feat(args): add --context flag for outputting context (#71)

README.md

@@ -146,6 +146,7 @@ git-cliff [FLAGS] [OPTIONS] [--] [RANGE]
     --current       Processes the commits that belong to the current tag
 -u, --unreleased    Processes the commits that do not belong to a tag
     --date-order    Sorts the tags chronologically
+    --context       Prints changelog context as JSON
 -h, --help          Prints help information
 -V, --version       Prints version information
 ```
@@ -260,6 +261,16 @@ Save the changelog file to the specified file:
 git cliff --output CHANGELOG.md
 ```
 
+Print the changelog [context](#context) as JSON:
+
+```sh
+# print context to stdout
+git cliff --context
+
+# save context to a file
+git cliff --context --output context.json
+```
+
 Prepend new changes to an existing changelog file:
 
 ```sh

git-cliff-core/Cargo.toml

@@ -12,6 +12,7 @@ edition = "2021"
 [dependencies]
 thiserror = "1.0.30"
 serde = { version = "1.0.136", features = ["derive"] }
+serde_json = "1.0.78"
 tera = "1.15.0"
 regex = "1.5.5"
 serde_regex = "1.1.0"

git-cliff-core/src/error.rs

@@ -44,6 +44,9 @@ pub enum Error {
 	/// Errors that may occur when deserializing types from TOML format.
 	#[error("Cannot parse TOML: `{0}`")]
 	DeserializeError(#[from] toml::de::Error),
+	/// Errors that may occur while de/serializing JSON format.
+	#[error("Cannot de/serialize JSON: `{0}`")]
+	JsonError(#[from] serde_json::Error),
 }
 
 /// Result type of the core library.

git-cliff-core/src/release.rs

@@ -1,4 +1,5 @@
 use crate::commit::Commit;
+use crate::error::Result;
 
 /// Representation of a release.
 #[derive(Default, Debug, Clone, PartialEq, serde::Serialize, serde::Deserialize)]
@@ -16,3 +17,13 @@ pub struct Release<'a> {
 	/// Previous release.
 	pub previous:  Option<Box<Release<'a>>>,
 }
+
+/// Representation of a list of releases.
+pub struct Releases<'a>(pub &'a Vec<Release<'a>>);
+
+impl<'a> Releases<'a> {
+	/// Returns the list of releases as JSON.
+	pub fn as_json(&self) -> Result<String> {
+		Ok(serde_json::to_string(self.0)?)
+	}
+}

git-cliff/src/args.rs

@@ -94,6 +94,9 @@ pub struct Opt {
 	/// Sorts the tags chronologically.
 	#[clap(long, help_heading = Some("FLAGS"))]
 	pub date_order:   bool,
+	/// Prints changelog context as JSON.
+	#[clap(long, help_heading = Some("FLAGS"))]
+	pub context:      bool,
 	/// Strips the given parts from the changelog.
 	#[clap(short, long, value_name = "PART", arg_enum)]
 	pub strip:        Option<Strip>,

git-cliff/src/changelog.rs

@@ -4,7 +4,10 @@ use git_cliff_core::error::{
 	Error,
 	Result,
 };
-use git_cliff_core::release::Release;
+use git_cliff_core::release::{
+	Release,
+	Releases,
+};
 use git_cliff_core::template::Template;
 use std::io::Write;
 
@@ -153,6 +156,13 @@ impl<'a> Changelog<'a> {
 		write!(out, "{}", changelog)?;
 		Ok(())
 	}
+
+	/// Prints the changelog context to the given output.
+	pub fn write_context<W: Write>(&self, out: &mut W) -> Result<()> {
+		let output = Releases(&self.releases).as_json()?;
+		writeln!(out, "{output}")?;
+		Ok(())
+	}
 }
 
 #[cfg(test)]

git-cliff/src/lib.rs

@@ -277,7 +277,14 @@ pub fn run(mut args: Opt) -> Result<()> {
 	if let Some(path) = args.prepend {
 		changelog.prepend(fs::read_to_string(&path)?, &mut File::create(path)?)
 	} else if let Some(path) = args.output {
-		changelog.generate(&mut File::create(path)?)
+		let mut output = File::create(path)?;
+		if args.context {
+			changelog.write_context(&mut output)
+		} else {
+			changelog.generate(&mut output)
+		}
+	} else if args.context {
+		changelog.write_context(&mut io::stdout())
 	} else {
 		changelog.generate(&mut io::stdout())
 	}