halide-cache: Add --base-dir option

Make the paths to generated files and dependencies relative to the value
of this argument. This makes it possible to share the halide cache
between repos or worktrees. If a path cannot be made relative then it
remains unchanged. Currently it is an Option<PathBuf> to avoid having
to make changes to the call site and if it is None then the path to the
repository is used. In the future we probably want to make this more
robust.

Author: Osse

halide-cache/src/main.rs

@@ -13,6 +13,8 @@ struct Args {
     generated_object: PathBuf,
     #[arg(long)]
     generated_header: PathBuf,
+    #[arg(long)]
+    base_dir: Option<PathBuf>,
     #[arg(last = true)]
     builder: Vec<String>,
 }
@@ -21,7 +23,7 @@ const MAX_CACHE_SIZE_BYTES: u64 = 10737418240; // 10 GiB
 
 struct Dependencies<'a> {
     path: &'a Path,
-    dependencies: &'a [PathBuf],
+    dependencies: &'a [&'a Path],
     env: &'a [String],
 }
 
@@ -60,19 +62,41 @@ fn main() -> anyhow::Result<()> {
     if !Path::new(&cache_dir).exists() {
         fs::create_dir_all(&cache_dir)?;
     }
+
     let lager = Lager::new(Path::new(&cache_dir))?;
 
     let zivid_env = collect_zivid_env();
 
+    let base_dir = match args.base_dir {
+        Some(d) => d,
+        None => find_repo_root()?,
+    };
+
+    let generated_object = args
+        .generated_object
+        .strip_prefix(&base_dir)
+        .unwrap_or(&args.generated_object);
+
+    let generated_header = args
+        .generated_header
+        .strip_prefix(&base_dir)
+        .unwrap_or(&args.generated_header);
+
+    let dependencies = args
+        .dependencies
+        .iter()
+        .map(|p| p.strip_prefix(&base_dir).unwrap_or(p))
+        .collect::<Vec<_>>();
+
     let object_dependencies = Dependencies {
-        path: &args.generated_object,
-        dependencies: &args.dependencies,
+        path: generated_object,
+        dependencies: &dependencies,
         env: &zivid_env,
     };
 
     let header_dependencies = Dependencies {
-        path: &args.generated_header,
-        dependencies: &args.dependencies,
+        path: generated_header,
+        dependencies: &dependencies,
         env: &zivid_env,
     };
 
@@ -149,3 +173,16 @@ fn cache_hit(
         (Err(e), Ok(_)) => Err(anyhow::anyhow!(e).context("Retrieving the header was successful")),
     }
 }
+
+fn find_repo_root() -> anyhow::Result<PathBuf> {
+    let mut cwd = std::env::current_dir()?;
+
+    loop {
+        if cwd.join(".git").exists() {
+            return Ok(cwd);
+        }
+        if !cwd.pop() {
+            anyhow::bail!("Could not determine root");
+        }
+    }
+}