Support escaping template variables in environment values (#6935)

## What's the problem this PR addresses?

<!-- Describe the rationale of your PR. -->
<!-- Link all issues that it closes. (Closes/Resolves #xxxx.) -->

Resolves #6491

```sh
$ yarn init -2
$ echo 'CYPRESS_DOWNLOAD_PATH_TEMPLATE="\${endpoint}/\${platform}-\${arch}/cypress.zip"' > .env.yarn
$ yarn node -p 'process.env.CYPRESS_DOWNLOAD_PATH_TEMPLATE'

# AS-IS
Usage Error: Environment variable not found (endpoint)

# TO-BE
${endpoint}/${platform}-${arch}/cypress.zip
```

## How did you fix it?

<!-- A detailed description of your implementation. -->

Support escaping template variables in environment variable values. When
a template variable is escaped with a backslash (e.g., `\${VAR}`), it is
now preserved as a literal string `${VAR}` instead of being replaced
with an actual environment variable value.

I updated the regex to match values starting with a backslash. When a
match starts with a backslash, it is treated as an escaped template and
returns the value with only the backslash removed (`match.slice(1)`).

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---------

Co-authored-by: Maël Nison <nison.mael@gmail.com>

Author: parksb

.yarn/versions/3e62b777.yml

@@ -0,0 +1,36 @@
+releases:
+  "@yarnpkg/cli": minor
+  "@yarnpkg/core": patch
+
+declined:
+  - "@yarnpkg/plugin-catalog"
+  - "@yarnpkg/plugin-compat"
+  - "@yarnpkg/plugin-constraints"
+  - "@yarnpkg/plugin-dlx"
+  - "@yarnpkg/plugin-essentials"
+  - "@yarnpkg/plugin-exec"
+  - "@yarnpkg/plugin-file"
+  - "@yarnpkg/plugin-git"
+  - "@yarnpkg/plugin-github"
+  - "@yarnpkg/plugin-http"
+  - "@yarnpkg/plugin-init"
+  - "@yarnpkg/plugin-interactive-tools"
+  - "@yarnpkg/plugin-jsr"
+  - "@yarnpkg/plugin-link"
+  - "@yarnpkg/plugin-nm"
+  - "@yarnpkg/plugin-npm"
+  - "@yarnpkg/plugin-npm-cli"
+  - "@yarnpkg/plugin-pack"
+  - "@yarnpkg/plugin-patch"
+  - "@yarnpkg/plugin-pnp"
+  - "@yarnpkg/plugin-pnpm"
+  - "@yarnpkg/plugin-stage"
+  - "@yarnpkg/plugin-typescript"
+  - "@yarnpkg/plugin-version"
+  - "@yarnpkg/plugin-workspace-tools"
+  - "@yarnpkg/builder"
+  - "@yarnpkg/doctor"
+  - "@yarnpkg/extensions"
+  - "@yarnpkg/nm"
+  - "@yarnpkg/pnpify"
+  - "@yarnpkg/sdks"

packages/yarnpkg-core/sources/miscUtils.ts

@@ -471,11 +471,13 @@ export function buildIgnorePattern(ignorePatterns: Array<string>) {
 }
 
 export function replaceEnvVariables(value: string, {env}: {env: {[key: string]: string | undefined}}) {
-  const regex = /\${(?<variableName>[\d\w_]+)(?<colon>:)?(?:-(?<fallback>[^}]*))?}/g;
+  const regex = /\\?\${(?<variableName>[\d\w_]+)(?<colon>:)?(?:-(?<fallback>[^}]*))?}/g;
 
-  return value.replace(regex, (...args) => {
-    const {variableName, colon, fallback} = args[args.length - 1];
+  return value.replace(regex, (match, ...args) => {
+    if (match.startsWith(`\\`))
+      return match.slice(1);
 
+    const {variableName, colon, fallback} = args[args.length - 1];
     const variableExist = Object.hasOwn(env, variableName);
     const variableValue = env[variableName];
 

packages/yarnpkg-core/tests/miscUtils.test.ts

@@ -3,6 +3,45 @@ import CJSON          from 'comment-json';
 import * as miscUtils from '../sources/miscUtils';
 
 describe(`miscUtils`, () => {
+  describe(`replaceEnvVariables`, () => {
+    it(`should replace environment variables with their values`, () => {
+      expect(
+        miscUtils.replaceEnvVariables(
+          `VAR_A: \${VAR_A}, VAR_B: \${VAR_B}`,
+          {
+            env: {
+              VAR_A: `ValueA`,
+              VAR_B: `ValueB`,
+            },
+          },
+        ),
+      ).toBe(`VAR_A: ValueA, VAR_B: ValueB`);
+    });
+
+    it(`should use fallback values when environment variables are not set`, () => {
+      expect(
+        miscUtils.replaceEnvVariables(
+          `VAR_A: \${VAR_A:-ValueA}, VAR_B: \${VAR_B:-ValueB}`,
+          {env: {}},
+        ),
+      ).toBe(`VAR_A: ValueA, VAR_B: ValueB`);
+    });
+
+    it(`should not replace escaped environment variables`, () => {
+      expect(
+        miscUtils.replaceEnvVariables(
+          `VAR_A: \\\${VAR_A}, VAR_B: \\\${VAR_B}`,
+          {
+            env: {
+              VAR_A: `ValueA`,
+              VAR_B: `ValueB`,
+            },
+          },
+        ),
+      ).toBe(`VAR_A: \${VAR_A}, VAR_B: \${VAR_B}`);
+    });
+  });
+
   describe(`mapAndFind`, () => {
     it(`should work with a simple example`, () => {
       expect(
@@ -135,7 +174,9 @@ describe(`miscUtils`, () => {
       const b = {n: [4, 5, 6]};
       const c = miscUtils.mergeIntoTarget(a, b);
 
-      expect(CJSON.stringify(c, null, 2)).toStrictEqual(CJSON.stringify(CJSON.parse(`{
+      expect(CJSON.stringify(c, null, 2)).toStrictEqual(
+        CJSON.stringify(
+          CJSON.parse(`{
         // n
         "n":
         // array
@@ -150,7 +191,11 @@ describe(`miscUtils`, () => {
           5,
           6
         ]
-      }`), null, 2));
+      }`),
+          null,
+          2,
+        ),
+      );
     });
   });
 });