Change ArrayBuffer.isView declaration to type guard for ArrayBufferView.

John Vilk · John Vilk · commit f10c7cc154cb · 2015-10-18T20:05:30.000-04:00
Also adds a test that checks that `ArrayBuffer.isView` appropriately narrows its argument to `ArrayBufferView`. Fixes microsoft#5308.
diff --git a/src/lib/core.d.ts b/src/lib/core.d.ts
@@ -1210,7 +1210,7 @@ interface ArrayBuffer {
 interface ArrayBufferConstructor {
     prototype: ArrayBuffer;
     new (byteLength: number): ArrayBuffer;
-    isView(arg: any): boolean;
+    isView(arg: any): arg is ArrayBufferView;
 }
 declare var ArrayBuffer: ArrayBufferConstructor;
 
diff --git a/tests/baselines/reference/arrayBufferIsViewNarrowsType.js b/tests/baselines/reference/arrayBufferIsViewNarrowsType.js
@@ -0,0 +1,13 @@
+//// [arrayBufferIsViewNarrowsType.ts]
+var obj: Object;
+if (ArrayBuffer.isView(obj)) {
+    // isView should be a guard that narrows type to ArrayBufferView.
+    var ab: ArrayBufferView = obj;
+}
+
+//// [arrayBufferIsViewNarrowsType.js]
+var obj;
+if (ArrayBuffer.isView(obj)) {
+    // isView should be a guard that narrows type to ArrayBufferView.
+    var ab = obj;
+}
diff --git a/tests/baselines/reference/arrayBufferIsViewNarrowsType.symbols b/tests/baselines/reference/arrayBufferIsViewNarrowsType.symbols
@@ -0,0 +1,17 @@
+=== tests/cases/compiler/arrayBufferIsViewNarrowsType.ts ===
+var obj: Object;
+>obj : Symbol(obj, Decl(arrayBufferIsViewNarrowsType.ts, 0, 3))
+>Object : Symbol(Object, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
+if (ArrayBuffer.isView(obj)) {
+>ArrayBuffer.isView : Symbol(ArrayBufferConstructor.isView, Decl(lib.d.ts, --, --))
+>ArrayBuffer : Symbol(ArrayBuffer, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>isView : Symbol(ArrayBufferConstructor.isView, Decl(lib.d.ts, --, --))
+>obj : Symbol(obj, Decl(arrayBufferIsViewNarrowsType.ts, 0, 3))
+
+    // isView should be a guard that narrows type to ArrayBufferView.
+    var ab: ArrayBufferView = obj;
+>ab : Symbol(ab, Decl(arrayBufferIsViewNarrowsType.ts, 3, 7))
+>ArrayBufferView : Symbol(ArrayBufferView, Decl(lib.d.ts, --, --))
+>obj : Symbol(obj, Decl(arrayBufferIsViewNarrowsType.ts, 0, 3))
+}
diff --git a/tests/baselines/reference/arrayBufferIsViewNarrowsType.types b/tests/baselines/reference/arrayBufferIsViewNarrowsType.types
@@ -0,0 +1,18 @@
+=== tests/cases/compiler/arrayBufferIsViewNarrowsType.ts ===
+var obj: Object;
+>obj : Object
+>Object : Object
+
+if (ArrayBuffer.isView(obj)) {
+>ArrayBuffer.isView(obj) : boolean
+>ArrayBuffer.isView : (arg: any) => arg is ArrayBufferView
+>ArrayBuffer : ArrayBufferConstructor
+>isView : (arg: any) => arg is ArrayBufferView
+>obj : Object
+
+    // isView should be a guard that narrows type to ArrayBufferView.
+    var ab: ArrayBufferView = obj;
+>ab : ArrayBufferView
+>ArrayBufferView : ArrayBufferView
+>obj : ArrayBufferView
+}
diff --git a/tests/cases/compiler/arrayBufferIsViewNarrowsType.ts b/tests/cases/compiler/arrayBufferIsViewNarrowsType.ts
@@ -0,0 +1,5 @@
+var obj: Object;
+if (ArrayBuffer.isView(obj)) {
+    // isView should be a guard that narrows type to ArrayBufferView.
+    var ab: ArrayBufferView = obj;
+}

Original file line number	Diff line number	Diff line change
`@@ -1210,7 +1210,7 @@ interface ArrayBuffer {`
`1210`	`1210`	`interface ArrayBufferConstructor {`
`1211`	`1211`	`prototype: ArrayBuffer;`
`1212`	`1212`	`new (byteLength: number): ArrayBuffer;`
`1213`		`- isView(arg: any): boolean;`
	`1213`	`+ isView(arg: any): arg is ArrayBufferView;`
`1214`	`1214`	`}`
`1215`	`1215`	`declare var ArrayBuffer: ArrayBufferConstructor;`
`1216`	`1216`