[gcc r15-3812] c++: diagnose this specifier in requires expr [PR116798]

[Marek Polacek]

https://gcc.gnu.org/g:4700ad1c78ccd7767f846802fca148b2ea9a1852

commit r15-3812-g4700ad1c78ccd7767f846802fca148b2ea9a1852
Author: Marek Polacek <polacek@redhat.com>
Date:   Mon Sep 23 12:19:40 2024 -0400

    c++: diagnose this specifier in requires expr [PR116798]
    
    We don't detect an explicit object parameter in a requires expression.
    We can get there by way of requires-expression -> requirement-parameter-list
    -> parameter-declaration-clause -> ... -> parameter-declaration with
    this[opt].  But [dcl.fct]/5 doesn't allow an explicit object parameter
    in this context.  So let's fix it like r14-9033 and not like r14-8832.
    
            PR c++/116798
    
    gcc/cp/ChangeLog:
    
            * parser.cc (cp_parser_parameter_declaration): Detect an explicit
            object parameter in a requires expression.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp23/explicit-obj-diagnostics12.C: New test.
    
    Reviewed-by: Jason Merrill <jason@redhat.com>

Diff:
---
 gcc/cp/parser.cc                                        | 11 ++++++++---
 gcc/testsuite/g++.dg/cpp23/explicit-obj-diagnostics12.C | 10 ++++++++++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 4dd9474cf609..dbc607027dfb 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -25982,10 +25982,15 @@ cp_parser_parameter_declaration (cp_parser *parser,
 
   bool xobj_param_p
     = decl_spec_seq_has_spec_p (&decl_specifiers, ds_this);
-  if (xobj_param_p && template_parm_p)
+  if (xobj_param_p
+      && (template_parm_p || current_binding_level->requires_expression))
     {
-      error_at (decl_specifiers.locations[ds_this],
-		"%<this%> specifier in template parameter declaration");
+      if (template_parm_p)
+	error_at (decl_specifiers.locations[ds_this],
+		  "%<this%> specifier in template parameter declaration");
+      else
+	error_at (decl_specifiers.locations[ds_this],
+		  "%<this%> specifier in a requires-expression parameter");
       xobj_param_p = false;
       decl_specifiers.locations[ds_this] = 0;
     }
diff --git a/gcc/testsuite/g++.dg/cpp23/explicit-obj-diagnostics12.C b/gcc/testsuite/g++.dg/cpp23/explicit-obj-diagnostics12.C
new file mode 100644
index 000000000000..ec0aced0fd9c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/explicit-obj-diagnostics12.C
@@ -0,0 +1,10 @@
+// PR c++/116798
+// { dg-do compile { target c++23 } }
+
+template<typename T>
+concept C = requires(this T u,	  // { dg-error "'this' specifier in a requires-expression parameter" }
+		     this T v) {  // { dg-error "'this' specifier in a requires-expression parameter" }
+    u + v;
+};
+
+static_assert(C<int>);