[clang-query] Add single-letter 'q' alias for 'quit'

[steveire]

Add test

[Szelethus]

I'd really enjoy this feature.

[steveire]

@Szelethus You can approve it and then you will get the feature :).

[aaron.ballman]

Please update HelpQuery::run() to print out the new mnemonic (it's the *only* form of public documentation we have for clang-query currently).

[steveire]

Add docs

[steveire]

In D52746#1252455, @aaron.ballman wrote:

Please update HelpQuery::run() to print out the new mnemonic (it's the *only* form of public documentation we have for clang-query currently).

Good point, thanks!

[aaron.ballman]

LGTM!

clang-query/Query.cpp

OS << "Available commands:\n\n"
         "                                    "
         "as part of other expressions.\n"
         "  set bind-root (true|false)        "
         "Set whether to bind the root matcher to \"root\".\n"
         "  set output (diag|print|dump)      "
         "Set whether to print bindings as diagnostics,\n"
         "                                    "
         "AST pretty prints or AST dumps.\n"
-        "  quit                              "
+        "  quit, q                           "
         "Terminates the query session.\n\n";
   return true;
 }
 
 bool QuitQuery::run(llvm::raw_ostream &OS, QuerySession &QS) const {
   QS.Terminate = true;
   return true;
 }

clang-query/QueryParser.cpp

QueryRef QueryParser::doParse() {
   StringRef CommandStr;
   ParsedQueryKind QKind = LexOrCompleteWord<ParsedQueryKind>(this, CommandStr)
                               .Case("", PQK_NoOp)
                               .Case("help", PQK_Help)
                               .Case("l", PQK_Let, /*IsCompletion=*/false)
                               .Case("let", PQK_Let)
                               .Case("m", PQK_Match, /*IsCompletion=*/false)
                               .Case("match", PQK_Match)
+                              .Case("q", PQK_Quit,  /*IsCompletion=*/false)
                               .Case("quit", PQK_Quit)
                               .Case("set", PQK_Set)
                               .Case("unlet", PQK_Unlet)
                               .Default(PQK_Invalid);
 
   switch (QKind) {
   case PQK_NoOp:
     return new NoOpQuery;

unittests/clang-query/QueryParserTest.cpp

TEST_F(QueryParserTest, Help) {
   ASSERT_TRUE(isa<InvalidQuery>(Q));
   EXPECT_EQ("unexpected extra input: ' me'", cast<InvalidQuery>(Q)->ErrStr);
 }
 
 TEST_F(QueryParserTest, Quit) {
   QueryRef Q = parse("quit");
   ASSERT_TRUE(isa<QuitQuery>(Q));
 
+  Q = parse("q");
+  ASSERT_TRUE(isa<QuitQuery>(Q));
+
   Q = parse("quit me");
   ASSERT_TRUE(isa<InvalidQuery>(Q));
   EXPECT_EQ("unexpected extra input: ' me'", cast<InvalidQuery>(Q)->ErrStr);
 }
 
 TEST_F(QueryParserTest, Set) {
   QueryRef Q = parse("set");
   ASSERT_TRUE(isa<InvalidQuery>(Q));