feat: add stripEnvFallback function

config/env-replace/env-replace.docs.mdx

@@ -16,3 +16,23 @@ import { envReplace } from '@pnpm/config.env-replace'
 
 envReplace('${foo}', process.env)
 ```
+
+## `stripEnvFallback`
+
+```ts
+function stripEnvFallback(settingValue: string): string;
+```
+
+Strips fallback values from environment variable placeholders, leaving only the variable name.
+
+Usage:
+
+```ts
+import { stripEnvFallback } from '@pnpm/config.env-replace'
+
+stripEnvFallback('${HOME-/default}/config')
+// Returns: '${HOME}/config'
+
+stripEnvFallback('${FOO:-fallback}')
+// Returns: '${FOO}'
+```

config/env-replace/env-replace.spec.ts

@@ -1,4 +1,4 @@
-import { envReplace } from './env-replace';
+import { envReplace, stripEnvFallback } from './env-replace';
 
 const ENV = {
   foo: 'foo_value',
@@ -25,3 +25,15 @@ test('fail when the env variable is not found', () => {
   expect(() => envReplace('${foo:-}', ENV)).toThrow(`Failed to replace env in config: \${foo:-}`);
 })
 
+test.each([
+  ['-${foo}-${bar}', '-${foo}-${bar}'],
+  ['-${foo-fallback-value}-${bar:-fallback-value}', '-${foo}-${bar}'],
+  ['-${qar-fallback-value}-${zoo:-fallback-for-empty-value}', '-${qar}-${zoo}'],
+  ['\\${foo}', '${foo}'],
+  ['\\\\${foo}', '\\${foo}'],
+  ['${foo}', '${foo}'],
+])('stripEnvFallback %s => %s', (settingValue, expected) => {
+  const actual = stripEnvFallback(settingValue);
+  expect(actual).toEqual(expected);
+})
+

config/env-replace/env-replace.ts

@@ -26,3 +26,22 @@ function getEnvValue (env: NodeJS.ProcessEnv, name: string): string | undefined
   }
   return fallback
 }
+
+export function stripEnvFallback (settingValue: string): string {
+  return settingValue.replace(ENV_EXPR, replaceEnvMatchForStrip)
+}
+
+function replaceEnvMatchForStrip (orig: string, escape: string, name: string): string {
+  if (escape.length % 2) {
+    return orig.slice((escape.length + 1) / 2)
+  }
+  const strippedName = getStrippedEnvName(name)
+  return `${escape.slice(escape.length / 2)}\${${strippedName}}`
+}
+
+function getStrippedEnvName (name: string): string {
+  const matched = name.match(ENV_VALUE)
+  if (!matched) return name
+  const [, variableName] = matched
+  return variableName
+}

config/env-replace/index.ts

@@ -1 +1 @@
-export { envReplace } from './env-replace';
+export { envReplace, stripEnvFallback } from './env-replace';