fix(changelog): include the root commit when --latest is used with one tag

.github/fixtures/test-latest-with-one-tag/commit.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -e
 
-GIT_COMMITTER_DATE="2021-01-23 01:23:45" git commit --allow-empty -m "Initial commit"
+GIT_COMMITTER_DATE="2021-01-23 01:23:45" git commit --allow-empty -m "feat: initial commit"
 
 GIT_COMMITTER_DATE="2021-01-23 01:23:46" git commit --allow-empty -m "feat: add feature 1"
 git tag v0.1.0

.github/fixtures/test-latest-with-one-tag/expected.md

@@ -6,6 +6,7 @@ All notable changes to this project will be documented in this file.
 
 ### Feat
 
+- Initial commit
 - Add feature 1
 
 <!-- generated by git-cliff -->

git-cliff-core/src/repo.rs

@@ -78,7 +78,12 @@ impl Repository {
 		let mut revwalk = self.inner.revwalk()?;
 		revwalk.set_sorting(Sort::TOPOLOGICAL)?;
 		if let Some(range) = range {
-			revwalk.push_range(range)?;
+			if range.contains("..") {
+				revwalk.push_range(range)?;
+			} else {
+				// When a single SHA is provided as the "range", start from the root.
+				revwalk.push(Oid::from_str(range)?)?;
+			}
 		} else {
 			revwalk.push_head()?;
 		}
@@ -464,6 +469,18 @@ mod test {
 		.to_string())
 	}
 
+	fn get_root_commit_hash() -> Result<String> {
+		Ok(str::from_utf8(
+			Command::new("git")
+				.args(["rev-list", "--max-parents=0", "HEAD"])
+				.output()?
+				.stdout
+				.as_ref(),
+		)?
+		.trim_ascii_end()
+		.to_string())
+	}
+
 	fn get_last_tag() -> Result<String> {
 		Ok(str::from_utf8(
 			Command::new("git")
@@ -586,6 +603,18 @@ mod test {
 		Ok(())
 	}
 
+	#[test]
+	fn includes_root_commit() -> Result<()> {
+		let repository = get_repository()?;
+		// a close descendant of the root commit
+		let range = Some("eea3914c7ab07472841aa85c36d11bdb2589a234");
+		let commits = repository.commits(range, None, None)?;
+		let root_commit =
+			AppCommit::from(&commits.last().expect("no commits found").clone());
+		assert_eq!(get_root_commit_hash()?, root_commit.id);
+		Ok(())
+	}
+
 	fn create_temp_repo() -> (Repository, TempDir) {
 		let temp_dir =
 			TempDir::with_prefix("git-cliff-").expect("failed to create temp dir");

git-cliff/src/lib.rs

@@ -171,7 +171,11 @@ fn process_repository<'a>(
 				commits.last().map(|c| c.id().to_string()),
 				tags.get_index(0).map(|(k, _)| k),
 			) {
-				commit_range = Some(format!("{tag1}..{tag2}"));
+				if tags.len() == 1 {
+					commit_range = Some(tag2.to_owned());
+				} else {
+					commit_range = Some(format!("{tag1}..{tag2}"));
+				}
 			}
 		} else {
 			let mut tag_index = tags.len() - 2;