Avoid calling indexOf when checking array element types

src/compiler/checker.ts

@@ -13198,16 +13198,11 @@ namespace ts {
         // the type of the property with the numeric name N in T, if one exists. Otherwise, if T has a numeric index signature,
         // it is the type of the numeric index signature in T. Otherwise, in ES6 and higher, the contextual type is the iterated
         // type of T.
-        function getContextualTypeForElementExpression(node: Expression): Type {
-            const arrayLiteral = <ArrayLiteralExpression>node.parent;
-            const type = getApparentTypeOfContextualType(arrayLiteral);
-            if (type) {
-                const index = indexOf(arrayLiteral.elements, node);
-                return getTypeOfPropertyOfContextualType(type, "" + index as __String)
-                    || getIndexTypeOfContextualType(type, IndexKind.Number)
-                    || getIteratedTypeOrElementType(type, /*errorNode*/ undefined, /*allowStringInput*/ false, /*allowAsyncIterables*/ false, /*checkAssignability*/ false);
-            }
-            return undefined;
+        function getContextualTypeForElementExpression(arrayContextualType: Type | undefined, index: number): Type | undefined {
+            return arrayContextualType && (
+                getTypeOfPropertyOfContextualType(arrayContextualType, "" + index as __String)
+                || getIndexTypeOfContextualType(arrayContextualType, IndexKind.Number)
+                || getIteratedTypeOrElementType(arrayContextualType, /*errorNode*/ undefined, /*allowStringInput*/ false, /*allowAsyncIterables*/ false, /*checkAssignability*/ false));
         }
 
         // In a contextually typed conditional expression, the true/false expressions are contextually typed by the same type.
@@ -13321,8 +13316,11 @@ namespace ts {
                     return getContextualTypeForObjectLiteralElement(<ObjectLiteralElementLike>parent);
                 case SyntaxKind.SpreadAssignment:
                     return getApparentTypeOfContextualType(parent.parent as ObjectLiteralExpression);
-                case SyntaxKind.ArrayLiteralExpression:
-                    return getContextualTypeForElementExpression(node);
+                case SyntaxKind.ArrayLiteralExpression: {
+                    const arrayLiteral = <ArrayLiteralExpression>parent;
+                    const type = getApparentTypeOfContextualType(arrayLiteral);
+                    return getContextualTypeForElementExpression(type, indexOfNode(arrayLiteral.elements, node));
+                }
                 case SyntaxKind.ConditionalExpression:
                     return getContextualTypeForConditionalOperand(node);
                 case SyntaxKind.TemplateSpan:
@@ -13451,12 +13449,14 @@ namespace ts {
                 (node.kind === SyntaxKind.BinaryExpression && (<BinaryExpression>node).operatorToken.kind === SyntaxKind.EqualsToken);
         }
 
-        function checkArrayLiteral(node: ArrayLiteralExpression, checkMode?: CheckMode): Type {
+        function checkArrayLiteral(node: ArrayLiteralExpression, checkMode: CheckMode | undefined): Type {
             const elements = node.elements;
             let hasSpreadElement = false;
             const elementTypes: Type[] = [];
             const inDestructuringPattern = isAssignmentTarget(node);
-            for (const e of elements) {
+            const contextualType = getApparentTypeOfContextualType(node);
+            for (let index = 0; index < elements.length; index++) {
+                const e = elements[index];
                 if (inDestructuringPattern && e.kind === SyntaxKind.SpreadElement) {
                     // Given the following situation:
                     //    var c: {};
@@ -13478,7 +13478,8 @@ namespace ts {
                     }
                 }
                 else {
-                    const type = checkExpressionForMutableLocation(e, checkMode);
+                    const elementContextualType = getContextualTypeForElementExpression(contextualType, index);
+                    const type = checkExpressionForMutableLocation(e, checkMode, elementContextualType);
                     elementTypes.push(type);
                 }
                 hasSpreadElement = hasSpreadElement || e.kind === SyntaxKind.SpreadElement;
@@ -18023,9 +18024,13 @@ namespace ts {
             return false;
         }
 
-        function checkExpressionForMutableLocation(node: Expression, checkMode?: CheckMode): Type {
+        function checkExpressionForMutableLocation(node: Expression, checkMode: CheckMode, contextualType?: Type): Type {
+            if (arguments.length === 2) {
+                contextualType = getContextualType(node);
+            }
             const type = checkExpression(node, checkMode);
-            return isTypeAssertion(node) || isLiteralContextualType(getContextualType(node)) ? type : getWidenedLiteralType(type);
+            const shouldWiden = isTypeAssertion(node) || isLiteralContextualType(contextualType);
+            return shouldWiden ? type : getWidenedLiteralType(type);
         }
 
         function checkPropertyAssignment(node: PropertyAssignment, checkMode?: CheckMode): Type {

src/compiler/utilities.ts

@@ -321,6 +321,18 @@ namespace ts {
         return getSourceTextOfNodeFromSourceFile(getSourceFileOfNode(node), node, includeTrivia);
     }
 
+    /**
+     * Note: it is expected that the `nodeArray` and the `node` are within the same file.
+     * For example, searching for a `SourceFile` in a `SourceFile[]` wouldn't work.
+     */
+    export function indexOfNode(nodeArray: ReadonlyArray<Node>, node: Node) {
+        return binarySearch(nodeArray, node, compareNodePos);
+    }
+
+    function compareNodePos({ pos: aPos }: Node, { pos: bPos}: Node) {
+        return aPos < bPos ? Comparison.LessThan : bPos < aPos ? Comparison.GreaterThan : Comparison.EqualTo;
+    }
+
     /**
      * Gets flags that control emit behavior of a node.
      */

src/services/textChanges.ts

@@ -224,7 +224,7 @@ namespace ts.textChanges {
                 Debug.fail("node is not a list element");
                 return this;
             }
-            const index = containingList.indexOf(node);
+            const index = indexOfNode(containingList, node);
             if (index < 0) {
                 return this;
             }
@@ -356,7 +356,7 @@ namespace ts.textChanges {
                 Debug.fail("node is not a list element");
                 return this;
             }
-            const index = containingList.indexOf(after);
+            const index = indexOfNode(containingList, after);
             if (index < 0) {
                 return this;
             }

src/services/utilities.ts

@@ -597,7 +597,7 @@ namespace ts {
         }
 
         const children = list.getChildren();
-        const listItemIndex = indexOf(children, node);
+        const listItemIndex = indexOfNode(children, node);
 
         return {
             listItemIndex,