[code-infra] Validate package.json fields before building

packages/code-infra/src/cli/cmdBuild.mjs

@@ -3,7 +3,7 @@ import { $ } from 'execa';
 import set from 'lodash-es/set.js';
 import * as fs from 'node:fs/promises';
 import * as path from 'node:path';
-import { getOutExtension, isMjsBuild } from '../utils/build.mjs';
+import { getOutExtension, isMjsBuild, validatePkgJson } from '../utils/build.mjs';
 
 /**
  * @typedef {Object} Args
@@ -16,6 +16,7 @@ import { getOutExtension, isMjsBuild } from '../utils/build.mjs';
  * @property {boolean} skipTsc - Whether to build types for the package.
  * @property {boolean} skipBabelRuntimeCheck - Whether to skip checking for Babel runtime dependencies in the package.
  * @property {boolean} skipPackageJson - Whether to skip generating the package.json file in the bundle output.
+ * @property {boolean} skipMainCheck - Whether to skip checking for main field in package.json.
  * @property {string[]} ignore - Globs to be ignored by Babel.
  */
 
@@ -291,6 +292,12 @@ export default /** @type {import('yargs').CommandModule<{}, Args>} */ ({
         type: 'boolean',
         default: false,
         description: 'Skip generating the package.json file in the bundle output.',
+      })
+      .option('skipMainCheck', {
+        // Currently added only to support @mui/icons-material. To be removed separately.
+        type: 'boolean',
+        default: false,
+        description: 'Skip checking for main field in package.json.',
       });
   },
   async handler(args) {
@@ -310,17 +317,9 @@ export default /** @type {import('yargs').CommandModule<{}, Args>} */ ({
     const cwd = process.cwd();
     const pkgJsonPath = path.join(cwd, 'package.json');
     const packageJson = JSON.parse(await fs.readFile(pkgJsonPath, { encoding: 'utf8' }));
-    const buildDirBase = packageJson.publishConfig?.directory;
-    if (!buildDirBase) {
-      throw new Error(
-        `No build directory specified in "${packageJson.name}" package.json. Specify it in the "publishConfig.directory" field.`,
-      );
-    }
-    if (packageJson.private === false) {
-      throw new Error(
-        `Remove the field "private": false from "${packageJson.name}" package.json. This is redundant.`,
-      );
-    }
+    validatePkgJson(packageJson, { skipMainCheck: args.skipMainCheck });
+
+    const buildDirBase = /** @type {string} */ (packageJson.publishConfig?.directory);
     const buildDir = path.join(cwd, buildDirBase);
 
     console.log(`Selected output directory: "${buildDirBase}"`);

packages/code-infra/src/utils/build.mjs

@@ -18,3 +18,53 @@ export function getOutExtension(bundle, isType = false) {
   }
   return bundle === 'esm' ? '.mjs' : '.js';
 }
+
+/**
+ * Validates the package.json before building.
+ * @param {Record<string, any>} packageJson
+ * @param {Object} [options]
+ * @param {boolean} [options.skipMainCheck=false] - Whether to skip checking for main field in package.json.
+ */
+export function validatePkgJson(packageJson, options = {}) {
+  const { skipMainCheck = false } = options;
+  /**
+   * @type {string[]}
+   */
+  const errors = [];
+  const buildDirBase = packageJson.publishConfig?.directory;
+  if (!buildDirBase) {
+    errors.push(
+      `No build directory specified in "${packageJson.name}" package.json. Specify it in the "publishConfig.directory" field.`,
+    );
+  }
+  if (packageJson.private === false) {
+    errors.push(
+      `Remove the field "private": false from "${packageJson.name}" package.json. This is redundant.`,
+    );
+  }
+
+  if (!skipMainCheck) {
+    if (packageJson.main) {
+      errors.push(
+        `Remove the field "main" from "${packageJson.name}" package.json. Add it as "exports["."]" instead.`,
+      );
+    }
+
+    if (packageJson.module) {
+      errors.push(
+        `Remove the field "module" from "${packageJson.name}" package.json. Add it as "exports["."]" instead.`,
+      );
+    }
+
+    if (packageJson.types || packageJson.typings) {
+      errors.push(
+        `Remove the field "types/typings" from "${packageJson.name}" package.json. Add it as "exports["."]" instead.`,
+      );
+    }
+  }
+
+  if (errors.length > 0) {
+    const error = new Error(errors.join('\n'));
+    throw error;
+  }
+}