Re: [PATCH] merge-file: fix build warning with gcc 4.8.5

[Jeff King <peff@peff.net>]

On Fri, Jul 29, 2022 at 08:48:46AM -0700, Junio C Hamano wrote:

> I think the concensus was that we should squelch the false warning
> on older compilers with -Wno-missing-braces, but then the discussion
> has stalled by a suggestion to introduce a way to detect older
> compilers that is different from how we do so at the same time, and
> went nowhere.
> 
> Hopefully we can add a simple -Wno-* without waiting for whole
> config.mak thing getting revamped this time?

Perhaps this?

-- >8 --
Subject: [PATCH] config.mak.dev: squelch -Wno-missing-braces for older gcc

Versions of gcc prior to 4.9 complain about an initialization like:

  struct inner { int x; };
  struct outer { struct inner; };
  struct outer foo = { 0 };

and insist on:

  struct outer foo = { { 0 } };

Newer compilers handle this just fine. And ignoring the window even on
older compilers is fine; the resulting code is correct, but we just get
caught by -Werror.

Let's relax this for older compilers to make developer lives easier (we
don't care much about non-developers on old compilers; they may see a
warning, but it won't stop compilation).

Signed-off-by: Jeff King <peff@peff.net>
---
Tested on a debian jessie chroot using gcc-4.8 and 4.9. Though note that
you also need to manually specify -std=gnu99 to get it to work at all
with those compilers these days! So I kind of wonder if it's even worth
catering to their warnings automatically.

 config.mak.dev | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/config.mak.dev b/config.mak.dev
index 335efd4620..b9878a4994 100644
--- a/config.mak.dev
+++ b/config.mak.dev
@@ -59,9 +59,13 @@ endif
 
 # uninitialized warnings on gcc 4.9.2 in xdiff/xdiffi.c and config.c
 # not worth fixing since newer compilers correctly stop complaining
+#
+# Likwise, gcc older than 4.9 complains about initializing a
+# struct-within-a-struct using just "{ 0 }"
 ifneq ($(filter gcc4,$(COMPILER_FEATURES)),)
 ifeq ($(filter gcc5,$(COMPILER_FEATURES)),)
 DEVELOPER_CFLAGS += -Wno-uninitialized
+DEVELOPER_CFLAGS += -Wno-missing-braces
 endif
 endif
 
-- 
2.37.1.804.g1775fa20e0