On Thu, 7 May 2020, Patrick Palka wrote:
> In fn_type_unifcation, we are passing NULL_TREE as the 'in_decl'
> parameter to coerce_template_parms, and this is causing template
> type/value mismatch error messages to get suppressed regardless of the
> value of 'complain'.
>
> This means that when substitution into a function template fails due to
> a type/value mismatch between a template parameter and the provided
> template argument, we just say "template argument deduction/substitution
> failed:" without a followup explanation of the failure.
>
> Fix this by passing 'fn' instead of NULL_TREE to coerce_template_parms.
> Passes 'make check-c++', does this look OK to commit after a full
> bootstrap and regtest?
I found an existing PR about this issue, 66439. Consider the patch
updated to refer to this PR.
>
> gcc/cp/ChangeLog:
>
> * pt.c (fn_type_unification): Pass 'fn' instead of NULL_TREE as
> the 'in_decl' parameter to coerce_template_parms.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp2a/concepts-ts4.C: Expect a "type/value mismatch"
> diagnostic.
> * g++.dg/cpp2a/concepts-ts6.C: Likewise.
> * g++.dg/template/error56.C: Likewise.
> * g++.dg/template/error59.C: New test.
>
> libstdc++-v3/ChangeLog:
>
> * testsuite/20_util/pair/astuple/get_neg.cc: Prune "type/value
> mismatch" messages.
> * testsuite/20_util/tuple/element_access/get_neg.cc: Likewise.
> ---
> gcc/cp/pt.c | 2 +-
> gcc/testsuite/g++.dg/cpp2a/concepts-ts4.C | 2 ++
> gcc/testsuite/g++.dg/cpp2a/concepts-ts6.C | 4 +++-
> gcc/testsuite/g++.dg/template/error56.C | 2 ++
> gcc/testsuite/g++.dg/template/error59.C | 11 +++++++++++
> .../testsuite/20_util/pair/astuple/get_neg.cc | 1 +
> .../testsuite/20_util/tuple/element_access/get_neg.cc | 1 +
> 7 files changed, 21 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/template/error59.C
>
> diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
> index c6091127225..52bb6f34d6a 100644
> --- a/gcc/cp/pt.c
> +++ b/gcc/cp/pt.c
> @@ -21088,7 +21088,7 @@ fn_type_unification (tree fn,
> /* Adjust any explicit template arguments before entering the
> substitution context. */
> explicit_targs
> - = (coerce_template_parms (tparms, explicit_targs, NULL_TREE,
> + = (coerce_template_parms (tparms, explicit_targs, fn,
> complain|tf_partial,
> /*require_all_args=*/false,
> /*use_default_args=*/false));
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-ts4.C
> b/gcc/testsuite/g++.dg/cpp2a/concepts-ts4.C
> index aa96621d9cf..2b0fd1b8deb 100644
> --- a/gcc/testsuite/g++.dg/cpp2a/concepts-ts4.C
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ts4.C
> @@ -31,4 +31,6 @@ void driver()
> fn<0>(); // OK
> fn<-1>(); // { dg-error "" }
> fn<int>(); // { dg-error "no matching function" }
> + // { dg-error "type/value mismatch at argument 1" "" { target *-*-* } .-1 }
> + // { dg-message "expected a constant of type .int., got .int." "" { target
> *-*-* } .-2 }
> }
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-ts6.C
> b/gcc/testsuite/g++.dg/cpp2a/concepts-ts6.C
> index bf665aa6308..e3dff54c83d 100644
> --- a/gcc/testsuite/g++.dg/cpp2a/concepts-ts6.C
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ts6.C
> @@ -25,6 +25,8 @@ void driver1() {
>
> f<X>();
> f<int>(); // { dg-error "no matching function for call" }
> + // { dg-error "type/value mismatch at argument 1" "" { target *-*-* } .-1 }
> + // { dg-message "expected a class template, got .int." "" { target *-*-* }
> .-2 }
>
> S2<int> s2a;
> S2<char, signed char, unsigned char> s2b;
> @@ -69,4 +71,4 @@ void driver2()
> S6<void, void> s6a;
> S6<void, int> s6c; // { dg-error "template constraint failure" }
> S6<void, void, void> s6b; // { dg-error "wrong number of template
> arguments" }
> -}
> \ No newline at end of file
> +}
> diff --git a/gcc/testsuite/g++.dg/template/error56.C
> b/gcc/testsuite/g++.dg/template/error56.C
> index 3eda04c3225..e85471a50b0 100644
> --- a/gcc/testsuite/g++.dg/template/error56.C
> +++ b/gcc/testsuite/g++.dg/template/error56.C
> @@ -9,4 +9,6 @@ struct A
> int main()
> {
> A().f<1>(); // { dg-error "f<1>" }
> + // { dg-error "type/value mismatch at argument 1" "" { target *-*-* } .-1 }
> + // { dg-message "expected a type, got .1." "" { target *-*-* } .-2 }
> }
> diff --git a/gcc/testsuite/g++.dg/template/error59.C
> b/gcc/testsuite/g++.dg/template/error59.C
> new file mode 100644
> index 00000000000..f81a28c2f1a
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/error59.C
> @@ -0,0 +1,11 @@
> +template<int N> struct S { };
> +
> +template<template<typename> class TT>
> +void foo();
> +
> +void bar()
> +{
> + foo<S>(); // { dg-error "no matching function" }
> + // { dg-error "type/value mismatch at argument 1" "" { target *-*-* } .-1 }
> + // { dg-message "expected a template of type .template<class> class TT.,
> got .template<int N> struct S." "" { target *-*-* } .-2 }
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/pair/astuple/get_neg.cc
> b/libstdc++-v3/testsuite/20_util/pair/astuple/get_neg.cc
> index bcf3940e16d..1f76aef6d73 100644
> --- a/libstdc++-v3/testsuite/20_util/pair/astuple/get_neg.cc
> +++ b/libstdc++-v3/testsuite/20_util/pair/astuple/get_neg.cc
> @@ -27,3 +27,4 @@ void test01()
> }
>
> // { dg-prune-output "tuple_element<2" }
> +// { dg-prune-output "type/value mismatch" }
> diff --git a/libstdc++-v3/testsuite/20_util/tuple/element_access/get_neg.cc
> b/libstdc++-v3/testsuite/20_util/tuple/element_access/get_neg.cc
> index 8488e287a98..03ad77215d2 100644
> --- a/libstdc++-v3/testsuite/20_util/tuple/element_access/get_neg.cc
> +++ b/libstdc++-v3/testsuite/20_util/tuple/element_access/get_neg.cc
> @@ -61,3 +61,4 @@ test03()
> }
>
> // { dg-prune-output "no type named .type" }
> +// { dg-prune-output "type/value mismatch" }
> --
> 2.26.2.561.g07d8ea56f2
>
>
