Allow builds from 'git archive' generated tarballs

CHANGELOG.md

@@ -23,6 +23,9 @@ but this also allows us now to define colors in the common hex format:
 
 Checkout [THEMES.md](./THEMES.md) for more info.
 
+### Added
+* support `TAR_COMMIT_ID` enabling builds from `git archive` generated source tarballs or other outside a git repo [[@alerque](https://github.com/alerque)] ([#2187](https://github.com/extrawurst/gitui/pull/2187))
+
 ### Fixes
 * update yanked dependency to `libc` to fix building with `--locked`.
 * document breaking change in theme file format.

build.rs

@@ -3,9 +3,14 @@ use chrono::TimeZone;
 fn get_git_hash() -> String {
 	use std::process::Command;
 
+	// Allow builds from `git archive` generated tarballs if output of `git get-tar-commit-id` is
+	// set in an env var.
+	if let Ok(commit) = std::env::var("TAR_COMMIT_ID") {
+		return commit[..7].to_string();
+	};
 	let commit = Command::new("git")
 		.arg("rev-parse")
-		.arg("--short")
+		.arg("--short=7")
 		.arg("--verify")
 		.arg("HEAD")
 		.output();