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PR c++/95999: Improved error recovery in enumeration lists.

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This patch resolves PR c++/95999 which is an ICE-after-error regression
in the g++ front-end.  When parsing an enumerator list, the C++ parser
assumes that cp_parser_constant_expression always returns either an
INTEGER_CST or error_mark_node, but in the testcase reported in the
PR, it actually returns a VAR_DECL.

The usual (but perhaps controversial) design philosophy is that the
routine that reports the error normally has a duty to indicate this to
the rest of the compiler (via error_mark_node), but here the return
value from calling require_rvalue_constant_expression (parser.cc:10666)
is ignored.  I initially experimented with setting EXPRESSION to
error_mark_node here in cp_parser_constant_expression but (perhaps
conveniently) that's insufficient to resolve the problem.  The simple
fix in this patch is to tweak the two places that require INTEGER_CST
to treat all other tree types as though they are error_mark_node.

2022-03-10  Roger Sayle  <roger@nextmovesoftware.com>

gcc/cp/ChangeLog
	PR c++/95999
	* decl.cc (finish_enum_value_list): If VALUE isn't an INTEGER_CST
	consider it to be zero (i.e. treat it like error_mark_node).
	(build_enumerator): Likewise, if PREV_VALUE isn't an INTEGER_CST,
	set VALUE to error_mark_node.

gcc/testsuite/ChangeLog
	PR c++/95999
	* g++.dg/parse/pr95999.C: New test case.
This commit is contained in:
Roger Sayle 2022-03-10 07:41:12 +00:00
parent 2185c9734a
commit bae10419f6
2 changed files with 10 additions and 2 deletions
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4
gcc/cp/decl.cc
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@ -16263,7 +16263,7 @@ finish_enum_value_list (tree enumtype)
/* Update the minimum and maximum values, if appropriate. */ /* Update the minimum and maximum values, if appropriate. */
value = DECL_INITIAL (decl); value = DECL_INITIAL (decl);
if (value == error_mark_node) if (TREE_CODE (value) != INTEGER_CST)
value = integer_zero_node; value = integer_zero_node;
/* Figure out what the minimum and maximum values of the /* Figure out what the minimum and maximum values of the
enumerators are. */ enumerators are. */
@ -16552,7 +16552,7 @@ build_enumerator (tree name, tree value, tree enumtype, tree attributes,
which case the type is an unspecified integral type which case the type is an unspecified integral type
sufficient to contain the incremented value. */ sufficient to contain the incremented value. */
prev_value = DECL_INITIAL (TREE_VALUE (TYPE_VALUES (enumtype))); prev_value = DECL_INITIAL (TREE_VALUE (TYPE_VALUES (enumtype)));
if (error_operand_p (prev_value)) if (TREE_CODE (prev_value) != INTEGER_CST)
value = error_mark_node; value = error_mark_node;
else else
{ {

8
gcc/testsuite/g++.dg/parse/pr95999.C Normal file
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@ -0,0 +1,8 @@
/* { dg-do compile } */
int a;
enum struct b;
template <typename = enum struct b { c = a d }
template <> enum struct b { e }; // { dg-error "explicit specialization" }
// { dg-excess-errors "note" }
// { dg-excess-errors "5:" }