Add Errors to warnings as well

packages/core/__tests__/core.test.ts

@@ -169,6 +169,12 @@ describe('@actions/core', () => {
     assertWriteCalls([`::warning::%0D%0Awarning%0A${os.EOL}`])
   })
 
+  it('warning handles an error object', () => {
+    const message = 'this is my error message'
+    core.warning(new Error(message))
+    assertWriteCalls([`::warning::Error: ${message}${os.EOL}`])
+  })
+
   it('startGroup starts a new group', () => {
     core.startGroup('my-group')
     assertWriteCalls([`::group::my-group${os.EOL}`])

packages/core/src/core.ts

@@ -33,7 +33,7 @@ export enum ExitCode {
 /**
  * Sets env variable for this action and future actions in the job
  * @param name the name of the variable to set
- * @param val the value of the variable. Will be converted to a string via JSON.stringify
+ * @param val the value of the variable. Non-string values will be converted to a string via JSON.stringify
  */
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 export function exportVariable(name: string, val: any): void {
@@ -80,7 +80,7 @@ export function getInput(name: string, options?: InputOptions): string {
  * Sets the value of an output.
  *
  * @param     name     name of the output to set
- * @param     value    value to store. Will be converted to a string via JSON.stringify
+ * @param     value    value to store. Non-string values will be converted to a string via JSON.stringify
  */
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 export function setOutput(name: string, value: any): void {
@@ -123,18 +123,18 @@ export function debug(message: string): void {
 
 /**
  * Adds an error issue
- * @param message error issue message
+ * @param message error issue message. Errors will be converted to string via toString()
  */
 export function error(message: string | Error): void {
   issue('error', message instanceof Error ? message.toString() : message)
 }
 
 /**
  * Adds an warning issue
- * @param message warning issue message
+ * @param message warning issue message. Errors will be converted to string via toString()
  */
-export function warning(message: string): void {
-  issue('warning', message)
+export function warning(message: string | Error): void {
+  issue('warning', message instanceof Error ? message.toString() : message)
 }
 
 /**