fix: use typescript library to resolve tsconfig files

example/inherited/tsconfig.base.json

@@ -0,0 +1,7 @@
+{
+  "compilerOptions": {
+    "paths": {
+      "@": []
+    }
+  }
+}

example/inherited/tsconfig.json

@@ -0,0 +1,3 @@
+{
+  "extends": "./tsconfig.preset.json"
+}

example/inherited/tsconfig.preset.json

@@ -0,0 +1,3 @@
+{
+  "extends": "./tsconfig.base.json"
+}

package.json

@@ -41,9 +41,10 @@
     "typescript": "^4.5.2"
   },
   "dependencies": {
-    "json5": "^2.2.2",
-    "minimist": "^1.2.6",
-    "strip-bom": "^3.0.0"
+    "minimist": "^1.2.6"
+  },
+  "peerDependencies": {
+    "typescript": "^4"
   },
   "scripts": {
     "start": "cd src && ts-node index.ts",

src/__tests__/tsconfig-loader.test.ts

@@ -1,9 +1,9 @@
 import {
-  loadTsconfig,
+  // loadTsconfig,
   tsConfigLoader,
   walkForTsConfig,
 } from "../tsconfig-loader";
-import { join } from "path";
+import { join, resolve } from "path";
 
 describe("tsconfig-loader", () => {
   it("should find tsconfig in cwd", () => {
@@ -167,172 +167,18 @@ describe("walkForTsConfig", () => {
   });
 });
 
-describe("loadConfig", () => {
-  it("It should load a config", () => {
-    const config = { compilerOptions: { baseUrl: "hej" } };
-    const res = loadTsconfig(
-      "/root/dir1/tsconfig.json",
-      (path) => path === "/root/dir1/tsconfig.json",
-      (_) => JSON.stringify(config)
-    );
-    expect(res).toStrictEqual(config);
-  });
-
-  it("It should load a config with comments", () => {
-    const config = { compilerOptions: { baseUrl: "hej" } };
-    const res = loadTsconfig(
-      "/root/dir1/tsconfig.json",
-      (path) => path === "/root/dir1/tsconfig.json",
-      (_) => `{
-          // my comment
-          "compilerOptions": { 
-            "baseUrl": "hej"
-          }
-        }`
-    );
-    expect(res).toStrictEqual(config);
-  });
-
-  it("It should load a config with trailing commas", () => {
-    const config = { compilerOptions: { baseUrl: "hej" } };
-    const res = loadTsconfig(
-      "/root/dir1/tsconfig.json",
-      (path) => path === "/root/dir1/tsconfig.json",
-      (_) => `{
-          "compilerOptions": { 
-            "baseUrl": "hej",
-          },
-        }`
-    );
-    expect(res).toStrictEqual(config);
-  });
-
-  it("It should throw an error including the file path when encountering invalid JSON5", () => {
-    expect(() =>
-      loadTsconfig(
-        "/root/dir1/tsconfig.json",
-        (path) => path === "/root/dir1/tsconfig.json",
-        (_) => `{
-            "compilerOptions": {
-          }`
-      )
-    ).toThrowError(
-      "/root/dir1/tsconfig.json is malformed JSON5: invalid end of input at 3:12"
-    );
-  });
-
-  it("It should load a config with extends and overwrite all options", () => {
-    const firstConfig = {
-      extends: "../base-config.json",
-      compilerOptions: { baseUrl: "kalle", paths: { foo: ["bar2"] } },
-    };
-    const firstConfigPath = join("/root", "dir1", "tsconfig.json");
-    const baseConfig = {
-      compilerOptions: {
-        baseUrl: "olle",
-        paths: { foo: ["bar1"] },
-        strict: true,
-      },
-    };
-    const baseConfigPath = join("/root", "base-config.json");
-    const res = loadTsconfig(
-      join("/root", "dir1", "tsconfig.json"),
-      (path) => path === firstConfigPath || path === baseConfigPath,
-      (path) => {
-        if (path === firstConfigPath) {
-          return JSON.stringify(firstConfig);
-        }
-        if (path === baseConfigPath) {
-          return JSON.stringify(baseConfig);
-        }
-        return "";
-      }
-    );
-
-    expect(res).toEqual({
-      extends: "../base-config.json",
-      compilerOptions: {
-        baseUrl: "kalle",
-        paths: { foo: ["bar2"] },
-        strict: true,
-      },
-    });
-  });
-
-  it("It should load a config with extends from node_modules and overwrite all options", () => {
-    const firstConfig = {
-      extends: "my-package/base-config.json",
-      compilerOptions: { baseUrl: "kalle", paths: { foo: ["bar2"] } },
-    };
-    const firstConfigPath = join("/root", "dir1", "tsconfig.json");
-    const baseConfig = {
-      compilerOptions: {
-        baseUrl: "olle",
-        paths: { foo: ["bar1"] },
-        strict: true,
-      },
-    };
-    const baseConfigPath = join(
-      "/root",
-      "dir1",
-      "node_modules",
-      "my-package",
-      "base-config.json"
-    );
-    const res = loadTsconfig(
-      join("/root", "dir1", "tsconfig.json"),
-      (path) => path === firstConfigPath || path === baseConfigPath,
-      (path) => {
-        if (path === firstConfigPath) {
-          return JSON.stringify(firstConfig);
-        }
-        if (path === baseConfigPath) {
-          return JSON.stringify(baseConfig);
-        }
-        return "";
-      }
-    );
-
-    expect(res).toEqual({
-      extends: "my-package/base-config.json",
-      compilerOptions: {
-        baseUrl: "kalle",
-        paths: { foo: ["bar2"] },
-        strict: true,
-      },
+describe("loadSyncDefault", () => {
+  it("should result multiple levels of tsconfig extension", () => {
+    const cwd = resolve(__dirname, "../../example/inherited");
+    const result = tsConfigLoader({
+      cwd,
+      getEnv: (_: string) => undefined,
     });
-  });
-
-  it("Should use baseUrl relative to location of extended tsconfig", () => {
-    const firstConfig = { compilerOptions: { baseUrl: "." } };
-    const firstConfigPath = join("/root", "first-config.json");
-    const secondConfig = { extends: "../first-config.json" };
-    const secondConfigPath = join("/root", "dir1", "second-config.json");
-    const thirdConfig = { extends: "../second-config.json" };
-    const thirdConfigPath = join("/root", "dir1", "dir2", "third-config.json");
-    const res = loadTsconfig(
-      join("/root", "dir1", "dir2", "third-config.json"),
-      (path) =>
-        path === firstConfigPath ||
-        path === secondConfigPath ||
-        path === thirdConfigPath,
-      (path) => {
-        if (path === firstConfigPath) {
-          return JSON.stringify(firstConfig);
-        }
-        if (path === secondConfigPath) {
-          return JSON.stringify(secondConfig);
-        }
-        if (path === thirdConfigPath) {
-          return JSON.stringify(thirdConfig);
-        }
-        return "";
-      }
-    );
 
-    expect(res).toEqual({
-      extends: "../second-config.json",
-      compilerOptions: { baseUrl: join("..", "..") },
+    expect(result).toEqual({
+      baseUrl: undefined,
+      paths: { "@": [] },
+      tsConfigPath: resolve(cwd, "tsconfig.json"),
     });
   });
 });

src/tsconfig-loader.ts

@@ -1,21 +1,6 @@
 import * as path from "path";
 import * as fs from "fs";
-// eslint-disable-next-line @typescript-eslint/no-require-imports
-import JSON5 = require("json5");
-// eslint-disable-next-line @typescript-eslint/no-require-imports
-import StripBom = require("strip-bom");
-
-/**
- * Typing for the parts of tsconfig that we care about
- */
-export interface Tsconfig {
-  extends?: string;
-  compilerOptions?: {
-    baseUrl?: string;
-    paths?: { [key: string]: Array<string> };
-    strict?: boolean;
-  };
-}
+import * as typescript from "typescript";
 
 export interface TsConfigLoaderResult {
   tsConfigPath: string | undefined;
@@ -47,7 +32,7 @@ export function tsConfigLoader({
   return loadResult;
 }
 
-function loadSyncDefault(
+export function loadSyncDefault(
   cwd: string,
   filename?: string,
   baseUrl?: string
@@ -63,14 +48,23 @@ function loadSyncDefault(
       paths: undefined,
     };
   }
-  const config = loadTsconfig(configPath);
+  const rawConfig = typescript.readConfigFile(
+    configPath,
+    typescript.sys.readFile
+  );
+
+  const config = typescript.parseJsonConfigFileContent(
+    rawConfig.config,
+    typescript.sys,
+    cwd,
+    {},
+    filename
+  );
 
   return {
     tsConfigPath: configPath,
-    baseUrl:
-      baseUrl ||
-      (config && config.compilerOptions && config.compilerOptions.baseUrl),
-    paths: config && config.compilerOptions && config.compilerOptions.paths,
+    baseUrl: baseUrl || config.options.baseUrl,
+    paths: config.options.paths,
   };
 }
 
@@ -111,70 +105,3 @@ export function walkForTsConfig(
 
   return walkForTsConfig(parentDirectory, readdirSync);
 }
-
-export function loadTsconfig(
-  configFilePath: string,
-  // eslint-disable-next-line no-shadow
-  existsSync: (path: string) => boolean = fs.existsSync,
-  readFileSync: (filename: string) => string = (filename: string) =>
-    fs.readFileSync(filename, "utf8")
-): Tsconfig | undefined {
-  if (!existsSync(configFilePath)) {
-    return undefined;
-  }
-
-  const configString = readFileSync(configFilePath);
-  const cleanedJson = StripBom(configString);
-  let config: Tsconfig;
-  try {
-    config = JSON5.parse(cleanedJson);
-  } catch (e) {
-    throw new Error(`${configFilePath} is malformed ${e.message}`);
-  }
-  let extendedConfig = config.extends;
-
-  if (extendedConfig) {
-    if (
-      typeof extendedConfig === "string" &&
-      extendedConfig.indexOf(".json") === -1
-    ) {
-      extendedConfig += ".json";
-    }
-    const currentDir = path.dirname(configFilePath);
-    let extendedConfigPath = path.join(currentDir, extendedConfig);
-    if (
-      extendedConfig.indexOf("/") !== -1 &&
-      extendedConfig.indexOf(".") !== -1 &&
-      !existsSync(extendedConfigPath)
-    ) {
-      extendedConfigPath = path.join(
-        currentDir,
-        "node_modules",
-        extendedConfig
-      );
-    }
-
-    const base =
-      loadTsconfig(extendedConfigPath, existsSync, readFileSync) || {};
-
-    // baseUrl should be interpreted as relative to the base tsconfig,
-    // but we need to update it so it is relative to the original tsconfig being loaded
-    if (base.compilerOptions && base.compilerOptions.baseUrl) {
-      const extendsDir = path.dirname(extendedConfig);
-      base.compilerOptions.baseUrl = path.join(
-        extendsDir,
-        base.compilerOptions.baseUrl
-      );
-    }
-
-    return {
-      ...base,
-      ...config,
-      compilerOptions: {
-        ...base.compilerOptions,
-        ...config.compilerOptions,
-      },
-    };
-  }
-  return config;
-}