Re: C warning in MSYS2 build

[Paul Eggert <eggert@cs.ucla.edu>]

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On 10/05/2017 11:54 AM, Eli Zaretskii wrote:
> Thanks, but it isn't new.

In my experience this kind of warning can appear and vanish almost at 
whim: compiling at a different optimization levels, or changing 
compilation in some other way, can cause GCC to omit or include the 
warning. So possibly Richard wasn't getting the warning a day ago, but 
got the warning after changing from -O2 to -O0 (or whatever), or by 
upgrading GCC.

If it's a major annoyance we could disable --Wnull-dereference for 
indent.c. I hope that's not needed, though.

Come to think of it, last year I filed a GCC bug report about a similar 
problem with lib-src/etags.c and -Wnull-dereference, here:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71157

The GCC bug is not fixed yet. etags.c confused GCC by using an 
assignment inside an 'if' expression, which is contrary to the usual GNU 
style, and last year I worked around the GCC bug by changing etags.c to 
use a cleaner style. I notice that indent.c also has an assignment 
inside an 'if' expression that is relevant to these warnings. Richard, 
does it help to recode indent.c to use the usual GNU style, as in the 
attached patch? If so, let's do that instead. (Perhaps we should do that 
anyway....)


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diff --git a/src/indent.c b/src/indent.c
index 26507b5eb5..79841a3d2c 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -76,15 +76,17 @@ buffer_display_table (void)
 static int
 character_width (int c, struct Lisp_Char_Table *dp)
 {
-  Lisp_Object elt;
-
   /* These width computations were determined by examining the cases
      in display_text_line.  */
 
   /* Everything can be handled by the display table, if it's
      present and the element is right.  */
-  if (dp && (elt = DISP_CHAR_VECTOR (dp, c), VECTORP (elt)))
-    return ASIZE (elt);
+  if (dp)
+    {
+      Lisp_Object elt = DISP_CHAR_VECTOR (dp, c);
+      if (VECTORP (elt))
+	return ASIZE (elt);
+    }
 
   /* Some characters are special.  */
   if (c == '\n' || c == '\t' || c == '\015')