Guess os_distros if none is specified to bot

.github/actions/bot/index.js

@@ -167,6 +167,41 @@ class CICommand {
         this.goal_args[goal] = args;
     }
 
+    // a map of file path prefixes to OS distros that are associated with the file paths
+    // a value of "*" implies multiple OS distros are associated with the path, and we should just rely on the workflow's default
+    // a value of null means no OS distros are associated with the path
+    osDistroPathPrefixHints = {
+        "templates/al2/": "al2",
+        "templates/al2023/": "al2023",
+        "templates/shared/": "*",
+        "nodeadm/": "al2023",
+        "doc/": null,
+    };
+
+    async guessOsDistrosForChangedFiles(github) {
+        const files = await github.rest.pulls.listFiles({
+            owner: this.repository_owner,
+            repo: this.repository_name,
+            pull_number: this.pr_number
+        });
+        let osDistros = [];
+        for (const file of files) {
+            for (const prefix of osDistroPathPrefixHints) {
+                if (file.filename.startsWith(prefix)) {
+                    osDistros = osDistros.concat(this.osDistroPathPrefixHints[prefix]);
+                } else {
+                    console.log("file does not match an OS distro hint, not attempting to guess os_distros!");
+                    return null;
+                }
+            }
+        }
+        if (osDistros.length != 1) {
+            console.log("changed files matched more than one OS distro prefix, not attempting to guess os_distros!");
+            return null;
+        }
+        return osDistros[0];
+    }
+
     async run(author, github) {
         const pr = await github.rest.pulls.get({
             owner: this.repository_owner,
@@ -198,6 +233,12 @@ class CICommand {
                 inputs[`${goal}_arguments`] = args;
             }
         }
+        if (!inputs.hasOwnProperty('os_distros')) {
+            osDistros = await this.guessOsDistrosForChangedFiles(github);
+            if (osDistros != null) {
+                inputs['os_distros'] = osDistros;
+            }
+        }
         console.log(`Dispatching workflow with inputs: ${JSON.stringify(inputs)}`);
         await github.rest.actions.createWorkflowDispatch({
             owner: this.repository_owner,