Merge pull request #5390 from maybejulian/declareOnTypeAliasInDts

Allow type aliases to omit 'declare' keyword in '.d.ts' files

Author: mhegazy

src/compiler/checker.ts

@@ -15979,11 +15979,14 @@ namespace ts {
             //  DeclarationElement:
             //     ExportAssignment
             //     export_opt   InterfaceDeclaration
+            //     export_opt   TypeAliasDeclaration
             //     export_opt   ImportDeclaration
             //     export_opt   ExternalImportDeclaration
             //     export_opt   AmbientDeclaration
             //
+            // TODO: The spec needs to be amended to reflect this grammar.
             if (node.kind === SyntaxKind.InterfaceDeclaration ||
+                node.kind === SyntaxKind.TypeAliasDeclaration ||
                 node.kind === SyntaxKind.ImportDeclaration ||
                 node.kind === SyntaxKind.ImportEqualsDeclaration ||
                 node.kind === SyntaxKind.ExportDeclaration ||

tests/baselines/reference/typeAliasDeclareKeyword01.d.symbols

@@ -0,0 +1,7 @@
+=== tests/cases/compiler/typeAliasDeclareKeyword01.d.ts ===
+type Foo = number;
+>Foo : Symbol(Foo, Decl(typeAliasDeclareKeyword01.d.ts, 0, 0))
+
+declare type Bar = string;
+>Bar : Symbol(Bar, Decl(typeAliasDeclareKeyword01.d.ts, 0, 18))
+

tests/baselines/reference/typeAliasDeclareKeyword01.d.types

@@ -0,0 +1,7 @@
+=== tests/cases/compiler/typeAliasDeclareKeyword01.d.ts ===
+type Foo = number;
+>Foo : number
+
+declare type Bar = string;
+>Bar : string
+

tests/cases/compiler/typeAliasDeclareKeyword01.d.ts

@@ -0,0 +1,2 @@
+type Foo = number;
+declare type Bar = string;