psy-repos-typescript
diff --git a/‎apps/rush-lib/src/cli/scriptActions/PhasedScriptAction.ts
Lines changed: 3 additions & 3 deletions b/‎apps/rush-lib/src/cli/scriptActions/PhasedScriptAction.ts
Lines changed: 3 additions & 3 deletions
diff --git a/‎apps/rush-lib/src/logic/operations/OperationExecutionManager.ts
Lines changed: 17 additions & 3 deletions b/‎apps/rush-lib/src/logic/operations/OperationExecutionManager.ts
Lines changed: 17 additions & 3 deletions
diff --git a/‎apps/rush-lib/src/logic/operations/test/OperationExecutionManager.test.ts
Lines changed: 16 additions & 0 deletions b/‎apps/rush-lib/src/logic/operations/test/OperationExecutionManager.test.ts
Lines changed: 16 additions & 0 deletions
diff --git a/‎apps/rush-lib/src/logic/operations/test/__snapshots__/OperationExecutionManager.test.ts.snap
Lines changed: 1 addition & 1 deletion b/‎apps/rush-lib/src/logic/operations/test/__snapshots__/OperationExecutionManager.test.ts.snap
Lines changed: 1 addition & 1 deletion
@@ -342,9 +342,9 @@ export class PhasedScriptAction extends BaseScriptAction<IPhasedCommandConfig> {
         environmentVariable: EnvironmentVariableNames.RUSH_PARALLELISM,
         description:
           'Specifies the maximum number of concurrent processes to launch during a build.' +
-          ' The COUNT should be a positive integer or else the word "max" to specify a count that is equal to' +
-          ' the number of CPU cores. If this parameter is omitted, then the default value depends on the' +
-          ' operating system and number of CPU cores.'
+          ' The COUNT should be a positive integer, a percentage value (eg. "50%") or the word "max"' +
+          ' to specify a count that is equal to the number of CPU cores. If this parameter is omitted,' +
+          ' then the default value depends on the operating system and number of CPU cores.'
       });
       this._timelineParameter = this.defineFlagParameter({
         parameterLongName: '--timeline',
 
@@ -157,10 +157,24 @@ export class OperationExecutionManager {
       if (parallelism === 'max') {
         this._parallelism = numberOfCores;
       } else {
-        const parallelismInt: number = parseInt(parallelism, 10);
+        const parsed: number = parseInt(parallelism, 10);
 
-        if (isNaN(parallelismInt)) {
-          throw new Error(`Invalid parallelism value of '${parallelism}', expected a number or 'max'`);
+        if (isNaN(parsed)) {
+          throw new Error(
+            `Invalid parallelism value of '${parallelism}', expected a number, a percentage, or 'max'`
+          );
+        }
+
+        let parallelismInt: number = parsed > 0 ? parsed : 1;
+
+        if (
+          typeof parallelism === 'string' &&
+          parallelism.trim().endsWith('%') &&
+          parsed > 0 &&
+          parsed <= 100
+        ) {
+          const workers: number = Math.floor((parsed / 100) * numberOfCores);
+          parallelismInt = Math.max(workers, 1);
         }
 
         this._parallelism = parallelismInt;
 
@@ -78,6 +78,22 @@ describe(OperationExecutionManager.name, () => {
     });
   });
 
+  describe('Constructor', () => {
+    it('createsWithPercentageBasedParallelism', () => {
+      expect(
+        () =>
+          new OperationExecutionManager(new Set(), {
+            quietMode: false,
+            debugMode: false,
+            parallelism: '50%',
+            changedProjectsOnly: false,
+            destination: mockWritable,
+            repoCommandLineConfiguration: undefined!
+          })
+      ).toBeInstanceOf(Function);
+    });
+  });
+
   describe('Error logging', () => {
     beforeEach(() => {
       executionManagerOptions = {
 
@@ -1,6 +1,6 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`OperationExecutionManager Constructor throwsErrorOnInvalidParallelism 1`] = `"Invalid para
4F85
llelism value of 'tequila', expected a number or 'max'"`;
+exports[`OperationExecutionManager Constructor throwsErrorOnInvalidParallelism 1`] = `"Invalid parallelism value of 'tequila', expected a number, a percentage, or 'max'"`;
 
 exports[`OperationExecutionManager Error logging printedStderrAfterError 1`] = `"An error occurred."`;