OK. On Tue, Nov 12, 2019 at 11:45 AM Marek Polacek <pola...@redhat.com> wrote:
> This is a complaint that we issue a [[nodiscard]] warning even in SFINAE > contexts. Here 'complain' is tf_decltype, but not tf_warning so I guess > we can fix it as below. > > Bootstrapped/regtested on x86_64-linux, ok for trunk? > > 2019-11-12 Marek Polacek <pola...@redhat.com> > > PR c++/89070 - bogus [[nodiscard]] warning in SFINAE. > * cvt.c (convert_to_void): Guard maybe_warn_nodiscard calls with > tf_warning. > > * g++.dg/cpp1z/nodiscard7.C: New test. > > diff --git gcc/cp/cvt.c gcc/cp/cvt.c > index d41aeb8f1fc..23facb77634 100644 > --- gcc/cp/cvt.c > +++ gcc/cp/cvt.c > @@ -1201,7 +1201,8 @@ convert_to_void (tree expr, impl_conv_void implicit, > tsubst_flags_t complain) > if (DECL_DESTRUCTOR_P (fn)) > return expr; > > - maybe_warn_nodiscard (expr, implicit); > + if (complain & tf_warning) > + maybe_warn_nodiscard (expr, implicit); > break; > > case INDIRECT_REF: > @@ -1357,7 +1358,8 @@ convert_to_void (tree expr, impl_conv_void implicit, > tsubst_flags_t complain) > && !is_reference) > warning_at (loc, OPT_Wunused_value, "value computed is not > used"); > expr = TREE_OPERAND (expr, 0); > - if (TREE_CODE (expr) == CALL_EXPR) > + if (TREE_CODE (expr) == CALL_EXPR > + && (complain & tf_warning)) > maybe_warn_nodiscard (expr, implicit); > } > > @@ -1435,7 +1437,8 @@ convert_to_void (tree expr, impl_conv_void implicit, > tsubst_flags_t complain) > AGGR_INIT_EXPR_ARGP (init)); > } > } > - maybe_warn_nodiscard (expr, implicit); > + if (complain & tf_warning) > + maybe_warn_nodiscard (expr, implicit); > break; > > default:; > diff --git gcc/testsuite/g++.dg/cpp1z/nodiscard7.C > gcc/testsuite/g++.dg/cpp1z/nodiscard7.C > new file mode 100644 > index 00000000000..80dac63e41e > --- /dev/null > +++ gcc/testsuite/g++.dg/cpp1z/nodiscard7.C > @@ -0,0 +1,18 @@ > +// PR c++/89070 - bogus [[nodiscard]] warning in SFINAE. > +// { dg-do compile { target c++11 } } > + > +struct A > +{ > + [[nodiscard]] static int match() { return 42; } > +}; > + > +template<typename T> > +auto g() -> decltype( T::match(), bool() ) > +{ > + return T::match(); > +} > + > +int main() > +{ > + g<A>(); > +} > >