build: fix missing GIT_COMMIT_HASH in some cases

Some people try to build without git, this adds a fallback so that
compilation still works in those cases.

Changelog-Fixed: Fix GIT_COMMIT_HASH compilation issue
Fixes: https://github.com/damus-io/notedeck/issues/634
Fixes: https://github.com/damus-io/notedeck/issues/633

crates/notedeck_columns/build.rs

@@ -1,10 +1,29 @@
 use std::process::Command;
 
-fn main() {
-    if let Ok(output) = Command::new("git").args(["rev-parse", "HEAD"]).output() {
-        if output.status.success() {
-            let hash = String::from_utf8_lossy(&output.stdout);
-            println!("cargo:rustc-env=GIT_COMMIT_HASH={}", hash.trim());
-        }
+fn fallback() {
+    if let Some(dirname) = std::env::current_dir()
+        .as_ref()
+        .ok()
+        .and_then(|cwd| cwd.file_name().and_then(|fname| fname.to_str()))
+    {
+        println!("cargo:rustc-env=GIT_COMMIT_HASH={}", dirname);
+    } else {
+        println!("cargo:rustc-env=GIT_COMMIT_HASH=unknown");
+    }
+}
+
+fn main() {
+    let output = if let Ok(output) = Command::new("git").args(["rev-parse", "HEAD"]).output() {
+        output
+    } else {
+        fallback();
+        return;
+    };
+
+    if output.status.success() {
+        let hash = String::from_utf8_lossy(&output.stdout);
+        println!("cargo:rustc-env=GIT_COMMIT_HASH={}", hash.trim());
+    } else {
+        fallback();
     }
 }