feat: add support for .corepack.env (#642)

Author: aduh95

README.md

@@ -297,6 +297,7 @@ same major line. Should you need to upgrade to a new major, use an explicit
   set to `1` to have the URL shown. By default, when Corepack is called
   explicitly (e.g. `corepack pnpm …`), it is set to `0`; when Corepack is called
   implicitly (e.g. `pnpm …`), it is set to `1`.
+  The default value cannot be overridden in a `.corepack.env` file.
   When standard input is a TTY and no CI environment is detected, Corepack will
   ask for user input before starting the download.
 
@@ -322,6 +323,14 @@ same major line. Should you need to upgrade to a new major, use an explicit
   project. This means that it will always use the system-wide package manager
   regardless of what is being specified in the project's `packageManager` field.
 
+- `COREPACK_ENV_FILE` can be set to `0` to request Corepack to not attempt to
+  load `.corepack.env`; it can be set to a path to specify a different env file.
+  Only keys that start with `COREPACK_` and are not in the exception list
+  (`COREPACK_ENABLE_DOWNLOAD_PROMPT` and `COREPACK_ENV_FILE` are ignored)
+  will be taken into account.
+  For Node.js 18.x users, this setting has no effect as that version doesn't
+  support parsing of `.env` files.
+
 - `COREPACK_HOME` can be set in order to define where Corepack should install
   the package managers. By default it is set to `%LOCALAPPDATA%\node\corepack`
   on Windows, and to `$HOME/.cache/node/corepack` everywhere else.

sources/specUtils.ts

@@ -4,12 +4,14 @@ import path                                    from 'path';
 import semverSatisfies                         from 'semver/functions/satisfies';
 import semverValid                             from 'semver/functions/valid';
 import semverValidRange                        from 'semver/ranges/valid';
+import {parseEnv}                              from 'util';
 
 import {PreparedPackageManagerInfo}            from './Engine';
 import * as debugUtils                         from './debugUtils';
 import {NodeError}                             from './nodeUtils';
 import * as nodeUtils                          from './nodeUtils';
 import {Descriptor, isSupportedPackageManager} from './types';
+import type {LocalEnvFile}                     from './types';
 
 const nodeModulesRegExp = /[\\/]node_modules[\\/](@[^\\/]*[\\/])?([^@\\/][^\\/]*)$/;
 
@@ -145,10 +147,17 @@ export async function setLocalPackageManager(cwd: string, info: PreparedPackageM
   };
 }
 
+interface FoundSpecResult {
+  type: `Found`;
+  target: string;
+  getSpec: () => Descriptor;
+  range?: Descriptor & {onFail?: DevEngineDependency['onFail']};
+  envFilePath?: string;
+}
 export type LoadSpecResult =
     | {type: `NoProject`, target: string}
     | {type: `NoSpec`, target: string}
-    | {type: `Found`, target: string, getSpec: () => Descriptor, range?: Descriptor & {onFail?: DevEngineDependency['onFail']}};
+    | FoundSpecResult;
 
 export async function loadSpec(initialCwd: string): Promise<LoadSpecResult> {
   let nextCwd = initialCwd;
@@ -157,6 +166,8 @@ export async function loadSpec(initialCwd: string): Promise<LoadSpecResult> {
   let selection: {
     data: any;
     manifestPath: string;
+    envFilePath?: string;
+    localEnv: LocalEnvFile;
   } | null = null;
 
   while (nextCwd !== currCwd && (!selection || !selection.data.packageManager)) {
@@ -184,12 +195,44 @@ export async function loadSpec(initialCwd: string): Promise<LoadSpecResult> {
     if (typeof data !== `object` || data === null)
       throw new UsageError(`Invalid package.json in ${path.relative(initialCwd, manifestPath)}`);
 
-    selection = {data, manifestPath};
+    let localEnv: LocalEnvFile;
+    const envFilePath = path.resolve(currCwd, process.env.COREPACK_ENV_FILE ?? `.corepack.env`);
+    if (process.env.COREPACK_ENV_FILE == `0`) {
+      debugUtils.log(`Skipping env file as configured with COREPACK_ENV_FILE`);
+      localEnv = process.env;
+    } else if (typeof parseEnv !== `function`) {
+      // TODO: remove this block when support for Node.js 18.x is dropped.
+      debugUtils.log(`Skipping env file as it is not supported by the current version of Node.js`);
+      localEnv = process.env;
+    } else {
+      debugUtils.log(`Checking ${envFilePath}`);
+      try {
+        localEnv = {
+          ...Object.fromEntries(Object.entries(parseEnv(await fs.promises.readFile(envFilePath, `utf8`))).filter(e => e[0].startsWith(`COREPACK_`))),
+          ...process.env,
+        };
+        debugUtils.log(`Successfully loaded env file found at ${envFilePath}`);
+      } catch (err) {
+        if ((err as NodeError)?.code !== `ENOENT`)
+          throw err;
+
+        debugUtils.log(`No env file found at ${envFilePath}`);
+        localEnv = process.env;
+      }
+    }
+
+    selection = {data, manifestPath, localEnv, envFilePath};
   }
 
   if (selection === null)
     return {type: `NoProject`, target: path.join(initialCwd, `package.json`)};
 
+  let envFilePath: string | undefined;
+  if (selection.localEnv !== process.env) {
+    envFilePath = selection.envFilePath;
+    process.env = selection.localEnv;
+  }
+
   const rawPmSpec = parsePackageJSON(selection.data);
   if (typeof rawPmSpec === `undefined`)
     return {type: `NoSpec`, target: selection.manifestPath};
@@ -199,6 +242,7 @@ export async function loadSpec(initialCwd: string): Promise<LoadSpecResult> {
   return {
     type: `Found`,
     target: selection.manifestPath,
+    envFilePath,
     range: selection.data.devEngines?.packageManager?.version && {
       name: selection.data.devEngines.packageManager.name,
       range: selection.data.devEngines.packageManager.version,

sources/types.ts

@@ -160,3 +160,5 @@ export interface LazyLocator {
      */
   reference: () => Promise<string>;
 }
+
+export type LocalEnvFile = Record<string, string | undefined>;