Resolve extended TypeScript configuration files

src/ExportMap.js

@@ -1,4 +1,5 @@
 import fs from 'fs';
+import path from 'path';
 
 import doctrine from 'doctrine';
 
@@ -18,7 +19,7 @@ import { tsConfigLoader } from 'tsconfig-paths/lib/tsconfig-loader';
 
 import includes from 'array-includes';
 
-let parseConfigFileTextToJson;
+let ts;
 
 const log = debug('eslint-plugin-import:ExportMap');
 
@@ -516,40 +517,17 @@ ExportMap.parse = function (path, content, context) {
 
   const source = makeSourceCode(content, ast);
 
-  function readTsConfig() {
-    const tsConfigInfo = tsConfigLoader({
-      cwd:
-        (context.parserOptions && context.parserOptions.tsconfigRootDir) ||
-        process.cwd(),
-      getEnv: (key) => process.env[key],
-    });
-    try {
-      if (tsConfigInfo.tsConfigPath !== undefined) {
-        const jsonText = fs.readFileSync(tsConfigInfo.tsConfigPath).toString();
-        if (!parseConfigFileTextToJson) {
-          // this is because projects not using TypeScript won't have typescript installed
-          ({ parseConfigFileTextToJson } = require('typescript'));
-        }
-        return parseConfigFileTextToJson(tsConfigInfo.tsConfigPath, jsonText).config;
-      }
-    } catch (e) {
-      // Catch any errors
-    }
-
-    return null;
-  }
-
   function isEsModuleInterop() {
     const cacheKey = hashObject({
       tsconfigRootDir: context.parserOptions && context.parserOptions.tsconfigRootDir,
     }).digest('hex');
     let tsConfig = tsConfigCache.get(cacheKey);
     if (typeof tsConfig === 'undefined') {
-      tsConfig = readTsConfig();
+      tsConfig = readTsConfig(context);
       tsConfigCache.set(cacheKey, tsConfig);
     }
 
-    return tsConfig && tsConfig.compilerOptions ? tsConfig.compilerOptions.esModuleInterop : false;
+    return tsConfig && tsConfig.options ? tsConfig.options.esModuleInterop : false;
   }
 
   ast.body.forEach(function (n) {
@@ -785,3 +763,32 @@ function makeSourceCode(text, ast) {
     return new SourceCode({ text, ast });
   }
 }
+
+/**
+ * Returns a project's TypeScript configuration.
+ */
+export function readTsConfig(context) {
+  const tsConfigInfo = tsConfigLoader({
+    cwd:
+      (context.parserOptions && context.parserOptions.tsconfigRootDir) ||
+      process.cwd(),
+    getEnv: (key) => process.env[key],
+  });
+  try {
+    if (tsConfigInfo.tsConfigPath !== undefined) {
+      // Projects not using TypeScript won't have `typescript` installed.
+      if (!ts) (ts = require('typescript'));
+
+      const configFile = ts.readConfigFile(tsConfigInfo.tsConfigPath, ts.sys.readFile);
+      return ts.parseJsonConfigFileContent(
+        configFile.config,
+        ts.sys,
+        path.dirname(tsConfigInfo.tsConfigPath),
+      );
+    }
+  } catch (e) {
+    // Catch any errors
+  }
+
+  return null;
+}

tests/files/typescript-extended-config/tsconfig.base.json

@@ -0,0 +1,8 @@
+{
+  "compilerOptions": {
+    "esModuleInterop": true,
+    "forceConsistentCasingInFileNames": true,
+    "skipLibCheck": true,
+    "strict": true
+  }
+}

tests/files/typescript-extended-config/tsconfig.json

@@ -0,0 +1,6 @@
+{
+  "extends": "./tsconfig.base.json",
+  "compilerOptions": {
+    "noEmit": true
+  }
+}

tests/src/ExportMap.js

@@ -0,0 +1,21 @@
+import { expect } from 'chai';
+import { readTsConfig } from '../../src/ExportMap';
+
+describe('ExportMap', function () {
+  describe('readTsConfig', function () {
+    const config = readTsConfig({
+      parserOptions: {
+        tsconfigRootDir: './tests/files/typescript-extended-config',
+      },
+    });
+    expect(config.options).to.contain({
+      // Rules from primary config.
+      noEmit: true,
+      // Rules from extended config.
+      esModuleInterop: true,
+      forceConsistentCasingInFileNames: true,
+      skipLibCheck: true,
+      strict: true,
+    });
+  });
+});