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[C++ PATCH] c++/89070 - bogus [[nodiscard]] warning in SFINAE.
- From: Marek Polacek <polacek at redhat dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>, Jason Merrill <jason at redhat dot com>
- Date: Tue, 12 Nov 2019 11:44:55 -0500
- Subject: [C++ PATCH] c++/89070 - bogus [[nodiscard]] warning in SFINAE.
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 <polacek@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>();
+}