bug#45536: [PATCH] Pretty-print keys without <> around modifiers

["Mattias Engdegård" <mattiase@acm.org>]

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It is a bit inconsistent that keys are described as C-x and <return> but <C-return>. It would be more logical to write C-<return>. The key parser will happily accept either, but descriptions without modifiers in <> brackets are more legible, and the result is easier to understand and explain.

Attached is a patch which adapts the code that pretty-prints keys. This is a change for human consumption only; it seems unlikely to affect compatibility. With the patch, <C-M-backspace> is now printed as C-M-<backspace>.

I'd be happy to update the manuals accordingly, and add a NEWS entry if required.


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From 18c9fc433f75a286abcd459abb77b2667d650021 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Tue, 29 Dec 2020 16:55:06 +0100
Subject: [PATCH] Pretty-print keys without <> around modifiers

Be consistent when pretty-printing keys: put modifiers outside <>,
thus the more logical C-M-<return> instead of <C-M-return>.

* src/keymap.c (Fsingle_key_description):
Skip modifier prefix before adding <>.
---
 src/keymap.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/keymap.c b/src/keymap.c
index ca2d33dba4..d3cde8e7ab 100644
--- a/src/keymap.c
+++ b/src/keymap.c
@@ -2260,11 +2260,21 @@ DEFUN ("single-key-description", Fsingle_key_description,
     {
       if (NILP (no_angles))
 	{
-	  Lisp_Object result;
-	  char *buffer = SAFE_ALLOCA (sizeof "<>"
-				      + SBYTES (SYMBOL_NAME (key)));
-	  esprintf (buffer, "<%s>", SDATA (SYMBOL_NAME (key)));
-	  result = build_string (buffer);
+	  Lisp_Object namestr = SYMBOL_NAME (key);
+	  const char *sym = SSDATA (namestr);
+	  ptrdiff_t len = SBYTES (namestr);
+	  /* Find the extent of the modifier prefix, like "C-M-". */
+	  int i = 0;
+	  while (i < len - 3 && sym[i + 1] == '-' && strchr ("CMSsHA", sym[i]))
+	    i += 2;
+	  /* First I bytes of SYM are modifiers; put <> around the rest. */
+	  char *buffer = SAFE_ALLOCA (len + 3);
+	  memcpy (buffer, sym, i);
+	  buffer[i] = '<';
+	  memcpy (buffer + i + 1, sym + i, len - i);
+	  buffer [len + 1] = '>';
+	  buffer [len + 2] = '\0';
+	  Lisp_Object result = build_string (buffer);
 	  SAFE_FREE ();
 	  return result;
 	}
-- 
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