[rush] Fix build cache ids when "enableSubPathScan" is enabled (#5045)

Co-authored-by: David Michon <[email protected]>

Author: dmichon-msft

common/changes/@microsoft/rush/git-filter-fixes_2024-12-14-00-09.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@microsoft/rush",
+      "comment": "Fix an issue with the `enableSubpathScan` experiment where the set of returned hashes would result in incorrect build cache identifiers when using `--only`.",
+      "type": "none"
+    }
+  ],
+  "packageName": "@microsoft/rush"
+}

libraries/rush-lib/src/cli/scriptActions/PhasedScriptAction.ts

@@ -556,7 +556,12 @@ export class PhasedScriptAction extends BaseScriptAction<IPhasedCommandConfig> {
 
     const analyzer: ProjectChangeAnalyzer = new ProjectChangeAnalyzer(this.rushConfiguration);
     const getInputsSnapshotAsync: GetInputsSnapshotAsyncFn | undefined =
-      await analyzer._tryGetSnapshotProviderAsync(projectConfigurations, terminal, projectSelection);
+      await analyzer._tryGetSnapshotProviderAsync(
+        projectConfigurations,
+        terminal,
+        // We need to include all dependencies, otherwise build cache id calculation will be incorrect
+        Selection.expandAllDependencies(projectSelection)
+      );
     const initialSnapshot: IInputsSnapshot | undefined = await getInputsSnapshotAsync?.();
 
     repoStateStopwatch.stop();

libraries/rush-lib/src/logic/ProjectChangeAnalyzer.ts

@@ -296,9 +296,10 @@ export class ProjectChangeAnalyzer {
 
       if (
         projectSelection &&
+        projectSelection.size > 0 &&
         this._rushConfiguration.experimentsConfiguration.configuration.enableSubpathScan
       ) {
-        filterPath = Array.from(projectSelection).map(({ projectFolder }) => projectFolder);
+        filterPath = Array.from(projectSelection, ({ projectFolder }) => projectFolder);
       }
 
       return async function tryGetSnapshotAsync(): Promise<IInputsSnapshot | undefined> {