C++ PATCHes for c++/82882, ICE with lambda in template default argument

This testcase was broken by the lambda rewrite.  This turned out to be
because the lambda in the template's default argument had namespace
scope, while the instantiation had function scope, because of
tsubst_default_argument calling push_access_scope and do_pushtag using
the resulting value of current_function_decl.

The fix is to teach do_pushtag to do better.  For GCC 8 I'm applying a
focused patch that just recognizes when we're trying to give a lambda
a function scope we aren't actually in.  This re-broke bug 59949, so
to avoid that I needed to fix tsubst_lambda_expr to use and update the
discriminator for global lambda scope when the template lambda has no
extra scope.

Looking at do_pushtag led me to wonder why we were relying on
current_* for the scope in the first place; since we're going to add
the tag to current_binding_level, we should get the scope from there
as well.  Making that change revealed a few more issues:

* With a lambda in a default argument, we would frequently be in the
binding_level for the calling function.  Fixed by calling
push_to_top_level.
* Redeclarations of C++11 enums with specified underlying type were
getting pushed into an arbitrary binding level.  Fixed by removing the
unnecessary permissiveness around such redeclarations with underlying
types that are not template-equivalent, so a redeclaration isn't
pushed anywhere.
* Lambdas in default member initializers were also getting pushed into
an arbitrary binding level, due to the code for allowing type
definition in a compound literal in a static data member initializer.
Fixed by no longer looking through the binding_level for a complete
class, but instead not pushing the tag anywhere if the class is
complete; a lambda type isn't found by name anyway.

Tested x86_64-pc-linux-gnu.  First patch applied to trunk and 8,
others only to trunk.

On Fri, Jun 15, 2018 at 4:21 PM, Jason Merrill <jason@redhat.com> wrote:
> This testcase was broken by the lambda rewrite.  This turned out to be
> because the lambda in the template's default argument had namespace
> scope, while the instantiation had function scope, because of
> tsubst_default_argument calling push_access_scope and do_pushtag using
> the resulting value of current_function_decl.
>
> The fix is to teach do_pushtag to do better.  For GCC 8 I'm applying a
> focused patch that just recognizes when we're trying to give a lambda
> a function scope we aren't actually in.  This re-broke bug 59949, so
> to avoid that I needed to fix tsubst_lambda_expr to use and update the
> discriminator for global lambda scope when the template lambda has no
> extra scope.
>
> Looking at do_pushtag led me to wonder why we were relying on
> current_* for the scope in the first place; since we're going to add
> the tag to current_binding_level, we should get the scope from there
> as well.  Making that change revealed a few more issues:
>
> * With a lambda in a default argument, we would frequently be in the
> binding_level for the calling function.  Fixed by calling
> push_to_top_level.
> * Redeclarations of C++11 enums with specified underlying type were
> getting pushed into an arbitrary binding level.  Fixed by removing the
> unnecessary permissiveness around such redeclarations with underlying
> types that are not template-equivalent, so a redeclaration isn't
> pushed anywhere.
> * Lambdas in default member initializers were also getting pushed into
> an arbitrary binding level, due to the code for allowing type
> definition in a compound literal in a static data member initializer.
> Fixed by no longer looking through the binding_level for a complete
> class, but instead not pushing the tag anywhere if the class is
> complete; a lambda type isn't found by name anyway.

One more: looking through one class binding level then stopped at its
enclosing template parms level even if that's still inside another
class binding level.

Tested x86_64-pc-linux-gnu, applying to trunk.
commit fa24a18a557cc0f7a7cb42416b0150a4847916c6
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Jun 27 12:25:07 2018 -0400

    Avoid crash on friend in nested class template.
    
            * name-lookup.c (do_pushtag): If we skip a class level, also skip
            its template level.

diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index a30c37428ad..e0500d83071 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -6509,20 +6509,30 @@ do_pushtag (tree name, tree type, tag_scope scope)
   tree decl;
 
   cp_binding_level *b = current_binding_level;
-  while (/* Cleanup scopes are not scopes from the point of view of
-	    the language.  */
-	 b->kind == sk_cleanup
-	 /* Neither are function parameter scopes.  */
-	 || b->kind == sk_function_parms
-	 /* Neither are the scopes used to hold template parameters
-	    for an explicit specialization.  For an ordinary template
-	    declaration, these scopes are not scopes from the point of
-	    view of the language.  */
-	 || (b->kind == sk_template_parms
-	     && (b->explicit_spec_p || scope == ts_global))
-	 || (b->kind == sk_class
-	     && scope != ts_current))
-    b = b->level_chain;
+  while (true)
+    {
+      if (/* Cleanup scopes are not scopes from the point of view of
+	     the language.  */
+	  b->kind == sk_cleanup
+	  /* Neither are function parameter scopes.  */
+	  || b->kind == sk_function_parms
+	  /* Neither are the scopes used to hold template parameters
+	     for an explicit specialization.  For an ordinary template
+	     declaration, these scopes are not scopes from the point of
+	     view of the language.  */
+	  || (b->kind == sk_template_parms
+	      && (b->explicit_spec_p || scope == ts_global)))
+	b = b->level_chain;
+      else if (b->kind == sk_class
+	       && scope != ts_current)
+	{
+	  b = b->level_chain;
+	  if (b->kind == sk_template_parms)
+	    b = b->level_chain;
+	}
+      else
+	break;
+    }
 
   gcc_assert (identifier_p (name));
 
diff --git a/gcc/testsuite/g++.dg/template/friend66.C b/gcc/testsuite/g++.dg/template/friend66.C
new file mode 100644
index 00000000000..f8c95f844b3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/friend66.C
@@ -0,0 +1,9 @@
+template <class T>
+struct A
+{
+  template <class U>
+  struct B
+  {
+    friend struct C;
+  };
+};
diff --git a/gcc/testsuite/g++.old-deja/g++.law/visibility13.C b/gcc/testsuite/g++.old-deja/g++.law/visibility13.C
index 025b0b1ef54..451ef1afaf8 100644
--- a/gcc/testsuite/g++.old-deja/g++.law/visibility13.C
+++ b/gcc/testsuite/g++.old-deja/g++.law/visibility13.C
@@ -15,9 +15,11 @@ using namespace std;
 
 const int ArraySize = 12;
 
+template <class> class Array_RC;
+
 template <class Type>
-class Array { // { dg-error "" } .struct Array_RC redecl.*
-friend class Array_RC;
+class Array {
+  friend class Array_RC<Type>;
 public:
     Array(const Type *ar, int sz) { init(ar,sz); }
     virtual ~Array() { delete [] ia; }
@@ -76,8 +78,8 @@ Array_RC<Type>::Array_RC(const Type *ar, int sz) : Array<Type>(ar, sz) {}
 
 template <class Type>
 Type &Array_RC<Type>::operator[](int ix) {
-    assert(ix >= 0 && ix < size);// { dg-error "" } member .size.*
-    return ia[ix];// { dg-error "" } member .ia.*
+    assert(ix >= 0 && ix < this->size);
+    return this->ia[ix];
 }
 
 //    -------------------   Test routine   ----------------------