Refactoring promises returning functions to use async and await

src/compiler/checker.ts

@@ -120,6 +120,7 @@ namespace ts {
                 return node ? getTypeFromTypeNode(node) : errorType;
             },
             getParameterType: getTypeAtPosition,
+            getPromisedTypeOfPromise,
             getReturnTypeOfSignature,
             getNullableType,
             getNonNullableType,

src/compiler/diagnosticMessages.json

@@ -4183,7 +4183,10 @@
         "category": "Suggestion",
         "code": 80005
     },
-
+    "This may be converted to an async function.": {
+        "category": "Suggestion",
+        "code": 80006
+    },
     "Add missing 'super()' call": {
         "category": "Message",
         "code": 90001
@@ -4556,12 +4559,21 @@
         "category": "Message",
         "code": 95062
     },
+
     "Add missing enum member '{0}'": {
         "category": "Message",
         "code": 95063
     },
     "Add all missing imports": {
         "category": "Message",
         "code": 95064
+    },
+    "Convert to async function":{
+        "category": "Message",
+         "code": 95065
+    },
+    "Convert all to async functions": {
+     "category": "Message",
+         "code": 95066
     }
-}
+}

src/compiler/types.ts

@@ -2911,6 +2911,8 @@ namespace ts {
         getBaseTypes(type: InterfaceType): BaseType[];
         getBaseTypeOfLiteralType(type: Type): Type;
         getWidenedType(type: Type): Type;
+        /* @internal */
+        getPromisedTypeOfPromise(promise: Type, errorNode?: Node): Type | undefined;
         getReturnTypeOfSignature(signature: Signature): Type;
         /**
          * Gets the type of a parameter at a given position in a signature.

src/services/suggestionDiagnostics.ts

@@ -3,6 +3,7 @@ namespace ts {
     export function computeSuggestionDiagnostics(sourceFile: SourceFile, program: Program, cancellationToken: CancellationToken): DiagnosticWithLocation[] {
         program.getSemanticDiagnostics(sourceFile, cancellationToken);
         const diags: DiagnosticWithLocation[] = [];
+        const checker = program.getDiagnosticsProducingTypeChecker();
 
         if (sourceFile.commonJsModuleIndicator &&
             (programContainsEs6Modules(program) || compilerOptionsIndicateEs6Modules(program.getCompilerOptions())) &&
@@ -68,6 +69,9 @@ namespace ts {
                 }
             }
 
+            if (isFunctionLikeDeclaration(node)) {
+                addConvertToAsyncFunctionDiagnostics(node, checker, diags);
+            }
             node.forEachChild(check);
         }
     }
@@ -109,7 +113,64 @@ namespace ts {
         }
     }
 
+    function addConvertToAsyncFunctionDiagnostics(node: FunctionLikeDeclaration, checker: TypeChecker, diags: DiagnosticWithLocation[]): void {
+
+        const functionType = node.type ? checker.getTypeFromTypeNode(node.type) : undefined;
+        if (isAsyncFunction(node) || !node.body || !functionType) {
+            return;
+        }
+
+        const callSignatures = checker.getSignaturesOfType(functionType, SignatureKind.Call);
+        const returnType = callSignatures.length ? checker.getReturnTypeOfSignature(callSignatures[0]) : undefined;
+
+        if (!returnType || !checker.getPromisedTypeOfPromise(returnType)) {
+            return;
+        }
+
+        // collect all the return statements
+        // check that a property access expression exists in there and that it is a handler
+        const returnStatements = getReturnStatementsWithPromiseHandlers(node);
+        if (returnStatements.length > 0) {
+            diags.push(createDiagnosticForNode(isVariableDeclaration(node.parent) ? node.parent.name : node, Diagnostics.This_may_be_converted_to_an_async_function));
+        }
+    }
+
     function getErrorNodeFromCommonJsIndicator(commonJsModuleIndicator: Node): Node {
         return isBinaryExpression(commonJsModuleIndicator) ? commonJsModuleIndicator.left : commonJsModuleIndicator;
     }
+
+    /** @internal */
+    export function getReturnStatementsWithPromiseHandlers(node: Node): Node[] {
+        const returnStatements: Node[] = [];
+        if (isFunctionLike(node)) {
+            forEachChild(node, visit);
+        }
+        else {
+            visit(node);
+        }
+
+        function visit(child: Node) {
+            if (isFunctionLike(child)) {
+                return;
+            }
+
+            if (isReturnStatement(child)) {
+                forEachChild(child, addHandlers);
+            }
+
+            function addHandlers(returnChild: Node) {
+                if (isPromiseHandler(returnChild)) {
+                    returnStatements.push(child as ReturnStatement);
+                }
+            }
+
+            forEachChild(child, visit);
+        }
+        return returnStatements;
+    }
+
+    function isPromiseHandler(node: Node): boolean {
+        return (isCallExpression(node) && isPropertyAccessExpression(node.expression) &&
+            (node.expression.name.text === "then" || node.expression.name.text === "catch"));
+    }
 }

src/services/tsconfig.json

@@ -46,6 +46,7 @@
         "codefixes/addMissingInvocationForDecorator.ts",
         "codefixes/annotateWithTypeFromJSDoc.ts",
         "codefixes/convertFunctionToEs6Class.ts",
+        "codefixes/convertToAsyncFunction.ts",
         "codefixes/convertToEs6Module.ts",
         "codefixes/correctQualifiedNameToIndexedAccessType.ts",
         "codefixes/fixClassIncorrectlyImplementsInterface.ts",

src/services/utilities.ts

@@ -226,7 +226,7 @@ namespace ts {
 
     export function isJumpStatementTarget(node: Node): node is Identifier & { parent: BreakOrContinueStatement } {
         return node.kind === SyntaxKind.Identifier && isBreakOrContinueStatement(node.parent) && node.parent.label === node;
-     }
+    }
 
     export function isLabelOfLabeledStatement(node: Node): node is Identifier {
         return node.kind === SyntaxKind.Identifier && isLabeledStatement(node.parent) && node.parent.label === node;
@@ -396,7 +396,7 @@ namespace ts {
     export function isThis(node: Node): boolean {
         switch (node.kind) {
             case SyntaxKind.ThisKeyword:
-            // case SyntaxKind.ThisType: TODO: GH#9267
+                // case SyntaxKind.ThisType: TODO: GH#9267
                 return true;
             case SyntaxKind.Identifier:
                 // 'this' as a parameter
@@ -1656,8 +1656,34 @@ namespace ts {
         return clone;
     }
 
-    function getSynthesizedDeepCloneWorker<T extends Node>(node: T): T {
-        const visited = visitEachChild(node, getSynthesizedDeepClone, nullTransformationContext);
+    export function getSynthesizedDeepCloneWithRenames<T extends Node | undefined>(node: T, includeTrivia = true, renameMap?: Map<Identifier>, checker?: TypeChecker, callback?: (originalNode: Node, clone: Node) => any): T {
+
+        let clone;
+        if (node && isIdentifier(node!) && renameMap && checker) {
+            const symbol = checker.getSymbolAtLocation(node!);
+            const renameInfo = symbol && renameMap.get(String(getSymbolId(symbol)));
+
+            if (renameInfo) {
+                clone = createIdentifier(renameInfo.text);
+            }
+        }
+
+        if (!clone) {
+            clone = node && getSynthesizedDeepCloneWorker(node as NonNullable<T>, renameMap, checker, callback);
+        }
+
+        if (clone && !includeTrivia) suppressLeadingAndTrailingTrivia(clone);
+        if (callback && node) callback(node!, clone);
+
+        return clone as T;
+    }
+
+
+    function getSynthesizedDeepCloneWorker<T extends Node>(node: T, renameMap?: Map<Identifier>, checker?: TypeChecker, callback?: (originalNode: Node, clone: Node) => any): T {
+        const visited = (renameMap || checker || callback) ?
+        visitEachChild(node, wrapper, nullTransformationContext) :
+        visitEachChild(node, getSynthesizedDeepClone, nullTransformationContext);
+
         if (visited === node) {
             // This only happens for leaf nodes - internal nodes always see their children change.
             const clone = getSynthesizedClone(node);
@@ -1675,6 +1701,10 @@ namespace ts {
         // would have made.
         visited.parent = undefined!;
         return visited;
+
+        function wrapper(node: T) {
+            return getSynthesizedDeepCloneWithRenames(node, /*includeTrivia*/ true, renameMap, checker, callback);
+        }
     }
 
     export function getSynthesizedDeepClones<T extends Node>(nodes: NodeArray<T>, includeTrivia?: boolean): NodeArray<T>;

src/testRunner/tsconfig.json

@@ -48,6 +48,7 @@
         "unittests/compileOnSave.ts",
         "unittests/configurationExtension.ts",
         "unittests/convertCompilerOptionsFromJson.ts",
+        "unittests/convertToAsyncFunction.ts",
         "unittests/convertToBase64.ts",
         "unittests/convertTypeAcquisitionFromJson.ts",
         "unittests/customTransforms.ts",