From 5188d6e366426d83934505296b585744f50e24a5 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Sun, 12 Mar 2017 23:59:19 -0400
Subject: [PATCH] Don't reparse the sexp in indent-sexp (Bug#25122)

* lisp/emacs-lisp/lisp-mode.el (calculate-lisp-indent): Let
PARSE-START be a parse state that can be reused.
(indent-sexp): Pass the running parse state to calculate-lisp-indent
instead of the sexp beginning position.
---
 lisp/emacs-lisp/lisp-mode.el | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/lisp/emacs-lisp/lisp-mode.el b/lisp/emacs-lisp/lisp-mode.el
index eb07c18b03..8d4abc24e8 100644
--- a/lisp/emacs-lisp/lisp-mode.el
+++ b/lisp/emacs-lisp/lisp-mode.el
@@ -781,6 +781,10 @@ calculate-lisp-indent
 If the value is nil, that means don't change the indentation
 because the line starts inside a string.
 
+PARSE-START may be a buffer position to start parsing from, or a
+parse state as returned by calling `parse-partial-sexp' up to the
+beginning of the current line.
+
 The value can also be a list of the form (COLUMN CONTAINING-SEXP-START).
 This means that following lines at the same level of indentation
 should not necessarily be indented the same as this line.
@@ -794,12 +798,14 @@ calculate-lisp-indent
           (desired-indent nil)
           (retry t)
           calculate-lisp-indent-last-sexp containing-sexp)
-      (if parse-start
-          (goto-char parse-start)
-          (beginning-of-defun))
-      ;; Find outermost containing sexp
-      (while (< (point) indent-point)
-        (setq state (parse-partial-sexp (point) indent-point 0)))
+      (cond ((or (markerp parse-start) (integerp parse-start))
+             (goto-char parse-start))
+            ((null parse-start) (beginning-of-defun))
+            (t (setq state parse-start)))
+      (unless state
+        ;; Find outermost containing sexp
+        (while (< (point) indent-point)
+          (setq state (parse-partial-sexp (point) indent-point 0))))
       ;; Find innermost containing sexp
       (while (and retry
 		  state
@@ -1070,11 +1076,6 @@ indent-sexp
 ENDPOS is encountered."
   (interactive)
   (let* ((indent-stack (list nil))
-         ;; If ENDPOS is non-nil, use beginning of defun as STARTING-POINT.
-         ;; If ENDPOS is nil, it is safe not to scan before point
-         ;; since every line we indent is more deeply nested than point is.
-         (starting-point (save-excursion (if endpos (beginning-of-defun))
-                                         (point)))
          ;; Use `syntax-ppss' to get initial state so we don't get
          ;; confused by starting inside a string.  We don't use
          ;; `syntax-ppss' in the loop, because this is measurably
@@ -1132,8 +1133,12 @@ indent-sexp
           (unless (or (eolp) (eq (char-syntax (char-after)) ?<))
             (let ((this-indent (car indent-stack)))
               (when (listp this-indent)
-                (let ((val (calculate-lisp-indent
-                            (or (car this-indent) starting-point))))
+                ;; The state here is actually to the end of the
+                ;; previous line, but that's fine for our purposes.
+                ;; And continuing the parse to the next line would
+                ;; destroy element 2 (last sexp position) which
+                ;; `calculate-lisp-indent' needs.
+                (let ((val (calculate-lisp-indent state)))
                   (setq
                    this-indent
                    (cond ((integerp val)
-- 
2.11.1