[v2] config.mak.dev: disable suggest braces error on old clang versions

Commit Message

Jeff Hostetler Oct. 10, 2022, 3:39 p.m. UTC

From: Jeff Hostetler <[e-mail]>

Add the "-Wno-missing-braces" option when building with an old version
of clang to suppress the "suggest braces around initialization" error
in developer mode.

For example, using an old version of clang gives the following errors
(when in DEVELOPER=1 mode):

$ make builtin/merge-file.o
    CC builtin/merge-file.o
builtin/merge-file.c:29:23: error: suggest braces around initialization \
			    of subobject [-Werror,-Wmissing-braces]
        mmfile_t mmfs[3] = { 0 };
                             ^
                             {}
builtin/merge-file.c:31:20: error: suggest braces around initialization \
			    of subobject [-Werror,-Wmissing-braces]
        xmparam_t xmp = { 0 };
                          ^
                          {}
2 errors generated.

This example compiles without error/warning with updated versions of
clang.  Since this is an obsolete error, use the -Wno-missing-braces
option to silence the warning when using an older compiler.  This
avoids the need to update the code to use "{{0}}" style
initializations.

Upstream clang version 8 has the problem.  It was fixed in version 9.

The version of clang distributed by Apple with XCode has its own
unique set of version numbers.  Apple clang version 11 has the
problem.  It was fixed in version 12.

Signed-off-by: Jeff Hostetler <[e-mail]>
---
    Fix syntax errors under clang 11.0.0 on MacOS
    
    Here is version 2. This version adds the "-Wno-missing-braces" compiler
    flag when we are using an old version of clang -- rather than updating
    the source files to use the "{{0}}" syntax that was expected by older
    versions of clang.
    
    I've expanded the scope to include fixes for Apple's clang 11 and below
    and non-Apple clang 8 and below.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1375%2Fjeffhostetler%2Ffix-clang11-warnings-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1375/jeffhostetler/fix-clang11-warnings-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1375

Range-diff vs v1:

 1:  7cee38788a7 < -:  ----------- builtin/merge-file: fix compiler error on MacOS with clang 11.0.0
 2:  e5009a325f2 < -:  ----------- builtin/unpack-objects.c: fix compiler error on MacOS with clang 11.0.0
 -:  ----------- > 1:  c6708ed9459 config.mak.dev: disable suggest braces error on old clang versions


 config.mak.dev | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)


base-commit: 3dcec76d9df911ed8321007b1d197c1a206dc164

Comments

Junio C Hamano Oct. 10, 2022, 6:13 p.m. UTC | #1

"Jeff Hostetler via GitGitGadget" <[e-mail]> writes:

>     Here is version 2. This version adds the "-Wno-missing-braces" compiler
>     flag when we are using an old version of clang -- rather than updating
>     the source files to use the "{{0}}" syntax that was expected by older
>     versions of clang.
>     
>     I've expanded the scope to include fixes for Apple's clang 11 and below
>     and non-Apple clang 8 and below.
>
> diff --git a/config.mak.dev b/config.mak.dev
> index 4fa19d361b7..981304727c5 100644
> --- a/config.mak.dev
> +++ b/config.mak.dev
> @@ -69,6 +69,31 @@ DEVELOPER_CFLAGS += -Wno-missing-braces
>  endif
>  endif
>  
> +# Old versions of clang complain about initializaing a
> +# struct-within-a-struct using just "{0}" rather than "{{0}}".  This
> +# error is considered a false-positive and not worth fixing, because
> +# new clang versions do not, so just disable it.
> +#
> +# The "bug" was fixed in upstream clang 9.
> +#
> +# Complicating this is that versions of clang released by Apple have
> +# their own version numbers (associated with the corresponding version
> +# of XCode) unrelated to the official clang version numbers.
> +#
> +# The bug was fixed in Apple clang 12.
> +#
> +ifneq ($(filter clang1,$(COMPILER_FEATURES)),)     # if we are using clang
> +ifeq ($(uname_S),Darwin)                           # if we are on darwin
> +ifeq ($(filter clang12,$(COMPILER_FEATURES)),)     # if version < 12
> +DEVELOPER_CFLAGS += -Wno-missing-braces
> +endif
> +else                                               # not darwin
> +ifeq ($(filter clang9,$(COMPILER_FEATURES)),)      # if version < 9
> +DEVELOPER_CFLAGS += -Wno-missing-braces
> +endif
> +endif
> +endif

Looks very straight-forward, albeit a tad verbose, and simple to
follow.  I think this is equivalent to René's original one-liner.

Will queue.  Thanks.

Junio C Hamano Oct. 11, 2022, 12:15 a.m. UTC | #2

Junio C Hamano <[e-mail]> writes:

> Looks very straight-forward, albeit a tad verbose, and simple to
> follow.  I think this is equivalent to René's original one-liner.
>
> Will queue.  Thanks.

Funny that during the whole time we were discussing this patch, I
never recalled b53a5f24 (config.mak.dev: squelch -Wno-missing-braces
for older gcc, 2022-07-29), which was a moral equivalent of this
change for older GCC, until I needed to decide the name of the topic
branch to queue this patch.

I had the topic branch jk/struct-zero-init-with-older-gcc for
b53a5f24 still lying around.  I reused a part of its name and queued
it on jh/struct-zero-init-with-older-clang branch.

Patch

diff --git a/config.mak.dev b/config.mak.dev
index 4fa19d361b7..981304727c5 100644
--- a/config.mak.dev
+++ b/config.mak.dev
@@ -69,6 +69,31 @@  DEVELOPER_CFLAGS += -Wno-missing-braces
 endif
 endif
 
+# Old versions of clang complain about initializaing a
+# struct-within-a-struct using just "{0}" rather than "{{0}}".  This
+# error is considered a false-positive and not worth fixing, because
+# new clang versions do not, so just disable it.
+#
+# The "bug" was fixed in upstream clang 9.
+#
+# Complicating this is that versions of clang released by Apple have
+# their own version numbers (associated with the corresponding version
+# of XCode) unrelated to the official clang version numbers.
+#
+# The bug was fixed in Apple clang 12.
+#
+ifneq ($(filter clang1,$(COMPILER_FEATURES)),)     # if we are using clang
+ifeq ($(uname_S),Darwin)                           # if we are on darwin
+ifeq ($(filter clang12,$(COMPILER_FEATURES)),)     # if version < 12
+DEVELOPER_CFLAGS += -Wno-missing-braces
+endif
+else                                               # not darwin
+ifeq ($(filter clang9,$(COMPILER_FEATURES)),)      # if version < 9
+DEVELOPER_CFLAGS += -Wno-missing-braces
+endif
+endif
+endif
+
 # https://bugzilla.redhat.com/show_bug.cgi?id=2075786
 ifneq ($(filter gcc12,$(COMPILER_FEATURES)),)
 DEVELOPER_CFLAGS += -Wno-error=stringop-overread