Re: Fix for configure error in 9.5/9.6 on macOS 11.0 Big Sur

On Thu, Sep 3, 2020 at 10:36 AM Tom Lane wrote:
>
> Jesse Zhang writes:
> >> Peter Eisentraut writes:
> >>> Where did the -Werror come from?
>
> > If you noticed the full invocation of clang, you'd notice that Werror is
> > nowhere on the command line, even though the error message suggests
> > otherwise. I think this is a behavior from the new AppleClang,
>
> Hmph. If you explicitly say -Wno-error, does the error drop back down
> to being a warning?

Yeah something like that, this is what works for me:

clang -Wno-error=implicit-function-declaration c.c

Then it became a warning.

Interestingly, it seems that AppleClang incorrectly forces this warning
on us:

$ clang --verbose c.c

| Apple clang version 12.0.0 (clang-1200.0.31.1)
| Target: x86_64-apple-darwin20.0.0
| Thread model: posix
| InstalledDir: /Library/Developer/CommandLineTools/usr/bin
| "/Library/Developer/CommandLineTools/usr/bin/clang" -cc1 -triple
x86_64-apple-macosx11.0.0 -Wdeprecated-objc-isa-usage
-Werror=deprecated-objc-isa-usage
-Werror=implicit-function-declaration -emit-obj -mrelax-all
-disable-free -disable-llvm-verifier -discard-value-names
-main-file-name c.c -mrelocation-model pic -pic-level 2 -mthread-model
posix -mframe-pointer=all -fno-strict-return -masm-verbose
-munwind-tables -target-sdk-version=11.0 -target-cpu penryn
-dwarf-column-info -debugger-tuning=lldb -target-linker-version 609 -v
-resource-dir /Library/Developer/CommandLineTools/usr/lib/clang/12.0.0
-isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk
-I/usr/local/include -internal-isystem
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/local/include
-internal-isystem
/Library/Developer/CommandLineTools/usr/lib/clang/12.0.0/include
-internal-externc-isystem
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include
-internal-externc-isystem
/Library/Developer/CommandLineTools/usr/include -Wno-reorder-init-list
-Wno-implicit-int-float-conversion -Wno-c99-designator
-Wno-final-dtor-non-final-class -Wno-extra-semi-stmt
-Wno-misleading-indentation -Wno-quoted-include-in-framework-header
-Wno-implicit-fallthrough -Wno-enum-enum-conversion
-Wno-enum-float-conversion -fdebug-compilation-dir /tmp -ferror-limit
19 -fmessage-length 193 -stack-protector 1 -fstack-check
-mdarwin-stkchk-strong-link -fblocks -fencode-extended-block-signature
-fregister-global-dtors-with-atexit -fgnuc-version=4.2.1
-fobjc-runtime=macosx-11.0.0 -fmax-type-align=16
-fdiagnostics-show-option -fcolor-diagnostics -o
/var/folders/ts/nxrsmhmd0xb5zdrlqb4jlkbr0000gn/T/c-e6802f.o -x c c.c
| clang -cc1 version 12.0.0 (clang-1200.0.31.1) default target
x86_64-apple-darwin20.0.0

Notice that -Werror=implicit-function-declaration up there? I spent a
few minutes digging in Apple's published fork of LLVM, they've been
forcing this error flag for quite a while, but this particular
warning-turned-error is guarded by a conditional along the lines of "is
this iOS-like" [1][2], so I cannot imagine such a code path is activated
(other than something like "goto fail;" from 2014)

>
> > I've heard reports of the same under the latest Xcode 12 on macOS
> > Catalina, but I don't have my hands on such an env.
>
> The latest thing available to the unwashed masses seems to be
> Xcode 11.7 with

Yes you're right. Xcode 12 is still beta.

>
> Smells like an Apple bug from here. Surely they're not expecting
> that anyone will appreciate -Werror suddenly being the default.

I think you've convinced me that this is an Apple bug indeed. I'll
probably just get by with a Wno-error=implicit-function-declaration in
my CFLAGS for now.

[1] https://github.com/apple/llvm-project/blob/swift-5.3-DEVELOPMENT-SNAPSHOT-2020-08-04-a/clang/lib/Driver/ToolChains/Darwin.cpp#L952-L962
[2] https://opensource.apple.com/source/clang/clang-800.0.42.1/src/tools/clang/lib/Driver/ToolChains.cpp