feat(config): 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

@@ -469,6 +469,7 @@ 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
@@ -652,6 +653,12 @@ 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
@@ -1018,6 +1025,38 @@ All notable changes to this project will be documented in this file.
 
 </details>
 
+#### [Limited Commits](./examples/limitedcommits.toml)
+
+<details>
+  <summary>Raw Output</summary>
+
+```
+## [unreleased]
+### Feat
+- Support multiple file formats
+- Use cache while fetching pages
+
+## [1.0.1] - 2021-07-18
+### Chore
+- Add release script
+```
+
+</details>
+
+<details>
+  <summary>Rendered Output</summary>
+
+## [unreleased]
+### Feat
+- Support multiple file formats
+- Use cache while fetching pages
+
+## [1.0.1] - 2021-07-18
+### Chore
+- Add release script
+
+</details>
+
 #### [Detailed](./examples/detailed.toml)
 
 <details>

config/cliff.toml

@@ -66,3 +66,5 @@ ignore_tags = ""
 date_order = false
 # sort the commits inside sections by oldest/newest order
 sort_commits = "oldest"
+# limit the number of commits included in the changelog.
+# limit_commits = 42

examples/limitedcommits.toml

@@ -0,0 +1,21 @@
+# 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

@@ -69,6 +69,8 @@ pub struct GitConfig {
 	pub date_order:               Option<bool>,
 	/// Sorting of the commits inside sections.
 	pub sort_commits:             Option<String>,
+	/// Limit the number of commits included in the changelog.
+	pub limit_commits:            Option<usize>,
 }
 
 /// Parser for grouping commits.

git-cliff-core/tests/integration_test.rs

@@ -91,6 +91,7 @@ fn generate_changelog() -> Result<()> {
 				text:    Some(String::from("$1")),
 			},
 		]),
+		limit_commits:            None,
 	};
 
 	let releases = vec![

git-cliff/src/changelog.rs

@@ -265,6 +265,7 @@ 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 +217,13 @@ pub fn run(mut args: Opt) -> Result<()> {
 			}
 		}
 	}
-	let commits =
+	let mut commits =
 		repository.commits(commit_range, args.include_path, args.exclude_path)?;
+	if let Some(commit_limit_value) = config.git.limit_commits {
+		commits = commits
+			.drain(..commit_limit_value)
+			.collect();
+	}
 
 	// Update tags.
 	if let Some(tag) = args.tag {