From: Philipp Stephani <phst@google.com>
Date: Fri, 16 Jun 2017 22:13:51 +0000 (+0200)
Subject: Say that side effect-free functions don't change the matchd data
X-Git-Tag: emacs-27.0.90~6262
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=f4995e7d36b576d9ed629b45dd3b09ba6d28cce7;p=emacs.git

Say that side effect-free functions don't change the matchd data

* lisp/help-fns.el (describe-function-1): Add note if a function is
known not to change the match data.
---

diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index d75fec2b564..788c03e9bf5 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -709,6 +709,10 @@ Returns a list of the form (REAL-FUNCTION DEF ALIASED REAL-DEF)."
                   real-function key-bindings-buffer)))
         (run-hook-with-args 'help-fns-describe-function-functions function)
         (insert "\n" (or doc "Not documented.")))
+      (when (or (function-get function 'pure)
+                (function-get function 'side-effect-free))
+        (insert "\nThis function does not change global state, "
+                "including the match data."))
       ;; Avoid asking the user annoying questions if she decides
       ;; to save the help buffer, when her locale's codeset
       ;; isn't UTF-8.