rustc_tools_util: rerun when git commit changes

Author: RalfJung

rustc_tools_util/src/lib.rs

@@ -1,3 +1,5 @@
+use std::path::PathBuf;
+use std::process::Command;
 use std::str;
 
 /// This macro creates the version string during compilation from the
@@ -32,6 +34,7 @@ macro_rules! get_version_info {
 #[macro_export]
 macro_rules! setup_version_info {
     () => {{
+        let _ = $crate::rerun_if_git_changes();
         println!(
             "cargo:rustc-env=GIT_HASH={}",
             $crate::get_commit_hash().unwrap_or_default()
@@ -100,19 +103,48 @@ impl std::fmt::Debug for VersionInfo {
 }
 
 #[must_use]
-pub fn get_commit_hash() -> Option<String> {
-    let output = std::process::Command::new("git")
-        .args(["rev-parse", "HEAD"])
+pub fn rerun_if_git_changes() -> Option<()> {
+    // Make sure we get rerun when the git commit changes.
+    // First, find the `HEAD` file. This should work even with worktrees.
+    let output = Command::new("git").args(["rev-parse", "--git-dir"]).output().ok()?;
+    let stdout = output.status.success().then_some(output.stdout)?;
+    let git_dir = PathBuf::from(String::from_utf8(stdout).ok()?.trim());
+    // Read the HEAD file to determine the name of the current ref.
+    let git_head_file = git_dir.join("HEAD");
+    let git_head_ref = String::from_utf8(std::fs::read(&git_head_file).ok()?).ok()?;
+    let git_head_ref = git_head_ref.strip_prefix("ref:")?.trim();
+    // Find the directory that stores the ref files.
+    // Refs *can* be packed, but the checked-out branch is not packed,
+    // so we should always be able to find this file.
+    let output = Command::new("git")
+        .args(["rev-parse", "--git-common-dir"])
         .output()
         .ok()?;
+    let stdout = output.status.success().then_some(output.stdout)?;
+    let git_common_dir = PathBuf::from(String::from_utf8(stdout).ok()?.trim());
+    // Determine the file where the target of that ref is stored.
+    let git_head_ref_file = git_common_dir.join(git_head_ref);
+    if !git_head_ref_file.exists() {
+        // Something went wrong.
+        return None;
+    }
+
+    println!("cargo::rerun-if-changed={}", git_head_file.display());
+    println!("cargo::rerun-if-changed={}", git_head_ref_file.display());
+    Some(())
+}
+
+#[must_use]
+pub fn get_commit_hash() -> Option<String> {
+    let output = Command::new("git").args(["rev-parse", "HEAD"]).output().ok()?;
     let mut stdout = output.status.success().then_some(output.stdout)?;
     stdout.truncate(10);
     String::from_utf8(stdout).ok()
 }
 
 #[must_use]
 pub fn get_commit_date() -> Option<String> {
-    let output = std::process::Command::new("git")
+    let output = Command::new("git")
         .args(["log", "-1", "--date=short", "--pretty=format:%cd"])
         .output()
         .ok()?;