clang-format: [JS] do not collapse short classes.

[mprobst]

Summary

clang-format does not collapse short records, interfaces, unions, etc.,
but fails to do so if the record is preceded by certain modifiers
(export, default, abstract, declare). This change skips over all
modifiers, and thus handles all record definitions uniformly.

Before:

export class Foo { bar: string; }
class Baz {
  bam: string;
}

After:

export class Foo {
  bar: string;
}
class Baz {
  bam: string;
}

[djasper]

Looks good.

lib/Format/UnwrappedLineFormatter.cpp

if (Line.Last->is(tok::l_brace)) {
            Tok->getNextNonComment()->is(tok::semi))) {
         // We merge empty blocks even if the line exceeds the column limit.
         Tok->SpacesRequiredBefore = 0;
         Tok->CanBreakBefore = true;
         return 1;
       } else if (Limit != 0 && !Line.startsWith(tok::kw_namespace) &&
                  !startsExternCBlock(Line)) {
         // We don't merge short records.
-        FormatToken *RecordTok =
-            Line.First->is(tok::kw_typedef) ? Line.First->Next : Line.First;
+        FormatToken *RecordTok = Line.First;
+        // Skip record modifiers.
+        while (RecordTok->Next &&
+               RecordTok->isOneOf(tok::kw_typedef, tok::kw_export,
+                                  Keywords.kw_declare, Keywords.kw_abstract,
+                                  tok::kw_default))
+          RecordTok = RecordTok->Next;
         if (RecordTok &&
             RecordTok->isOneOf(tok::kw_class, tok::kw_union, tok::kw_struct,
                                Keywords.kw_interface))
           return 0;
 
         // Check that we still have three lines and they fit into the limit.
         if (I + 2 == E || I[2]->Type == LT_Invalid)
           return 0;

unittests/Format/FormatTestJS.cpp

verifyFormat("export {\n"
                "  someSurprisinglyLongVariable as\n"
                "      from\n"
                "};",
                getGoogleJSStyleWithColumns(20));
   verifyFormat("export class C {\n"
                "  x: number;\n"
                "  y: string;\n"
                "}");
-  verifyFormat("export class X { y: number; }");
-  verifyFormat("export abstract class X { y: number; }");
-  verifyFormat("export default class X { y: number }");
+  verifyFormat("export class X {\n"
+               "  y: number;\n"
+               "}");
+  verifyFormat("export abstract class X {\n"
+               "  y: number;\n"
+               "}");
+  verifyFormat("export default class X {\n"
+               "  y: number\n"
+               "}");
   verifyFormat("export default function() {\n  return 1;\n}");
   verifyFormat("export var x = 12;");
   verifyFormat("class C {}\n"
                "export function f() {}\n"
                "var v;");
   verifyFormat("export var x: number = 12;");
   verifyFormat("export const y = {\n"
                "  a: 1,\n"
                "  b: 2\n"
                "};");
   verifyFormat("export enum Foo {\n"
                "  BAR,\n"
                "  // adsdasd\n"
                "  BAZ\n"
                "}");
   verifyFormat("export default [\n"
                "  aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa,\n"
                "  bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\n"
                "];");
   verifyFormat("export default [];");
   verifyFormat("export default () => {};");
-  verifyFormat("export interface Foo { foo: number; }\n"
+  verifyFormat("export interface Foo {\n"
+               "  foo: number;\n"
+               "}\n"
                "export class Bar {\n"
                "  blah(): string {\n"
                "    return this.blah;\n"
                "  };\n"
                "}");
 }
 
 TEST_F(FormatTestJS, ImportWrapping) {