Re: [bug-gawk] Warning message issued with no source line number [PATCH]

[Arnold Robbins]

Hi.

> Date: Wed, 17 May 2017 13:41:49 -0400
> From: "Andrew J. Schorr" <address@hidden>
> To: "Peter J. Farley III" <address@hidden>
> Subject: Re: [bug-gawk] Warning message issued with no source line number
>  [PATCH]
> Cc: address@hidden
> Errors-To: address@hidden
>
> On Tue, May 16, 2017 at 11:34:25PM -0400, Peter J. Farley III wrote:
> > > Here's a simpler version:
> > > 
> > > bash-4.2$ cat /tmp/test.awk
> > > BEGIN {
> > >       "a" 1
> > > }
> > > bash-4.2$ gawk --lint -f /tmp/test.awk
> > > gawk: warning: statement may have no effect
> > > 
> > > Interestingly, if the "1" is removed, there is no warning at all:
> > > 
> > > bash-4.2$ cat /tmp/test.awk
> > > BEGIN {
> > >       "a"
> > > }
> > > bash-4.2$ gawk --lint -f /tmp/test.awk
> > > bash-4.2$
> > > 
> > > But still we need to find the bug...
> > 
> > Interesting bug.  Thanks for the update.
>
> The problem is due to an Op_concat instruction that has source_line set to 0.
> The message printed by msg.c:err includes the source filename and line only if
> sourceline is positive. The attached patch seems to fix this particular
> problem, but it seems like a bit of a hack. I await confirmation from Arnold
> that this is the right way to solve this issue.
>
> Regards,
> Andy

Hi Andy,

Your patch fixes the problem locally. The following change looks to be more
general and catches the issue.

The byte code for 'BEGIN { "a" }' seems to not be caught by add_lint().
That's more work than I have time for right now.

Andy - does this look OK to you to commit?

Thanks,

Arnold
-----------------------------------------------------
diff --git a/awkgram.y b/awkgram.y
index b72d1c8..e4cedca 100644
--- a/awkgram.y
+++ b/awkgram.y
@@ -5886,6 +5886,7 @@ add_lint(INSTRUCTION *list, LINTTYPE linttype)
 {
 #ifndef NO_LINT
        INSTRUCTION *ip;
+       int line = 0;
 
        switch (linttype) {
        case LINT_assign_in_cond:
@@ -5904,12 +5905,16 @@ add_lint(INSTRUCTION *list, LINTTYPE linttype)
 
        case LINT_no_effect:
                if (list->lasti->opcode == Op_pop && list->nexti != 
list->lasti) {
-                       for (ip = list->nexti; ip->nexti != list->lasti; ip = 
ip->nexti)
-                               ;
-
+                       for (ip = list->nexti; ip->nexti != list->lasti; ip = 
ip->nexti) {
+                               if (line == 0 && ip->source_line != 0)
+                                       line = ip->source_line;
+                       } 
                        if (do_lint) {          /* compile-time warning */
-                               if (isnoeffect(ip->opcode))
-                                       lintwarn_ln(ip->source_line, 
("statement may have no effect"));
+                               if (isnoeffect(ip->opcode)) {
+                                       if (ip->source_line != 0)
+                                               line = ip->source_line;
+                                       lintwarn_ln(line, ("statement may have 
no effect"));
+                               }
                        }
 
                        if (ip->opcode == Op_push) {            /* run-time 
warning */