feat: Add lifecycle hooks for publish (#656)

This PR adds lifecycle hooks (pre and post) to the publish command.
It runs pre once before publishing runs and post once afterwards (even though several packages might be published).

It also runs in --dry-run mode, to better emulate a real publish.
The environment variable MELOS_PUBLISH_DRY_RUN is introduced so that the user can know whether it is in dry-run mode or not in the scripts.

docs/commands/publish.mdx

@@ -49,3 +49,30 @@ Note that tags are automatically created as part of `melos version` (unless
 `--no-git-tag-version` is specified when running the version command) so this is
 usually not required on `melos publish` unless you're doing a manual version and
 publish of packages.
+
+## Hooks
+
+Melos supports various command [lifecycle hooks](/configuration/scripts#hooks)
+that can be defined in your `melos.yaml`.
+
+For example, if you need to run something such as a build runner automatically
+before `melos publish` is run and then remove the generated files after
+publishing is done, you can add `pre` and `post` hook scripts to your
+`melos.yaml` file:
+
+```yaml
+# melos.yaml
+# ...
+command:
+  publish:
+    hooks:
+      pre: dart pub run build_runner build
+      post: dart pub run build_runner clean
+# ...
+```
+
+The pre-hook will run before `melos publish` and the post-hook will run after
+`melos publish` is done. It only runs once, even if multiple packages are
+published and it also runs when you are doing a `dry-run` publish.
+You can detect whether it is a dry-run by checking the `MELOS_PUBLISH_DRY_RUN`
+environment variable.

docs/configuration/scripts.mdx

@@ -156,3 +156,4 @@ Currently, the following Melos commands support hooks:
 - [`bootstrap`](/commands/bootstrap)
 - [`clean`](/commands/clean)
 - [`version`](/commands/version)
+- [`publish`](/commands/publish)

docs/environment-variables.mdx

@@ -48,6 +48,11 @@ executing a script (when using `melos exec`).
 The path of the parent package of the current package that's currently executing
 a script (when using `melos exec`).
 
+### `MELOS_PUBLISH_DRY_RUN`
+
+Whether the current publish is a dry run or not. This is `true` when running
+`melos publish --dry-run` and `false` otherwise.
+
 #### What is a 'parent package'
 
 If a package exists in a directory that is also a child of another package, then

packages/melos/lib/src/command_configs/command_configs.dart

@@ -4,6 +4,7 @@ import '../common/utils.dart';
 import '../common/validation.dart';
 import 'bootstrap.dart';
 import 'clean.dart';
+import 'publish.dart';
 import 'version.dart';
 
 export 'bootstrap.dart';
@@ -17,6 +18,7 @@ class CommandConfigs {
     this.bootstrap = BootstrapCommandConfigs.empty,
     this.clean = CleanCommandConfigs.empty,
     this.version = VersionCommandConfigs.empty,
+    this.publish = PublishCommandConfigs.empty,
   });
 
   factory CommandConfigs.fromYaml(
@@ -42,6 +44,12 @@ class CommandConfigs {
       path: 'command',
     );
 
+    final publishMap = assertKeyIsA<Map<Object?, Object?>?>(
+      key: 'publish',
+      map: yaml,
+      path: 'command',
+    );
+
     return CommandConfigs(
       bootstrap: BootstrapCommandConfigs.fromYaml(
         bootstrapMap ?? const {},
@@ -56,6 +64,11 @@ class CommandConfigs {
         workspacePath: workspacePath,
         repositoryIsConfigured: repositoryIsConfigured,
       ),
+      publish: PublishCommandConfigs.fromYaml(
+        publishMap ?? const {},
+        workspacePath: workspacePath,
+        repositoryIsConfigured: repositoryIsConfigured,
+      ),
     );
   }
 
@@ -64,12 +77,14 @@ class CommandConfigs {
   final BootstrapCommandConfigs bootstrap;
   final CleanCommandConfigs clean;
   final VersionCommandConfigs version;
+  final PublishCommandConfigs publish;
 
   Map<String, Object?> toJson() {
     return {
       'bootstrap': bootstrap.toJson(),
       'clean': clean.toJson(),
       'version': version.toJson(),
+      'publish': publish.toJson(),
     };
   }
 
@@ -79,14 +94,17 @@ class CommandConfigs {
       runtimeType == other.runtimeType &&
       other.bootstrap == bootstrap &&
       other.clean == clean &&
-      other.version == version;
+      other.version == version &&
+      other.publish == publish;
 
   @override
-  int get hashCode =>
-      runtimeType.hashCode ^
-      bootstrap.hashCode ^
-      clean.hashCode ^
-      version.hashCode;
+  int get hashCode => Object.hash(
+        runtimeType,
+        bootstrap,
+        clean,
+        version,
+        publish,
+      );
 
   @override
   String toString() {
@@ -95,6 +113,7 @@ CommandConfigs(
   bootstrap: ${bootstrap.toString().indent('  ')},
   clean: ${clean.toString().indent('  ')},
   version: ${version.toString().indent('  ')},
+  publish: ${publish.toString().indent('  ')},
 )
 ''';
   }