1256642 - Make the build system infer LIB_IS_C_ONLY

Status: RESOLVED FIXED

(Firefox Build System :: General, defect)

Description

[(not currently active) Ted Mielczarek]

This Makefile only contains `LIB_IS_C_ONLY    = 1`:
https://hg.mozilla.org/mozilla-central/file/5e14887312d4523ab59c3f6c6c94a679cf42b496/config/external/sqlite/Makefile.in

The only function of that is to use the C compiler instead of the C++ compiler for linking the library:
https://dxr.mozilla.org/mozilla-central/rev/d6ee82b9a74155b6bfd544166f036fc572ae8c56/config/rules.mk#151

But note:
https://dxr.mozilla.org/mozilla-central/rev/d6ee82b9a74155b6bfd544166f036fc572ae8c56/build/templates.mozbuild#15

Comment 1

[Mike Hommey [:glandium]]

(In reply to Ted Mielczarek [:ted.mielczarek] from comment #0)
> This Makefile only contains `LIB_IS_C_ONLY    = 1`:
> https://hg.mozilla.org/mozilla-central/file/
> 5e14887312d4523ab59c3f6c6c94a679cf42b496/config/external/sqlite/Makefile.in
> 
> The only function of that is to use the C compiler instead of the C++
> compiler for linking the library:
> https://dxr.mozilla.org/mozilla-central/rev/
> d6ee82b9a74155b6bfd544166f036fc572ae8c56/config/rules.mk#151
> 
> But note:
> https://dxr.mozilla.org/mozilla-central/rev/
> d6ee82b9a74155b6bfd544166f036fc572ae8c56/build/templates.mozbuild#15

But that's just for the explicit stuff. We'd be adding a dependency on libstdc++ from sqlite on the platforms where it's a separate shared library (which I think is just linux nowaways).

BTW, this makes me think that since we're now building nspr with the gecko build system, the nspr libraries are linked to libstdc++ too...

Comment 2

[(not currently active) Ted Mielczarek]

I have a candidate patch. It does correctly add this for the NSPR libs, as well as a few other things I hadn't considered:
```
luser@eye7:/build/mozilla-central$ find /build/debug-mozilla-central/ -name backend.mk | xargs grep LIB_IS_C_ONLY
/build/debug-mozilla-central/media/ffvpx/libavcodec/backend.mk:LIB_IS_C_ONLY := 1
/build/debug-mozilla-central/media/ffvpx/libavutil/backend.mk:LIB_IS_C_ONLY := 1
/build/debug-mozilla-central/config/external/nspr/ds/backend.mk:LIB_IS_C_ONLY := 1
/build/debug-mozilla-central/config/external/nspr/pr/backend.mk:LIB_IS_C_ONLY := 1
/build/debug-mozilla-central/config/external/nspr/libc/backend.mk:LIB_IS_C_ONLY := 1
/build/debug-mozilla-central/config/external/sqlite/backend.mk:LIB_IS_C_ONLY := 1
/build/debug-mozilla-central/widget/gtk/mozgtk/gtk3/backend.mk:LIB_IS_C_ONLY := 1
/build/debug-mozilla-central/widget/gtk/mozgtk/gtk2/backend.mk:LIB_IS_C_ONLY := 1
/build/debug-mozilla-central/widget/gtk/mozgtk/stub/backend.mk:LIB_IS_C_ONLY := 1
```

However, if you --enable-stdcxx-compat they disappear because the build frontend notices the dependency on stdc++compat from the Library template. I think we should get my patch landed anyway since it's no worse than the current situation, and then we can sort out how to fix the template thing in a followup.

Comment 3

[(not currently active) Ted Mielczarek]

Attachment: bug 1256642 - have the build system automatically detect LIB_IS_C_ONLY.

Review commit: https://reviewboard.mozilla.org/r/73926/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/73926/

Comment 4

[(not currently active) Ted Mielczarek]

The try push was green.

Comment 5

[Mike Hommey [:glandium]]

Comment on attachment 8784480 [details]
bug 1256642 - have the build system automatically detect LIB_IS_C_ONLY.

https://reviewboard.mozilla.org/r/73926/#review73438

::: python/mozbuild/mozbuild/frontend/emitter.py:817
(Diff revision 1)
>              UNIFIED_SOURCES=(UnifiedSources, None, ['.c', '.mm', '.cpp']),
>          )
> +        # Track whether there are any C++ source files.
> +        # Technically this won't do the right thing for SIMPLE_PROGRAMS in
> +        # a directory with mixed C and C++ source, but it's not that important.
> +        cxx_sources = dict((k, False) for k in varmap.keys())

defaultdict(bool)

Or you can just use a dict and .get() from it in the loop setting cxx_link.

Comment 6

[(not currently active) Ted Mielczarek]

https://hg.mozilla.org/integration/mozilla-inbound/rev/83f3a00b2a1905bfbad4dd74358423969ed181d0
bug 1256642 - have the build system automatically detect LIB_IS_C_ONLY. r=glandium

Comment 7

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/83f3a00b2a19