feat(transformer): Support overloaded functions by attaching signatures on use

Add overloads feature flag that enables this feature.

Enabling it makes the transformer process function calls if their declaration
was previously marked for mocking (via getMethod).

From a type-perspective, typed methods shouldn't bother to consider their inputs
in order to determine the output in runtime. At transformation time, the type
checker resolves the matching overload and that information can be used to
attach to the function, by utilizing the "instance" (`this`) of it. The
transformer changes transform functions in the following way.

```
mockedFunction() -> mockedFunction.apply(<signature>, [])
```

As for constructor instantiation signatures in interfaces, those can be wrapped
by an intermediate function that will copy the mocked properties to preserve the
instantiation behavior.

```
new mockedNewFunction()
    |
    `-> new (mockedNewFunction[<signature>] || (mockedNewFunction[<signature>] = function() {
               Object.assign(this, mockedNewFunction.apply(<signature>, []));
            }))()
```

These attached interfaces will determine the branching at runtime and to reduce
as much overhead as possible, all signatures of an overloaded function are
mapped to the resolved return type and stored in a jump table, i.e.:

```
getMethod("functionName", function () {
  const jt = {
    ['<signature-1>']: () => <signature-1-return-descriptor>,
    ['<signature-2>']: () => <signature-2-return-descriptor>,
    ...
  };

  return jt[this]();
})
```

It should be noted, that if spies are introduced using the method provider, then
`this` will be occupied by the signature key.

Author: martinjlowm

config/utils/features.js

@@ -6,7 +6,8 @@ function DetermineFeaturesFromEnvironment() {
 
     if (features) {
        return [
-           'random'
+           'overloads',
+           'random',
        ];
     }
 

src/extension/method/provider/functionMethod.ts

@@ -1,5 +1,7 @@
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
-export function functionMethod(name: string, value: () => any): any {
+export function functionMethod(name: string, value: (...args: any[]) => any): any {
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  return (): any => value();
+  return function(...args: any[]): any {
+    return value.apply(this, args);
+  };
 }

src/merge/merge.ts

@@ -1,4 +1,4 @@
-import { merge} from 'lodash-es';
+import { merge } from 'lodash-es';
 import { DeepPartial } from '../partial/deepPartial';
 
 export class Merge {

src/options/features.ts

@@ -1 +1 @@
-export type TsAutoMockFeaturesOption = 'random';
+export type TsAutoMockFeaturesOption = 'random' | 'overloads';

src/options/overloads.ts

@@ -0,0 +1,5 @@
+import { GetOptionByKey } from './options';
+
+export function IsTsAutoMockOverloadsEnabled(): boolean {
+  return GetOptionByKey('features').includes('overloads');
+}

src/transformer/base/base.ts

@@ -1,15 +1,17 @@
-import * as ts from 'typescript';
+import ts from 'typescript';
+import { IsTsAutoMockOverloadsEnabled } from '../../options/overloads';
 import { SetTsAutoMockOptions, TsAutoMockOptions } from '../../options/options';
 import { SetTypeChecker } from '../typeChecker/typeChecker';
 import { MockDefiner } from '../mockDefiner/mockDefiner';
 import { SetProgram } from '../program/program';
 import { TypescriptHelper } from '../descriptor/helper/helper';
+import { TypescriptCreator } from '../helper/creator';
 import {
   CustomFunction,
   isFunctionFromThisLibrary,
 } from '../matcher/matcher';
 
-export type Visitor = (node: ts.CallExpression & { typeArguments: ts.NodeArray<ts.TypeNode> }, declaration: ts.FunctionDeclaration) => ts.Node;
+export type Visitor = (node: ts.CallLikeExpression & { typeArguments: ts.NodeArray<ts.TypeNode> }, declaration: ts.SignatureDeclaration) => ts.Node;
 
 export function baseTransformer(visitor: Visitor, customFunctions: CustomFunction[]): (program: ts.Program, options?: TsAutoMockOptions) => ts.TransformerFactory<ts.SourceFile> {
   return (program: ts.Program, options?: TsAutoMockOptions): ts.TransformerFactory<ts.SourceFile> => {
@@ -47,14 +49,69 @@ function isObjectWithProperty<T extends {}, K extends keyof T>(
   return typeof obj[key] !== 'undefined';
 }
 
+function isMockedByThisLibrary(declaration: ts.Declaration): boolean {
+  return MockDefiner.instance.hasKeyForDeclaration(declaration);
+}
+
 function visitNode(node: ts.Node, visitor: Visitor, customFunctions: CustomFunction[]): ts.Node {
-  if (!ts.isCallExpression(node)) {
+  if (!ts.isCallExpression(node) && !ts.isNewExpression(node)) {
     return node;
   }
 
   const signature: ts.Signature | undefined = TypescriptHelper.getSignatureOfCallExpression(node);
+  const declaration: ts.Declaration | undefined = signature?.declaration;
+
+  if (!declaration || !ts.isFunctionLike(declaration)) {
+    return node;
+  }
+
+  if (IsTsAutoMockOverloadsEnabled() && isMockedByThisLibrary(declaration)) {
+    const mockKey: string = MockDefiner.instance.getDeclarationKeyMap(declaration);
+    const mockKeyLiteral: ts.StringLiteral = ts.createStringLiteral(mockKey);
+
+    const boundSignatureCall: ts.CallExpression  = TypescriptCreator.createCall(
+      ts.createPropertyAccess(
+        node.expression,
+        ts.createIdentifier('apply'),
+      ),
+      [mockKeyLiteral, ts.createArrayLiteral(node.arguments)],
+    );
+
+    if (ts.isCallExpression(node)) {
+      return boundSignatureCall;
+    }
 
-  if (!signature || !isFunctionFromThisLibrary(signature, customFunctions)) {
+    return ts.createNew(
+      TypescriptCreator.createCachedAssignment(
+        ts.createElementAccess(
+          node.expression,
+          mockKeyLiteral,
+        ),
+        TypescriptCreator.createFunctionExpression(
+          ts.createBlock(
+            [
+              ts.createExpressionStatement(
+                TypescriptCreator.createCall(
+                  ts.createPropertyAccess(
+                    ts.createIdentifier('Object'),
+                    ts.createIdentifier('assign'),
+                  ),
+                  [
+                    ts.createIdentifier('this'),
+                    boundSignatureCall,
+                  ]
+                ),
+              ),
+            ],
+          )
+        ),
+      ),
+      undefined,
+      undefined,
+    );
+  }
+
+  if (!isFunctionFromThisLibrary(declaration, customFunctions)) {
     return node;
   }
 
@@ -73,7 +130,5 @@ function visitNode(node: ts.Node, visitor: Visitor, customFunctions: CustomFunct
   MockDefiner.instance.setFileNameFromNode(nodeToMock);
   MockDefiner.instance.setTsAutoMockImportIdentifier();
 
-  const declaration: ts.FunctionDeclaration = signature.declaration as ts.FunctionDeclaration;
-
   return visitor(node, declaration);
 }

src/transformer/descriptor/helper/helper.ts

@@ -104,7 +104,7 @@ export namespace TypescriptHelper {
   }
 
 
-  export function getSignatureOfCallExpression(node: ts.CallExpression): ts.Signature | undefined {
+  export function getSignatureOfCallExpression(node: ts.CallLikeExpression): ts.Signature | undefined {
     const typeChecker: ts.TypeChecker = TypeChecker();
 
     return typeChecker.getResolvedSignature(node);

src/transformer/descriptor/method/bodyReturnType.ts

@@ -7,30 +7,28 @@ export function GetReturnTypeFromBodyDescriptor(node: ts.ArrowFunction | ts.Func
   return GetDescriptor(GetReturnNodeFromBody(node), scope);
 }
 
-export function GetReturnNodeFromBody(node: ts.FunctionLikeDeclaration): ts.Node {
-  let returnValue: ts.Node | undefined;
-
+export function GetReturnNodeFromBody<T extends ts.Node & { body?: ts.ConciseBody }>(node: T): ts.Expression {
   const functionBody: ts.ConciseBody | undefined = node.body;
 
-  if (functionBody && ts.isBlock(functionBody)) {
-    const returnStatement: ts.ReturnStatement = GetReturnStatement(functionBody);
+  if (!functionBody) {
+    return GetNullDescriptor();
+  }
 
-    if (returnStatement) {
-      returnValue = returnStatement.expression;
-    } else {
-      returnValue = GetNullDescriptor();
-    }
-  } else {
-    returnValue = node.body;
+  if (!ts.isBlock(functionBody)) {
+    return functionBody;
   }
 
-  if (!returnValue) {
-    throw new Error(`Failed to determine the return value of ${node.getText()}.`);
+  const returnStatement: ts.ReturnStatement | undefined = GetReturnStatement(functionBody);
+
+  if (!returnStatement?.expression) {
+    return GetNullDescriptor();
   }
 
-  return returnValue;
+  return returnStatement.expression;
 }
 
-function GetReturnStatement(body: ts.FunctionBody): ts.ReturnStatement {
-  return body.statements.find((statement: ts.Statement) => statement.kind === ts.SyntaxKind.ReturnStatement) as ts.ReturnStatement;
+function GetReturnStatement(body: ts.FunctionBody): ts.ReturnStatement | undefined {
+  return body.statements.find(
+    (statement: ts.Statement): statement is ts.ReturnStatement => statement.kind === ts.SyntaxKind.ReturnStatement,
+  );
 }

src/transformer/descriptor/method/functionAssignment.ts

@@ -1,14 +1,12 @@
-import * as ts from 'typescript';
+import ts from 'typescript';
 import { Scope } from '../../scope/scope';
 import { PropertySignatureCache } from '../property/cache';
-import { GetReturnTypeFromBodyDescriptor } from './bodyReturnType';
 import { GetMethodDescriptor } from './method';
 
 type FunctionAssignment = ts.ArrowFunction | ts.FunctionExpression;
 
 export function GetFunctionAssignmentDescriptor(node: FunctionAssignment, scope: Scope): ts.Expression {
   const property: ts.PropertyName = PropertySignatureCache.instance.get();
-  const returnValue: ts.Expression = GetReturnTypeFromBodyDescriptor(node, scope);
 
-  return GetMethodDescriptor(property, returnValue);
+  return GetMethodDescriptor(property, [node], scope);
 }

src/transformer/descriptor/method/functionType.ts

@@ -1,6 +1,5 @@
 import * as ts from 'typescript';
 import { Scope } from '../../scope/scope';
-import { GetDescriptor } from '../descriptor';
 import { PropertySignatureCache } from '../property/cache';
 import { GetMethodDescriptor } from './method';
 
@@ -11,7 +10,5 @@ export function GetFunctionTypeDescriptor(node: ts.FunctionTypeNode | ts.CallSig
     throw new Error(`No type was declared for ${node.getText()}.`);
   }
 
-  const returnValue: ts.Expression = GetDescriptor(node.type, scope);
-
-  return GetMethodDescriptor(property, returnValue);
+  return GetMethodDescriptor(property, [node], scope);
 }