Re: [PATCH Rust front-end v2 31/37] gccrs: Add GCC Rust front-end Make-lang.in

[Thomas Schwinge <thomas@codesourcery.com>]

Hi!

On 2022-09-14T15:34:10+0200, Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> On Wed, Aug 24, 2022 at 2:22 PM <herron.philip@googlemail.com> wrote:
>> --- /dev/null
>> +++ b/gcc/rust/Make-lang.in

>> +# TODO: possibly find a way to ensure C++11 compilation level here?
>> +RUST_CXXFLAGS = -std=c++11 -Wno-unused-parameter -Werror=overloaded-virtual
>
> You probably should inherit from $(CXXFLAGS) here which ensures C++11
> compatibility.

That was done in GCC/Rust commit da13bf4bbc46b399419c3e7f2c358a0efe3bdfdd
"make: Inherit CXXFLAGS, remove compiler-specific warnings", which
changed this to just 'RUST_CXXFLAGS = $(CXXFLAGS)'.

> Note you have to deal with non-g++ host compilers when not
> bootstrapping so adding -Wno-unused-parameter -Werror=overload-virtual
> needs to be guarded.

'-Werror=overloaded-virtual' is implied as by default, we have
'-Woverloaded-virtual' and '-Werror'.  (I've verified via putting
'class tmp : public Dump { void visit (int) {} };' into
'gcc/rust/ast/rust-ast-dump.cc', and getting a number of
'error: ‘virtual void Rust::AST::Dump::visit([...])’ was hidden'.)
(Maybe that isn't active for '--disable-bootstrap' builds, but that's
"OK".)

Remains only '-Wno-unused-parameter'.  That one should move into
'rust-warn', where we currently have:

>> +# Use strict warnings for this front end.
>> +rust-warn = $(STRICT_WARN)

Per GCC 4.8 documentation (baseline version to bootstrap GCC), we may use
'-Wno-[...]' without checking whether the corresponding '-W[...]' is
actually supported, so we may specify '-Wno-unused-parameter'
unconditionally, like existing ones, for example in 'gcc/Makefile.in':

    # These files are to have specific diagnostics suppressed, [...]
    gimple-match.o-warn = -Wno-unused
    generic-match.o-warn = -Wno-unused
    dfp.o-warn = -Wno-strict-aliasing

I thus understand that non-GCC compilers implement the same '-Wno-[...]'
behavior -- or maybe warning flags are not passed to those at all, at
stage 1 build where this is (only) relevant.

I've thus proposed <https://github.com/Rust-GCC/gccrs/pull/1670>
"'rust-warn += -Wno-unused-parameter'".


Grüße
 Thomas
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