feat(changelog): add --topo-order flag for sorting tags (#29)

README.md

@@ -136,6 +136,7 @@ git-cliff [FLAGS] [OPTIONS] [RANGE]
 -i, --init          Writes the default configuration file to cliff.toml
 -l, --latest        Processes the commits starting from the latest tag
 -u, --unreleased    Processes the commits that do not belong to a tag
+    --topo-order    Sorts the tags topologically
 -h, --help          Prints help information
 -V, --version       Prints version information
 ```
@@ -218,6 +219,13 @@ git cliff --sort oldest
 git cliff --sort newest
 ```
 
+Sort the tags in topological order:
+
+```sh
+# Process in topological order instead of chronological.
+git cliff --topo-order
+```
+
 Save the changelog file to the specified file:
 
 ```sh

git-cliff-core/src/repo.rs

@@ -82,6 +82,7 @@ impl Repository {
 	pub fn tags(
 		&self,
 		pattern: &Option<String>,
+		topo_order: bool,
 	) -> Result<IndexMap<String, String>> {
 		let mut tags: Vec<(Commit, String)> = Vec::new();
 		let tag_names = self.inner.tag_names(pattern.as_deref())?;
@@ -100,7 +101,9 @@ impl Repository {
 				}
 			}
 		}
-		tags.sort_by(|a, b| a.0.time().seconds().cmp(&b.0.time().seconds()));
+		if !topo_order {
+			tags.sort_by(|a, b| a.0.time().seconds().cmp(&b.0.time().seconds()));
+		}
 		Ok(tags
 			.into_iter()
 			.map(|(a, b)| (a.id().to_string(), b))
@@ -164,7 +167,7 @@ mod test {
 				}
 			}
 		}
-		let tags = repository.tags(&None)?;
+		let tags = repository.tags(&None, false)?;
 		assert_eq!(&get_last_tag()?, tags.last().unwrap().1);
 		Ok(())
 	}

git-cliff/src/args.rs

@@ -66,6 +66,9 @@ pub struct Opt {
 	/// Processes the commits that do not belong to a tag.
 	#[structopt(short, long)]
 	pub unreleased:  bool,
+	/// Sorts the tags topologically.
+	#[structopt(long)]
+	pub topo_order:  bool,
 	/// Strips the given parts from the changelog.
 	#[structopt(
 		short,
@@ -77,12 +80,11 @@ pub struct Opt {
 	/// Sets the commit range to process.
 	#[structopt(value_name = "RANGE")]
 	pub range:       Option<String>,
-
 	/// Sets sorting of the commits inside sections.
 	#[structopt(
 		long,
 		possible_values = &["oldest", "newest"],
 		default_value = "oldest"
 	)]
-	pub sort: String,
+	pub sort:        String,
 }

git-cliff/src/lib.rs

@@ -102,7 +102,7 @@ pub fn run(mut args: Opt) -> Result<()> {
 		Repository::init(args.repository.unwrap_or(env::current_dir()?))?;
 
 	// Parse tags.
-	let mut tags = repository.tags(&config.git.tag_pattern)?;
+	let mut tags = repository.tags(&config.git.tag_pattern, args.topo_order)?;
 
 	// Parse commits.
 	let mut commit_range = args.range;