In this testcase, in C++17 mode after parsing the template-id fails, we try to treat the template-name as a class template deduction placeholder, producing an auto type, and then we try to take its TREE_TYPE when calling cp_parser_check_for_invalid_type_id, which doesn't work because it's a type, not a TYPE_DECL. Fixed by removing the TREE_TYPE and adjusting cp_parser_check_for_invalid_type_id to handle TYPE_DECL.
Really we shouldn't be creating a deduction placeholder in the first place when the template name is followed by <, but that distinction shouldn't affect well-formed code since we try to parse a template-id first. I still want to improve our handling of parse errors in template-ids; we never actually diagnose the syntax error here because it's swallowed by tentative parsing, we just say "argument 1 is invalid". Tested x86_64-pc-linux-gnu, applying to trunk.
commit bbea244e8042460d49970b7fffce13f79e58d8e9 Author: Jason Merrill <ja...@redhat.com> Date: Tue Jun 20 15:32:06 2017 -0400 PR c++/79056 - C++17 ICE with invalid template syntax. * parser.c (cp_parser_simple_type_specifier): Don't assume that type is a TYPE_DECL. (cp_parser_check_for_invalid_template_id): Handle TYPE_DECL. * pt.c (template_placeholder_p): New. * cp-tree.h: Declare it. diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index 40c113b..33dde15 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -6413,6 +6413,7 @@ extern void check_template_variable (tree); extern tree make_auto (void); extern tree make_decltype_auto (void); extern tree make_template_placeholder (tree); +extern bool template_placeholder_p (tree); extern tree do_auto_deduction (tree, tree, tree); extern tree do_auto_deduction (tree, tree, tree, tsubst_flags_t, diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c index ddb1cf3..97cd923 100644 --- a/gcc/cp/parser.c +++ b/gcc/cp/parser.c @@ -2983,7 +2983,9 @@ cp_parser_check_for_invalid_template_id (cp_parser* parser, if (cp_lexer_next_token_is (parser->lexer, CPP_LESS)) { - if (TYPE_P (type)) + if (TREE_CODE (type) == TYPE_DECL) + type = TREE_TYPE (type); + if (TYPE_P (type) && !template_placeholder_p (type)) error_at (location, "%qT is not a template", type); else if (identifier_p (type)) { @@ -17060,7 +17062,7 @@ cp_parser_simple_type_specifier (cp_parser* parser, /* There is no valid C++ program where a non-template type is followed by a "<". That usually indicates that the user thought that the type was a template. */ - cp_parser_check_for_invalid_template_id (parser, TREE_TYPE (type), + cp_parser_check_for_invalid_template_id (parser, type, none_type, token->location); } diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index fba7fb1..392fba0 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -24799,6 +24799,14 @@ make_template_placeholder (tree tmpl) return t; } +/* True iff T is a C++17 class template deduction placeholder. */ + +bool +template_placeholder_p (tree t) +{ + return is_auto (t) && CLASS_PLACEHOLDER_TEMPLATE (t); +} + /* Make a "constrained auto" type-specifier. This is an auto type with constraints that must be associated after deduction. The constraint is formed from the given diff --git a/gcc/testsuite/g++.dg/parse/template28.C b/gcc/testsuite/g++.dg/parse/template28.C new file mode 100644 index 0000000..6868bc8 --- /dev/null +++ b/gcc/testsuite/g++.dg/parse/template28.C @@ -0,0 +1,10 @@ +// PR c++/79056 + +template<class> struct A {}; + +template<class T> void foo(A<T>=A<T>()) {} // { dg-error "" } + +void bar() +{ + foo(A<int>()); // { dg-error "" } +}