Merge branch 'release-2.0'

src/compiler/checker.ts

@@ -13277,7 +13277,7 @@ namespace ts {
                         checkAsyncFunctionReturnType(<FunctionLikeDeclaration>node);
                     }
                 }
-                if (!(<FunctionDeclaration>node).body) {
+                if (noUnusedIdentifiers && !(<FunctionDeclaration>node).body) {
                     checkUnusedTypeParameters(node);
                 }
             }
@@ -14612,8 +14612,15 @@ namespace ts {
         function checkUnusedTypeParameters(node: ClassDeclaration | ClassExpression | FunctionDeclaration | MethodDeclaration | FunctionExpression | ArrowFunction | ConstructorDeclaration | SignatureDeclaration | InterfaceDeclaration) {
             if (compilerOptions.noUnusedLocals && !isInAmbientContext(node)) {
                 if (node.typeParameters) {
+                    // Only report errors on the last declaration for the type parameter container;
+                    // this ensures that all uses have been accounted for.
+                    const symbol = getSymbolOfNode(node);
+                    const lastDeclaration = symbol && symbol.declarations && lastOrUndefined(symbol.declarations);
+                    if (lastDeclaration !== node) {
+                        return;
+                    }
                     for (const typeParameter of node.typeParameters) {
-                        if (!typeParameter.symbol.isReferenced) {
+                        if (!getMergedSymbol(typeParameter.symbol).isReferenced) {
                             error(typeParameter.name, Diagnostics._0_is_declared_but_never_used, typeParameter.symbol.name);
                         }
                     }
@@ -16122,7 +16129,7 @@ namespace ts {
 
             if (produceDiagnostics) {
                 checkTypeForDuplicateIndexSignatures(node);
-                checkUnusedTypeParameters(node);
+                registerForUnusedIdentifiersCheck(node);
             }
         }
 

src/compiler/emitter.ts

@@ -2749,7 +2749,7 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
              *   if we should also export the value after its it changed
              * - check if node is a source level declaration to emit it differently,
              *   i.e non-exported variable statement 'var x = 1' is hoisted so
-             *   we we emit variable statement 'var' should be dropped.
+             *   when we emit variable statement 'var' should be dropped.
              */
             function isSourceFileLevelDeclarationInSystemJsModule(node: Node, isExported: boolean): boolean {
                 if (!node || !isCurrentFileSystemExternalModule()) {
@@ -5503,16 +5503,15 @@ const _super = (function (geti, seti) {
                             write("export ");
                         }
 
-                        if (!isHoistedDeclarationInSystemModule) {
-                            write("let ");
-                        }
                         if (decoratedClassAlias !== undefined) {
-                            write(`${decoratedClassAlias}`);
+                            write(`let ${decoratedClassAlias}`);
                         }
                         else {
+                            if (!isHoistedDeclarationInSystemModule) {
+                                write("let ");
+                            }
                             emitDeclarationName(node);
                         }
-
                         write(" = ");
                     }
                     else if (isES6ExportedDeclaration(node)) {
@@ -5530,7 +5529,9 @@ const _super = (function (geti, seti) {
                 //
                 // We'll emit:
                 //
-                //      (_temp = class C { ... }, _temp.a = 1, _temp.b = 2, _temp)
+                //      let C_1 = class C{};
+                //      C_1.a = 1;
+                //      C_1.b = 2; // so forth and so on
                 //
                 // This keeps the expression as an expression, while ensuring that the static parts
                 // of it have been initialized by the time it is used.

src/compiler/types.ts

@@ -2912,7 +2912,6 @@ namespace ts {
         getCancellationToken?(): CancellationToken;
         getDefaultLibFileName(options: CompilerOptions): string;
         getDefaultLibLocation?(): string;
-        getDefaultTypeDirectiveNames?(rootPath: string): string[];
         writeFile: WriteFileCallback;
         getCurrentDirectory(): string;
         getDirectories(path: string): string[];