[PR c++/86610] lambda captures in templates

[Nathan Sidwell <nathan@acm.org>]

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This PR reports a bug where we select a non-const operator function and 
then apply it to a const object.  That's happening because the 
expression 'c[0]' is not dependent, so we figure end up resolving it. 
But the lambda capture logic doesn't capture 'c' at that point and we 
have a non-const qualified 'c'.  At instantiation time we do the capture 
and the by-value lambda results in const-qualified captures.

Jason, the orginal test in process_outer_var_ref looked a little funky 
-- why not just processing_template_decl? That would satisfy what the 
comment says it checking.  Anyway changing the test to check DECL's 
type-dependency makes the right things happen, and a bootstrap passes. 
Could you review please.

nathan
-- 
Nathan Sidwell

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2019-01-16  Nathan Sidwell  <nathan@acm.org>

	PR c++/86610
	* semantics.c (process_outer_var_ref): Only skip dependent types
	in templates.

	PR c++/86610
	* g++.dg/cpp0x/pr86610.C: New.

Index: cp/semantics.c
===================================================================
--- cp/semantics.c	(revision 267983)
+++ cp/semantics.c	(working copy)
@@ -3438,10 +3438,9 @@ process_outer_var_ref (tree decl, tsubst
     }
 
   /* In a lambda within a template, wait until instantiation
-     time to implicitly capture.  */
+     time to implicitly capture a dependent type.  */
   if (context == containing_function
-      && DECL_TEMPLATE_INFO (containing_function)
-      && uses_template_parms (DECL_TI_ARGS (containing_function)))
+      && dependent_type_p (TREE_TYPE (decl)))
     return decl;
 
   if (lambda_expr && VAR_P (decl)
Index: testsuite/g++.dg/cpp0x/pr86610.C
===================================================================
--- testsuite/g++.dg/cpp0x/pr86610.C	(revision 0)
+++ testsuite/g++.dg/cpp0x/pr86610.C	(working copy)
@@ -0,0 +1,31 @@
+// { dg-do run { target c++11 } }
+// PR c++86610 lambda capture inside template
+
+struct C
+{
+  int operator[](int)
+  { return 1; }
+
+  int operator[](int) const
+  { return 0; } // Want this one
+};
+
+int q()
+{
+  C c;
+  return [=] { return c[0]; }();
+}
+
+template <typename T>
+int f()
+{
+  C c;
+  T d;
+  return [=] { return c[0]; }() 
+    + [=] { return c[0] + d[0]; }();
+}
+
+int main()
+{
+  return q () + f<C>();
+}