c++: change -fconcepts to mean C++20 concepts

It was always weird that -fconcepts in C++17 mode meant the same thing as
-fconcepts-ts in C++20 mode; this patch harmonizes the flags so that for TS
concepts you always need to write -fconcepts-ts.

In the unlikely event anyone is still using -fconcepts in C++17 mode, they
can either fix their code to work with C++20 concepts or adjust the compiler
flag.

gcc/c-family/ChangeLog:

	* c-opts.cc (c_common_post_options): -fconcepts no longer implies
	-fconcepts-ts before C++20.

gcc/ChangeLog:

	* doc/invoke.texi: -fconcepts no longer implies
	-fconcepts-ts before C++20.

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_template_declaration_after_parameters): Fix
	concept parsing below C++20.

gcc/testsuite/ChangeLog:

	* g++.dg/concepts/auto1.C:
	* g++.dg/concepts/auto3.C:
	* g++.dg/concepts/auto4.C:
	* g++.dg/concepts/class-deduction1.C:
	* g++.dg/concepts/class5.C:
	* g++.dg/concepts/class6.C:
	* g++.dg/concepts/debug1.C:
	* g++.dg/concepts/decl-diagnose.C:
	* g++.dg/concepts/deduction-constraint1.C:
	* g++.dg/concepts/diagnostic1.C:
	* g++.dg/concepts/dr1430.C:
	* g++.dg/concepts/equiv.C:
	* g++.dg/concepts/equiv2.C:
	* g++.dg/concepts/expression.C:
	* g++.dg/concepts/expression2.C:
	* g++.dg/concepts/expression3.C:
	* g++.dg/concepts/fn-concept1.C:
	* g++.dg/concepts/fn-concept2.C:
	* g++.dg/concepts/fn-concept3.C:
	* g++.dg/concepts/fn1.C:
	* g++.dg/concepts/fn10.C:
	* g++.dg/concepts/fn2.C:
	* g++.dg/concepts/fn3.C:
	* g++.dg/concepts/fn4.C:
	* g++.dg/concepts/fn5.C:
	* g++.dg/concepts/fn6.C:
	* g++.dg/concepts/fn8.C:
	* g++.dg/concepts/fn9.C:
	* g++.dg/concepts/generic-fn-err.C:
	* g++.dg/concepts/generic-fn.C:
	* g++.dg/concepts/inherit-ctor1.C:
	* g++.dg/concepts/inherit-ctor3.C:
	* g++.dg/concepts/intro1.C:
	* g++.dg/concepts/intro2.C:
	* g++.dg/concepts/intro3.C:
	* g++.dg/concepts/intro4.C:
	* g++.dg/concepts/intro5.C:
	* g++.dg/concepts/intro6.C:
	* g++.dg/concepts/intro7.C:
	* g++.dg/concepts/locations1.C:
	* g++.dg/concepts/partial-concept-id1.C:
	* g++.dg/concepts/partial-concept-id2.C:
	* g++.dg/concepts/partial-spec5.C:
	* g++.dg/concepts/placeholder2.C:
	* g++.dg/concepts/placeholder3.C:
	* g++.dg/concepts/placeholder4.C:
	* g++.dg/concepts/placeholder5.C:
	* g++.dg/concepts/placeholder6.C:
	* g++.dg/concepts/pr65634.C:
	* g++.dg/concepts/pr65636.C:
	* g++.dg/concepts/pr65681.C:
	* g++.dg/concepts/pr65848.C:
	* g++.dg/concepts/pr67249.C:
	* g++.dg/concepts/pr67595.C:
	* g++.dg/concepts/pr68434.C:
	* g++.dg/concepts/pr71127.C:
	* g++.dg/concepts/pr71128.C:
	* g++.dg/concepts/pr71131.C:
	* g++.dg/concepts/pr71385.C:
	* g++.dg/concepts/pr85065.C:
	* g++.dg/concepts/template-parm11.C:
	* g++.dg/concepts/template-parm12.C:
	* g++.dg/concepts/template-parm2.C:
	* g++.dg/concepts/template-parm3.C:
	* g++.dg/concepts/template-parm4.C:
	* g++.dg/concepts/template-template-parm1.C:
	* g++.dg/concepts/var-concept1.C:
	* g++.dg/concepts/var-concept2.C:
	* g++.dg/concepts/var-concept3.C:
	* g++.dg/concepts/var-concept4.C:
	* g++.dg/concepts/var-concept5.C:
	* g++.dg/concepts/var-concept6.C:
	* g++.dg/concepts/var-concept7.C:
	* g++.dg/concepts/var-templ2.C:
	* g++.dg/concepts/var-templ3.C:
	* g++.dg/concepts/variadic1.C:
	* g++.dg/concepts/variadic2.C:
	* g++.dg/concepts/variadic3.C:
	* g++.dg/concepts/variadic4.C:
	* g++.dg/cpp2a/concepts-pr65575.C:
	* g++.dg/cpp2a/concepts-pr66091.C:
	* g++.dg/cpp2a/concepts-pr84980.C:
	* g++.dg/cpp2a/concepts-pr85265.C: Pass -fconcepts-ts.
	* g++.dg/cpp2a/concepts-pr84979-2.C:
	* g++.dg/cpp2a/concepts-pr84979-3.C: Same diagnostics
	in C++20 and below.

1 files changed, 8 insertions, 8 deletions

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index c6323a53ad2..2b29db831ae 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -3075,14 +3075,14 @@ exhaustion is signalled by throwing @code{std::bad_alloc}.  See also
 @itemx -fconcepts-ts
 @opindex fconcepts
 @opindex fconcepts-ts
-Below @option{-std=c++20}, @option{-fconcepts} enables support for the
-C++ Extensions for Concepts Technical Specification, ISO 19217 (2015).
-
-With @option{-std=c++20} and above, Concepts are part of the language
-standard, so @option{-fconcepts} defaults to on.  But the standard
-specification of Concepts differs significantly from the TS, so some
-constructs that were allowed in the TS but didn't make it into the
-standard can still be enabled by @option{-fconcepts-ts}.
+Enable support for the C++ Concepts feature for constraining template
+arguments.  With @option{-std=c++20} and above, Concepts are part of
+the language standard, so @option{-fconcepts} defaults to on.
+
+Some constructs that were allowed by the earlier C++ Extensions for
+Concepts Technical Specification, ISO 19217 (2015), but didn't make it
+into the standard, can additionally be enabled by
+@option{-fconcepts-ts}.
 
 @item -fconstexpr-depth=@var{n}
 @opindex fconstexpr-depth