Re: git grep --show-function treats GOTO labels as function names

[Jeff King <peff@peff.net>]

On Wed, May 27, 2020 at 06:04:21PM -0500, Zach Riggle wrote:

> It looks like that does the trick for "goto" labels, but there are
> also some issue on function name parsing with attributes when they are
> split onto a second line.
> 
> $ cat attr.cpp
> int main() __attribute__ ( (no_sanitize("alignment")) )
> {
>     FOO
> }
> $ git grep --no-index --show-function -e FOO attr.cpp
> attr.cpp=2=__attribute__ ( (no_sanitize("alignment")) )
> attr.cpp:4:    FOO

From your output, I assume the problematic input actually splits the
attribute onto the second line?

I agree that's not ideal. The baked-in regex we use for matching C
function lines is:

  $ git grep -nA4 cpp userdiff.c
  userdiff.c:173:PATTERNS("cpp",
  userdiff.c-174-  /* Jump targets or access declarations */
  userdiff.c-175-  "!^[ \t]*[A-Za-z_][A-Za-z_0-9]*:[[:space:]]*($|/[/*])\n"
  userdiff.c-176-  /* functions/methods, variables, and compounds at top level */
  userdiff.c-177-  "^((::[[:space:]]*)?[A-Za-z_].*)$",

so we mistake it for a function name. I'm not sure how easy it is to do
better, though. We can add a line like:

diff --git a/userdiff.c b/userdiff.c
index 1df884ef0b..de8e1a3d72 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -173,6 +173,8 @@ PATTERNS("tex", "^(\\\\((sub)*section|chapter|part)\\*{0,1}\\{.*)$",
 PATTERNS("cpp",
 	 /* Jump targets or access declarations */
 	 "!^[ \t]*[A-Za-z_][A-Za-z_0-9]*:[[:space:]]*($|/[/*])\n"
+	 /* skip over attribute declarations are on their own lines */
+	 "!((::[[:space:]]*))?__attribute__\n"
 	 /* functions/methods, variables, and compounds at top level */
 	 "^((::[[:space:]]*)?[A-Za-z_].*)$",
 	 /* -- */

which works for your case, but would regress:

  __attribute__((whatever) int main()
  {
  FOO
  }

Handling both means skipping past the attribute, not counting it as a
function, and then checking for a plausible function afterwards. That's
a much trickier regex. But if you come up with something that works, I
think we'd be happy to take a patch. :)

You can also just override this regex via config for your personal use.
If you know you'd never use that style, then the problem becomes much
easier.

-Peff