clang-format: [JS] avoid indent after ambient function declarations.

Summary:
Before:
  declare function foo();
    let x = 1;

After:
  declare function foo();
  let x = 1;

The problem was that clang-format would unconditionally try to parse a child block, even though ambient function declarations do not have a body (similar to forward declarations).

Reviewers: djasper

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D28246

llvm-svn: 290959
diff --git a/clang/unittests/Format/FormatTestJS.cpp b/clang/unittests/Format/FormatTestJS.cpp
index 6f494db..90c9931 100644
--- a/clang/unittests/Format/FormatTestJS.cpp
+++ b/clang/unittests/Format/FormatTestJS.cpp
@@ -377,6 +377,16 @@
       "declare function\n"
       "x();",  // TODO(martinprobst): should ideally be indented.
       NineCols);
+  verifyFormat("declare function foo();\n"
+               "let x = 1;\n");
+  verifyFormat("declare function foo(): string;\n"
+               "let x = 1;\n");
+  verifyFormat("declare function foo(): {x: number};\n"
+               "let x = 1;\n");
+  verifyFormat("declare class X {}\n"
+               "let x = 1;\n");
+  verifyFormat("declare interface Y {}\n"
+               "let x = 1;\n");
   verifyFormat(
       "declare enum X {\n"
       "}",