[PATCH v2 0/2] Makefile: "pedantic" fallout on .depend and "compdb"

In this v2 I just added an unconditional -Wno-pedantic and omitted the
change to spew error on STDERR. This more narrowly fixes the immediate
issue and doesn't get into whether we should use /dev/null or whatever
as input.

I then noticed that the same bug was present in
"GENERATE_COMPILATION_DATABASE=yes", so there's now a 2nd patch to fix
that.

Ævar Arnfjörð Bjarmason (2):
  Makefile: make COMPUTE_HEADER_DEPENDENCIES=auto work with
    DEVOPTS=pedantic
  Makefile: pass -Wno-pendantic under GENERATE_COMPILATION_DATABASE=yes

 Makefile | 2 ++
 1 file changed, 2 insertions(+)

Range-diff against v1:
1:  3ff8ea12bf3 ! 1:  31c871e9bf6 Makefile: make COMPUTE_HEADER_DEPENDENCIES=auto work with DEVOPTS=pedantic
    @@ Commit message
         Makefile: make COMPUTE_HEADER_DEPENDENCIES=auto work with DEVOPTS=pedantic
     
         The "COMPUTE_HEADER_DEPENDENCIES" feature added in [1] was extended to
    -    use auto-detection in [2]. Then when -Wpedantic support was added to
    -    DEVOPTS in [3] we started passing -Wpedantic in combination with
    -    -Werror to the compiler here.
    +    use auto-detection in [2], that "auto" detection has always piped
    +    STDERR to /dev/null, so any failures on compilers that didn't support
    +    these GCC flags would silently fall back to
    +    "COMPUTE_HEADER_DEPENDENCIES=no".
     
    -    This broke the auto-detection, but since we'd quieted it in [4] we
    -    didn't find out. It was emitting all of this on STDERR under GCC:
    +    Later when -Wpedantic support was added to DEVOPTS in [3] we started
    +    passing -Wpedantic in combination with -Werror to the compiler
    +    here. Note (to the pedantic): [3] actually passed "-pedantic", but it
    +    and "-Wpedantic" are synonyms.
    +
    +    Turning on -Wpedantic in [3] broke the auto-detection, since this
    +    relies on compiling an empty program. GCC would loudly complain on
    +    STDERR:
     
             /dev/null:1: error: ISO C forbids an empty translation unit
             [-Werror=pedantic]
    @@ Commit message
             earlier diagnostics
             cc1: all warnings being treated as errors
     
    -    Let's fix that bug by maintaining a NON_DEVELOPER_CFLAGS, it's like
    -    ALL_CFLAGS but without anything we add in config.mak.dev, and
    -    furthermore stop redirecting STDERR to /dev/null, this means that
    -    someone whose compiler doesn't support this will see this output, but
    -    also this new message:
    +    But as that ended up in the "$(dep_check)" variable due to the "2>&1"
    +    in [2] we didn't see it.
     
    -        Non-zero 1 exit with COMPUTE_HEADER_DEPENDENCIES=auto, set it to "yes" or "no" to quiet auto-detect
    +    Then when [4] made DEVOPTS=pedantic the default specifying
    +    "DEVELOPER=1" would effectively set "COMPUTE_HEADER_DEPENDENCIES=no".
    +
    +    To fix these issues let's unconditionally pass -Wno-pedantic after
    +    $(ALL_CFLAGS), we might get a -Wpedantic via config.mak.dev after, or
    +    the builder might specify it via CFLAGS. In either case this will undo
    +    current and future problems with -Wpedantic.
     
    -    It's also possible that some compilers will emit warnings but still
    -    give a zero exit code, anyone using a compiler like that will
    -    potentially get more verbose output from the Makefile until they set
    -    COMPUTE_HEADER_DEPENDENCIES=no. E.g. on AIX's xlc we'll now emit:
    +    I think it would make sense to simply remove the "2>&1", it would mean
    +    that anyone using a non-GCC-like compiler would get warnings under
    +    COMPUTE_HEADER_DEPENDENCIES=auto, e.g on AIX's xlc would emit:
     
             /opt/IBM/xlc/13.1.3/bin/.orig/xlc: 1501-208 (S) command option D is missing a subargument
             Non-zero 40 exit with COMPUTE_HEADER_DEPENDENCIES=auto, set it to "yes" or "no" to quiet auto-detect
    @@ Commit message
             cc: refused to overwrite input file by output file: /dev/null
             Non-zero 1 exit with COMPUTE_HEADER_DEPENDENCIES=auto, set it to "yes" or "no" to quiet auto-detect
     
    -    Both are quieted by setting COMPUTE_HEADER_DEPENDENCIES=no as
    -    suggested.
    -
    -    I considered piping the output and the exit code to a variable
    -    instead, but e.g. under GCC that would lose the coloring in the error
    -    messages.
    +    Both could be quieted by setting COMPUTE_HEADER_DEPENDENCIES=no
    +    explicitly, as suggested, but let's see if this'll fix it without
    +    emitting too much noise at those that aren't using "gcc" or "clang".
     
         1. f2fabbf76e4 (Teach Makefile to check header dependencies,
            2010-01-26)
    @@ Commit message
         Signed-off-by: Ævar Arnfjörð Bjarmason [off-list ref]
     
      ## Makefile ##
    -@@ Makefile: ALL_COMMANDS_TO_INSTALL += git-upload-archive$(X)
    - ALL_COMMANDS_TO_INSTALL += git-upload-pack$(X)
    - endif
    - 
    --ALL_CFLAGS = $(DEVELOPER_CFLAGS) $(CPPFLAGS) $(CFLAGS)
    -+NON_DEVELOPER_CFLAGS = $(CPPFLAGS) $(CFLAGS)
    -+ALL_CFLAGS = $(DEVELOPER_CFLAGS) $(NON_DEVELOPER_CFLAGS)
    - ALL_LDFLAGS = $(LDFLAGS)
    - 
    - comma := ,
    -@@ Makefile: COMPUTE_HEADER_DEPENDENCIES = auto
    - endif
    +@@ Makefile: endif
      
      ifeq ($(COMPUTE_HEADER_DEPENDENCIES),auto)
    --dep_check = $(shell $(CC) $(ALL_CFLAGS) \
    -+dep_check = $(shell $(CC) $(NON_DEVELOPER_CFLAGS) \
    + dep_check = $(shell $(CC) $(ALL_CFLAGS) \
    ++	-Wno-pedantic \
      	-c -MF /dev/null -MQ /dev/null -MMD -MP \
    --	-x c /dev/null -o /dev/null 2>&1; \
    -+	-x c /dev/null -o /dev/null; \
    + 	-x c /dev/null -o /dev/null 2>&1; \
      	echo $$?)
    - ifeq ($(dep_check),0)
    - override COMPUTE_HEADER_DEPENDENCIES = yes
    - else
    -+$(info Non-zero $(dep_check) exit with COMPUTE_HEADER_DEPENDENCIES=auto, set it to "yes" or "no" to quiet auto-detect)
    - override COMPUTE_HEADER_DEPENDENCIES = no
    - endif
    - endif
-:  ----------- > 2:  6b18bd08894 Makefile: pass -Wno-pendantic under GENERATE_COMPILATION_DATABASE=yes
-- 
2.33.0.1225.g9f062250122