bug#50236: 27.2; electric-pair-mode is inconvenient in comint

From ca8bb2aaff67e3663628eb814800b81b0c1160b4 Mon Sep 17 00:00:00 2001
From: Andrew Hyatt <[email protected]>
Date: Sun, 16 Aug 2026 12:31:55 +0100
Subject: [PATCH] Make electric-pair-mode respect field boundaries (bug#50236)
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Among other potential benefits, this makes e-p-m work correctly in all
comint-based modes.

* lisp/elec-pair.el (electric-pair-field-search-size): New variable.
(electric-pair-post-self-insert-function): Tweak.
(electric--pair-psif-1)

* etc/NEWS: Call out change.

* lisp/comint.el (electric-pair-field-search-size): forward-declare.
(comint-mode): Set electric-pair-field-search-size to 1000.

* test/lisp/electric-tests.el (preserve-balance)
(preserve-balance-not-across-fields): New tests.

Co-authored-by: João Távora <[email protected]>
---
 etc/NEWS                    |  7 +++++++
 lisp/comint.el              |  5 ++++-
 lisp/elec-pair.el           | 24 +++++++++++++++++++++++-
 test/lisp/electric-tests.el | 26 +++++++++++++++++++++++++-
 4 files changed, 59 insertions(+), 3 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 5f5f59d2a9f..fe662e4421d 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -972,6 +972,13 @@ To use this, add a list to both electric pair user options: '("/*" . "*/")'.
 You can also specify that an extra space should be inserted after the
 first string, like this: '("/*" " */" t)'.
 
+*** Electric pair mode can restrict operation to nearby fields
+This is particularly useful in comint-based modes (like Eshell) and
+other situations where process output may contain unpaired delimiters,
+while keeping delimiters you insert balanced. The
+''electric-pair-field-search-size'' variable controls the search
+distance for nearby fields.
+
 ---
 ** New user option 'electric-indent-actions'.
 This user option specifies a list of actions to reindent.  The possible
diff --git a/lisp/comint.el b/lisp/comint.el
index e5418f4ee67..3018717c937 100644
--- a/lisp/comint.el
+++ b/lisp/comint.el
@@ -702,6 +702,8 @@ comint-stored-incomplete-input
 
 (put 'comint-mode 'mode-class 'special)
 
+(defvar electric-pair-field-search-size)
+
 (define-derived-mode comint-mode fundamental-mode "Comint"
   "Major mode for interacting with an inferior interpreter.
 Interpreter name is same as buffer name, sans the asterisks.
@@ -792,7 +794,8 @@ comint-mode
   (add-hook 'isearch-mode-hook #'comint-history-isearch-setup nil t)
   (add-hook 'completion-at-point-functions #'comint-completion-at-point nil t)
   ;; This behavior is not useful in comint buffers, and is annoying
-  (setq-local next-line-add-newlines nil))
+  (setq-local next-line-add-newlines nil)
+  (setq electric-pair-field-search-size 1000))
 
 (defun comint-check-proc (buffer)
   "Return non-nil if there is a living process associated w/buffer BUFFER.
diff --git a/lisp/elec-pair.el b/lisp/elec-pair.el
index 54fbc960b0f..d7ae555e408 100644
--- a/lisp/elec-pair.el
+++ b/lisp/elec-pair.el
@@ -596,10 +596,32 @@ electric-pair-default-inhibit
       (electric-pair-inhibit-if-helps-balance char)
     (electric-pair-conservative-inhibit char)))
 
+(defvar electric-pair-field-search-size nil
+  "How far to look for nearby fields to restrict `electric-pair-mode'.
+
+If nil, do not look for nearby fields and use the accessible portion of
+the buffer.  If a integer number of characters, look at most that far
+backward and forward for a field boundary.  If one isn't found, use the
+accessible portion of the buffer in that direction.")
+
 (defun electric-pair-post-self-insert-function ()
   "Do main work for `electric-pair-mode'.
 This function is added to `post-self-insert-hook' when
-`electric-pair-mode' is enabled.
+`electric-pair-mode' is enabled."
+  ;; First, figure out whether to restrit the buffer (bug#50236)
+  (if (or (null electric-pair-field-search-size)
+          (use-region-p))
+      (electric--pair-psif-1)
+    (let* ((min (- (point) electric-pair-field-search-size))
+           (max (+ (point) electric-pair-field-search-size))
+           (beg (field-beginning nil nil (max (point-min) min)))
+           (end (field-end nil nil (min (point-max) max))))
+      (with-restriction
+          (if (= min beg) (point-min) beg) (if (= max end) (point-max) end)
+        (electric--pair-psif-1)))))
+
+(defun electric--pair-psif-1 ()
+  "Do main work for `electric-pair-post-self-insert-function.'
 
 If the newly inserted character C has delimiter syntax, this
 function may decide to insert additional paired delimiters, or
diff --git a/test/lisp/electric-tests.el b/test/lisp/electric-tests.el
index 9209e1739fd..d678279c8cc 100644
--- a/test/lisp/electric-tests.el
+++ b/test/lisp/electric-tests.el
@@ -703,7 +703,31 @@ autowrapping-multi-2
                 (goto-char (point-max))
                 (skip-chars-backward "\"")
                 (mark-sexp -1)))
-
+
+(define-electric-pair-test preserve-balance
+ "\"\n\n" "---\""
+ :expected-string "\"\n\n\""
+ :expected-point 5
+ :modes '(fundamental-mode)
+ :test-in-comments nil
+ :test-in-strings nil
+ :bindings '((electric-pair-preserve-balance . t))
+ :fixture-fn (lambda ()
+               (electric-pair-mode 1)))
+
+(define-electric-pair-test preserve-balance-not-across-fields
+ "\"\n\n" "---\""
+ :expected-string "\"\n\n\"\""
+ :expected-point 5
+ :modes '(fundamental-mode)
+ :test-in-comments nil
+ :test-in-strings nil
+ :bindings '((electric-pair-preserve-balance . t)
+             (electric-pair-field-search-size . 100))
+ :fixture-fn (lambda ()
+               (electric-pair-mode 1)
+               (add-text-properties (point-min) (+ (point-min) 2)
+                                    '(field t))))
 
 ;;; Electric quotes
 (define-electric-pair-test electric-quote-string
-- 
2.54.0