[PATCH] c++: Fix tentative parsing of enum-specifier [PR96077]

[Marek Polacek via Gcc-patches]

Here's an interesting issue: in this code a ) is missing:

  enum { E = (2 } e;

but we compile the code anyway, and E is set to 0 in build_enumerator,
which is sneaky.

The problem is that cp_parser_enum_specifier parses tentatively, because
when we see the enum keyword, we don't know yet if we'll find an
enum-specifier, opaque-enum-declaration, or elaborated-enum-specifier.

In this test when we call cp_parser_enumerator_list we're still parsing
tentatively, and as a consequence, parens.require_close (parser) in
cp_parser_primary_expression doesn't report any errors.  But we only go
on to parse the enumerator-list after we've seen a {, at which point we
might as well commit -- we know we're dealing with an enum-specifier.

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

gcc/cp/ChangeLog:

        PR c++/96077
        * parser.c (cp_parser_enum_specifier): Commit to tentative parse
        after we've seen an opening brace.

gcc/testsuite/ChangeLog:

        PR c++/96077
        * g++.dg/parse/enum14.C: New test.
---
 gcc/cp/parser.c                     | 7 ++++++-
 gcc/testsuite/g++.dg/parse/enum14.C | 7 +++++++
 2 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/parse/enum14.C

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 528b41b7170..ee6a956aea9 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -19412,7 +19412,12 @@ cp_parser_enum_specifier (cp_parser* parser)
                     "ISO C++ forbids empty unnamed enum");
        }
       else
-       cp_parser_enumerator_list (parser, type);
+       {
+         /* We've seen a '}' so we know we're in an enum-specifier.
+            Commit to any tentative parse to get syntax errors.  */
+         cp_parser_commit_to_tentative_parse (parser);
+         cp_parser_enumerator_list (parser, type);
+       }
 
       /* Consume the final '}'.  */
       braces.require_close (parser);
diff --git a/gcc/testsuite/g++.dg/parse/enum14.C 
b/gcc/testsuite/g++.dg/parse/enum14.C
new file mode 100644
index 00000000000..be09cca5211
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/enum14.C
@@ -0,0 +1,7 @@
+// PR c++/96077
+
+int main ()
+{
+  enum { E = (2 } e; // { dg-error "expected" }
+  enum { F = true ? 2 : (3 /* missing ")" here */ } f; // { dg-error 
"expected" }
+}

base-commit: c6b7ba5de624f2a17d799bac5ff017cd065ce035
-- 
2.26.2