diff --git a/clang-tools-extra/unittests/clang-query/QueryParserTest.cpp b/clang-tools-extra/unittests/clang-query/QueryParserTest.cpp
index 1088be0..ace095d 100644
--- a/clang-tools-extra/unittests/clang-query/QueryParserTest.cpp
+++ b/clang-tools-extra/unittests/clang-query/QueryParserTest.cpp
@@ -16,95 +16,139 @@
 using namespace clang;
 using namespace clang::query;
 
-TEST(QueryParser, NoOp) {
-  QueryRef Q = QueryParser::parse("");
+class QueryParserTest : public ::testing::Test {
+protected:
+  QueryParserTest() {}
+  QueryRef parse(StringRef Code) { return QueryParser::parse(Code, QS); }
+
+  QuerySession QS{llvm::ArrayRef<ASTUnit*>()};
+};
+
+TEST_F(QueryParserTest, NoOp) {
+  QueryRef Q = parse("");
   EXPECT_TRUE(isa<NoOpQuery>(Q));
 
-  Q = QueryParser::parse("\n");
+  Q = parse("\n");
   EXPECT_TRUE(isa<NoOpQuery>(Q));
 }
 
-TEST(QueryParser, Invalid) {
-  QueryRef Q = QueryParser::parse("foo");
+TEST_F(QueryParserTest, Invalid) {
+  QueryRef Q = parse("foo");
   ASSERT_TRUE(isa<InvalidQuery>(Q));
   EXPECT_EQ("unknown command: foo", cast<InvalidQuery>(Q)->ErrStr);
 }
 
-TEST(QueryParser, Help) {
-  QueryRef Q = QueryParser::parse("help");
+TEST_F(QueryParserTest, Help) {
+  QueryRef Q = parse("help");
   ASSERT_TRUE(isa<HelpQuery>(Q));
 
-  Q = QueryParser::parse("help me");
+  Q = parse("help me");
   ASSERT_TRUE(isa<InvalidQuery>(Q));
   EXPECT_EQ("unexpected extra input: ' me'", cast<InvalidQuery>(Q)->ErrStr);
 }
 
-TEST(QueryParser, Set) {
-  QueryRef Q = QueryParser::parse("set");
+TEST_F(QueryParserTest, Set) {
+  QueryRef Q = parse("set");
   ASSERT_TRUE(isa<InvalidQuery>(Q));
   EXPECT_EQ("expected variable name", cast<InvalidQuery>(Q)->ErrStr);
 
-  Q = QueryParser::parse("set foo bar");
+  Q = parse("set foo bar");
   ASSERT_TRUE(isa<InvalidQuery>(Q));
   EXPECT_EQ("unknown variable: 'foo'", cast<InvalidQuery>(Q)->ErrStr);
 
-  Q = QueryParser::parse("set output");
+  Q = parse("set output");
   ASSERT_TRUE(isa<InvalidQuery>(Q));
   EXPECT_EQ("expected 'diag', 'print' or 'dump', got ''",
             cast<InvalidQuery>(Q)->ErrStr);
 
-  Q = QueryParser::parse("set bind-root true foo");
+  Q = parse("set bind-root true foo");
   ASSERT_TRUE(isa<InvalidQuery>(Q));
   EXPECT_EQ("unexpected extra input: ' foo'", cast<InvalidQuery>(Q)->ErrStr);
 
-  Q = QueryParser::parse("set output foo");
+  Q = parse("set output foo");
   ASSERT_TRUE(isa<InvalidQuery>(Q));
   EXPECT_EQ("expected 'diag', 'print' or 'dump', got 'foo'",
             cast<InvalidQuery>(Q)->ErrStr);
 
-  Q = QueryParser::parse("set output dump");
+  Q = parse("set output dump");
   ASSERT_TRUE(isa<SetQuery<OutputKind> >(Q));
   EXPECT_EQ(&QuerySession::OutKind, cast<SetQuery<OutputKind> >(Q)->Var);
   EXPECT_EQ(OK_Dump, cast<SetQuery<OutputKind> >(Q)->Value);
 
-  Q = QueryParser::parse("set bind-root foo");
+  Q = parse("set bind-root foo");
   ASSERT_TRUE(isa<InvalidQuery>(Q));
   EXPECT_EQ("expected 'true' or 'false', got 'foo'",
             cast<InvalidQuery>(Q)->ErrStr);
 
-  Q = QueryParser::parse("set bind-root true");
+  Q = parse("set bind-root true");
   ASSERT_TRUE(isa<SetQuery<bool> >(Q));
   EXPECT_EQ(&QuerySession::BindRoot, cast<SetQuery<bool> >(Q)->Var);
   EXPECT_EQ(true, cast<SetQuery<bool> >(Q)->Value);
 }
 
-TEST(QueryParser, Match) {
-  QueryRef Q = QueryParser::parse("match decl()");
+TEST_F(QueryParserTest, Match) {
+  QueryRef Q = parse("match decl()");
   ASSERT_TRUE(isa<MatchQuery>(Q));
   EXPECT_TRUE(cast<MatchQuery>(Q)->Matcher.canConvertTo<Decl>());
 
-  Q = QueryParser::parse("m stmt()");
+  Q = parse("m stmt()");
   ASSERT_TRUE(isa<MatchQuery>(Q));
   EXPECT_TRUE(cast<MatchQuery>(Q)->Matcher.canConvertTo<Stmt>());
 }
 
-TEST(QueryParser, Complete) {
+TEST_F(QueryParserTest, LetUnlet) {
+  QueryRef Q = parse("let foo decl()");
+  ASSERT_TRUE(isa<LetQuery>(Q));
+  EXPECT_EQ("foo", cast<LetQuery>(Q)->Name);
+  EXPECT_TRUE(cast<LetQuery>(Q)->Value.isMatcher());
+  EXPECT_TRUE(cast<LetQuery>(Q)->Value.getMatcher().hasTypedMatcher<Decl>());
+
+  Q = parse("let bar \"str\"");
+  ASSERT_TRUE(isa<LetQuery>(Q));
+  EXPECT_EQ("bar", cast<LetQuery>(Q)->Name);
+  EXPECT_TRUE(cast<LetQuery>(Q)->Value.isString());
+  EXPECT_EQ("str", cast<LetQuery>(Q)->Value.getString());
+
+  Q = parse("let");
+  ASSERT_TRUE(isa<InvalidQuery>(Q));
+  EXPECT_EQ("expected variable name", cast<InvalidQuery>(Q)->ErrStr);
+
+  Q = parse("unlet x");
+  ASSERT_TRUE(isa<LetQuery>(Q));
+  EXPECT_EQ("x", cast<LetQuery>(Q)->Name);
+  EXPECT_FALSE(cast<LetQuery>(Q)->Value.hasValue());
+
+  Q = parse("unlet");
+  ASSERT_TRUE(isa<InvalidQuery>(Q));
+  EXPECT_EQ("expected variable name", cast<InvalidQuery>(Q)->ErrStr);
+
+  Q = parse("unlet x bad_data");
+  ASSERT_TRUE(isa<InvalidQuery>(Q));
+  EXPECT_EQ("unexpected extra input: ' bad_data'",
+            cast<InvalidQuery>(Q)->ErrStr);
+}
+
+TEST_F(QueryParserTest, Complete) {
   std::vector<llvm::LineEditor::Completion> Comps =
-      QueryParser::complete("", 0);
-  ASSERT_EQ(3u, Comps.size());
+      QueryParser::complete("", 0, QS);
+  ASSERT_EQ(5u, Comps.size());
   EXPECT_EQ("help ", Comps[0].TypedText);
   EXPECT_EQ("help", Comps[0].DisplayText);
-  EXPECT_EQ("match ", Comps[1].TypedText);
-  EXPECT_EQ("match", Comps[1].DisplayText);
-  EXPECT_EQ("set ", Comps[2].TypedText);
-  EXPECT_EQ("set", Comps[2].DisplayText);
+  EXPECT_EQ("let ", Comps[1].TypedText);
+  EXPECT_EQ("let", Comps[1].DisplayText);
+  EXPECT_EQ("match ", Comps[2].TypedText);
+  EXPECT_EQ("match", Comps[2].DisplayText);
+  EXPECT_EQ("set ", Comps[3].TypedText);
+  EXPECT_EQ("set", Comps[3].DisplayText);
+  EXPECT_EQ("unlet ", Comps[4].TypedText);
+  EXPECT_EQ("unlet", Comps[4].DisplayText);
 
-  Comps = QueryParser::complete("set o", 5);
+  Comps = QueryParser::complete("set o", 5, QS);
   ASSERT_EQ(1u, Comps.size());
   EXPECT_EQ("utput ", Comps[0].TypedText);
   EXPECT_EQ("output", Comps[0].DisplayText);
 
-  Comps = QueryParser::complete("match while", 11);
+  Comps = QueryParser::complete("match while", 11, QS);
   ASSERT_EQ(1u, Comps.size());
   EXPECT_EQ("Stmt(", Comps[0].TypedText);
   EXPECT_EQ("Matcher<Stmt> whileStmt(Matcher<WhileStmt>...)",