feat(args): add --current flag for processing the current tag (#37)

README.md

@@ -137,6 +137,7 @@ git-cliff [FLAGS] [OPTIONS] [RANGE]
 -v, --verbose       Increases the logging verbosity
 -i, --init          Writes the default configuration file to cliff.toml
 -l, --latest        Processes the commits starting from the latest tag
+    --current       Processes the commits that belong to the current tag
 -u, --unreleased    Processes the commits that do not belong to a tag
     --topo-order    Sorts the tags topologically
 -h, --help          Prints help information
@@ -195,6 +196,11 @@ Generate a changelog for a certain part of git history:
 # (requires at least 2 tags)
 git cliff --latest
 
+# only takes the current tag into account
+# useful if you checkout a specific tag (e.g. `git checkout v0.0.1`)
+# (requires a tag to be present for the current commit (i.e. HEAD))
+git cliff --current
+
 # generate changelog for unreleased commits
 git cliff --unreleased
 git cliff --unreleased --tag 1.0.0

git-cliff-core/src/repo.rs

@@ -4,6 +4,7 @@ use crate::error::{
 };
 use git2::{
 	Commit,
+	DescribeOptions,
 	Repository as GitRepository,
 	Sort,
 };
@@ -90,6 +91,16 @@ impl Repository {
 		Ok(commits)
 	}
 
+	/// Returns the current tag.
+	///
+	/// It is the same as running `git describe --tags`
+	pub fn current_tag(&self) -> Option<String> {
+		self.inner
+			.describe(DescribeOptions::new().describe_tags())
+			.ok()
+			.and_then(|describe| describe.format(None).ok())
+	}
+
 	/// Parses and returns a commit-tag map.
 	///
 	/// It collects lightweight and annotated tags.

git-cliff/src/args.rs

@@ -67,6 +67,9 @@ pub struct Opt {
 	/// Processes the commits starting from the latest tag.
 	#[structopt(short, long)]
 	pub latest:       bool,
+	/// Processes the commits that belong to the current tag.
+	#[structopt(long)]
+	pub current:      bool,
 	/// Processes the commits that do not belong to a tag.
 	#[structopt(short, long)]
 	pub unreleased:   bool,

git-cliff/src/lib.rs

@@ -116,14 +116,31 @@ pub fn run(mut args: Opt) -> Result<()> {
 		if let Some(last_tag) = tags.last().map(|(k, _)| k) {
 			commit_range = Some(format!("{}..HEAD", last_tag));
 		}
-	} else if args.latest {
+	} else if args.latest || args.current {
 		if tags.len() < 2 {
 			return Err(Error::ChangelogError(String::from(
-				"Latest tag cannot be processed",
+				"Not enough tags exist for processing the latest/current tag",
 			)));
-		} else if let (Some(tag1), Some(tag2)) = (
-			tags.get_index(tags.len() - 2).map(|(k, _)| k),
-			tags.get_index(tags.len() - 1).map(|(k, _)| k),
+		}
+		let mut tag_index = tags.len() - 2;
+		if args.current {
+			if let Some(current_tag_index) =
+				repository.current_tag().as_ref().and_then(|tag| {
+					tags.iter()
+						.enumerate()
+						.find(|(_, (_, v))| v == &tag)
+						.map(|(i, _)| i)
+				}) {
+				tag_index = current_tag_index - 1;
+			} else {
+				return Err(Error::ChangelogError(String::from(
+					"No tag exists for the current commit",
+				)));
+			}
+		}
+		if let (Some(tag1), Some(tag2)) = (
+			tags.get_index(tag_index).map(|(k, _)| k),
+			tags.get_index(tag_index + 1).map(|(k, _)| k),
 		) {
 			commit_range = Some(format!("{}..{}", tag1, tag2));
 		}