fix(config)!: nested environment config overrides (#157)

* chore: update env variable override format

* tests: add a copule env override assertions

* docs: add a doc for env overrides

* docs: wording

* docs: wording

* fix: prefix

* docs: format first

git-cliff-core/src/config.rs

@@ -144,7 +144,9 @@ impl Config {
 			config::Config::builder().add_source(config::File::from(path))
 		};
 		Ok(config_builder
-			.add_source(config::Environment::with_prefix("CLIFF").separator("_"))
+			.add_source(
+				config::Environment::with_prefix("GIT_CLIFF").separator("__"),
+			)
 			.build()?
 			.try_deserialize()?)
 	}
@@ -164,9 +166,29 @@ mod test {
 			.to_path_buf()
 			.join("config")
 			.join(crate::DEFAULT_CONFIG);
-		env::set_var("CLIFF_CHANGELOG_FOOTER", "test");
+
+		const FOOTER_VALUE: &str = "test";
+		const TAG_PATTERN_VALUE: &str = "*[0-9]*";
+		const IGNORE_TAGS_VALUE: &str = "v[0-9]+.[0-9]+.[0-9]+-rc[0-9]+";
+
+		env::set_var("GIT_CLIFF__CHANGELOG__FOOTER", FOOTER_VALUE);
+		env::set_var("GIT_CLIFF__GIT__TAG_PATTERN", TAG_PATTERN_VALUE);
+		env::set_var("GIT_CLIFF__GIT__IGNORE_TAGS", IGNORE_TAGS_VALUE);
+
 		let config = Config::parse(&path)?;
-		assert_eq!(Some(String::from("test")), config.changelog.footer);
+
+		assert_eq!(Some(String::from(FOOTER_VALUE)), config.changelog.footer);
+		assert_eq!(
+			Some(String::from(TAG_PATTERN_VALUE)),
+			config.git.tag_pattern
+		);
+		assert_eq!(
+			Some(String::from(IGNORE_TAGS_VALUE)),
+			config
+				.git
+				.ignore_tags
+				.map(|ignore_tags| ignore_tags.to_string())
+		);
 		Ok(())
 	}
 }

website/docs/configuration.md

@@ -276,3 +276,26 @@ Examples:
 `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.
+
+### Environment Configuration Overrides
+
+It's possible to use environment variables to override configuration elements. If an environment variable matches a configuration element the variable's value will be used instead of the element's.
+
+Format:
+```
+[PREFIX]__[CONFIG SECTION]__[FIELD NAME]
+```
+
+Examples:
+
+To override the `footer` element:
+
+```bash
+export GIT_CLIFF__CHANGELOG__FOOTER="<!-- footer from env -->"
+```
+
+To override the `ignore_tags` element:
+
+```bash
+export GIT_CLIFF__GIT__IGNORE_TAGS="v[0-9]+.[0-9]+.[0-9]+-rc[0-9]+"
+```