Go through alias template to handle aliased template specialization (issue #150).

Test case created with the help of Kim Gräsman.

iwyu.cc

@@ -3095,6 +3095,12 @@ class InstantiatedTemplateVisitor
     if (current_ast_node()->in_forward_declare_context())
       return true;
 
+    while (type->isTypeAlias()) {
+      type = DynCastFrom(type->getAliasedType().getTypePtr());
+      if (!type)
+        return true;
+    }
+
     // If we're a dependent type, we only try to be analyzed if we're
     // in the precomputed list -- in general, the only thing clang
     // tells us about dependent types is their name (which is all we

run_iwyu_tests.py

@@ -79,6 +79,7 @@ class OneIwyuTest(unittest.TestCase):
                       self.Include('prefix_header_includes-d3.h'),
                       self.Include('prefix_header_includes-d4.h')]
     clang_flags_map = {
+      'alias_template.cc': ['-std=c++11'],
       'auto_type_within_template.cc': ['-std=c++11'],
       'conversion_ctor.cc': ['-std=c++11'],
       'ms_inline_asm.cc': ['-fms-extensions'],

tests/cxx/alias_template.cc

@@ -0,0 +1,47 @@
+//===--- alias_template.cc - test input file for iwyu ---------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// Tests alias templates.  Does not test type aliases.
+
+#include "tests/cxx/direct.h"
+
+template<class T> struct FullUseTemplateArg {
+  char argument[sizeof(T)];
+};
+
+// Test that we go through alias template and handle aliased template
+// specialization.
+template<class T> using Alias = FullUseTemplateArg<T>;
+// IWYU: IndirectClass needs a declaration
+// IWYU: IndirectClass is...*indirect.h
+Alias<IndirectClass> alias;
+
+// Test following through entire chain of aliases.
+template<class T> using AliasChain1 = FullUseTemplateArg<T>;
+template<class T> using AliasChain2 = AliasChain1<T>;
+// IWYU: IndirectClass needs a declaration
+// IWYU: IndirectClass is...*indirect.h
+AliasChain2<IndirectClass> aliasChain;
+
+// Test the case when aliased type isn't a template specialization.
+template<class T> using Pointer = T*;
+Pointer<int> intPtr;
+
+/**** IWYU_SUMMARY
+
+tests/cxx/alias_template.cc should add these lines:
+#include "tests/cxx/indirect.h"
+
+tests/cxx/alias_template.cc should remove these lines:
+- #include "tests/cxx/direct.h"  // lines XX-XX
+
+The full include-list for tests/cxx/alias_template.cc:
+#include "tests/cxx/indirect.h"  // for IndirectClass
+
+***** IWYU_SUMMARY */