Re: [PATCH] c++: undeclared identifier in requires-clause [PR99678]

[Jason Merrill]

On 6/12/24 14:22, Patrick Palka wrote:

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
for trunk/14?

OK.

-- >8 --

Since the terms of a requires-clause are grammatically primary-expressions
rather than e.g. postfix-expressions, it seems we need to explicitly
handle and diagnose the case where a term parses to bare unresolved
unqualified-id, like cp_parser_postfix_expression does, since
cp_parser_primary_expression doesn't do so itself.  Otherwise we fail to
reject the first three requires-clauses those below.

Note that the only users of primary-expression in the C++ grammar are
indeed postfix-expression and constraint-logical-and-expression, so it
seems not so surprising that we need this special handling here.

        PR c++/99678

gcc/cp/ChangeLog:

        * parser.cc (cp_parser_constraint_primary_expression): Reject
        a bare unresolved unqualified-id.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/concepts-requires38.C: New test.
---
  gcc/cp/parser.cc                                 |  2 ++
  gcc/testsuite/g++.dg/cpp2a/concepts-requires38.C | 14 ++++++++++++++
  2 files changed, 16 insertions(+)
  create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires38.C

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index bc4a2359153..0d59f7d2690 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -31496,6 +31496,8 @@ cp_parser_constraint_primary_expression (cp_parser 
*parser, bool lambda_p)
      }
    if (pce == pce_ok)
      {
+      if (idk == CP_ID_KIND_UNQUALIFIED && identifier_p (expr))
+       expr = unqualified_name_lookup_error (expr);
        cp_lexer_commit_tokens (parser->lexer);
        return finish_constraint_primary_expr (expr);
      }
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires38.C 
b/gcc/testsuite/g++.dg/cpp2a/concepts-requires38.C
new file mode 100644
index 00000000000..663195b79cc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires38.C
@@ -0,0 +1,14 @@
+// PR c++/99678
+// { dg-do compile { target c++20 } }
+
+template<class T>
+void f1() requires undeclared_identifier; // { dg-error "not declared" }
+
+template<class T>
+void f2() requires true && undeclared_identifier; // { dg-error "not declared" 
}
+
+template<class T>
+void f3() requires false || undeclared_identifier; // { dg-error "not 
declared" }
+
+template<class T>
+void f4() requires undeclared_identifier(T{}); // { dg-error "must be enclosed in 
parentheses" }