Document that flymake-diag-region saves match data

The typical use of this function (which is parsing compiler diagnostic
messages), lends itself too easily to one the problems in bug#29193.
Make it a friendlier API.

* doc/misc/flymake.texi (Flymake utility functions): Document that
flymake-diag-region saves match data.

* lisp/progmodes/flymake.el (flymake-diag-region): Document that
this saves match data.

2 files changed, 2 insertions, 2 deletions

diff --git a/doc/misc/flymake.texi b/doc/misc/flymake.texi
index b4757938e99..f4fc26d896b 100644
--- a/doc/misc/flymake.texi
+++ b/doc/misc/flymake.texi
@@ -581,7 +581,7 @@ can use the following function:
 Compute @var{buffer}'s region (@var{beg} .  @var{end}) corresponding
 to @var{line} and @var{col}.  If @var{col} is @code{nil}, return a
 region just for @var{line}.  Return @code{nil} if the region is
-invalid.
+invalid.  This function saves match data (@pxref{Saving Match Data}).
 @end deffn
 
 @cindex add a log message
diff --git a/lisp/progmodes/flymake.el b/lisp/progmodes/flymake.el
index dfb4f18cff7..40bb90d0f15 100644
--- a/lisp/progmodes/flymake.el
+++ b/lisp/progmodes/flymake.el
@@ -412,7 +412,7 @@ verify FILTER, a function, and sort them by COMPARE (using KEY)."
 (defun flymake-diag-region (buffer line &optional col)
   "Compute BUFFER's region (BEG . END) corresponding to LINE and COL.
 If COL is nil, return a region just for LINE.  Return nil if the
-region is invalid."
+region is invalid.  This function saves match data."
   (condition-case-unless-debug _err
       (with-current-buffer buffer
         (let ((line (min (max line 1)