Allow logging functions to accept string[] directly

src/logging.ts

@@ -1,10 +1,16 @@
 import * as core from "@actions/core";
 
+/** Types that all of our logging functions accept. */
+export type Loggable = string | string[];
+
+/** Some logging functions also accept errors directly. */
+export type LoggableError = Loggable | Error;
+
 export interface Logger {
-  debug: (message: string) => void;
-  info: (message: string) => void;
-  warning: (message: string | Error) => void;
-  error: (message: string | Error) => void;
+  debug: (message: Loggable) => void;
+  info: (message: Loggable) => void;
+  warning: (message: LoggableError) => void;
+  error: (message: LoggableError) => void;
 
   isDebug: () => boolean;
 
@@ -12,12 +18,33 @@ export interface Logger {
   endGroup: () => void;
 }
 
+/** If `message` is an array of strings, the array is `join`-ed into one string separated by spaces. */
+export const joinMessageStrings = <T>(
+  message: string[] | string | T,
+): string | T => {
+  if (Array.isArray(message)) {
+    return message.join(" ");
+  } else {
+    return message;
+  }
+};
+
+/**
+ * Wraps a logging function so that `joinMessageStrings` is applied to the input before
+ * calling the wrapped logging function.
+ */
+const autoJoinMessageStrings = <T>(fn: (msg: string | T) => void) => {
+  return (message: string[] | string | T) => {
+    return fn(joinMessageStrings(message));
+  };
+};
+
 export function getActionsLogger(): Logger {
   return {
-    debug: core.debug,
-    info: core.info,
-    warning: core.warning,
-    error: core.error,
+    debug: autoJoinMessageStrings(core.debug),
+    info: autoJoinMessageStrings(core.info),
+    warning: autoJoinMessageStrings(core.warning),
+    error: autoJoinMessageStrings(core.error),
     isDebug: core.isDebug,
     startGroup: core.startGroup,
     endGroup: core.endGroup,