Compile-time warning when git is missing (#187)

build.rs

@@ -1,16 +1,50 @@
+use std::env;
 use std::process::Command;
 
-fn main() {
-    let git_describe = Command::new("git")
-        .args(&["describe", "--tags", "--broken"])
-        .output()
-        .ok()
-        .and_then(|proc| String::from_utf8(proc.stdout).ok());
+macro_rules! warn {
+    ($fmt:tt) => ({
+        ::std::println!(::std::concat!("cargo:warning=", $fmt));
+    });
+    ($fmt:tt, $($arg:tt)*) => ({
+        ::std::println!(::std::concat!("cargo:warning=", $fmt), $($arg)*);
+    });
+}
 
-    let version_info = match git_describe {
-        Some(description) if !description.is_empty() => description,
-        _ => format!("v{}", env!("CARGO_PKG_VERSION")),
+fn git_version() -> Option<String> {
+    let mut git = Command::new("git");
+    git.args(&["describe", "--tags", "--broken"]);
+
+    let output = match git.output() {
+        Err(e) => {
+            warn!("when retrieving version: git failed to start: {}", e);
+            return None;
+        }
+        Ok(output) if !output.status.success() => {
+            warn!(
+                "when retrieving version: git exited with code: {:?}",
+                output.status.code()
+            );
+            return None;
+        }
+        Ok(output) => output,
     };
 
-    println!("cargo:rustc-env=ZOXIDE_VERSION={}", version_info);
+    match String::from_utf8(output.stdout) {
+        Ok(version) => Some(version),
+        Err(e) => {
+            warn!("when retrieving version: git returned invalid utf-8: {}", e);
+            None
+        }
+    }
+}
+
+fn crate_version() -> String {
+    warn!("falling back to crate version");
+    // unwrap is safe here, since Cargo will always supply this variable.
+    format!("v{}", env::var("CARGO_PKG_VERSION").unwrap())
+}
+
+fn main() {
+    let version = git_version().unwrap_or_else(crate_version);
+    println!("cargo:rustc-env=ZOXIDE_VERSION={}", version);
 }