unofficial mirror of emacs-devel@gnu.org 
 help / color / mirror / code / Atom feed
blob c510e5a848beeed12a9004cc135ebea7c4bd2d26 64550 bytes (raw)
name: lisp/follow.el 	 # note: path name is non-authoritative(*)

   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
 
;;; follow.el --- synchronize windows showing the same buffer

;; Copyright (C) 1995-1997, 1999, 2001-2016 Free Software Foundation,
;; Inc.

;; Author: Anders Lindgren
;; Maintainer: emacs-devel@gnu.org
;; Created: 1995-05-25
;; Keywords: display, window, minor-mode, convenience

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; `Follow mode' is a minor mode for Emacs and XEmacs that
;; combines windows into one tall virtual window.
;;
;; The feeling of a "virtual window" has been accomplished by the use
;; of two major techniques:
;;
;; * The windows always display adjacent sections of the buffer.
;;   This means that whenever one window is moved, all the
;;   others will follow.  (Hence the name Follow mode.)
;;
;; * Should point (cursor) end up outside a window, another
;;   window displaying that point is selected, if possible.  This
;;   makes it possible to walk between windows using normal cursor
;;   movement commands.
;;
;; Follow mode comes to its prime when a large screen and two
;; side-by-side window are used.  The user can, with the help of Follow
;; mode, use two full-height windows as though they are one.
;; Imagine yourself editing a large function, or section of text,
;; and being able to use 144 lines instead of the normal 72... (your
;; mileage may vary).

;; To test this package, make sure `follow' is loaded, or will be
;; autoloaded when activated (see below).  Then do the following:
;;
;; * Find your favorite file (preferably a long one).
;;
;; * Resize Emacs so that it will be wide enough for two full size
;;   columns.  Delete the other windows and split the window with
;;   the commands `C-x 1 C-x 3'.
;;
;; * Give the command:
;;	M-x follow-mode <RETURN>
;;
;; * Now the display should look something like (assuming the text "71"
;;   is on line 71):
;;
;;		    +----------+----------+
;;		    |1         |73        |
;;		    |2         |74        |
;;		    |3         |75        |
;;		         ...        ...
;;		    |71        |143       |
;;		    |72        |144       |
;;		    +----------+----------+
;;
;;   As you can see, the right-hand window starts at line 73, the line
;;   immediately below the end of the left-hand window.  As long as
;;   `follow-mode' is active, the two windows will follow each other!
;;
;; * Play around and enjoy! Scroll one window and watch the other.
;;   Jump to the beginning or end.  Press `Cursor down' at the last
;;   line of the left-hand window.  Enter new lines into the
;;   text.  Enter long lines spanning several lines, or several
;;   windows.
;;
;; * Should you find `Follow' mode annoying, just type
;;	M-x follow-mode <RETURN>
;;   to turn it off.


;; The command `follow-delete-other-windows-and-split' maximizes the
;; visible area of the current buffer.
;;
;; I recommend adding it, and `follow-mode', to hotkeys in the global
;; key map.  To do so, add the following lines (replacing `[f7]' and
;; `[f8]' with your favorite keys) to the init file:
;;
;; (global-set-key [f8] 'follow-mode)
;; (global-set-key [f7] 'follow-delete-other-windows-and-split)


;; There exist two system variables that control the appearance of
;; lines wider than the window containing them.  The default is to
;; truncate long lines whenever a window isn't as wide as the frame.
;;
;; To make sure lines are never truncated, please place the following
;; lines in your init file:
;;
;; (setq truncate-lines nil)
;; (setq truncate-partial-width-windows nil)


;; The correct way to configure Follow mode, or any other mode for
;; that matter, is to create one or more functions that do
;; whatever you would like to do.  These functions are then added to
;; a hook.
;;
;; The keymap `follow-key-map' contains key bindings activated by
;; `follow-mode'.
;;
;; Example:
;; (add-hook 'follow-mode-hook 'my-follow-mode-hook)
;;
;; (defun my-follow-mode-hook ()
;;    (define-key follow-mode-map "\C-ca" 'your-favorite-function)
;;    (define-key follow-mode-map "\C-cb" 'another-function))


;; Usage:
;;
;; To activate, issue the command "M-x follow-mode"
;; and press Return.  To deactivate, do it again.
;;
;; The following is a list of commands useful when follow-mode is active.
;;
;;	follow-scroll-up			 C-c . C-v
;;		Scroll text in a Follow mode window chain up.
;;
;;	follow-scroll-down			 C-c . v
;;		Like `follow-scroll-up', but in the other direction.
;;
;;	follow-delete-other-windows-and-split	 C-c . 1
;;		Maximize the visible area of the current buffer,
;;		and enter Follow mode. 	This is a very convenient
;;		way to start Follow mode, hence we recommend that
;;		this command be added to the global keymap.
;;
;;	follow-recenter				 C-c . C-l
;;		Place point in the center of the middle window,
;;		or a specified number of lines from either top or bottom.
;;
;;	follow-switch-to-buffer			 C-c . b
;;		Switch buffer in all windows displaying the current buffer
;;		in this frame.
;;
;;	follow-switch-to-buffer-all		 C-c . C-b
;;		Switch buffer in all windows in the selected frame.
;;
;;	follow-switch-to-current-buffer-all
;;		Show the current buffer in all windows on the current
;;		frame and turn on `follow-mode'.
;;
;;	follow-first-window			 C-c . <
;;		Select the first window in the frame showing the same buffer.
;;
;;	follow-last-window			 C-c . >
;;		Select the last window in the frame showing the same buffer.
;;
;;	follow-next-window			 C-c . n
;;		Select the next window in the frame showing the same buffer.
;;
;;	follow-previous-window			 C-c . p
;;		Select the previous window showing the same buffer.


;; Well, it seems ok, but what if I really want to look at two different
;; positions in the text? Here are two simple methods to use:
;;
;; 1) Use multiple frames; `follow' mode only affects windows displayed
;;    in the same frame. (My apologies to you who can't use frames.)
;;
;; 2) Bind `follow-mode' to key so you can turn it off whenever
;;    you want to view two locations.  Of course, `follow' mode can
;;    be reactivated by hitting the same key again.
;;
;;    Example from my ~/.emacs:
;;	(global-set-key [f8] 'follow-mode)

;; Implementation:
;;
;; The main method by which Follow mode aligns windows is via the
;; function `follow-post-command-hook', which is run after each
;; command.  This "fixes up" the alignment of other windows which are
;; showing the same Follow mode buffer, on the same frame as the
;; selected window.  It does not try to deal with buffers other than
;; the buffer of the selected frame, or windows on other frames.
;;
;; Comint mode specially calls `follow-comint-scroll-to-bottom' on
;; Follow mode buffers.  This function scrolls the bottom-most window
;; in a window chain and aligns the other windows accordingly.  Follow
;; mode adds a function to `compilation-filter-hook' to align
;; compilation buffers.

;;; Code:

(require 'easymenu)
(eval-when-compile (require 'cl-lib))

;;; Variables

(defgroup follow nil
  "Synchronize windows showing the same buffer."
  :group 'windows
  :group 'convenience)

(defcustom follow-mode-hook nil
  "Normal hook run by `follow-mode'."
  :type 'hook
  :group 'follow)

;;; Keymap/Menu

;; Define keys for the follow-mode minor mode map and replace some
;; functions in the global map.  All Follow mode special functions can
;; be found on the `C-c .' prefix key.
;;
;; To change the prefix, redefine `follow-mode-prefix' before `follow'
;; is loaded, or see the section on `follow-mode-hook' above for an
;; example of how to bind the keys the way you like.

(defcustom follow-mode-prefix "\C-c."
  "Prefix key to use for follow commands in Follow mode.
The value of this variable is checked as part of loading Follow mode.
After that, changing the prefix key requires manipulating keymaps."
  :type 'string
  :group 'follow)

(defvar follow-mode-map
  (let ((mainmap (make-sparse-keymap))
        (map (make-sparse-keymap)))
    (define-key map "\C-v"	'follow-scroll-up)
    (define-key map "\M-v"	'follow-scroll-down)
    (define-key map "v"		'follow-scroll-down)
    (define-key map "1"		'follow-delete-other-windows-and-split)
    (define-key map "b"		'follow-switch-to-buffer)
    (define-key map "\C-b"	'follow-switch-to-buffer-all)
    (define-key map "\C-l"	'follow-recenter)
    (define-key map "<"		'follow-first-window)
    (define-key map ">"		'follow-last-window)
    (define-key map "n"		'follow-next-window)
    (define-key map "p"		'follow-previous-window)

    (define-key mainmap follow-mode-prefix map)

    ;; Replace the standard `end-of-buffer', when in Follow mode.  (I
    ;; don't see the point in trying to replace every function that
    ;; could be enhanced in Follow mode.  End-of-buffer is a special
    ;; case since it is very simple to define and it greatly enhances
    ;; the look and feel of Follow mode.)
    (define-key mainmap [remap end-of-buffer] 'follow-end-of-buffer)

    (define-key mainmap [remap scroll-bar-toolkit-scroll] 'follow-scroll-bar-toolkit-scroll)
    (define-key mainmap [remap scroll-bar-drag] 'follow-scroll-bar-drag)
    (define-key mainmap [remap scroll-bar-scroll-up] 'follow-scroll-bar-scroll-up)
    (define-key mainmap [remap scroll-bar-scroll-down] 'follow-scroll-bar-scroll-down)
    (define-key mainmap [remap mwheel-scroll] 'follow-mwheel-scroll)

    mainmap)
  "Minor mode keymap for Follow mode.")

;; When the mode is not activated, only one item is visible to activate
;; the mode.
(defun follow-menu-filter (menu)
  (if (bound-and-true-p follow-mode)
      menu
    '(["Follow mode"	follow-mode
       :style toggle :selected follow-mode])))

(easy-menu-add-item nil '("Tools")
  '("Follow"
    :filter follow-menu-filter
    ["Scroll Up"	follow-scroll-up	follow-mode]
    ["Scroll Down"	follow-scroll-down	follow-mode]
    "--"
    ["Delete Other Windows and Split" follow-delete-other-windows-and-split follow-mode]
    "--"
    ["Switch To Buffer"	follow-switch-to-buffer	follow-mode]
    ["Switch To Buffer (all windows)" follow-switch-to-buffer-all follow-mode]
    "--"
    ["First Window"	follow-first-window	follow-mode]
    ["Last Window"	follow-last-window	follow-mode]
    ["Next Window"	follow-next-window	follow-mode]
    ["Previous Window"	follow-previous-window	follow-mode]
    "--"
    ["Recenter"		follow-recenter		follow-mode]
    "--"
    ["Follow mode"	follow-mode :style toggle :selected follow-mode]))

(defcustom follow-mode-line-text " Follow"
  "Text shown in the mode line when Follow mode is active.
Defaults to \" Follow\".  Examples of other values
are \" Fw\", or simply \"\"."
  :type 'string
  :group 'follow)

(defcustom follow-auto nil
  "Non-nil activates Follow mode whenever a file is loaded."
  :type 'boolean
  :group 'follow
  :set (lambda (symbol value)
	 (if value
	     (add-hook 'find-file-hook 'follow-find-file-hook t)
	   (remove-hook 'find-file-hook 'follow-find-file-hook))
	 (set-default symbol value)))

(defvar follow-cache-command-list
  '(next-line previous-line forward-char backward-char right-char left-char)
  "List of commands that don't require recalculation.

In order to be able to use the cache, a command should not change the
contents of the buffer, nor should it change selected window or current
buffer.

The commands in this list are checked at load time.

To mark other commands as suitable for caching, set the symbol
property `follow-mode-use-cache' to non-nil.")

(defcustom follow-debug nil
  "If non-nil, emit Follow mode debugging messages."
  :type 'boolean
  :group 'follow)

;; Internal variables:

(defvar follow-internal-force-redisplay nil
  "True when Follow mode should redisplay the windows.")

(defvar follow-active-menu nil
  "The menu visible when Follow mode is active.")

(defvar follow-inactive-menu nil
  "The menu visible when Follow mode is inactive.")

(defvar follow-inside-post-command-hook nil
  "Non-nil when inside Follow modes `post-command-hook'.
Used by `follow-window-size-change'.")

(defvar follow-windows-start-end-cache nil
  "Cache used by `follow-window-start-end'.")

(defvar follow-fixed-window nil
  "If non-nil, the current window must not be scrolled.
This is typically set by explicit scrolling commands.")
;;; Debug messages

;; This inline function must be as small as possible!
;; Maybe we should define a macro that expands to nil if
;; the variable is not set.

(defsubst follow-debug-message (&rest args)
  "Like `message', but only active when `follow-debug' is non-nil."
  (if (and (boundp 'follow-debug) follow-debug)
      (apply 'message args)))

;;; Cache

(dolist (cmd follow-cache-command-list)
  (put cmd 'follow-mode-use-cache t))

;;; The mode

;;;###autoload
(defun turn-on-follow-mode ()
  "Turn on Follow mode.  Please see the function `follow-mode'."
  (follow-mode 1))


;;;###autoload
(defun turn-off-follow-mode ()
  "Turn off Follow mode.  Please see the function `follow-mode'."
  (follow-mode -1))

(put 'follow-mode 'permanent-local t)
;;;###autoload
(define-minor-mode follow-mode
  "Toggle Follow mode.
With a prefix argument ARG, enable Follow mode if ARG is
positive, and disable it otherwise.  If called from Lisp, enable
the mode if ARG is omitted or nil.

Follow mode is a minor mode that combines windows into one tall
virtual window.  This is accomplished by two main techniques:

* The windows always displays adjacent sections of the buffer.
  This means that whenever one window is moved, all the
  others will follow.  (Hence the name Follow mode.)

* Should point (cursor) end up outside a window, another
  window displaying that point is selected, if possible.  This
  makes it possible to walk between windows using normal cursor
  movement commands.

Follow mode comes to its prime when used on a large screen and two or
more side-by-side windows are used.  The user can, with the help of
Follow mode, use these full-height windows as though they were one.
Imagine yourself editing a large function, or section of text, and
being able to use 144 or 216 lines instead of the normal 72... (your
mileage may vary).

To split one large window into two side-by-side windows, the commands
`\\[split-window-right]' or \
`\\[follow-delete-other-windows-and-split]' can be used.

Only windows displayed in the same frame follow each other.

This command runs the normal hook `follow-mode-hook'.

Keys specific to Follow mode:
\\{follow-mode-map}"
  :keymap follow-mode-map
  (if follow-mode
      (progn
	(add-hook 'compilation-filter-hook 'follow-align-compilation-windows t t)
	(add-hook 'post-command-hook 'follow-post-command-hook t)
	(add-hook 'window-size-change-functions 'follow-window-size-change t)
        (add-hook 'after-change-functions 'follow-after-change nil t)
        (add-hook 'isearch-update-post-hook 'follow-post-command-hook nil t)
        (add-hook 'replace-update-post-hook 'follow-post-command-hook nil t)
        (add-hook 'ispell-update-post-hook 'follow-post-command-hook nil t)

        (setq window-group-start-function 'follow-window-start)
        (setq window-group-end-function 'follow-window-end)
        (setq set-window-group-start-function 'follow-set-window-start)
        (setq recenter-window-group-function 'follow-recenter)
        (setq pos-visible-in-window-group-p-function
              'follow-pos-visible-in-window-p)
        (setq selected-window-group-function 'follow-all-followers)
        (setq move-to-window-group-line-function 'follow-move-to-window-line))

    ;; Remove globally-installed hook functions only if there is no
    ;; other Follow mode buffer.
    (let ((buffers (buffer-list))
	  following)
      (while (and (not following) buffers)
	(setq following (buffer-local-value 'follow-mode (car buffers))
	      buffers (cdr buffers)))
      (unless following
	(remove-hook 'post-command-hook 'follow-post-command-hook)
	(remove-hook 'window-size-change-functions 'follow-window-size-change)))

    (kill-local-variable 'move-to-window-group-line-function)
    (kill-local-variable 'selected-window-group-function)
    (kill-local-variable 'pos-visible-in-window-group-p-function)
    (kill-local-variable 'recenter-window-group-function)
    (kill-local-variable 'set-window-group-start-function)
    (kill-local-variable 'window-group-end-function)
    (kill-local-variable 'window-group-start-function)

    (remove-hook 'ispell-update-post-hook 'follow-post-command-hook t)
    (remove-hook 'replace-update-post-hook 'follow-post-command-hook t)
    (remove-hook 'isearch-update-post-hook 'follow-post-command-hook t)
    (remove-hook 'after-change-functions 'follow-after-change t)
    (remove-hook 'compilation-filter-hook 'follow-align-compilation-windows t)))

(defun follow-find-file-hook ()
  "Find-file hook for Follow mode.  See the variable `follow-auto'."
  (if follow-auto (follow-mode 1)))

;;; User functions

;;; Scroll

(defun follow-get-scrolled-point (dest windows)
  "Calculate the correct value for point after a scrolling operation.

DEST is our default position, typically where point was before the scroll.
If `scroll-preserve-screen-position' is non-nil and active, DEST will be
in the same screen position as before the scroll.  WINDOWS is the list of
windows in the follow chain.

This function attempts to duplicate the point placing from
`window_scroll_line_based' in the Emacs core source window.c.

Return the new position."
  (if (and scroll-preserve-screen-position
	   (get this-command 'scroll-command))
      dest
    (let ((dest-column
	   (save-excursion
	     (goto-char dest)
	     (- (current-column)
		(progn (vertical-motion 0) (current-column)))))
	  (limit0
	   (with-selected-window (car windows)
	     (save-excursion
	       (goto-char (window-start))
	       (vertical-motion 0)
	       (point))))
	  (limitn
	   (with-selected-window (car (reverse windows))
	     (save-excursion
	       (goto-char (window-end nil t))
	       (if (pos-visible-in-window-p)
		   (point)		; i.e. (point-max)
		 (1- (point)))))))
      (cond
       ((< dest limit0)
	(with-selected-window (car windows)
	  (save-excursion
	    (goto-char limit0)
	    (vertical-motion (cons dest-column 0))
	    (point))))
       ((> dest limitn)
	(with-selected-window (car (reverse windows))
	  (save-excursion
	    (goto-char limitn)
	    (vertical-motion (cons dest-column 0))
	    (point))))
       (t dest)))))

;; `scroll-up' and `-down', but for windows in Follow mode.
;;
;; Almost like the real thing, except when the cursor ends up outside
;; the top or bottom...  In our case however, we end up outside the
;; window and hence we are recentered.  Should we let `recenter' handle
;; the point position we would never leave the selected window.  To do
;; it ourselves we would need to do our own redisplay, which is easier
;; said than done.  (Why didn't I do a real display abstraction from
;; the beginning?)
;;
;; We must sometimes set `follow-internal-force-redisplay', otherwise
;; our post-command-hook will move our windows back into the old
;; position...  (This would also be corrected if we would have had a
;; good redisplay abstraction.)

(defun follow-scroll-up-arg (arg)
  "Scroll the text in a follow mode window chain up by ARG lines.
If ARG is nil, scroll the size of the current window.

This is an internal function for `follow-scroll-up' and
`follow-scroll-up-window'."
  (let ((opoint (point))  (owin (selected-window)))
    (while
        ;; If we are too near EOB, try scrolling the previous window.
        (condition-case nil (progn (scroll-up arg) nil)
          (end-of-buffer
           (condition-case nil (progn (follow-previous-window) t)
             (error
              (select-window owin)
              (goto-char opoint)
              (signal 'end-of-buffer nil))))))
    (unless (and scroll-preserve-screen-position
                 (get this-command 'scroll-command))
      (goto-char opoint))
    (setq follow-fixed-window t)))

(defun follow-scroll-down-arg (arg)
  "Scroll the text in a follow mode window chain down by ARG lines.
If ARG is nil, scroll the size of the current window.

This is an internal function for `follow-scroll-down' and
`follow-scroll-down-window'."
  (let ((opoint (point)))
    (scroll-down arg)
    (unless (and scroll-preserve-screen-position
                 (get this-command 'scroll-command))
      (goto-char opoint))
    (setq follow-fixed-window t)))

;;;###autoload
(defun follow-scroll-up-window (&optional arg)
  "Scroll text in a Follow mode window up by that window's size.
The other windows in the window chain will scroll synchronously.

If called with no ARG, the `next-screen-context-lines' last lines of
the window will be visible after the scroll.

If called with an argument, scroll ARG lines up.
Negative ARG means scroll downward.

Works like `scroll-up' when not in Follow mode."
  (interactive "P")
  (cond ((not follow-mode)
	 (scroll-up arg))
	((eq arg '-)
	 (follow-scroll-down-window))
	(t (follow-scroll-up-arg arg))))
(put 'follow-scroll-up-window 'scroll-command t)

;;;###autoload
(defun follow-scroll-down-window (&optional arg)
  "Scroll text in a Follow mode window down by that window's size.
The other windows in the window chain will scroll synchronously.

If called with no ARG, the `next-screen-context-lines' top lines of
the window in the chain will be visible after the scroll.

If called with an argument, scroll ARG lines down.
Negative ARG means scroll upward.

Works like `scroll-down' when not in Follow mode."
  (interactive "P")
  (cond ((not follow-mode)
	 (scroll-down arg))
	((eq arg '-)
	 (follow-scroll-up-window))
	(t (follow-scroll-down-arg arg))))
(put 'follow-scroll-down-window 'scroll-command t)

;;;###autoload
(defun follow-scroll-up (&optional arg)
  "Scroll text in a Follow mode window chain up.

If called with no ARG, the `next-screen-context-lines' last lines of
the bottom window in the chain will be visible in the top window.

If called with an argument, scroll ARG lines up.
Negative ARG means scroll downward.

Works like `scroll-up' when not in Follow mode."
  (interactive "P")
  (cond ((not follow-mode)
	 (scroll-up arg))
	(arg (follow-scroll-up-arg arg))
        (t
	 (let* ((windows (follow-all-followers))
		(end (window-end (car (reverse windows)))))
	   (if (eq end (point-max))
	       (signal 'end-of-buffer nil)
	     (select-window (car windows))
	     ;; `window-end' might return nil.
	     (if end
		 (goto-char end))
	     (vertical-motion (- next-screen-context-lines))
	     (set-window-start (car windows) (point)))))))
(put 'follow-scroll-up 'scroll-command t)

;;;###autoload
(defun follow-scroll-down (&optional arg)
  "Scroll text in a Follow mode window chain down.

If called with no ARG, the `next-screen-context-lines' top lines of
the top window in the chain will be visible in the bottom window.

If called with an argument, scroll ARG lines down.
Negative ARG means scroll upward.

Works like `scroll-down' when not in Follow mode."
  (interactive "P")
  (cond ((not follow-mode)
	 (scroll-down arg))
	(arg (follow-scroll-down-arg arg))
        (t
	 (let* ((windows (follow-all-followers))
		(win (car (reverse windows)))
		(start (window-start (car windows))))
	   (if (eq start (point-min))
	       (signal 'beginning-of-buffer nil)
	     (select-window win)
	     (goto-char start)
	     (vertical-motion (- (- (window-height win)
				    (if header-line-format 2 1)
				    next-screen-context-lines)))
	     (set-window-start win (point))
	     (goto-char start)
	     (vertical-motion (- next-screen-context-lines 1))
	     (setq follow-internal-force-redisplay t))))))
(put 'follow-scroll-down 'scroll-command t)

(declare-function comint-adjust-point "comint" (window))
(defvar comint-scroll-show-maximum-output)

(defun follow-comint-scroll-to-bottom (&optional _window)
  "Scroll the bottom-most window in the current Follow chain.
This is to be called by `comint-postoutput-scroll-to-bottom'."
  (let* ((buffer (current-buffer))
	 (selected (selected-window))
	 (is-selected (eq (window-buffer) buffer))
	 some-window)
    (when (or is-selected
	      (setq some-window (get-buffer-window)))
      (let* ((pos (progn (comint-adjust-point nil) (point)))
	     (win (if is-selected
		      selected
		    (car (last (follow-all-followers some-window))))))
	(select-window win)
	(goto-char pos)
	(setq follow-windows-start-end-cache nil)
	(follow-adjust-window win)
	(unless is-selected
	  (select-window selected)
	  (set-buffer buffer))))))

(defun follow-align-compilation-windows ()
  "Align the windows of the current Follow mode buffer.
This is to be called from `compilation-filter-hook'."
  (let ((buffer (current-buffer))
	(win (get-buffer-window))
	(selected (selected-window)))
    (when (and follow-mode (waiting-for-user-input-p) win)
      (let ((windows (follow-all-followers win)))
	(unless (eq (window-buffer selected) buffer)
	  (setq win (car windows))
	  (select-window win))
	(follow-redisplay windows win t)
	(setq follow-windows-start-end-cache nil)
	(unless (eq selected win)
	  (select-window selected)
	  (set-buffer buffer))))))

;;; Buffer

;;;###autoload
(defun follow-delete-other-windows-and-split (&optional arg)
  "Create two side by side windows and enter Follow mode.

Execute this command to display as much as possible of the text
in the selected window.  All other windows, in the current
frame, are deleted and the selected window is split in two
side-by-side windows.  Follow mode is activated, hence the
two windows always will display two successive pages.
\(If one window is moved, the other one will follow.)

If ARG is positive, the leftmost window is selected.  If negative,
the rightmost is selected.  If ARG is nil, the leftmost window is
selected if the original window is the first one in the frame."
  (interactive "P")
  (let ((other (or (and (null arg)
			(not (eq (selected-window)
				 (frame-first-window))))
		   (and arg
			(< (prefix-numeric-value arg) 0))))
	(start (window-start)))
    (delete-other-windows)
    (split-window-right)
    (if other
	(progn
	  (other-window 1)
	  (set-window-start (selected-window) start)
	  (setq follow-internal-force-redisplay t)))
    (follow-mode 1)))

(defun follow-switch-to-buffer (buffer)
  "Show BUFFER in all windows in the current Follow mode window chain."
  (interactive "BSwitch to Buffer: ")
  (let ((orig-window (selected-window))
	(windows (follow-all-followers)))
    (while windows
      (select-window (car windows))
      (switch-to-buffer buffer)
      (setq windows (cdr windows)))
    (select-window orig-window)))


(defun follow-switch-to-buffer-all (&optional buffer)
  "Show BUFFER in all windows on this frame.
Defaults to current buffer."
  (interactive (list (read-buffer "Switch to Buffer: "
				  (current-buffer))))
  (or buffer (setq buffer (current-buffer)))
  (let ((orig-window (selected-window)))
    (walk-windows (lambda (win)
		    (select-window win)
		    (switch-to-buffer buffer))
		  'no-minibuf)
    (select-window orig-window)
    (follow-redisplay)))


(defun follow-switch-to-current-buffer-all ()
  "Show current buffer in all windows on this frame, and enter Follow mode."
  (interactive)
  (unless follow-mode
    (follow-mode 1))
  (follow-switch-to-buffer-all))

;;; Movement

;; Note, these functions are not very useful, at least not unless you
;; rebind the rather cumbersome key sequence `C-c . p'.

(defun follow-next-window ()
  "Select the next window showing the same buffer."
  (interactive)
  (let ((succ (cdr (follow-split-followers (follow-all-followers)))))
    (if succ
	(select-window (car succ))
      (error "%s" "No more windows"))))


(defun follow-previous-window ()
  "Select the previous window showing the same buffer."
  (interactive)
  (let ((pred (car (follow-split-followers (follow-all-followers)))))
    (if pred
	(select-window (car pred))
      (error "%s" "No more windows"))))


(defun follow-first-window ()
  "Select the first window in the frame showing the same buffer."
  (interactive)
  (select-window (car (follow-all-followers))))


(defun follow-last-window ()
  "Select the last window in the frame showing the same buffer."
  (interactive)
  (select-window (car (reverse (follow-all-followers)))))

;;; Redraw

(defun follow-recenter (&optional arg)
  "Recenter the middle window around point.
Rearrange all other windows around the middle window.

With a positive argument, place the current line ARG lines
from the top.  With a negative argument, place it -ARG lines
from the bottom."
  (interactive "P")
  (if arg
      (let ((p (point))
	    (arg (prefix-numeric-value arg)))
	(if (>= arg 0)
	    ;; Recenter relative to the top.
	    (progn
	      (follow-first-window)
	      (goto-char p)
	      (recenter arg))
	  ;; Recenter relative to the bottom.
	  (follow-last-window)
	  (goto-char p)
	  (recenter arg)
	  ;; Otherwise, our post-command-hook will move the window
	  ;; right back.
	  (setq follow-internal-force-redisplay t)))
    ;; Recenter in the middle.
    (let* ((dest (point))
	   (windows (follow-all-followers))
	   (win (nth (/ (- (length windows) 1) 2) windows)))
      (select-window win)
      (goto-char dest)
      (recenter))))


(defun follow-redraw ()
  "Arrange windows displaying the same buffer in successor order.
This function can be called even if the buffer is not in Follow mode.

Hopefully, there should be no reason to call this function when in
Follow mode since the windows should always be aligned."
  (interactive)
  (sit-for 0)
  (follow-redisplay))

;;; End of buffer

(defun follow-end-of-buffer (&optional arg)
  "Move point to the end of the buffer, Follow mode style.

If the end is not visible, it will be displayed in the last possible
window in the Follow mode window chain.

The mark is left at the previous position.  With arg N, put point N/10
of the way from the true end."
  (interactive "P")
  (let ((followers (follow-all-followers))
	(pos (point)))
    (cond (arg
	   (select-window (car (reverse followers))))
	  ((follow-select-if-end-visible
	    (follow-windows-start-end followers)))
	  (t
	   (select-window (car (reverse followers)))))
    (goto-char pos)
    (with-no-warnings
      (end-of-buffer arg))))

;;; Display

(defun follow--window-sorter (w1 w2)
  "Sorting function for W1 and W2 based on their positions.
Return non-nil if W1 is above W2; if their top-lines
are at the same position, return non-nil if W1 is to the
left of W2."
  (let* ((edge-1 (window-pixel-edges w1))
	 (edge-2 (window-pixel-edges w2))
	 (y1 (nth 1 edge-1))
	 (y2 (nth 1 edge-2)))
    (if (= y1 y2)
	(< (car edge-1) (car edge-2))
      (< y1 y2))))

(defun follow-all-followers (&optional win)
  "Return all windows displaying the same buffer as the WIN.
The list is sorted with topmost and leftmost windows first, and
contains only windows in the same frame as WIN.  If WIN is nil,
it defaults to the selected window."
  (unless (window-live-p win)
    (setq win (selected-window)))
  (let ((windows (get-buffer-window-list
                  (window-buffer win) 'no-minibuf (window-frame win))))
    (sort windows #'follow--window-sorter)))

(defun follow-split-followers (windows &optional win)
  "Split WINDOWS into two sets: predecessors and successors.
Return `(PRED . SUCC)' where `PRED' and `SUCC' are ordered starting
from the selected window."
  (or win
      (setq win (selected-window)))
  (let ((pred '()))
    (while (not (eq (car windows) win))
      (setq pred (cons (car windows) pred))
      (setq windows (cdr windows)))
    (cons pred (cdr windows))))

(defun follow-calc-win-end (&optional win)
  "Calculate the end position for window WIN.
Return (END-POS END-OF-BUFFER).

Actually, the position returned is the start of the line after
the last fully-visible line in WIN.  END-OF-BUFFER is t when EOB
is fully-visible in WIN.  If WIN is nil, the selected window is
used."
  (let* ((win (or win (selected-window)))
	 (edges (window-inside-pixel-edges win))
	 (ht (- (nth 3 edges) (nth 1 edges)))
	 (last-line-pos (posn-point (posn-at-x-y 0 (1- ht) win))))
    (if (pos-visible-in-window-p last-line-pos win)
	(let ((end (window-end win t)))
	  (list end (pos-visible-in-window-p (point-max) win)))
      (list last-line-pos nil))))

(defun follow-calc-win-start (windows pos win)
  "Determine the start of window WIN in a Follow mode window chain.
WINDOWS is a list of chained windows, and POS is the starting
position for the first window in the list.  If WIN is nil, return
the point below all windows."
  (while (and windows (not (eq (car windows) win)))
    (let ((old-start (window-start (car windows))))
      ;; Can't use `save-window-excursion' since it triggers a redraw.
      (set-window-start (car windows) pos 'noforce)
      (setq pos (car (follow-calc-win-end (car windows))))
      (set-window-start (car windows) old-start 'noforce)
      (setq windows (cdr windows))))
  pos)

;; The result from `follow-windows-start-end' is cached when using
;; a handful simple commands, like cursor movement commands.

(defsubst follow-cache-valid-p (windows)
  "Test if the cached value of `follow-windows-start-end' can be used.
Note that this handles the case when the cache has been set to nil."
  (let ((res t)
	(cache follow-windows-start-end-cache))
    (while (and res windows cache)
      (setq res (and (eq (car windows)
			 (car (car cache)))
		     (eq (window-start (car windows))
			 (car (cdr (car cache))))))
      (setq windows (cdr windows))
      (setq cache (cdr cache)))
    (and res (null windows) (null cache))))

(defun follow-windows-start-end (windows)
  "Return a list of (WIN START END BUFFER-END-P) for window list WINDOWS."
  (if (follow-cache-valid-p windows)
      follow-windows-start-end-cache
    (let ((orig-win (selected-window))
	  win-start-end)
      (dolist (w windows)
	(select-window w 'norecord)
	(push (cons w (cons (window-start) (follow-calc-win-end)))
	      win-start-end))
      (select-window orig-win 'norecord)
      (setq follow-windows-start-end-cache (nreverse win-start-end)))))

(defsubst follow-pos-visible (pos win win-start-end)
  "Non-nil when POS is visible in WIN."
  (let ((wstart-wend-bend (cdr (assq win win-start-end))))
    (and (>= pos (car wstart-wend-bend))
	 (or (< pos (cadr wstart-wend-bend))
	     (nth 2 wstart-wend-bend)))))


;; By `aligned' we mean that for all adjacent windows, the end of the
;; first is equal with the start of the successor.  The first window
;; should start at a full screen line.

(defsubst follow-windows-aligned-p (win-start-end)
  "Non-nil if the follower windows are aligned.
The argument, WIN-START-END, should be a list of the form
returned by `follow-windows-start-end'."
  (let ((result t))
    (while (and win-start-end result)
      (if (cdr win-start-end)
	  (setq result (eq (nth 2 (car win-start-end))
			   (nth 1 (cadr win-start-end)))))
      (setq win-start-end (cdr win-start-end)))
    result))

;; Check if point is visible in all windows. (So that
;; no one will be recentered.)

(defun follow-point-visible-all-windows-p (win-start-end)
  "Non-nil when the `window-point' is visible in all windows."
  (let ((res t))
    (while (and res win-start-end)
      (setq res (follow-pos-visible (window-point (car (car win-start-end)))
				    (car (car win-start-end))
				    win-start-end))
      (setq win-start-end (cdr win-start-end)))
    res))


;; Make sure WIN always starts at the beginning of a whole screen
;; line. If WIN is not aligned the start is updated which probably
;; will lead to a redisplay of the screen later on.
;;
;; This is used with the first window in a follow chain.  The reason
;; is that we want to detect that point is outside the window.
;; (Without the update, the start of the window will move as the
;; user presses BackSpace, and the other window redisplay routines
;; will move the start of the window in the wrong direction.)

(defun follow-update-window-start (win)
  "Make sure that the start of WIN starts at a full screen line."
  (save-excursion
    (goto-char (window-start win))
    (unless (bolp)
      (vertical-motion 0 win)
      (unless (eq (point) (window-start win))
	(vertical-motion 1 win)
	(set-window-start win (point) 'noforce)))))

(defun follow-select-if-visible (dest win-start-end)
  "Select and return a window, if DEST is visible in it.
Return the selected window."
  (let (win wse)
    (while (and (not win) win-start-end)
      ;; Don't select a window that was just moved. This makes it
      ;; possible to later select the last window after a
      ;; `end-of-buffer' command.
      (setq wse (car win-start-end))
      (when (follow-pos-visible dest (car wse) win-start-end)
	(setq win (car wse))
	(select-window win))
      (setq win-start-end (cdr win-start-end)))
    win))

;; Lets select a window showing the end. Make sure we only select it if
;; it wasn't just moved here. (I.e. M-> shall not unconditionally place
;; point in the selected window.)
;;
;; (Compatibility kludge: in Emacs `window-end' is equal to `point-max';
;; in XEmacs, it is equal to `point-max + 1'. Should I really bother
;; checking `window-end' now when I check `end-of-buffer' explicitly?)

(defun follow-select-if-end-visible (win-start-end)
  "Select and return a window, if end is visible in it."
  (let ((win nil))
    (while (and (not win) win-start-end)
      ;; Don't select a window that was just moved. This makes it
      ;; possible to later select the last window after a `end-of-buffer'
      ;; command.
      (if (and (eq (point-max) (nth 2 (car win-start-end)))
	       (nth 3 (car win-start-end))
	       ;; `window-end' might return nil.
	       (let ((end (window-end (car (car win-start-end)))))
		 (and end
		      (eq (point-max) (min (point-max) end)))))
	  (progn
	    (setq win (car (car win-start-end)))
	    (select-window win)))
      (setq win-start-end (cdr win-start-end)))
    win))


;; Select a window that will display point if the windows would
;; be redisplayed with the first window fixed. This is useful for
;; example when the user has pressed return at the bottom of a window
;; as point is not visible in any window.

(defun follow-select-if-visible-from-first (dest windows)
  "Try to select one of WINDOWS without repositioning the topmost window.
If one of the windows in WINDOWS contains DEST, select it, call
`follow-redisplay', move point to DEST, and return that window.
Otherwise, return nil."
  (let (win end-pos-end-p)
    (save-excursion
      (goto-char (window-start (car windows)))
      ;; Make sure the line start in the beginning of a real screen
      ;; line.
      (vertical-motion 0 (car windows))
      (when (>= dest (point))
	;; At or below the start. Check the windows.
	(save-window-excursion
	  (let ((windows windows))
	    (while (and (not win) windows)
	      (set-window-start (car windows) (point) 'noforce)
	      (setq end-pos-end-p (follow-calc-win-end (car windows)))
	      (goto-char (car end-pos-end-p))
	      ;; Visible, if dest above end, or if eob is visible
	      ;; inside the window.
	      (if (or (car (cdr end-pos-end-p))
		      (< dest (point)))
		  (setq win (car windows))
		(setq windows (cdr windows))))))))
    (when win
      (select-window win)
      (follow-redisplay windows (car windows))
      (goto-char dest))
    win))

;;; Redisplay

;; Redraw all the windows on the screen, starting with the top window.
;; The window used as as marker is WIN, or the selected window if WIN
;; is nil.  Start every window directly after the end of the previous
;; window, to make sure long lines are displayed correctly.

(defvar follow-start-end-invalid t
  "When non-nil, indicates `follow-windows-start-end-cache' is invalid.")
(make-variable-buffer-local 'follow-start-end-invalid)

(defun follow-redisplay (&optional windows win preserve-win)
  "Reposition the WINDOWS around WIN.
Should point be too close to the roof we redisplay everything
from the top.  WINDOWS should contain a list of windows to
redisplay; it is assumed that WIN is a member of the list.
Should WINDOWS be nil, the windows displaying the
same buffer as WIN, in the current frame, are used.
Should WIN be nil, the selected window is used.
If PRESERVE-WIN is non-nil, keep WIN itself unchanged while
repositioning the other windows."
  (or win (setq win (selected-window)))
  (or windows (setq windows (follow-all-followers win)))
  ;; Calculate the start of the first window.
  (let* ((old-win-start (window-start win))
	 (try-first-start (follow-estimate-first-window-start
			   windows win old-win-start))
	 (try-win-start (follow-calc-win-start
			 windows try-first-start win))
	 (start (cond ((= try-win-start old-win-start)
		       (follow-debug-message "exact")
		       try-first-start)
		      ((< try-win-start old-win-start)
		       (follow-debug-message "above")
		       (follow-calculate-first-window-start-from-above
			windows try-first-start win old-win-start))
		      (t
		       (follow-debug-message "below")
		       (follow-calculate-first-window-start-from-below
			windows try-first-start win old-win-start)))))
    (dolist (w windows)
      (unless (and preserve-win (eq w win))
	(set-window-start w start))
      (setq start (car (follow-calc-win-end w))))
    (setq follow-start-end-invalid nil)))

(defun follow-estimate-first-window-start (windows win start)
  "Estimate the position of the first window.
The estimate is computed by assuming that the window WIN, which
should be a member of WINDOWS, starts at position START."
  (let ((windows-before (car (follow-split-followers windows win))))
    (save-excursion
      (goto-char start)
      (vertical-motion 0 win)
      (dolist (w windows-before)
	(vertical-motion (- (window-text-height w)) w))
      (point))))


;; Find the starting point, start at GUESS and search downward.
;; The returned point is always a point below GUESS.

(defun follow-calculate-first-window-start-from-above
       (windows guess win start)
  (save-excursion
    (let ((done nil)
	  win-start
	  res)
      (goto-char guess)
      (while (not done)
	(if (not (= (vertical-motion 1 (car windows)) 1))
	    ;; Hit bottom! (Can we really do this?)
	    ;; We'll keep it, since it ensures termination.
	    (progn
	      (setq done t)
	      (setq res (point-max)))
	  (setq win-start (follow-calc-win-start windows (point) win))
	  (if (>= win-start start)
	      (setq done t res (point)))))
      res)))


;; Find the starting point, start at GUESS and search upward.  Return
;; a point on the same line as GUESS, or above.

(defun follow-calculate-first-window-start-from-below
       (windows guess &optional win start)
  (setq win (or win (selected-window)))
  (setq start (or start (window-start win)))
  (save-excursion
    (let (done win-start res opoint)
      ;; Always calculate what happens when no line is displayed in the first
      ;; window. (The `previous' res is needed below!)
      (goto-char guess)
      (vertical-motion 0 (car windows))
      (setq res (point))
      (while (not done)
	(setq opoint (point))
	(if (not (= (vertical-motion -1 (car windows)) -1))
	    ;; Hit roof!
	    (setq done t res (point-min))
	  (setq win-start (follow-calc-win-start windows (point) win))
	  (cond ((>= (point) opoint)
		 ;; In some pathological cases, vertical-motion may
		 ;; return -1 even though point has not decreased.  In
		 ;; that case, avoid looping forever.
		 (setq done t res (point)))
		((= win-start start)	; Perfect match, use this value
		 (setq done t res (point)))
		((< win-start start)	; Walked to far, use previous result
		 (setq done t))
		(t			; Store result for next iteration
		 (setq res (point))))))
      res)))

;;; Avoid tail recenter

;; This sets the window internal flag `force_start'. The effect is
;; that windows only displaying the tail aren't recentered.
;;
;; A window displaying only the tail, is a window whose window-start
;; position is equal to (point-max) of the buffer it displays.

(defun follow-avoid-tail-recenter (&rest _rest)
  "Make sure windows displaying the end of a buffer aren't recentered.
This is done by reading and rewriting the start position of
non-first windows in Follow mode."
  (let* ((orig-buffer (current-buffer))
	 (top (frame-first-window))
	 (win top)
	 who) ; list of (buffer . frame)
    ;; If the only window in the frame is a minibuffer
    ;; window, `next-window' will never find it again...
    (unless (window-minibuffer-p top)
      (while  ;; look, no body!
	  (let ((start (window-start win))
		(pair (cons (window-buffer win) (window-frame win))))
	    (set-buffer (window-buffer win))
	    (cond ((null (member pair who))
		   (setq who (cons pair who)))
		  ((and follow-mode (eq (point-max) start))
		   ;; Write the same window start back, but don't
		   ;; set the NOFORCE flag.
		   (set-window-start win start)))
	    (setq win (next-window win 'not t))
	    (not (eq win top))))  ;; Loop while this is true.
      (set-buffer orig-buffer))))

;;; Post Command Hook

;; The magic little box. This function is called after every command.

;; This is not as complicated as it seems. It is simply a list of common
;; display situations and the actions to take, plus commands for redrawing
;; the screen if it should be unaligned.
;;
;; We divide the check into two parts; whether we are at the end or not.
;; This is due to the fact that the end can actually be visible
;; in several window even though they are aligned.

(defun follow-post-command-hook ()
  "Ensure that the windows in Follow mode are adjacent after each command."
  (unless (input-pending-p)
    (let ((follow-inside-post-command-hook t)
	  (win (selected-window)))
      ;; Work in the selected window, not in the current buffer.
      (with-current-buffer (window-buffer win)
	(unless (and (symbolp this-command)
		     (get this-command 'follow-mode-use-cache))
	  (setq follow-windows-start-end-cache nil))
        (follow-adjust-window win)))))

(defun follow-adjust-window (win)
  ;; Adjust the window WIN and its followers.
  (cl-assert (eq (window-buffer win) (current-buffer)))
  (when (and follow-mode
             (not (window-minibuffer-p win)))
    (let ((windows (follow-all-followers win)))
      ;; If we've explicitly scrolled, align the windows first.
      (when follow-fixed-window
	(follow-debug-message "fixed")
	(follow-redisplay windows win)
	(goto-char (follow-get-scrolled-point (point) windows))
	(setq follow-fixed-window nil))
      (let* ((dest (point))
	     (win-start-end (progn
			      (follow-update-window-start (car windows))
			      (follow-windows-start-end windows)))
	     (aligned (follow-windows-aligned-p win-start-end))
	     (visible (follow-pos-visible dest win win-start-end))
	     selected-window-up-to-date)
	(unless (and aligned visible)
	  (setq follow-windows-start-end-cache nil))

	;; Select a window to display point.
	(unless follow-internal-force-redisplay
	  (if (eq dest (point-max))
	      ;; Be careful at point-max: the display can be aligned
	      ;; while DEST can be visible in several windows.
	      (cond
	       ;; Select the current window, but only when the display
	       ;; is correct. (When inserting characters in a tail
	       ;; window, the display is not correct, as they are
	       ;; shown twice.)
	       ;;
	       ;; Never stick to the current window after a deletion.
	       ;; Otherwise, when typing `DEL' in a window showing
	       ;; only the end of the file, a character would be
	       ;; removed from the window above, which is very
	       ;; unintuitive.
	       ((and visible
		     aligned
		     (not (memq this-command
				'(backward-delete-char
				  delete-backward-char
				  backward-delete-char-untabify
				  kill-region))))
		(follow-debug-message "Max: same"))
	       ;; If the end is visible, and the window doesn't
	       ;; seems like it just has been moved, select it.
	       ((follow-select-if-end-visible win-start-end)
		(follow-debug-message "Max: end visible")
		(setq visible t aligned nil)
		(goto-char dest))
	       ;; Just show the end...
	       (t
		(follow-debug-message "Max: default")
		(select-window (car (last windows)))
		(goto-char dest)
		(setq visible nil aligned nil)))

	    ;; We're not at the end, here life is much simpler.
	    (cond
	     ;; This is the normal case!
	     ;; It should be optimized for speed.
	     ((and visible aligned)
	      (follow-debug-message "same"))
	     ;; Pick a position in any window.  If the display is ok,
	     ;; this picks the `correct' window.
	     ((follow-select-if-visible dest win-start-end)
	      (follow-debug-message "visible")
	      (goto-char dest)
	      ;; Perform redisplay, in case line is partially visible.
	      (setq visible nil))
	     ;; Not visible anywhere else, lets pick this one.
	     (visible
	      (follow-debug-message "visible in selected."))
	     ;; If DEST is before the first window start, select the
	     ;; first window.
	     ((< dest (nth 1 (car win-start-end)))
	      (follow-debug-message "before first")
	      (select-window (car windows))
	      (goto-char dest)
	      (setq visible nil aligned nil))
	     ;; If we can position the cursor without moving the first
	     ;; window, do it. This is the case that catches `RET' at
	     ;; the bottom of a window.
	     ((follow-select-if-visible-from-first dest windows)
	      (follow-debug-message "Below first")
	      (setq visible t aligned t))
	     ;; None of the above.  Stick to the selected window.
	     (t
	      (follow-debug-message "None")
	      (setq visible nil aligned nil))))

	  ;; If a new window was selected, make sure that the old is
	  ;; not scrolled when point is outside the window.
	  (unless (eq win (selected-window))
	    (let ((p (window-point win)))
	      (set-window-start win (window-start win) nil)
	      (set-window-point win p))))

	(unless visible
	  ;; If point may not be visible in the selected window,
	  ;; perform a redisplay; this ensures scrolling.
	  (let ((opoint (point)))
	    (redisplay)
	    ;; If this `redisplay' moved point, we got clobbered by a
	    ;; previous call to `set-window-start'.  Try again.
	    (when (/= (point) opoint)
	      (goto-char opoint)
	      (redisplay)))

	  (setq selected-window-up-to-date t)
	  (follow-avoid-tail-recenter)
	  (setq win-start-end (follow-windows-start-end windows)
		follow-windows-start-end-cache nil
		aligned nil))

	;; Now redraw the windows around the selected window.
	(unless (and (not follow-internal-force-redisplay)
		     (or aligned
			 (follow-windows-aligned-p win-start-end))
		     (follow-point-visible-all-windows-p win-start-end))
	  (setq follow-internal-force-redisplay nil)
	  (follow-redisplay windows (selected-window)
			    selected-window-up-to-date)
	  (setq win-start-end (follow-windows-start-end windows)
		follow-windows-start-end-cache nil)
	  ;; Point can end up in another window when DEST is at
	  ;; the beginning of the buffer and the selected window is
	  ;; not the first.  It can also happen when long lines are
	  ;; used and there is a big difference between the width of
	  ;; the windows.  (When scrolling one line in a wide window
	  ;; which will cause a move larger that an entire small
	  ;; window.)
	  (unless (follow-pos-visible dest win win-start-end)
	    (follow-select-if-visible dest win-start-end)
	    (goto-char dest)))

	;; If the region is visible, make it look good when spanning
	;; multiple windows.
	(when (region-active-p)
	  (follow-maximize-region
	   (selected-window) windows win-start-end))))

    ;; Whether or not the buffer was in follow mode, update windows
    ;; displaying the tail so that Emacs won't recenter them.
    (follow-avoid-tail-recenter)))

;;; The region

;; Tries to make the highlighted area representing the region look
;; good when spanning several windows.
;;
;; Not perfect, as point can't be placed at window end, only at
;; end-1.  This will highlight a little bit in windows above
;; the current.

(defun follow-maximize-region (win windows win-start-end)
  "Make a highlighted region stretching multiple windows look good."
  (let* ((all (follow-split-followers windows win))
	 (pred (car all))
	 (succ (cdr all))
	 data)
    (while pred
      (setq data (assq (car pred) win-start-end))
      (set-window-point (car pred) (max (nth 1 data) (- (nth 2 data) 1)))
      (setq pred (cdr pred)))
    (while succ
      (set-window-point (car succ) (nth 1 (assq (car succ) win-start-end)))
      (setq succ (cdr succ)))))

;;; Scroll bar

;;;; Scroll-bar support code.

;; This handles the case where the user drags the scroll bar of a
;; non-selected window whose buffer is in Follow mode.

(declare-function scroll-bar-toolkit-scroll "scroll-bar" (event))
(declare-function scroll-bar-drag "scroll-bar" (event))
(declare-function scroll-bar-scroll-up "scroll-bar" (event))
(declare-function scroll-bar-scroll-down "scroll-bar" (event))
(declare-function mwheel-scroll "mwheel" (event))

(defun follow-scroll-bar-toolkit-scroll (event)
  (interactive "e")
  (scroll-bar-toolkit-scroll event)
  (follow-redraw-after-event event))

(defun follow-scroll-bar-drag (event)
  (interactive "e")
  (scroll-bar-drag event)
  (follow-redraw-after-event event))

(defun follow-scroll-bar-scroll-up (event)
  (interactive "e")
  (scroll-bar-scroll-up event)
  (follow-redraw-after-event event))

(defun follow-scroll-bar-scroll-down (event)
  (interactive "e")
  (scroll-bar-scroll-down event)
  (follow-redraw-after-event event))

(defun follow-mwheel-scroll (event)
  (interactive "e")
  (mwheel-scroll event)
  (follow-redraw-after-event event))

(defun follow-redraw-after-event (event)
  "Re-align the Follow mode windows affected by EVENT."
  (let* ((window (nth 0 (event-end event)))
	 (buffer (window-buffer window))
	 (orig-win (selected-window)))
    (when (and (buffer-local-value 'follow-mode buffer)
	       ;; Ignore the case where we scroll the selected window;
	       ;; that is handled by the post-command hook function.
	       (not (eq window (selected-window))))
      (select-window window)
      (follow-redisplay)
      (unless (eq (window-buffer orig-win) buffer)
	(select-window orig-win)))))

;;; Window size change

;; The functions in `window-size-change-functions' are called every
;; time a window in a frame changes size, most notably after the frame
;; has been resized.  We call `follow-post-command-hook' for every
;; Follow mode buffer visible in any window in the resized frame.
;;
;; Since `follow-window-size-change' can be called indirectly from
;; `follow-post-command-hook' we have a potential infinite loop.  To
;; avoid this, we simply do not do anything in this situation.  The
;; variable `follow-inside-post-command-hook' contains information
;; about whether the execution actually is inside the
;; post-command-hook or not.

(defun follow-window-size-change (frame)
  "Redraw all windows in FRAME, when in Follow mode."
  ;; Below, we call `post-command-hook'.  Avoid an infloop.
  (unless follow-inside-post-command-hook
    (save-current-buffer
      (let ((orig-frame (selected-frame)))
        (select-frame frame)
        (let ((picked-window (selected-window))   ; Note: May change below.
              (seen-buffers '()))
          (unwind-protect
              (walk-windows
               (lambda (win)
                 (let ((buf (window-buffer win)))
                   (unless (memq buf seen-buffers)
                     (set-buffer buf)
                     (when follow-mode
                       (let ((windows (follow-all-followers win)))
                         (if (not (memq picked-window windows))
                             (follow-redisplay windows win)
                           ;; Make sure we're redrawing around the selected
                           ;; window.
                           (select-window picked-window 'norecord)
                           (follow-post-command-hook)
                           (setq picked-window (selected-window))))
                       (push buf seen-buffers)))))
               'no-minibuf)
            (select-window picked-window 'norecord)))
        (select-frame orig-frame)))))

(add-hook 'window-scroll-functions 'follow-avoid-tail-recenter t)

;;; Low level window start and end.

;; These routines are the Follow Mode versions of the low level
;; functions described on page "Window Start and End" of the elisp
;; manual, e.g. `window-group-start'.  The aim is to be able to handle
;; Follow Mode windows by replacing `window-start' by
;; `window-group-start', etc.

(defun follow-after-change (_beg _end _old-len)
  "After change function: set `follow-start-end-invalid'."
  (setq follow-start-end-invalid t))

(defun follow-window-start (&optional window)
  "Return position at which display currently starts in the
Follow Mode group of windows which includes WINDOW.

WINDOW must be a live window and defaults to the selected one.
This is updated by redisplay or by calling
`follow-set-window-start'."
  (let ((windows (follow-all-followers window)))
    (window-start (car windows))))

(defun follow-window-end (&optional window update)
  "Return position at which display currently ends in the Follow
  Mode group of windows which includes WINDOW.

  WINDOW must be a live window and defaults to the selected one.
  This is updated by redisplay, when it runs to completion.
  Simply changing the buffer text or setting `window-start' does
  not update this value.

  Return nil if there is no recorded value.  (This can happen if
  the last redisplay of WINDOW was preempted, and did not
  finish.)  If UPDATE is non-nil, compute the up-to-date position
  if it isn't already recorded."
  (let* ((windows (follow-all-followers window))
         (last (car (last windows))))
    (when (and update follow-start-end-invalid)
      (follow-redisplay windows (car windows)))
    (window-end last update)))

(defun follow-set-window-start (window pos &optional noforce)
  "Make display in the Follow Mode group of windows which includes
WINDOW start at position POS in WINDOW's buffer.

WINDOW must be a live window and defaults to the selected one.  Return
POS.  Optional third arg NOFORCE non-nil inhibits next redisplay from
overriding motion of point in order to display at this exact start."
  (let ((windows (follow-all-followers window)))
    (setq follow-start-end-invalid t)
    (set-window-start (car windows) pos noforce)))

(defun follow-pos-visible-in-window-p (&optional pos window partially)
  "Return non-nil if position POS is currently on the frame in one of
  the windows in the Follow Mode group which includes WINDOW.

WINDOW must be a live window and defaults to the selected one.

Return nil if that position is scrolled vertically out of view.  If a
character is only partially visible, nil is returned, unless the
optional argument PARTIALLY is non-nil.  If POS is only out of view
because of horizontal scrolling, return non-nil.  If POS is t, it
specifies the position of the last visible glyph in WINDOW.  POS
defaults to point in WINDOW; WINDOW defaults to the selected window.

If POS is visible, return t if PARTIALLY is nil; if PARTIALLY is non-nil,
the return value is a list of 2 or 6 elements (X Y [RTOP RBOT ROWH VPOS]),
where X and Y are the pixel coordinates relative to the top left corner
of the actual window containing it.  The remaining elements are
omitted if the character after POS is fully visible; otherwise, RTOP
and RBOT are the number of pixels off-window at the top and bottom of
the screen line (\"row\") containing POS, ROWH is the visible height
of that row, and VPOS is the row number \(zero-based)."
  (let* ((windows (follow-all-followers window))
         (last (car (last windows))))
    (when follow-start-end-invalid
      (follow-redisplay windows (car windows)))
    (let* ((cache (follow-windows-start-end windows))
           (last-elt (car (last cache)))
           our-pos pertinent-elt)
      (setq pertinent-elt
            (if (eq pos t)
                last-elt
              (setq our-pos (or pos (point)))
              (catch 'element
                (while cache
                  (when (< our-pos (nth 2 (car cache)))
                    (throw 'element (car cache)))
                  (setq cache (cdr cache)))
                last-elt)))
      (pos-visible-in-window-p our-pos (car pertinent-elt) partially))))

(defun follow-move-to-window-line (arg)
  "Position point relative to the Follow mode group containing the selected window.
ARG nil means position point at center of the window group.
Else, ARG specifies vertical position within the window group;
zero means top of the first window in the group, negative means
  relative to bottom of the last window in the group."
  (let* ((windows (follow-all-followers))
         (start-end (follow-windows-start-end windows))
         (rev-start-end (reverse start-end))
         (lines 0)
         middle-window elt count)
    (select-window
     (cond
      ((null arg)
       (setq rev-start-end (nthcdr (/ (length windows) 2) rev-start-end))
       (prog1 (car (car rev-start-end))
         (while (setq rev-start-end (cdr rev-start-end))
           (setq elt (car rev-start-end)
                 count (count-screen-lines (cadr elt) (nth 2 elt)
                                           nil (car elt))
                 lines (+ lines count)))))
      ((>= arg 0)
       (while (and (cdr start-end)
                   (progn
                     (setq elt (car start-end)
                           count (count-screen-lines (cadr elt) (nth 2 elt)
                                                     nil (car elt)))
                     (>= arg count)))
         (setq arg (- arg count)
               lines (+ lines count)
               start-end (cdr start-end)))
       (car (car start-end)))
      (t                                ; (< arg 0)
       (while (and (cadr rev-start-end)
                   (progn
                     (setq elt (car rev-start-end)
                           count (count-lines (cadr elt) (nth 2 elt)))
                     (<= arg (- count))))
         (setq arg (+ arg count)
               rev-start-end (cdr rev-start-end)))
       (prog1 (car (car rev-start-end))
         (while (setq rev-start-end (cdr rev-start-end))
           (setq elt (car rev-start-end)
                 count (count-screen-lines (cadr elt) (nth 2 elt)
                                           nil (car elt))
                 lines (+ lines count)))))))
    (+ lines (move-to-window-line arg))))

;;; Profile support

;; The following (non-evaluated) section can be used to
;; profile this package using `elp'.
;;
;; Invalid indentation on purpose!

;; (setq elp-function-list
;;       '(window-end
;; 	vertical-motion
;; 	follow-mode
;; 	follow-all-followers
;; 	follow-split-followers
;; 	follow-redisplay
;; 	follow-estimate-first-window-start
;; 	follow-calculate-first-window-start-from-above
;; 	follow-calculate-first-window-start-from-below
;; 	follow-calc-win-end
;; 	follow-calc-win-start
;; 	follow-pos-visible
;; 	follow-windows-start-end
;; 	follow-cache-valid-p
;; 	follow-select-if-visible
;; 	follow-select-if-visible-from-first
;; 	follow-windows-aligned-p
;; 	follow-point-visible-all-windows-p
;; 	follow-avoid-tail-recenter
;; 	follow-update-window-start
;; 	follow-post-command-hook))

(provide 'follow)

;; /------------------------------------------------------------------------\
;; | "I [..] am rarely happier then when spending an entire day programming |
;; | my computer to perform automatically a task that it would otherwise    |
;; | take me a good ten seconds to do by hand. Ten seconds, I tell myself,  |
;; | is ten seconds. Time is valuable and ten seconds' worth of it is well  |
;; | worth the investment of a day's happy activity working out a way to    |
;; | save it".             -- Douglas Adams, "Last Chance to See"           |
;; \------------------------------------------------------------------------/

;;; follow.el ends here

debug log:

solving c510e5a ...
found c510e5a in https://git.savannah.gnu.org/cgit/emacs.git

(*) Git path names are given by the tree(s) the blob belongs to.
    Blobs themselves have no identifier aside from the hash of its contents.^

Code repositories for project(s) associated with this public inbox

	https://git.savannah.gnu.org/cgit/emacs.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).