feat(changelog_cmd): add semver v2 proposal for generating changelog

Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

packages/changelog-cmd/lib/fetcher/github_fetcher.dart

@@ -55,11 +55,15 @@ class GithubFetcher extends GenericFetcher {
     )));
 
     var rawLastTags = QueryGetLastTag.fromJson(lastTag).repository;
-    var lastRelease = cleanListOfTags(rawLastTags).first;
-    if (lastRelease == null) {
+    var releases = cleanListOfTags(rawLastTags);
+    if (releases.isEmpty) {
       return commits;
     }
 
+    var lastRelease = releases.first;
+    if (lastRelease == null) {
+      return commits;
+    }
     var listCommits = await _client!.query(
         query: GQLOptionsQueryGetLastCommits(
             variables: VariablesQueryGetLastCommits(

packages/changelog-cmd/lib/method/semver_v2_msg.dart

@@ -0,0 +1,59 @@
+/// Header Msg is the method generator to generate the changelog
+/// from the message header like this example here
+/// https://github.com/invertase/melos/blob/main/packages/melos/CHANGELOG.md
+///
+/// Where a message header contains the content of the changelog
+/// an example `FIX: don't use Enum.name (#PR) commit_hash`
+///
+/// The filter keywords are:
+/// - `fix: message` to document a fix;
+/// - `feat: message ` to document a feature;
+/// - `docs: message ` to document a new doc addition.
+///
+/// author: https://github.com/vincenzopalazzo
+import 'package:changelog_cmd/method/method_generation.dart';
+import 'package:changelog_lib/changelog_lib.dart';
+
+class SemVerV2Generator extends MethodGenerator {
+  @override
+  void apply(
+      {required ChangelogGenerator generator,
+      String? exactMatchHeader,
+      RegExp? regexHeader,
+      bool strictly = false}) {
+    generator.addFilterRule(
+        rule: FilterRule(headerExactMatch: "fix:", nameSection: "Fixed"));
+    generator.addFilterRule(
+        rule:
+            FilterRule(headerExactMatch: "feat:", nameSection: "Added"));
+    generator.addFilterRule(
+        rule: FilterRule(headerExactMatch: "doc:", nameSection: "Docs"));
+
+    generator.addFilterRule(
+        rule: FilterRule(headerExactMatch: "deprecate:", nameSection: "Deprecated"));
+
+    generator.addFilterRule(
+        rule: FilterRule(headerExactMatch: "remove:", nameSection: "Removed"));
+
+    generator.addFilterRule(
+        rule: FilterRule(
+            headerExactMatch: "fix(${generator.packageName}):",
+            nameSection: "Fixed"));
+    generator.addFilterRule(
+        rule: FilterRule(
+            headerExactMatch: "feat(${generator.packageName}):",
+            nameSection: "Added"));
+    generator.addFilterRule(
+        rule: FilterRule(
+            headerExactMatch: "doc(${generator.packageName}):",
+            nameSection: "Docs"));
+    generator.addFilterRule(
+        rule: FilterRule(
+            headerExactMatch: "deprecate(${generator.packageName}):",
+            nameSection: "Deprecated"));
+    generator.addFilterRule(
+        rule: FilterRule(
+            headerExactMatch: "remove(${generator.packageName}):",
+            nameSection: "Removed"));
+  }
+}