Add support for extends as array of strings to v3 (backport of #245) (#…

…260)

TypeScript 5.0 added support for defining "extends" as an array of
strings. This commit adds support for this use case.

src/__tests__/tsconfig-loader.test.ts

@@ -133,7 +133,7 @@ describe("walkForTsConfig", () => {
 });
 
 describe("loadConfig", () => {
-  it("It should load a config", () => {
+  it("should load a config", () => {
     const config = { compilerOptions: { baseUrl: "hej" } };
     const res = loadTsconfig(
       "/root/dir1/tsconfig.json",
@@ -144,7 +144,7 @@ describe("loadConfig", () => {
     expect(res).toStrictEqual(config);
   });
 
-  it("It should load a config with comments", () => {
+  it("should load a config with comments", () => {
     const config = { compilerOptions: { baseUrl: "hej" } };
     const res = loadTsconfig(
       "/root/dir1/tsconfig.json",
@@ -160,7 +160,7 @@ describe("loadConfig", () => {
     expect(res).toStrictEqual(config);
   });
 
-  it("It should load a config with trailing commas", () => {
+  it("should load a config with trailing commas", () => {
     const config = { compilerOptions: { baseUrl: "hej" } };
     const res = loadTsconfig(
       "/root/dir1/tsconfig.json",
@@ -175,7 +175,21 @@ describe("loadConfig", () => {
     expect(res).toStrictEqual(config);
   });
 
-  it("It should load a config with extends and overwrite all options", () => {
+  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("should load a config with string extends and overwrite all options", () => {
     const firstConfig = {
       extends: "../base-config.json",
       compilerOptions: { baseUrl: "kalle", paths: { foo: ["bar2"] } },
@@ -221,7 +235,7 @@ describe("loadConfig", () => {
     });
   });
 
-  it("It should load a config with extends from node_modules and overwrite all options", () => {
+  it("should load a config with string extends from node_modules and overwrite all options", () => {
     const firstConfig = {
       extends: "my-package/base-config.json",
       compilerOptions: { baseUrl: "kalle", paths: { foo: ["bar2"] } },
@@ -273,7 +287,7 @@ describe("loadConfig", () => {
     });
   });
 
-  it("Should use baseUrl relative to location of extended tsconfig", () => {
+  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" };
@@ -309,4 +323,94 @@ describe("loadConfig", () => {
       compilerOptions: { baseUrl: join("..", "..") },
     });
   });
+
+  it("should load a config with array extends and overwrite all options", () => {
+    const baseConfig1 = {
+      compilerOptions: { baseUrl: ".", paths: { foo: ["bar"] } },
+    };
+    const baseConfig1Path = join("/root", "base-config-1.json");
+    const baseConfig2 = { compilerOptions: { baseUrl: "." } };
+    const baseConfig2Path = join("/root", "dir1", "base-config-2.json");
+    const baseConfig3 = {
+      compilerOptions: { baseUrl: ".", paths: { foo: ["bar2"] } },
+    };
+    const baseConfig3Path = join("/root", "dir1", "dir2", "base-config-3.json");
+    const actualConfig = {
+      extends: [
+        "./base-config-1.json",
+        "./dir1/base-config-2.json",
+        "./dir1/dir2/base-config-3.json",
+      ],
+    };
+    const actualConfigPath = join("/root", "tsconfig.json");
+
+    const res = loadTsconfig(
+      join("/root", "tsconfig.json"),
+      (path) =>
+        [
+          baseConfig1Path,
+          baseConfig2Path,
+          baseConfig3Path,
+          actualConfigPath,
+        ].indexOf(path) >= 0,
+      (path) => {
+        if (path === baseConfig1Path) {
+          return JSON.stringify(baseConfig1);
+        }
+        if (path === baseConfig2Path) {
+          return JSON.stringify(baseConfig2);
+        }
+        if (path === baseConfig3Path) {
+          return JSON.stringify(baseConfig3);
+        }
+        if (path === actualConfigPath) {
+          return JSON.stringify(actualConfig);
+        }
+        return "";
+      }
+    );
+
+    expect(res).toEqual({
+      extends: [
+        "./base-config-1.json",
+        "./dir1/base-config-2.json",
+        "./dir1/dir2/base-config-3.json",
+      ],
+      compilerOptions: {
+        baseUrl: join("dir1", "dir2"),
+        paths: { foo: ["bar2"] },
+      },
+    });
+  });
+
+  it("should load a config with array extends without .json extension", () => {
+    const baseConfig = {
+      compilerOptions: { baseUrl: ".", paths: { foo: ["bar"] } },
+    };
+    const baseConfigPath = join("/root", "base-config-1.json");
+    const actualConfig = { extends: ["./base-config-1"] };
+    const actualConfigPath = join("/root", "tsconfig.json");
+
+    const res = loadTsconfig(
+      join("/root", "tsconfig.json"),
+      (path) => [baseConfigPath, actualConfigPath].indexOf(path) >= 0,
+      (path) => {
+        if (path === baseConfigPath) {
+          return JSON.stringify(baseConfig);
+        }
+        if (path === actualConfigPath) {
+          return JSON.stringify(actualConfig);
+        }
+        return "";
+      }
+    );
+
+    expect(res).toEqual({
+      extends: ["./base-config-1"],
+      compilerOptions: {
+        baseUrl: ".",
+        paths: { foo: ["bar"] },
+      },
+    });
+  });
 });

src/tsconfig-loader.ts

@@ -9,7 +9,7 @@ import StripBom = require("strip-bom");
  * Typing for the parts of tsconfig that we care about
  */
 export interface Tsconfig {
-  extends?: string;
+  extends?: string | string[];
   compilerOptions?: {
     baseUrl?: string;
     paths?: { [key: string]: Array<string> };
@@ -122,51 +122,105 @@ export function loadTsconfig(
 
   const configString = readFileSync(configFilePath);
   const cleanedJson = StripBom(configString);
-  const config: Tsconfig = JSON5.parse(cleanedJson);
-  let extendedConfig = config.extends;
+  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
+    let base: Tsconfig;
+
+    if (Array.isArray(extendedConfig)) {
+      base = extendedConfig.reduce(
+        (currBase, extendedConfigElement) =>
+          mergeTsconfigs(
+            currBase,
+            loadTsconfigFromExtends(
+              configFilePath,
+              extendedConfigElement,
+              existsSync,
+              readFileSync
+            )
+          ),
+        {}
+      );
+    } else {
+      base = loadTsconfigFromExtends(
+        configFilePath,
+        extendedConfig,
+        existsSync,
+        readFileSync
       );
     }
 
-    const base =
-      loadTsconfig(extendedConfigPath, existsSync, readFileSync) || {};
+    return mergeTsconfigs(base, config);
+  }
+  return config;
+}
 
-    // 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
-      );
-    }
+/**
+ * Intended to be called only from loadTsconfig.
+ * Parameters don't have defaults because they should use the same as loadTsconfig.
+ */
+function loadTsconfigFromExtends(
+  configFilePath: string,
+  extendedConfigValue: string,
+  // eslint-disable-next-line no-shadow
+  existsSync: (path: string) => boolean,
+  readFileSync: (filename: string) => string
+): Tsconfig {
+  if (
+    typeof extendedConfigValue === "string" &&
+    extendedConfigValue.indexOf(".json") === -1
+  ) {
+    extendedConfigValue += ".json";
+  }
+  const currentDir = path.dirname(configFilePath);
+  let extendedConfigPath = path.join(currentDir, extendedConfigValue);
+  if (
+    extendedConfigValue.indexOf("/") !== -1 &&
+    extendedConfigValue.indexOf(".") !== -1 &&
+    !existsSync(extendedConfigPath)
+  ) {
+    extendedConfigPath = path.join(
+      currentDir,
+      "node_modules",
+      extendedConfigValue
+    );
+  }
 
-    return {
-      ...base,
-      ...config,
-      compilerOptions: {
-        ...base.compilerOptions,
-        ...config.compilerOptions,
-      },
-    };
+  const config =
+    loadTsconfig(extendedConfigPath, existsSync, readFileSync) || {};
+
+  // baseUrl should be interpreted as relative to extendedConfigPath,
+  // but we need to update it so it is relative to the original tsconfig being loaded
+  if (config.compilerOptions?.baseUrl) {
+    const extendsDir = path.dirname(extendedConfigValue);
+    config.compilerOptions.baseUrl = path.join(
+      extendsDir,
+      config.compilerOptions.baseUrl
+    );
   }
+
   return config;
 }
+
+function mergeTsconfigs(
+  base: Tsconfig | undefined,
+  config: Tsconfig | undefined
+): Tsconfig {
+  base = base || {};
+  config = config || {};
+
+  return {
+    ...base,
+    ...config,
+    compilerOptions: {
+      ...base.compilerOptions,
+      ...config.compilerOptions,
+    },
+  };
+}