C++ PATCH for c++/47687 (infinite recursion with lambda returning lambda)

C++ PATCH for c++/47687 (infinite recursion with lambda returning lambda)

[Jason Merrill]

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Here, deciding whether the nested lambda was dependent meant checking 
the enclosing function, which meant checking the function's type, which 
meant checking its return type, the nested lambda.  I've broken this 
cycle by looking not at whether the enclosing function is a dependent 
expression, but whether it is a template.

Tested x86_64-pc-linux-gnu, applying to trunk.

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commit 5656f70c3b34354e29de75db6dad0a0b44ef6f04
Author: Jason Merrill <jason@redhat.com>
Date:   Fri May 27 12:05:59 2011 -0400

    	PR c++/47687
    	* pt.c (dependent_type_p_r): Avoid infinite recursion.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 71fe0a0..ae3d83d 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -18260,8 +18260,15 @@ dependent_type_p_r (tree type)
   scope = TYPE_CONTEXT (type);
   if (scope && TYPE_P (scope))
     return dependent_type_p (scope);
-  else if (scope && TREE_CODE (scope) == FUNCTION_DECL)
-    return type_dependent_expression_p (scope);
+  /* Don't use type_dependent_expression_p here, as it can lead
+     to infinite recursion trying to determine whether a lambda
+     nested in a lambda is dependent (c++/47687).  */
+  else if (scope && TREE_CODE (scope) == FUNCTION_DECL
+	   && DECL_LANG_SPECIFIC (scope)
+	   && DECL_TEMPLATE_INFO (scope)
+	   && (any_dependent_template_arguments_p
+	       (INNERMOST_TEMPLATE_ARGS (DECL_TI_ARGS (scope)))))
+    return true;
 
   /* Other types are non-dependent.  */
   return false;
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested4.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested4.C
new file mode 100644
index 0000000..a5bd1a2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested4.C
@@ -0,0 +1,9 @@
+// PR c++/47687
+// { dg-options -std=c++0x }
+
+template <class T> struct A { };
+
+auto inl = []{ return []{}; }();
+typedef decltype(inl) inlt;
+
+A<inlt> a;