Re: [PATCH] c++: Don't allow defining types in enum-base [PR96380]

[Jason Merrill via Gcc-patches]

On 4/20/21 3:33 PM, Marek Polacek wrote:

In r11-2064 I made cp_parser_enum_specifier commit to tentative parse
when seeing a '{'.  That still looks like the correct thing to do, but
it caused an ICE-on-invalid as well as accepts-invalid.

When we have something sneaky like this, which is broken in multiple
ways:

   template 
   enum struct c : union enum struct c { e = b, f = a };

we parse the "enum struct c" part (that's OK) and then we see that
we have an enum-base, so we consume ':' and then parse the type-specifier
that follows the :.  "union enum" is clearly invalid, but we're still
parsing tentatively and we parse everything up to the ;, and then
throw away the underlying type.  We parsed everything because we were
tricked into parsing an enum-specifier in an enum-base of another
enum-specifier!  Not good.

Since the grammar for enum-base doesn't allow a defining-type-specifier,
only a type-specifier, we should set type_definition_forbidden_message
which fixes all the problems in this PR.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk (GCC 12)?
This may be too obscure to fix in 11.2, but it looks like a reasonable
change to backport.


OK for trunk, 11.2, and 10.4, since this is a regression from 10.1.


gcc/cp/ChangeLog:

PR c++/96380
* parser.c (cp_parser_enum_specifier): Don't allow defining
types in enum-base.

gcc/testsuite/ChangeLog:

PR c++/96380
* g++.dg/cpp0x/enum_base4.C: New test.
* g++.dg/cpp0x/enum_base5.C: New test.
---
  gcc/cp/parser.c | 4 
  gcc/testsuite/g++.dg/cpp0x/enum_base4.C | 8 
  gcc/testsuite/g++.dg/cpp0x/enum_base5.C | 7 +++
  3 files changed, 19 insertions(+)
  create mode 100644 gcc/testsuite/g++.dg/cpp0x/enum_base4.C
  create mode 100644 gcc/testsuite/g++.dg/cpp0x/enum_base5.C

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 99eccf0c5e4..fba516efa23 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -19942,6 +19942,10 @@ cp_parser_enum_specifier (cp_parser* parser)
/* Consume the `:'.  */
cp_lexer_consume_token (parser->lexer);
  
+  auto tdf

+   = make_temp_override (parser->type_definition_forbidden_message,
+ G_("types may not be defined in enum-base"));
+
/* Parse the type-specifier-seq.  */
cp_parser_type_specifier_seq (parser, CP_PARSER_FLAGS_NONE,
/*is_declaration=*/false,
diff --git a/gcc/testsuite/g++.dg/cpp0x/enum_base4.C 
b/gcc/testsuite/g++.dg/cpp0x/enum_base4.C
new file mode 100644
index 000..b3015256386
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/enum_base4.C
@@ -0,0 +1,8 @@
+// PR c++/96380
+// { dg-do compile { target c++11 } }
+
+extern const int a, b;
+enum struct c;
+template 
+enum struct c : union enum struct c { e = b, f = a };  // { dg-error "types may not 
be defined|expected|elaborated-type-specifier" }
+enum class c {};
diff --git a/gcc/testsuite/g++.dg/cpp0x/enum_base5.C 
b/gcc/testsuite/g++.dg/cpp0x/enum_base5.C
new file mode 100644
index 000..c01e857e612
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/enum_base5.C
@@ -0,0 +1,7 @@
+// PR c++/96380
+// { dg-do compile { target c++11 } }
+
+extern const int a, b;
+enum struct c;
+template 
+enum struct c : union enum struct c { e = b, f = a }; // { dg-error "types may not 
be defined|expected|elaborated-type-specifier" }

base-commit: 5491da23088734d516aae220810f253b9922c98c

[PATCH] c++: Don't allow defining types in enum-base [PR96380]

[Marek Polacek via Gcc-patches]

In r11-2064 I made cp_parser_enum_specifier commit to tentative parse
when seeing a '{'.  That still looks like the correct thing to do, but
it caused an ICE-on-invalid as well as accepts-invalid.

When we have something sneaky like this, which is broken in multiple
ways:

  template 
  enum struct c : union enum struct c { e = b, f = a };

we parse the "enum struct c" part (that's OK) and then we see that
we have an enum-base, so we consume ':' and then parse the type-specifier
that follows the :.  "union enum" is clearly invalid, but we're still
parsing tentatively and we parse everything up to the ;, and then
throw away the underlying type.  We parsed everything because we were
tricked into parsing an enum-specifier in an enum-base of another
enum-specifier!  Not good.

Since the grammar for enum-base doesn't allow a defining-type-specifier,
only a type-specifier, we should set type_definition_forbidden_message
which fixes all the problems in this PR.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk (GCC 12)?
This may be too obscure to fix in 11.2, but it looks like a reasonable
change to backport.

gcc/cp/ChangeLog:

PR c++/96380
* parser.c (cp_parser_enum_specifier): Don't allow defining
types in enum-base.

gcc/testsuite/ChangeLog:

PR c++/96380
* g++.dg/cpp0x/enum_base4.C: New test.
* g++.dg/cpp0x/enum_base5.C: New test.
---
 gcc/cp/parser.c | 4 
 gcc/testsuite/g++.dg/cpp0x/enum_base4.C | 8 
 gcc/testsuite/g++.dg/cpp0x/enum_base5.C | 7 +++
 3 files changed, 19 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/enum_base4.C
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/enum_base5.C

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 99eccf0c5e4..fba516efa23 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -19942,6 +19942,10 @@ cp_parser_enum_specifier (cp_parser* parser)
   /* Consume the `:'.  */
   cp_lexer_consume_token (parser->lexer);
 
+  auto tdf
+   = make_temp_override (parser->type_definition_forbidden_message,
+ G_("types may not be defined in enum-base"));
+
   /* Parse the type-specifier-seq.  */
   cp_parser_type_specifier_seq (parser, CP_PARSER_FLAGS_NONE,
/*is_declaration=*/false,
diff --git a/gcc/testsuite/g++.dg/cpp0x/enum_base4.C 
b/gcc/testsuite/g++.dg/cpp0x/enum_base4.C
new file mode 100644
index 000..b3015256386
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/enum_base4.C
@@ -0,0 +1,8 @@
+// PR c++/96380
+// { dg-do compile { target c++11 } }
+
+extern const int a, b;
+enum struct c;
+template 
+enum struct c : union enum struct c { e = b, f = a };  // { dg-error "types 
may not be defined|expected|elaborated-type-specifier" }
+enum class c {};
diff --git a/gcc/testsuite/g++.dg/cpp0x/enum_base5.C 
b/gcc/testsuite/g++.dg/cpp0x/enum_base5.C
new file mode 100644
index 000..c01e857e612
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/enum_base5.C
@@ -0,0 +1,7 @@
+// PR c++/96380
+// { dg-do compile { target c++11 } }
+
+extern const int a, b;
+enum struct c;
+template 
+enum struct c : union enum struct c { e = b, f = a }; // { dg-error "types may 
not be defined|expected|elaborated-type-specifier" }

base-commit: 5491da23088734d516aae220810f253b9922c98c
-- 
2.30.2