Check for flake-dirs clash with inputs

README.md

@@ -138,7 +138,7 @@ jobs:
           path-to-flake-dir: 'nix/' # in this example our flake doesn't sit at the root of the repository, it sits under 'nix/flake.nix'
 ```
 
-You can also run the update operation in multiple directories, provide that each directory is a valid flake:
+You can also run the update operation in multiple directories, provided that each directory is a valid flake:
 
 ```yaml
 - name: Update flake.lock
@@ -150,6 +150,11 @@ You can also run the update operation in multiple directories, provide that each
       flake3
 ```
 
+> **Warning**: If you choose multiple directories, `update-flake-lock` can only update all flake inputs,
+> meaning that you can't set the `inputs` parameter. This is due to limitations in input handling in
+> GitHub Actions, which only allows for strings, numbers, Booleans, and arrays but not objects, which
+> would be the much preferred data type for expressing per-directory inputs.
+
 ## Example using a different Git user
 
 If you want to change the author and / or committer of the flake.lock update commit, you can tweak the `git-{author,committer}-{name,email}` options:

dist/index.js

@@ -94848,7 +94848,7 @@ var UpdateFlakeLockAction = class extends DetSysAction {
   validateInputs() {
     if (this.flakeDirs !== null && this.flakeDirs.length > 0 && this.pathToFlakeDir !== null && this.pathToFlakeDir !== "") {
       throw new Error(
-        "Both `path-to-flake-dir` and `flake-dirs` are set, whereas only one can be set"
+        "Both `path-to-flake-dir` and `flake-dirs` are set, whereas only one can be"
       );
     }
     if (this.flakeDirs !== null && this.flakeDirs.length === 0) {
@@ -94856,6 +94856,11 @@ var UpdateFlakeLockAction = class extends DetSysAction {
         "The `flake-dirs` input is set to an empty array; it must contain at least one directory"
       );
     }
+    if (this.flakeDirs !== null && this.flakeDirs.length > 0 && this.flakeInputs.length > 0) {
+      throw new Error(
+        `You've set both \`flake-dirs\` and \`inputs\` but you can only set one`
+      );
+    }
   }
   ensureDirectoryExists(flakeDir) {
     core.debug(`Checking that flake directory \`${flakeDir}\` exists`);

src/index.ts

@@ -107,25 +107,35 @@ class UpdateFlakeLockAction extends DetSysAction {
   }
 
   private validateInputs(): void {
-    // Ensure that either path-to-flake-dir or flake-dirs is set to a meaningful value but not both
+    // 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 !== null &&
       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",
+        "Both `path-to-flake-dir` and `flake-dirs` are set, whereas only one can be",
       );
     }
 
-    // Ensure that flake-dirs isn't an empty array if 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",
       );
     }
+
+    // Ensure that both `flake-dirs` and `inputs` aren't set at the same time
+    if (
+      this.flakeDirs !== null &&
+      this.flakeDirs.length > 0 &&
+      this.flakeInputs.length > 0
+    ) {
+      throw new Error(
+        `You've set both \`flake-dirs\` and \`inputs\` but you can only set one`,
+      );
+    }
   }
 
   private ensureDirectoryExists(flakeDir: string): void {