support ts4

packages/example-ts4/.babelrc

@@ -0,0 +1,3 @@
+{
+  "presets": ["@babel/preset-env", "@babel/preset-typescript"]
+}

packages/example-ts4/README.md

@@ -0,0 +1,18 @@
+# ts-overrides-plugin example
+
+Before all:
+
+```bash
+yarn ts-patch install
+```
+
+Commands:
+
+```bash
+yarn build:tsc
+yarn build:ts-loader
+yarn build:fork-ts
+yarn watch:tsc
+yarn watch:ts-loader
+yarn watch:fork-ts
+```

packages/example-ts4/package.json

@@ -0,0 +1,29 @@
+{
+  "name": "example-ts4",
+  "scripts": {
+    "build:tsc": "tsc",
+    "build:ts-loader": "webpack --config webpack.config.ts-loader.js",
+    "build:fork-ts": "webpack --config webpack.config.fork-ts.js",
+    "watch:tsc": "tsc --watch",
+    "watch:ts-loader": "webpack --config webpack.config.ts-loader.js --watch",
+    "watch:fork-ts": "webpack --config webpack.config.fork-ts.js --watch",
+    "prepare": "ts-patch install -s"
+  },
+  "devDependencies": {
+    "@babel/core": "^7.23.6",
+    "@babel/preset-env": "^7.23.6",
+    "@babel/preset-typescript": "^7.23.3",
+    "@types/babel__core": "^7",
+    "@types/babel__preset-env": "^7",
+    "babel-loader": "^9.1.3",
+    "fork-ts-checker-webpack-plugin": "^9.0.2",
+    "ts-loader": "^9.5.1",
+    "ts-node": "^10.9.2",
+    "ts-overrides-plugin": "workspce:*",
+    "ts-patch": "2.1.0",
+    "typescript": "4.2.4",
+    "webpack": "^5.89.0",
+    "webpack-cli": "^5.1.4"
+  },
+  "packageManager": "[email protected]"
+}

packages/example-ts4/src/index.ts

@@ -0,0 +1,4 @@
+import { getDate as getDateLegacy } from './legacy/getDate';
+import { getDate as getDateModern } from './modern/getDate';
+
+console.log({ getDateLegacy, getDateModern });

packages/example-ts4/src/legacy/getDate.ts

@@ -0,0 +1,16 @@
+// ok with strict: false
+export const getDate = (date) => {
+  const modern: string | undefined = undefined;
+
+  // ok with strict: false
+  modern.split('');
+
+  return date.toLocaleDateString('ru-RU', {
+    day: 'numeric',
+    month: 'long',
+    year: 'numeric',
+  });
+}
+
+// show `string` on hover in IDE
+export const someVar: string | undefined = undefined;

packages/example-ts4/src/modern/getDate.ts

@@ -0,0 +1,18 @@
+import { someVar } from '../legacy/getDate';
+
+// Parameter 'date' implicitly has an 'any' type.
+export const getDate = (date) => {
+  const modern: string | undefined = undefined;
+
+  // Show `string | undefined` on hover in IDE
+  console.log(someVar);
+
+  // 'modern' is possibly 'undefined'
+  modern.split('');
+
+  return date.toLocaleDateString('ru-RU', {
+    day: 'numeric',
+    month: 'long',
+    year: 'numeric',
+  });
+}

packages/example-ts4/tsconfig.json

@@ -0,0 +1,25 @@
+{
+  "compilerOptions": {
+    "module": "ESNext",
+    "outDir": "./dist",
+    "baseUrl": "./src",
+    "strict": false,
+    "noEmit": false,
+    "skipLibCheck": true,
+    "plugins": [
+      {
+        "name": "ts-overrides-plugin",
+        "transform": "ts-overrides-plugin/cli",
+        "transformProgram": true,
+        "overrides": [
+          {
+            "files": ["src/modern/**/*.{ts,tsx}"],
+            "compilerOptions": {
+              "strict": true,
+            },
+          },
+        ]
+      },
+    ]
+  },
+}

packages/example-ts4/webpack.config.fork-ts.js

@@ -0,0 +1,29 @@
+const path = require('path');
+const ForkTsCheckerWebpackPlugin = require('fork-ts-checker-webpack-plugin');
+
+module.exports = [
+    {
+        mode: 'production',
+        entry: './src/index.ts',
+        output: {
+            path: path.join(__dirname, 'build'),
+            filename: 'main.js',
+        },
+        module: {
+            rules: [
+                {
+                    test: /\.ts$/,
+                    exclude: /node_modules/,
+                    loader: 'babel-loader',
+                },
+            ],
+        },
+        plugins: [
+          new ForkTsCheckerWebpackPlugin(),
+        ],
+        resolve: {
+            extensions: ['.ts', '.js'],
+        },
+        target: 'web',
+    }
+];

packages/example-ts4/webpack.config.ts-loader.js

@@ -0,0 +1,25 @@
+const path = require('path');
+
+module.exports = [
+    {
+        mode: 'production',
+        entry: './src/index.ts',
+        output: {
+            path: path.join(__dirname, 'build'),
+            filename: 'main.js',
+        },
+        module: {
+            rules: [
+                {
+                    test: /\.ts$/,
+                    exclude: /node_modules/,
+                    loader: 'ts-loader',
+                },
+            ],
+        },
+        resolve: {
+            extensions: ['.ts', '.js'],
+        },
+        target: 'web',
+    }
+];

packages/plugin/README.md

@@ -29,6 +29,7 @@ any other cases where you need to override the `tsconfig` settings for specific
 ## Installation and setup
 
 Examples can be seen in the [`example`](https://github.com/DiFuks/ts-overrides-plugin/tree/main/packages/example) folder.
+Specially for TS4, a separate [`example`](https://github.com/DiFuks/ts-overrides-plugin/tree/main/packages/example-ts4) folder.
 
 ### For using the plugin only in the IDE
 
@@ -111,7 +112,11 @@ In the `tsconfig.json` file, add:
 ```
 
 If you are using [`Persistent Patch`](https://github.com/nonara/ts-patch?tab=readme-ov-file#method-2-persistent-patch)
-with `ts-patch`, then there is nothing more to do. If, however, you are using [`Live Compiler`](https://github.com/nonara/ts-patch?tab=readme-ov-file#method-1-live-compiler), the
+with `ts-patch`, then there is nothing more to do.
+
+For TS4 version, it is possible to use only the Persistent Patch option with [ts-patch version 2.1.0](https://github.com/nonara/ts-patch/tree/v2.1.0).
+
+If, however, you are using [`Live Compiler`](https://github.com/nonara/ts-patch?tab=readme-ov-file#method-1-live-compiler), the
 following steps are necessary:
 
 For the `tsc` command – replace it with `tspc` in `package.json`:

packages/plugin/package.json

@@ -43,8 +43,8 @@
 		"typescript": "5.5.1-rc"
 	},
 	"peerDependencies": {
-		"ts-patch": "^3.0.0",
-		"typescript": "^5.0.0"
+		"ts-patch": "^3.0.0 || ^2.0.0",
+		"typescript": "^5.0.0 || ^4.0.0"
 	},
 	"license": "MIT",
 	"packageManager": "[email protected]"

packages/plugin/src/ide/index.ts

@@ -2,7 +2,7 @@ import { relative } from 'node:path';
 import outmatch from 'outmatch';
 import type ts from 'typescript/lib/tsserverlibrary';
 
-import { type Override } from '../types/Override';
+import type { Override } from '../types/Override';
 
 interface IdePluginConfig {
 	overrides: Override[];
@@ -16,13 +16,17 @@ const getOverrideLanguageServices = (
 ): ts.LanguageService[] =>
 	[...overridesFromConfig].reverse().map(override => {
 		const overrideLanguageServiceHost: ts.LanguageServiceHost = {
-			fileExists: path => languageServiceHost.fileExists(path),
+			// don't remove this, it's needed for TS 4
+			// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+			fileExists: path => !!languageServiceHost.fileExists?.(path),
 			getCurrentDirectory: (): string => languageServiceHost.getCurrentDirectory(),
 			getDefaultLibFileName: (options: ts.CompilerOptions): string =>
 				languageServiceHost.getDefaultLibFileName(options),
 			getScriptSnapshot: fileName => languageServiceHost.getScriptSnapshot(fileName),
 			getScriptVersion: fileName => languageServiceHost.getScriptVersion(fileName),
-			readFile: (path, encoding) => languageServiceHost.readFile(path, encoding),
+			// don't remove this, it's needed for TS 4
+			// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+			readFile: (path, encoding) => languageServiceHost.readFile?.(path, encoding),
 			getCompilationSettings: () => ({
 				...languageServiceHost.getCompilationSettings(),
 				...typescript.convertCompilerOptionsFromJson(

packages/plugin/src/types/Override.ts

@@ -1,4 +1,4 @@
-import type ts from 'typescript';
+import type ts from 'typescript/lib/tsserverlibrary';
 
 export interface Override {
 	files: string[];