Index: cfe/trunk/include/clang/AST/NestedNameSpecifier.h
===================================================================
--- cfe/trunk/include/clang/AST/NestedNameSpecifier.h
+++ cfe/trunk/include/clang/AST/NestedNameSpecifier.h
@@ -212,9 +212,12 @@
   /// parameter pack (for C++11 variadic templates).
   bool containsUnexpandedParameterPack() const;
 
-  /// Print this nested name specifier to the given output
-  /// stream.
-  void print(raw_ostream &OS, const PrintingPolicy &Policy) const;
+  /// Print this nested name specifier to the given output stream. If
+  /// `ResolveTemplateArguments` is true, we'll print actual types, e.g.
+  /// `ns::SomeTemplate<int, MyClass>` instead of
+  /// `ns::SomeTemplate<Container::value_type, T>`.
+  void print(raw_ostream &OS, const PrintingPolicy &Policy,
+             bool ResolveTemplateArguments = false) const;
 
   void Profile(llvm::FoldingSetNodeID &ID) const {
     ID.AddPointer(Prefix.getOpaqueValue());
Index: cfe/trunk/lib/AST/NestedNameSpecifier.cpp
===================================================================
--- cfe/trunk/lib/AST/NestedNameSpecifier.cpp
+++ cfe/trunk/lib/AST/NestedNameSpecifier.cpp
@@ -16,6 +16,7 @@
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
+#include "clang/AST/DeclTemplate.h"
 #include "clang/AST/PrettyPrinter.h"
 #include "clang/AST/TemplateName.h"
 #include "clang/AST/Type.h"
@@ -270,9 +271,8 @@
 
 /// Print this nested name specifier to the given output
 /// stream.
-void
-NestedNameSpecifier::print(raw_ostream &OS,
-                           const PrintingPolicy &Policy) const {
+void NestedNameSpecifier::print(raw_ostream &OS, const PrintingPolicy &Policy,
+                                bool ResolveTemplateArguments) const {
   if (getPrefix())
     getPrefix()->print(OS, Policy);
 
@@ -305,6 +305,15 @@
     LLVM_FALLTHROUGH;
 
   case TypeSpec: {
+    const auto *Record =
+            dyn_cast_or_null<ClassTemplateSpecializationDecl>(getAsRecordDecl());
+    if (ResolveTemplateArguments && Record) {
+        // Print the type trait with resolved template parameters.
+        Record->printName(OS);
+        printTemplateArgumentList(OS, Record->getTemplateArgs().asArray(),
+                                  Policy);
+        break;
+    }
     const Type *T = getAsType();
 
     PrintingPolicy InnerPolicy(Policy);
Index: cfe/trunk/lib/Sema/SemaTemplate.cpp
===================================================================
--- cfe/trunk/lib/Sema/SemaTemplate.cpp
+++ cfe/trunk/lib/Sema/SemaTemplate.cpp
@@ -3052,6 +3052,28 @@
   return Cond;
 }
 
+// Print a diagnostic for the failing static_assert expression. Defaults to
+// pretty-printing the expression.
+static void prettyPrintFailedBooleanCondition(llvm::raw_string_ostream &OS,
+                                              const Expr *FailedCond,
+                                              const PrintingPolicy &Policy) {
+  const auto *DR = dyn_cast<DeclRefExpr>(FailedCond);
+  if (DR && DR->getQualifier()) {
+    // If this is a qualified name, expand the template arguments in nested
+    // qualifiers.
+    DR->getQualifier()->print(OS, Policy, true);
+    // Then print the decl itself.
+    const ValueDecl *VD = DR->getDecl();
+    OS << VD->getName();
+    if (const auto *IV = dyn_cast<VarTemplateSpecializationDecl>(VD)) {
+      // This is a template variable, print the expanded template arguments.
+      printTemplateArgumentList(OS, IV->getTemplateArgs().asArray(), Policy);
+    }
+    return;
+  }
+  FailedCond->printPretty(OS, nullptr, Policy);
+}
+
 std::pair<Expr *, std::string>
 Sema::findFailedBooleanCondition(Expr *Cond, bool AllowTopLevelCond) {
   Cond = lookThroughRangesV3Condition(PP, Cond);
@@ -3093,7 +3115,7 @@
   std::string Description;
   {
     llvm::raw_string_ostream Out(Description);
-    FailedCond->printPretty(Out, nullptr, getPrintingPolicy());
+    prettyPrintFailedBooleanCondition(Out, FailedCond, getPrintingPolicy());
   }
   return { FailedCond, Description };
 }
Index: cfe/trunk/test/SemaCXX/static-assert-cxx17.cpp
===================================================================
--- cfe/trunk/test/SemaCXX/static-assert-cxx17.cpp
+++ cfe/trunk/test/SemaCXX/static-assert-cxx17.cpp
@@ -0,0 +1,47 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++1z -triple=x86_64-linux-gnu
+
+template <typename U, typename V>
+struct S1 {
+  static constexpr const bool value = false;
+};
+
+template <typename U, typename V>
+inline constexpr bool global_inline_var = S1<U, V>::value;
+
+template <typename T>
+struct S2 {
+  template <typename U, typename V>
+  static inline constexpr bool var = global_inline_var<U, V>;
+};
+
+template <typename U, typename V>
+void foo() {
+  static_assert(S1<U, V>::value);
+  // expected-error@-1{{static_assert failed due to requirement 'S1<int, float>::value'}}
+}
+template void foo<int, float>();
+// expected-note@-1{{in instantiation of function template specialization 'foo<int, float>' requested here}}
+
+template <typename U, typename V>
+void foo2() {
+  static_assert(global_inline_var<U, V>);
+  // expected-error@-1{{static_assert failed due to requirement 'global_inline_var<int, float>'}}
+}
+template void foo2<int, float>();
+// expected-note@-1{{in instantiation of function template specialization 'foo2<int, float>' requested here}}
+
+template <typename T, typename U, typename V>
+void foo3() {
+  static_assert(T::template var<U, V>);
+  // expected-error@-1{{static_assert failed due to requirement 'S2<long>::var<int, float>'}}
+}
+template void foo3<S2<long>, int, float>();
+// expected-note@-1{{in instantiation of function template specialization 'foo3<S2<long>, int, float>' requested here}}
+
+template <typename T>
+void foo4() {
+  static_assert(S1<T[sizeof(T)], int[4]>::value, "");
+  // expected-error@-1{{static_assert failed due to requirement 'S1<float [4], int [4]>::value'}}
+};
+template void foo4<float>();
+// expected-note@-1{{in instantiation of function template specialization 'foo4<float>' requested here}}
Index: cfe/trunk/test/SemaCXX/static-assert.cpp
===================================================================
--- cfe/trunk/test/SemaCXX/static-assert.cpp
+++ cfe/trunk/test/SemaCXX/static-assert.cpp
@@ -68,3 +68,100 @@
 };
 
 static_assert(first_trait<X>::value && second_trait<X>::value, "message"); // expected-error{{static_assert failed due to requirement 'second_trait<X>::value' "message"}}
+
+namespace std {
+
+template <class Tp, Tp v>
+struct integral_constant {
+  static const Tp value = v;
+  typedef Tp value_type;
+  typedef integral_constant type;
+};
+
+template <class Tp, Tp v>
+const Tp integral_constant<Tp, v>::value;
+
+typedef integral_constant<bool, true> true_type;
+typedef integral_constant<bool, false> false_type;
+
+template <class Tp>
+struct is_const : public false_type {};
+template <class Tp>
+struct is_const<Tp const> : public true_type {};
+
+// We do not define is_same in terms of integral_constant to check that both implementations are supported.
+template <typename T, typename U>
+struct is_same {
+  static const bool value = false;
+};
+
+template <typename T>
+struct is_same<T, T> {
+  static const bool value = true;
+};
+
+} // namespace std
+
+struct ExampleTypes {
+  using T = int;
+  using U = float;
+};
+
+static_assert(std::is_same<ExampleTypes::T, ExampleTypes::U>::value, "message");
+// expected-error@-1{{static_assert failed due to requirement 'std::is_same<int, float>::value' "message"}}
+static_assert(std::is_const<ExampleTypes::T>::value, "message");
+// expected-error@-1{{static_assert failed due to requirement 'std::is_const<int>::value' "message"}}
+
+struct BI_tag {};
+struct RAI_tag : BI_tag {};
+struct MyIterator {
+  using tag = BI_tag;
+};
+struct MyContainer {
+  using iterator = MyIterator;
+};
+template <class Container>
+void foo() {
+  static_assert(std::is_same<RAI_tag, typename Container::iterator::tag>::value, "message");
+  // expected-error@-1{{static_assert failed due to requirement 'std::is_same<RAI_tag, BI_tag>::value' "message"}}
+}
+template void foo<MyContainer>();
+// expected-note@-1{{in instantiation of function template specialization 'foo<MyContainer>' requested here}}
+
+namespace ns {
+template <typename T, int v>
+struct NestedTemplates1 {
+  struct NestedTemplates2 {
+    template <typename U>
+    struct NestedTemplates3 : public std::is_same<T, U> {};
+  };
+};
+} // namespace ns
+
+template <typename T, typename U, int a>
+void foo2() {
+  static_assert(::ns::NestedTemplates1<T, a>::NestedTemplates2::template NestedTemplates3<U>::value, "message");
+  // expected-error@-1{{static_assert failed due to requirement '::ns::NestedTemplates1<int, 3>::NestedTemplates2::NestedTemplates3<float>::value' "message"}}
+}
+template void foo2<int, float, 3>();
+// expected-note@-1{{in instantiation of function template specialization 'foo2<int, float, 3>' requested here}}
+
+template <class T>
+void foo3(T t) {
+  static_assert(std::is_const<T>::value, "message");
+  // expected-error-re@-1{{static_assert failed due to requirement 'std::is_const<(lambda at {{.*}}static-assert.cpp:{{[0-9]*}}:{{[0-9]*}})>::value' "message"}}
+  static_assert(std::is_const<decltype(t)>::value, "message");
+  // expected-error-re@-1{{static_assert failed due to requirement 'std::is_const<(lambda at {{.*}}static-assert.cpp:{{[0-9]*}}:{{[0-9]*}})>::value' "message"}}
+}
+void callFoo3() {
+  foo3([]() {});
+  // expected-note@-1{{in instantiation of function template specialization 'foo3<(lambda at }}
+}
+
+template <class T>
+void foo4(T t) {
+  static_assert(std::is_const<typename T::iterator>::value, "message");
+  // expected-error@-1{{type 'int' cannot be used prior to '::' because it has no members}}
+}
+void callFoo4() { foo4(42); }
+// expected-note@-1{{in instantiation of function template specialization 'foo4<int>' requested here}}