bug#58601: 29.0.50; Infinite loop in byte-compile--first-symbol-with-pos

["Basil L. Contovounesios" via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Given this sample input file:


[-- Attachment #2: my.el --]
[-- Type: application/emacs-lisp, Size: 429 bytes --]

[-- Attachment #3: Type: text/plain, Size: 240 bytes --]


Byte-compiling it as follows hangs indefinitely:
  
  emacs -Q -batch -f batch-byte-compile my.el

While it's hanging, might as well poke it:

  pkill -f 'batch-byte-compile my\.el' -SIGUSR2  

To which it yields the following backtrace:


[-- Attachment #4: backtrace.txt --]
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Debugger entered--Lisp error: (quit)
  byte-compile--first-symbol-with-pos((t . #1))
  byte-compile--first-symbol-with-pos('(t . #2))
  byte-compile--first-symbol-with-pos((progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #5)))
  byte-compile--first-symbol-with-pos(((my-cycle) (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) (progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #8)) (setcar value-0 (progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #12))) (unwind-protect (setcar value-0 (progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #15))) :fun-body (internal-make-closure nil (form-description-1 value-0) nil (setcar (internal-get-closed-var 0) (list '(should ...) :form '(progn ... ...) :value (car-safe (internal-get-closed-var 1)))) (ert--signal-should-execution (car-safe (internal-get-closed-var 0))))) (let ((form-description-1 (list nil))) (unwind-protect (setcar value-0 (progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #19))) :fun-body (internal-make-closure nil (form-description-1 value-0) nil (setcar (internal-get-closed-var 0) (list '... :form '... :value (car-safe ...))) (ert--signal-should-execution (car-safe (internal-get-closed-var 0)))))) (let ((value-0 (list (gensym "ert-form-evaluation-aborted-")))) (let ((form-description-1 (list nil))) (unwind-protect (setcar value-0 (progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '...)) :fun-body (internal-make-closure nil (form-description-1 value-0) nil (setcar (internal-get-closed-var 0) (list ... :form ... :value ...)) (ert--signal-should-execution (car-safe ...))))) (car-safe value-0)) #'(lambda nil (let ((value-0 (list ...))) (let ((form-description-1 ...)) (if (unwind-protect ... :fun-body ...) nil (ert-fail ...))) (car-safe value-0))) (record 'ert-test 'my-test nil #'(lambda nil (let ((value-0 ...)) (let (...) (if ... nil ...)) (car-safe value-0))) nil :passed nil "/tmp/my.el") (ert-set-test 'my-test (record 'ert-test 'my-test nil #'(lambda nil (let (...) (let ... ...) (car-safe value-0))) nil :passed nil "/tmp/my.el")) (ert-deftest my-test nil (should (my-identity (my-cycle))))))
  byte-compile--warning-source-offset()
  byte-compile-log-warning("Oh dear" t :warning)
  byte-compile-warn("%s" "Oh dear")
  apply(byte-compile-warn "%s" "Oh dear")
  byte-compile-warn-x((my-cycle) "%s" "Oh dear")
  #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)()
  #f(compiled-function (form) #<bytecode -0x384fa88d0504449>)((macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)))
  byte-compile-form((macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) t)
  byte-compile-body(((macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #4)) nil)
  byte-compile-progn((progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #5)))
  byte-compile-form((progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #5)))
  byte-compile-two-args((setcar value-0 (progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #8))))
  byte-compile-form((setcar value-0 (progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #8))) t)
  byte-compile-unwind-protect((unwind-protect (setcar value-0 (progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #10))) :fun-body (internal-make-closure nil (form-description-1 value-0) nil (setcar (internal-get-closed-var 0) (list '(should (my-identity ...)) :form '(progn (macroexp--funcall-if-compiled ...) (my-cycle)) :value (car-safe (internal-get-closed-var 1)))) (ert--signal-should-execution (car-safe (internal-get-closed-var 0))))))
  byte-compile-form((unwind-protect (setcar value-0 (progn (macroexp--funcall-if-compiled #f(compiled-function () #<bytecode 0xe3f7c0047f6bb37>)) '(t . #10))) :fun-body (internal-make-closure nil (form-description-1 value-0) nil (setcar (internal-get-closed-var 0) (list '(should (my-identity ...)) :form '(progn (macroexp--funcall-if-compiled ...) (my-cycle)) :value (car-safe (internal-get-closed-var 1)))) (ert--signal-should-execution (car-safe (internal-get-closed-var 0))))) t)
...
  byte-compile-form((record 'ert-test 'my-test nil #'(lambda nil (let ((value-0 (list ...))) (let ((form-description-1 ...)) (if (unwind-protect ... :fun-body ...) nil (ert-fail ...))) (car-safe value-0))) nil :passed nil "/tmp/my.el"))
  mapc(byte-compile-form ('my-test (record 'ert-test 'my-test nil #'(lambda nil (let ((value-0 ...)) (let (...) (if ... nil ...)) (car-safe value-0))) nil :passed nil "/tmp/my.el")))
  byte-compile-normal-call((ert-set-test 'my-test (record 'ert-test 'my-test nil #'(lambda nil (let ((value-0 ...)) (let (...) (if ... nil ...)) (car-safe value-0))) nil :passed nil "/tmp/my.el")))
  byte-compile-form((ert-set-test 'my-test (record 'ert-test 'my-test nil #'(lambda nil (let ((value-0 ...)) (let (...) (if ... nil ...)) (car-safe value-0))) nil :passed nil "/tmp/my.el")) t)
  byte-compile-keep-pending((ert-set-test 'my-test (record 'ert-test 'my-test nil #'(lambda nil (let ((value-0 ...)) (let (...) (if ... nil ...)) (car-safe value-0))) nil ':passed 'nil "/tmp/my.el")))
  byte-compile-file-form((ert-set-test 'my-test (record 'ert-test 'my-test nil #'(lambda nil (let ((value-0 ...)) (let (...) (if ... nil ...)) (car-safe value-0))) nil ':passed 'nil "/tmp/my.el")))
  #f(compiled-function (form) #<bytecode -0x1079b636bff336ff>)((ert-set-test 'my-test (record 'ert-test 'my-test nil #'(lambda nil (let ((value-0 ...)) (let (form-description-1) (if ... nil ...)) value-0)) nil ':passed 'nil "/tmp/my.el")))
  byte-compile-recurse-toplevel((ert-set-test 'my-test (record 'ert-test 'my-test nil #'(lambda nil (let ((value-0 ...)) (let (form-description-1) (if ... nil ...)) value-0)) nil ':passed 'nil "/tmp/my.el")) #f(compiled-function (form) #<bytecode -0x1079b636bff336ff>))
  #f(compiled-function (subform) #<bytecode -0x88ecb93aa9a0d82>)((ert-set-test 'my-test (record 'ert-test 'my-test nil #'(lambda nil (let ((value-0 ...)) (let (form-description-1) (if ... nil ...)) value-0)) nil ':passed 'nil "/tmp/my.el")))
  mapcar(#f(compiled-function (subform) #<bytecode -0x88ecb93aa9a0d82>) ((ert-set-test 'my-test (record 'ert-test 'my-test nil #'(lambda nil (let (...) (let ... ...) value-0)) nil ':passed 'nil "/tmp/my.el")) 'my-test))
  byte-compile-recurse-toplevel((ert-deftest my-test nil (should (my-identity (my-cycle)))) #f(compiled-function (form) #<bytecode -0x1079b636bff336ff>))
  byte-compile-toplevel-file-form((ert-deftest my-test nil (should (my-identity (my-cycle)))))
  #f(compiled-function (inbuffer) #<bytecode 0x1c4a7e9ef683d101>)(#<buffer  *Compiler Input*>)
  byte-compile-from-buffer(#<buffer  *Compiler Input*>)
  byte-compile-file("my.el")
  batch-byte-compile-file("my.el")
  batch-byte-compile()
  command-line-1(("-f" "batch-byte-compile" "my.el"))
  command-line()
  normal-top-level()

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I.e. the 'pure' compile-time form has a cycle, and the DFS of
byte-compile--first-symbol-with-pos gets lost.  Paraphrasing Stefan,
it's acceptable if the compiler mishandles circular source code, but it
should be able to handle circular data.

I don't know why, but I can reproduce the hang only when the form is inside
ert-deftest+should, and not inside a plain defun.

Perhaps byte-compile--first-symbol-with-pos needs to employ something
like byte-run--ssp-seen?  Or does ERT somehow come into play?

Thanks,

-- 
Basil

In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.16.0, Xaw3d scroll bars) of 2022-10-18 built on tia
Repository revision: c2b79d9148f21c3717f1eaa2d37b837b0922b94c
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101004
System Description: Debian GNU/Linux bookworm/sid

Configured using:
 'configure 'CFLAGS=-Og -ggdb3' -C --prefix=/home/blc/.local
 --enable-checking=structs --with-file-notification=yes
 --with-x-toolkit=lucid --with-x'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS WEBP X11 XAW3D XDBE XIM XINPUT2 XPM LUCID ZLIB

Important settings:
  value of $LANG: en_IE.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
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  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
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  indent-tabs-mode: t
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Load-path shadows:
None found.

Features:
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Memory information:
((conses 16 36538 7652)
 (symbols 48 5112 0)
 (strings 32 13853 1864)
 (string-bytes 1 382346)
 (vectors 16 9260)
 (vector-slots 8 147212 11667)
 (floats 8 23 25)
 (intervals 56 242 0)
 (buffers 1000 10))