feat(args): set CHANGELOG.md as default missing value for output op…

…tion (#354)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

git-cliff-core/src/lib.rs

@@ -37,3 +37,5 @@ extern crate log;
 
 /// Default configuration file.
 pub const DEFAULT_CONFIG: &str = "cliff.toml";
+/// Default output file.
+pub const DEFAULT_OUTPUT: &str = "CHANGELOG.md";

git-cliff/src/args.rs

@@ -3,7 +3,10 @@ use clap::{
 	Parser,
 	ValueEnum,
 };
-use git_cliff_core::DEFAULT_CONFIG;
+use git_cliff_core::{
+	DEFAULT_CONFIG,
+	DEFAULT_OUTPUT,
+};
 use glob::Pattern;
 use std::path::PathBuf;
 
@@ -130,7 +133,9 @@ pub struct Opt {
 	    long,
 	    env = "GIT_CLIFF_OUTPUT",
 	    value_name = "PATH",
-	    value_parser = Opt::parse_dir
+	    value_parser = Opt::parse_dir,
+	    num_args = 0..=1,
+	    default_missing_value = DEFAULT_OUTPUT
 	)]
 	pub output:       Option<PathBuf>,
 	/// Sets the tag for the latest version.

website/docs/usage/examples.md

@@ -102,7 +102,11 @@ git cliff --topo-order
 Save the changelog file to the specified file:
 
 ```bash
+# Set output path
 git cliff --output CHANGELOG.md
+
+# Without path, the default is `CHANGELOG.md`
+git cliff -o
 ```
 
 Print the changelog [context](/docs/templating/context) as JSON:

website/docs/usage/usage.md

@@ -33,7 +33,7 @@ git-cliff [FLAGS] [OPTIONS] [--] [RANGE]
     --exclude-path <PATTERN>...  Sets the path to exclude related commits [env: GIT_CLIFF_EXCLUDE_PATH=]
     --with-commit <MSG>...       Sets custom commit messages to include in the changelog [env: GIT_CLIFF_WITH_COMMIT=]
 -p, --prepend <PATH>             Prepends entries to the given changelog file [env: GIT_CLIFF_PREPEND=]
--o, --output <PATH>              Writes output to the given file [env: GIT_CLIFF_OUTPUT=]
+-o, --output [<PATH>]            Writes output to the given file [env: GIT_CLIFF_OUTPUT=]
 -t, --tag <TAG>                  Sets the tag for the latest version [env: GIT_CLIFF_TAG=]
 -b, --body <TEMPLATE>            Sets the template for the changelog body [env: GIT_CLIFF_TEMPLATE=]
 -s, --strip <PART>               Strips the given parts from the changelog [possible values: header, footer, all]