[rush-lib] Fix .npmrc syncing cache bug that strips pnpm hoisting properties (#5642)

Author: iclanton

common/changes/@microsoft/rush-lib/fix-npmrc-syncing_2026-02-19-02-14.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@microsoft/rush",
+      "comment": "Fix .npmrc syncing to common/temp incorrectly caching results, which caused pnpm-specific properties like hoist-pattern to be stripped when the same .npmrc was processed with different options.",
+      "type": "none"
+    }
+  ],
+  "packageName": "@microsoft/rush"
+}

libraries/rush-lib/src/utilities/npmrcUtilities.ts

@@ -19,9 +19,6 @@ export interface ILogger {
  * The text of the the .npmrc.
  */
 
-// create a global _combinedNpmrc for cache purpose
-const _combinedNpmrcMap: Map<string, string> = new Map();
-
 function _trimNpmrcFile(
   options: Pick<
     INpmrcTrimOptions,
@@ -41,10 +38,6 @@ function _trimNpmrcFile(
     filterNpmIncompatibleProperties,
     env = process.env
   } = options;
-  const combinedNpmrcFromCache: string | undefined = _combinedNpmrcMap.get(sourceNpmrcPath);
-  if (combinedNpmrcFromCache !== undefined) {
-    return combinedNpmrcFromCache;
-  }
 
   let npmrcFileLines: string[] = [];
   if (linesToPrepend) {
@@ -70,9 +63,6 @@ function _trimNpmrcFile(
 
   const combinedNpmrc: string = resultLines.join('\n');
 
-  //save the cache
-  _combinedNpmrcMap.set(sourceNpmrcPath, combinedNpmrc);
-
   return combinedNpmrc;
 }