clang-format: [JS] more precisely detect enums.

[mprobst]

Summary

The current enum detection is overly aggressive. As NestingLevel only applies per line (?) it classifies many if not most object literals as enum declarations and adds superfluous line breaks into them. This change narrows the heuristic by requiring an assignment just before the open brace and requiring the line to start with an identifier.

[djasper]

Submitted as r232320.

lib/Format/TokenAnnotator.cpp

         Left.Previous->is(tok::char_constant))
       return true;
     if (Left.is(TT_DictLiteral) && Left.is(tok::l_brace) &&
-        Left.NestingLevel == 0)
+        Left.NestingLevel == 0 && Left.Previous &&
+        Left.Previous->is(tok::equal) &&
+        Line.First->isOneOf(tok::identifier, Keywords.kw_import,
+                            tok::kw_export) &&
+        // kw_var is a pseudo-token that's a tok::identifier, so matches above.
+        !Line.First->is(Keywords.kw_var))
+      // Enum style object literal.
       return true;
   } else if (Style.Language == FormatStyle::LK_Java) {
     if (Right.is(tok::plus) && Left.is(tok::string_literal) && Right.Next &&

unittests/Format/FormatTestJS.cpp

 
 TEST_F(FormatTestJS, ES6DestructuringAssignment) {
   verifyFormat("var [a, b, c] = [1, 2, 3];");
-  verifyFormat("var {a, b} = {\n"
-               "  a: 1,\n"
-               "  b: 2\n"
-               "};");
+  verifyFormat("var {a, b} = {a: 1, b: 2};");
 }
 
 TEST_F(FormatTestJS, ContainerLiterals) {

                "    return x.zIsTooLongForOneLineWithTheDeclarationLine();\n"
                "  }\n"
                "};");
+  // Simple object literal, as opposed to enum style below.
+  verifyFormat("var obj = {a: 123};");
+  // Enum style top level assignment.
+  verifyFormat("X = {\n  a: 123\n};");
+  verifyFormat("X.Y = {\n  a: 123\n};");
+  verifyFormat("x = foo && {a: 123};");
 }
 
 TEST_F(FormatTestJS, SpacesInContainerLiterals) {

                getGoogleJSStyleWithColumns(20));
   verifyFormat("import {X as myLocalX, Y as myLocalY} from 'some/module.js';");
   verifyFormat("import * as lib from 'some/module.js';");
-  verifyFormat("var x = {\n  import: 1\n};\nx.import = 2;");
+  verifyFormat("var x = {import: 1};\nx.import = 2;");
 
   verifyFormat("export function fn() {\n"
                "  return 'fn';\n"