feat: changelog for the last n commits

Adds a additional configuration variable `limit_commits` to the
configuration struct.
`limit_commits` can be set to a positive integer number to limit the
commits contained in the generated changelog.

Also adjusts the default config file to contain `limit_commits` as a
commented out line.

Extends documentation in README.md to also cover the introduced
configuration value.

issue: #102

README.md

@@ -468,6 +468,7 @@ link_parsers = [
     { pattern = "#(\\d+)", href = "https://github.com/orhun/git-cliff/issues/$1"},
     { pattern = "RFC(\\d+)", text = "ietf-rfc$1", href = "https://datatracker.ietf.org/doc/html/rfc$1"},
 ]
+limit_commits = 42
 ```
 
 #### conventional_commits
@@ -645,6 +646,12 @@ Examples:
 - `{ pattern = "RFC(\\d+)", text = "ietf-rfc$1", href = "https://datatracker.ietf.org/doc/html/rfc$1"}`,
   - Extract mentions of IETF RFCs and generate URLs linking to them. It also rewrites the text as "ietf-rfc...".
 
+#### limit_commits
+
+`limit_commits` is a **optional** positive integer number that limits the number of included commits in the generated changelog.
+
+`limit_commits` is not part of the default configuration.
+
 ## Project Integration
 
 ### Rust

config/cliff.toml

@@ -64,3 +64,5 @@ ignore_tags = ""
 date_order = false
 # sort the commits inside sections by oldest/newest order
 sort_commits = "oldest"
+# limit the number of commits inlcuded in the changelog.
+# limit_commits = 42

examples/limitedcommits.toml

@@ -0,0 +1,22 @@
+# configuration file for git-cliff (0.1.0)
+
+[changelog]
+# template for the changelog body
+# https://tera.netlify.app/docs/#introduction
+body = """
+{% if version %}\
+    ## [{{ version | trim_start_matches(pat="v") }}] - {{ timestamp | date(format="%Y-%m-%d") }}\
+{% else %}\
+    ## [unreleased]\
+{% endif %}\
+{% for group, commits in commits | group_by(attribute="group") %}
+    ### {{ group | upper_first }}
+    {% for commit in commits %}\
+        - {% if commit.breaking %}[**breaking**] {% endif %}{{ commit.message | upper_first }}
+    {% endfor %}\
+{% endfor %}\n
+"""
+
+[git]
+limit_commits = 3
+

git-cliff-core/src/config.rs

@@ -66,6 +66,8 @@ pub struct GitConfig {
 	pub date_order:           Option<bool>,
 	/// Sorting of the commits inside sections.
 	pub sort_commits:         Option<String>,
+	/// Limit the number of commits inlcuded in the changelog.
+	pub limit_commits:        Option<usize>,
 }
 
 /// Parser for grouping commits.

git-cliff-core/tests/integration_test.rs

@@ -90,6 +90,7 @@ fn generate_changelog() -> Result<()> {
 				text:    Some(String::from("$1")),
 			},
 		]),
+		limit_commits:         None,
 	};
 
 	let releases = vec![

git-cliff/src/changelog.rs

@@ -264,6 +264,7 @@ mod test {
 				date_order:            Some(false),
 				sort_commits:          Some(String::from("oldest")),
 				link_parsers:          None,
+				limit_commits:         None,
 			},
 		};
 		let test_release = Release {

git-cliff/src/lib.rs

@@ -217,8 +217,15 @@ pub fn run(mut args: Opt) -> Result<()> {
 			}
 		}
 	}
-	let commits =
-		repository.commits(commit_range, args.include_path, args.exclude_path)?;
+	let commits = if let Some(commit_limit_value) = config.git.limit_commits {
+		repository
+			.commits(commit_range, args.include_path, args.exclude_path)?
+			.into_iter()
+			.take(commit_limit_value)
+			.collect()
+	} else {
+		repository.commits(commit_range, args.include_path, args.exclude_path)?
+	};
 
 	// Update tags.
 	if let Some(tag) = args.tag {