Allow decorators in JavaScript files

src/compiler/diagnosticMessages.json

@@ -2729,11 +2729,6 @@
         "category": "Error",
         "code": 8016
     },
-    "'decorators' can only be used in a .ts file.": {
-        "category": "Error",
-        "code": 8017
-    },
-
     "Only identifiers/qualified-names with optional type arguments are currently supported in a class 'extends' clauses.": {
         "category": "Error",
         "code": 9002

src/compiler/program.ts

@@ -1168,9 +1168,6 @@ namespace ts {
                             let typeAssertionExpression = <TypeAssertion>node;
                             diagnostics.push(createDiagnosticForNode(typeAssertionExpression.type, Diagnostics.type_assertion_expressions_can_only_be_used_in_a_ts_file));
                             return true;
-                        case SyntaxKind.Decorator:
-                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.decorators_can_only_be_used_in_a_ts_file));
-                            return true;
                     }
 
                     return forEachChild(node, walk);

tests/baselines/reference/jsFileCompilationDecoratorSyntax.errors.txt

@@ -1,9 +0,0 @@
-error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
-tests/cases/compiler/a.js(1,1): error TS8017: 'decorators' can only be used in a .ts file.
-
-
-!!! error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
-==== tests/cases/compiler/a.js (1 errors) ====
-    @internal class C { }
-    ~~~~~~~~~
-!!! error TS8017: 'decorators' can only be used in a .ts file.

tests/baselines/reference/jsFileCompilationDecoratorSyntax.symbols

@@ -0,0 +1,4 @@
+=== tests/cases/compiler/a.js ===
+@internal class C { }
+>C : Symbol(C, Decl(a.js, 0, 0))
+

tests/baselines/reference/jsFileCompilationDecoratorSyntax.types

@@ -0,0 +1,5 @@
+=== tests/cases/compiler/a.js ===
+@internal class C { }
+>internal : any
+>C : C
+

tests/cases/compiler/jsFileCompilationDecoratorSyntax.ts

@@ -1,3 +1,4 @@
 // @allowJs: true
+// @noEmit: true
 // @filename: a.js
 @internal class C { }

tests/cases/fourslash/getJavaScriptSemanticDiagnostics21.ts

@@ -4,12 +4,4 @@
 // @Filename: a.js
 //// @internal class C {}
 
-verify.getSemanticDiagnostics(`[
-  {
-    "message": "'decorators' can only be used in a .ts file.",
-    "start": 0,
-    "length": 9,
-    "category": "error",
-    "code": 8017
-  }
-]`);
+verify.getSemanticDiagnostics(`[]`);