[gcc r14-8832] c++: Disallow this specifier except for parameter declarations [PR113788]

[gcc r14-8832] c++: Disallow this specifier except for parameter declarations [PR113788]

[Jakub Jelinek]

https://gcc.gnu.org/g:40485378ade83102d7aa30c317f5d6c90c1d232b

commit r14-8832-g40485378ade83102d7aa30c317f5d6c90c1d232b
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Feb 6 22:34:55 2024 +0100

    c++: Disallow this specifier except for parameter declarations [PR113788]
    
    The deducing this patchset added parsing of this specifier to
    cp_parser_decl_specifier_seq unconditionally, but in the C++ grammar
    this[opt] only appears in the parameter-declaration non-terminal, so
    rather than checking in all the callers of cp_parser_decl_specifier_seq
    except for cp_parser_parameter_declaration that this specifier didn't
    appear I think it is far easier and closer to what the standard says
    to only parse this specifier when called from
    cp_parser_parameter_declaration.
    
    2024-02-06  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/113788
            * parser.cc (CP_PARSER_FLAGS_PARAMETER): New enumerator.
            (cp_parser_decl_specifier_seq): Parse RID_THIS only if
            CP_PARSER_FLAGS_PARAMETER is set in flags.
            (cp_parser_parameter_declaration): Or in CP_PARSER_FLAGS_PARAMETER
            when calling cp_parser_decl_specifier_seq.
    
            * g++.dg/parse/pr113788.C: New test.

Diff:
---
 gcc/cp/parser.cc                      |  8 +++++---
 gcc/testsuite/g++.dg/parse/pr113788.C | 20 ++++++++++++++++++++
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 3748ccd49ff3..c4292c49ce26 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -2088,7 +2088,9 @@ enum
   /* When parsing of the noexcept-specifier should be delayed.  */
   CP_PARSER_FLAGS_DELAY_NOEXCEPT = 0x40,
   /* When parsing a consteval declarator.  */
-  CP_PARSER_FLAGS_CONSTEVAL = 0x80
+  CP_PARSER_FLAGS_CONSTEVAL = 0x80,
+  /* When parsing a parameter declaration.  */
+  CP_PARSER_FLAGS_PARAMETER = 0x100
 };
 
 /* This type is used for parameters and variables which hold
@@ -16342,7 +16344,7 @@ cp_parser_decl_specifier_seq (cp_parser* parser,
       /* Special case for "this" specifier, indicating a parm is an xobj parm.
 	 The "this" specifier must be the first specifier in the declaration,
 	 after any attributes.  */
-      if (token->keyword == RID_THIS)
+      if (token->keyword == RID_THIS && (flags & CP_PARSER_FLAGS_PARAMETER))
 	{
 	  cp_lexer_consume_token (parser->lexer);
 	  if (token != first_specifier)
@@ -25607,7 +25609,7 @@ cp_parser_parameter_declaration (cp_parser *parser,
   /* Parse the declaration-specifiers.  */
   cp_token *decl_spec_token_start = cp_lexer_peek_token (parser->lexer);
   cp_parser_decl_specifier_seq (parser,
-				flags,
+				flags | CP_PARSER_FLAGS_PARAMETER,
 				&decl_specifiers,
 				&declares_class_or_enum);
 
diff --git a/gcc/testsuite/g++.dg/parse/pr113788.C b/gcc/testsuite/g++.dg/parse/pr113788.C
new file mode 100644
index 000000000000..d255037a514b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/pr113788.C
@@ -0,0 +1,20 @@
+// PR c++/113788
+// { dg-do compile { target c++11 } }
+
+struct S { int a, b; };
+struct U {
+  void foo () { this int g = 1; }	// { dg-error "expected ';' before 'int'" }
+};
+this auto h = 1;			// { dg-error "expected unqualified-id before 'this'" }
+
+int
+main ()
+{
+  S s = { 1, 2 };
+  short t[3] = { 3, 4, 5 };
+  this auto &[a, b] = s;		// { dg-error "invalid use of 'this' in non-member function" }
+  this auto &[c, d, e] = t;		// { dg-error "invalid use of 'this' in non-member function" }
+  this int f = 1;			// { dg-error "invalid use of 'this' in non-member function" }
+  for (this auto &i : t)		// { dg-error "invalid use of 'this' in non-member function" }
+    ;					// { dg-error "expected" }
+}					// { dg-error "expected" }