Check that each directory is a valid flake

src/index.ts

@@ -2,6 +2,7 @@ import { makeNixCommandArgs } from "./nix.js";
 import * as actionsCore from "@actions/core";
 import * as actionsExec from "@actions/exec";
 import { DetSysAction, inputs } from "detsys-ts";
+import * as fs from "fs";
 
 const EVENT_EXECUTION_FAILURE = "execution_failure";
 
@@ -25,15 +26,7 @@ class UpdateFlakeLockAction extends DetSysAction {
     this.pathToFlakeDir = inputs.getStringOrNull("path-to-flake-dir");
     this.flakeDirs = inputs.getArrayOfStrings("flake-dirs", "space");
 
-    // Ensure that either path-to-flake-dir or flake-dirs is set to a meaningful value but not both
-    if (
-      this.flakeDirs !== null &&
-      this.flakeDirs.length > 0 &&
-      this.pathToFlakeDir !== ""
-    ) {
-      // TODO: improve this error message
-      throw new Error("Both path-to-flake-dir and flake-dirs is defined");
-    }
+    this.validateInputs();
   }
 
   async main(): Promise<void> {
@@ -46,7 +39,7 @@ class UpdateFlakeLockAction extends DetSysAction {
   async update(): Promise<void> {
     if (this.flakeDirs !== null && this.flakeDirs.length > 0) {
       actionsCore.debug(
-        `Running flake lock update in multiple directories: ${this.flakeDirs}`,
+        `Running flake lock update in multiple directories: ${this.flakeDirs.map((dir) => `\`${dir}\``).join(" ")}`,
       );
 
       for (const directory of this.flakeDirs) {
@@ -60,7 +53,10 @@ class UpdateFlakeLockAction extends DetSysAction {
   }
 
   private async updateFlake(flakeDir: string): Promise<void> {
-    actionsCore.debug(`Running flake lock update in directory ${flakeDir}`);
+    this.ensureDirectoryExists(flakeDir);
+    this.ensureDirectoryIsFlake(flakeDir);
+
+    actionsCore.debug(`Running flake lock update in directory \`${flakeDir}\``);
 
     // Nix command of this form:
     // nix ${maybe nix options} flake ${"update" or "lock"} ${maybe --update-input flags} --commit-lock-file --commit-lockfile-summary ${commit message}
@@ -94,14 +90,59 @@ class UpdateFlakeLockAction extends DetSysAction {
         exitCode,
       });
       actionsCore.setFailed(
-        `non-zero exit code of ${exitCode} detected while updating directory ${flakeDir}`,
+        `non-zero exit code of ${exitCode} detected while updating directory \`${flakeDir}\``,
       );
     } else {
       actionsCore.info(
-        `flake.lock file in ${flakeDir} was successfully updated`,
+        `flake.lock file in \`${flakeDir}\` was successfully updated`,
       );
     }
   }
+
+  private validateInputs(): void {
+    // Ensure that either path-to-flake-dir or flake-dirs is set to a meaningful value but not both
+    if (
+      this.flakeDirs !== null &&
+      this.flakeDirs.length > 0 &&
+      this.pathToFlakeDir !== ""
+    ) {
+      // TODO: improve this error message
+      throw new Error(
+        "Both `path-to-flake-dir` and `flake-dirs` are set, whereas only one can be set",
+      );
+    }
+
+    // Ensure that flake-dirs isn't an empty array if set
+    if (this.flakeDirs !== null && this.flakeDirs.length === 0) {
+      throw new Error(
+        "The `flake-dirs` input is set to an empty array; it must contain at least one directory",
+      );
+    }
+  }
+
+  private ensureDirectoryExists(flakeDir: string): void {
+    actionsCore.debug(`Checking that flake directory \`${flakeDir}\` exists`);
+
+    // Ensure the directory exists
+    fs.access(flakeDir, fs.constants.F_OK, (err) => {
+      if (err !== null) {
+        throw new Error(`Directory \`${flakeDir}\` doesn't exist`);
+      } else {
+        actionsCore.debug(`Flake directory \`${flakeDir}\` exists`);
+      }
+    });
+  }
+
+  private ensureDirectoryIsFlake(flakeDir: string): void {
+    const flakeDotNix = `${flakeDir}/flake.nix`;
+    if (!fs.existsSync(flakeDotNix)) {
+      throw new Error(
+        `Directory \`${flakeDir}\` is not a valid flake as it doesn't contain a \`flake.nix\``,
+      );
+    } else {
+      actionsCore.debug(`Directory \`${flakeDir}\` is a valid flake`);
+    }
+  }
 }
 
 function main(): void {