firmware: don't bail out if building not from a git checkout (#783).

artiq/firmware/libbuild_artiq/lib.rs

@@ -3,13 +3,23 @@ extern crate walkdir;
 use std::env;
 use std::fs::File;
 use std::io::{Write, BufRead, BufReader};
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use std::process::Command;
 
 use walkdir::WalkDir;
 
 pub fn git_describe() {
-    let id =
+    let git_dir = Path::new("../../../.git");
+
+    println!("cargo:rerun-if-changed={}", git_dir.join("HEAD").display());
+    for entry in WalkDir::new(git_dir.join("refs")) {
+        let entry = entry.unwrap();
+        println!("cargo:rerun-if-changed={}", entry.path().display());
+    }
+
+    let version;
+    if git_dir.exists() {
+        let git_describe =
             Command::new("git")
                     .arg("describe")
                     .arg("--tags")
@@ -26,21 +36,17 @@ pub fn git_describe() {
                         s
                     })
                     .unwrap();
-    let id = id.split("-").collect::<Vec<_>>();
+        let parts = git_describe.split("-").collect::<Vec<_>>();
-    let id = format!("{}+{}.{}", id[0], id[1], id[2]);
+        version = format!("{}+{}.{}", parts[0], parts[1], parts[2]);
-
+    } else {
-    let out_dir = env::var("OUT_DIR").unwrap();
+        version = "unknown".to_owned();
-    let dest_path = Path::new(&out_dir).join("git-describe");
-    let mut f = File::create(&dest_path).unwrap();
-    f.write(id.as_bytes()).unwrap();
-
-    println!("cargo:rust-cfg=git_describe={:?}", id);
-
-    println!("cargo:rerun-if-changed=../../../.git/HEAD");
-    for entry in WalkDir::new("../../../.git/refs") {
-        let entry = entry.unwrap();
-        println!("cargo:rerun-if-changed={}", entry.path().display());
     }
+
+    let out_dir = PathBuf::from(env::var("OUT_DIR").unwrap());
+    let mut f = File::create(out_dir.join("git-describe")).unwrap();
+    write!(f, "{}", version).unwrap();
+
+    println!("cargo:rust-cfg=git_describe={:?}", version);
 }
 
 pub fn misoc_cfg() {