Refactor source of Git commit build info (closes #661)

editor/build.rs

@@ -0,0 +1,22 @@
+use std::process::Command;
+
+const GRAPHITE_RELEASE_SERIES: &str = "Alpha Milestone 1";
+
+fn main() {
+	// Execute a Git command for its stdout. Early exit if it fails for any of the possible reasons.
+	let try_git_command = |args: &[&str]| -> Option<String> {
+		let git_output = Command::new("git").args(args).output().ok()?;
+		let maybe_empty = String::from_utf8(git_output.stdout).ok()?;
+		let command_result = (!maybe_empty.is_empty()).then(|| maybe_empty)?;
+		Some(command_result)
+	};
+	// Execute a Git command for its output. Return "unknown" if it fails for any of the possible reasons.
+	let git_command = |args| -> String { try_git_command(args).unwrap_or_else(|| String::from("unknown")) };
+
+	// Rather than printing to any terminal, these commands set environment variables in the Cargo toolchain.
+	// They are accessed with the `env!("...")` macro in the codebase.
+	println!("cargo:rustc-env=GRAPHITE_GIT_COMMIT_DATE={}", git_command(&["log", "-1", "--format=%cd"]));
+	println!("cargo:rustc-env=GRAPHITE_GIT_COMMIT_HASH={}", git_command(&["rev-parse", "HEAD"]));
+	println!("cargo:rustc-env=GRAPHITE_GIT_COMMIT_BRANCH={}", git_command(&["rev-parse", "--abbrev-ref", "HEAD"]));
+	println!("cargo:rustc-env=GRAPHITE_RELEASE_SERIES={}", GRAPHITE_RELEASE_SERIES);
+}