[PATCH] c++: diagnose this specifier in requires expr [PR116798]

[Marek Polacek]

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

-- >8 --
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.
---
 gcc/cp/parser.cc                                      | 11 ++++++++---
 .../g++.dg/cpp23/explicit-obj-diagnostics12.C         | 10 ++++++++++
 2 files changed, 18 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp23/explicit-obj-diagnostics12.C

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 4dd9474cf60..7b54586fce6 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");
       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 00000000000..84db2166cc2
--- /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" }
+                    this T v) {  // { dg-error "'this' specifier in a requires 
expression" }
+    u + v;
+};
+
+static_assert(C<int>);

base-commit: c1fb78fb03caede01b02a1ebb3275ac98343d468
-- 
2.46.1