From 6677b4193d3f4884686a1abba792debfdff6ea0d Mon Sep 17 00:00:00 2001
From: Siddarth Kumar <siddarthkay@gmail.com>
Date: Mon, 5 Jun 2023 07:24:05 +0530
Subject: [PATCH 1/2] implement fn `resolvePackageTargetsFromImports`

Implement `resolvePackageTargetsFromImports`as per spec at :
https://nodejs.org/api/esm.html#resolver-algorithm-specification
---
 .../src/PackageImportsResolve.js              | 269 ++++++++++++++++++
 1 file changed, 269 insertions(+)
 create mode 100644 packages/metro-resolver/src/PackageImportsResolve.js

diff --git a/packages/metro-resolver/src/PackageImportsResolve.js b/packages/metro-resolver/src/PackageImportsResolve.js
new file mode 100644
index 0000000000..2cfea3d236
--- /dev/null
+++ b/packages/metro-resolver/src/PackageImportsResolve.js
@@ -0,0 +1,269 @@
+import path from 'path';
+import fs from 'fs';
+import * as url from 'url';
+export function resolvePackageTargetsFromImports(specifier: string, parentURL, conditions){
+
+  if (!specifier.startsWith('#')) {
+    throw new Error("Specifier must start with '#'.");
+  }
+
+  if(specifier.startsWith('#/') || specifier === '#') {
+    throw Error('Invalid Module Specifier.');
+  }
+  const packageURL = lookupParentScope(parentURL);
+
+  if (packageURL) {
+    const pjson = readPackageJSON(packageURL);
+
+    // If pjson.imports is a non-null Object, then
+    if (pjson.imports && typeof pjson.imports === 'object') {
+      const resolved = packageImportsExportsResolver(specifier, pjson.imports, packageURL, true, conditions);
+
+      // If resolved is not null or undefined, return resolved.
+      if (resolved != null && typeof resolved !== 'undefined') {
+        return resolved;
+      }
+    }
+
+    throw new Error('Package Import Not Defined.');
+  }
+}
+
+function lookupParentScope(url: string): string {
+  let scopeURL = url;
+
+  while (scopeURL !== path.parse(scopeURL).root) {
+    scopeURL = path.dirname(scopeURL);
+
+    // If scopeURL ends in a "node_modules" path segment, return null.
+    if (scopeURL.endsWith('node_modules')) {
+      return null;
+    }
+
+    const pjsonURL = path.resolve(scopeURL, 'package.json');
+
+    // If the file at pjsonURL exists, then
+    if (fs.existsSync(pjsonURL)) {
+      return scopeURL;
+    }
+  }
+  return null;
+}
+
+function readPackageJSON(url: string): string {
+  const pjsonURL = path.resolve(packageURL, 'package.json');
+
+  // If the file at pjsonURL does not exist, then
+  if (!fs.existsSync(pjsonURL)) {
+    return null;
+  }
+
+  try {
+    // Parse JSON from file
+    const packageJson = fs.readFileSync(pjsonURL, 'utf-8');
+    const parsedJson = JSON.parse(packageJson);
+
+    // If the file at pjsonURL does not parse as valid JSON, then
+    // Throw an Invalid Package Configuration error.
+    return parsedJson;
+  } catch (e) {
+    throw new Error('Invalid Package Configuration');
+  }
+}
+
+function packageImportsExportsResolver(matchKey, matchObj, packageURL, isImports, conditions) {
+  if (matchObj.hasOwnProperty(matchKey) && !matchKey.includes('*')) {
+    const target = matchObj[matchKey];
+    return packageTargetResolve(packageURL, target, null, isImports, conditions);
+  }
+
+  const expansionKeys = Object.keys(matchObj).filter(key => key.split('*').length - 1 === 1).sort(PATTERN_KEY_COMPARE);
+
+  for (const expansionKey of expansionKeys) {
+    const patternBase = expansionKey.split('*')[0];
+    if (matchKey.startsWith(patternBase) && matchKey !== patternBase) {
+      const patternTrailer = expansionKey.split('*')[1];
+      if (patternTrailer.length === 0 || (matchKey.endsWith(patternTrailer) && matchKey.length >= expansionKey.length)) {
+        const target = matchObj[expansionKey];
+        const patternMatch = matchKey.substring(patternBase.length, matchKey.length - patternTrailer.length);
+        return packageTargetResolve(packageURL, target, patternMatch, isImports, conditions);
+      }
+    }
+  }
+
+  return null;
+}
+
+function packageTargetResolve(packageURL, target, patternMatch, isImports, conditions) {
+  if (typeof target === 'string') {
+    if (!target.startsWith('./')) {
+      if (!isImports || target.startsWith('../') || target.startsWith('/') || isValidURL(target)) {
+        throw new Error('Invalid Package Target');
+      }
+    }
+
+    if (patternMatch) {
+      return packageResolve(target.replace(/\*/g, patternMatch), `${packageURL}/`);
+    }
+
+    return packageResolve(target, `${packageURL}/`);
+  } else if (target && typeof target === 'object' && !Array.isArray(target)) {
+    if (Object.keys(target).some(key => /^\d+$/.test(key))) {
+      throw new Error('Invalid Package Configuration');
+    }
+
+    for (const p in target) {
+      if (p === 'default' || conditions.includes(p)) {
+        const targetValue = target[p];
+        const resolved = packageTargetResolve(packageURL, targetValue, patternMatch, isImports, conditions);
+        if (resolved != null) {
+          return resolved;
+        }
+      }
+    }
+
+    return undefined;
+  } else if (Array.isArray(target)) {
+    if (target.length === 0) {
+      return null;
+    }
+
+    for (const targetValue of target) {
+      try {
+        const resolved = packageTargetResolve(packageURL, targetValue, patternMatch, isImports, conditions);
+        if (resolved != null) {
+          return resolved;
+        }
+      } catch (e) {
+        if (e.message !== 'Invalid Package Target') {
+          throw e;
+        }
+      }
+    }
+
+    throw new Error('Invalid Package Target');
+  } else if (target == null) {
+    return null;
+  }
+
+  throw new Error('Invalid Package Target');
+}
+
+function isValidURL(str) {
+  try {
+    new URL(str);
+    return true;
+  } catch (e) {
+    return false;
+  }
+}
+
+function packageResolve(packageSpecifier, parentURL) {
+  if (packageSpecifier === '') {
+    throw new Error('Invalid Module Specifier');
+  }
+
+  if (isBuiltinModule(packageSpecifier)) {
+    return `node:${packageSpecifier}`;
+  }
+
+  let packageName;
+  if (!packageSpecifier.startsWith('@')) {
+    packageName = packageSpecifier.split('/')[0];
+  } else {
+    if (!packageSpecifier.includes('/')) {
+      throw new Error('Invalid Module Specifier');
+    }
+    packageName = packageSpecifier.split('/').slice(0, 2).join('/');
+  }
+
+  if (packageName.startsWith('.') || packageName.includes('\\') || packageName.includes('%')) {
+    throw new Error('Invalid Module Specifier');
+  }
+
+  const packageSubpath = '.' + packageSpecifier.slice(packageName.length);
+
+  if (packageSubpath.endsWith('/')) {
+    throw new Error('Invalid Module Specifier');
+  }
+
+  const selfUrl = PackageSelfResolve(packageName, packageSubpath, parentURL);
+
+  if (selfUrl != null) {
+    return selfUrl;
+  }
+
+  while (parentURL !== path.parse(parentURL).root) {
+    const packageURL = url.resolve(parentURL, `node_modules/${packageSpecifier}`);
+    parentURL = path.dirname(parentURL);
+
+    if (!fs.existsSync(packageURL)) {
+      continue;
+    }
+
+    const pjson = readPackageJSON(packageURL);
+
+    if (pjson != null && pjson.exports != null) {
+      return PackageExportsResolve(packageURL, packageSubpath, pjson.exports, ['default']);
+    } else if (packageSubpath === '.') {
+      if (typeof pjson.main === 'string') {
+        return url.resolve(packageURL, pjson.main);
+      } else {
+        return url.resolve(packageURL, packageSubpath);
+      }
+    }
+  }
+
+  throw new Error('Module Not Found');
+}
+
+function isBuiltinModule(moduleName) {
+  // Check if moduleName is a Node.js builtin module
+  return require('module').builtinModules.includes(moduleName);
+}
+
+function PackageSelfResolve(packageName, packageSubpath, parentURL) {
+  const packageURL = lookupParentScope(parentURL);
+  if (packageURL == null) {
+    return undefined;
+  }
+  const pjson = readPackageJSON(packageURL);
+  if (pjson == null || pjson.exports == null || pjson.exports == null) {
+    return undefined;
+  }
+  if (pjson.name === packageName) {
+    return PackageExportsResolve(packageURL, packageSubpath, pjson.exports, defaultConditions);
+  }
+  return undefined;
+}
+
+function PackageExportsResolve(packageURL, subpath, exports, conditions) {
+  if (typeof exports === 'object' && Object.keys(exports).some(key => key.startsWith('.')) && Object.keys(exports).some(key => !key.startsWith('.'))) {
+    throw new Error('Invalid Package Configuration');
+  }
+
+  if (subpath === '.') {
+    let mainExport = undefined;
+
+    if (typeof exports === 'string' || Array.isArray(exports) || (typeof exports === 'object' && !Object.keys(exports).some(key => key.startsWith('.')))) {
+      mainExport = exports;
+    } else if (typeof exports === 'object' && exports.hasOwnProperty('.')) {
+      mainExport = exports['.'];
+    }
+
+    if (mainExport != null) {
+      const resolved = packageTargetResolve(packageURL, mainExport, null, false, conditions);
+      if (resolved != null && resolved != null) {
+        return resolved;
+      }
+    }
+  } else if (typeof exports === 'object' && Object.keys(exports).every(key => key.startsWith('.'))) {
+    const matchKey = './' + subpath;
+    const resolved = packageImportsExportsResolver(matchKey, exports, packageURL, false, conditions);
+    if (resolved != null && resolved != null) {
+      return resolved;
+    }
+  }
+
+  throw new Error('Package Path Not Exported');
+}

From 4481ccc1fa539064d0f6ffa950b95e2ef2af4603 Mon Sep 17 00:00:00 2001
From: Siddarth Kumar <siddarthkay@gmail.com>
Date: Mon, 5 Jun 2023 07:25:27 +0530
Subject: [PATCH 2/2] add optional `imports` type to PackageJson

---
 packages/metro-resolver/src/types.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/packages/metro-resolver/src/types.js b/packages/metro-resolver/src/types.js
index 69b1c8c3bb..1ea6de2d3c 100644
--- a/packages/metro-resolver/src/types.js
+++ b/packages/metro-resolver/src/types.js
@@ -76,6 +76,7 @@ export type PackageJson = $ReadOnly<{
   name?: string,
   main?: string,
   exports?: ExportsField,
+  imports?: ExportMap,
   ...
 }>;