Allow passing in GIT_DESCRIBE/GIT_REV to avoid git repo

This should allow building inside a flake

build.rs

@@ -3,11 +3,26 @@ use std::env;
 use git2::Repository;
 
 fn main() {
-    if let Ok(repo) = Repository::open(".") {
-        let head = repo.head().expect("should get git HEAD");
-        let commit = head.peel_to_commit().expect("should get git HEAD commit");
-        println!("cargo::rustc-env=GIT_REV={}", commit.id());
-    }
+    let branch = if let Ok(describe) = env::var("GIT_DESCRIBE") {
+        describe
+    } else {
+        let repo = Repository::open(".").expect("should open git repository");
+        let head = repo.head().expect("should get HEAD");
+        head.shorthand()
+            .expect("should get branch name")
+            .to_string()
+    };
+    println!("cargo::rustc-env=GIT_DESCRIBE={branch}");
+
+    let rev = if let Ok(rev) = env::var("GIT_REV") {
+        rev
+    } else {
+        let repo = Repository::open(".").expect("should open git repository");
+        let head = repo.head().expect("should get HEAD");
+        let commit = head.peel_to_commit().expect("should get HEAD commit");
+        commit.id().to_string()
+    };
+    println!("cargo::rustc-env=GIT_REV={rev}");
 
     let os = env::var("CARGO_CFG_TARGET_OS").expect("should get CARGO_CFG_TARGET_OS");
     println!("cargo::rustc-env=TARGET_OS={os}");

flake.nix

@@ -134,7 +134,8 @@
             nativeBuildInputs = with pkgs; [ pkg-config ];
             CARGO_BUILD_TARGET = targetConfig.rustTarget;
             CARGO_BUILD_RUSTFLAGS = [ "-Ctarget-feature=+crt-static" ];
-            GIT_REV = self.rev or self.dirtyRev or "dirty";
+            GIT_REV = self.rev or self.dirtyRev or "unknown-rev";
+            GIT_DESCRIBE = "flake-" + self.shortRev or self.dirtyShortRev or "unknown";
             postInstall = ''
               export WINEPREFIX="$(mktemp -d)"
 

src/cli.rs

@@ -84,7 +84,9 @@ impl Cli {
         env!("TARGET_ENV"),
         " ",
         env!("TARGET_ARCH"),
-        ", git rev ",
+        ", git ",
+        env!("GIT_DESCRIBE"),
+        " rev ",
         env!("GIT_REV"),
     );
 }