c++: Update TYPE_FIELDS of variant types if cp_parser_late_parsing_default_args etc. modify it [PR98533]

The following testcases ICE during type verification, because TYPE_FIELDS
of e.g. S RECORD_TYPE in pr119123.C is different from TYPE_FIELDS of const S.
Various decls are added to S's TYPE_FIELDS first, then finish_struct
indirectly calls fixup_type_variants to sync the variant copies.
But later on cp_parser_class_specifier calls
cp_parser_late_parsing_default_args and that apparently adds a lambda
type (from default argument) to TYPE_FIELDS of S.
Dunno if that is right or not, assuming it is right, the following
patch fixes it by updating TYPE_FIELDS of variant types if there were
any changes in the various functions cp_parser_class_specifier defers and
calls on the outermost enclosing class.
There was quite a lot of code repetition already before, so the patch
uses a lambda to avoid the repetitions.
To my surprise, in some of the contract testcases (
g++.dg/contracts/contracts-friend1.C
g++.dg/contracts/contracts-nested-class1.C
g++.dg/contracts/contracts-nested-class2.C
g++.dg/contracts/contracts-redecl7.C
g++.dg/contracts/contracts-redecl8.C
) it is actually setting class_type and pushing TRANSLATION_UNIT_DECL
rather than some class types in some cases.

Or should the lambda pushing into the containing class be somehow avoided?

2025-03-06  Jakub Jelinek  <jakub@redhat.com>

	PR c++/98533
	PR c++/119123
	* parser.cc (cp_parser_class_specifier): Update TYPE_FIELDS of
	variant types in case cp_parser_late_parsing_default_args etc. change
	TYPE_FIELDS on the main variant.  Add switch_to_class lambda and
	use it to simplify repeated class switching code.

	* g++.dg/cpp0x/pr98533.C: New test.
	* g++.dg/cpp0x/pr119123.C: New test.

2 files changed, 35 insertions, 0 deletions

diff --git a/gcc/testsuite/g++.dg/cpp0x/pr119123.C b/gcc/testsuite/g++.dg/cpp0x/pr119123.C
new file mode 100644
index 0000000..bbc1ca0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/pr119123.C
@@ -0,0 +1,10 @@
+// PR c++/119123
+// { dg-do compile { target c++11 } }
+// { dg-options "-O2 -g" }
+
+struct S {
+  template <typename> void foo (int = [] {}) const;
+};
+struct T {
+  static void bar (const S &);
+};
diff --git a/gcc/testsuite/g++.dg/cpp0x/pr98533.C b/gcc/testsuite/g++.dg/cpp0x/pr98533.C
new file mode 100644
index 0000000..c279d02
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/pr98533.C
@@ -0,0 +1,25 @@
+// PR c++/98533
+// { dg-do compile { target c++11 } }
+// { dg-options "-g" }
+
+class IR;
+struct Pass {
+  explicit Pass(IR *ir) : ir_(ir) {}
+  virtual ~Pass() = default;
+  IR *ir_ {nullptr};
+};
+struct PassManager {
+  template <typename T> void RunPass() { T pass(ir_); }
+  IR *ir_ {nullptr};
+};
+struct IR final {
+  template <typename T> void RunPass() { pass_manager_.RunPass<T>(); }
+  PassManager pass_manager_;
+};
+struct ThePass : Pass {
+  explicit ThePass(IR *ir) : Pass(ir) {}
+  ThePass(const ThePass &) = delete;
+  template <typename Func = bool (*)(void *)> void Bar(void *inst, Func func = [](void *) {});
+};
+
+void foo(IR *ir) { ir->RunPass<ThePass>(); }