[rust_verify] fix: rerun-if-changed paths in build.rs (#2826)

Author: mkovaxx

source/cargo-verus-toolchains/src/versions.rs

@@ -1,4 +1,4 @@
-use std::process::Command;
+use std::{path::PathBuf, process::Command};
 
 use anyhow::{Context, Result, bail};
 
@@ -69,6 +69,33 @@ fn get_git_rev(abbreviate_to: Option<usize>) -> Result<String> {
     Ok(raw_rev.trim().to_owned())
 }
 
+/// Get the existing Git files that determine the current `HEAD` commit.
+///
+/// This works for ordinary repositories, linked worktrees, both symbolic and detached `HEAD`s,
+/// and packed refs.
+pub fn get_git_head_paths() -> Result<Vec<PathBuf>> {
+    let mut paths = vec![get_git_path("HEAD")?.context("Git HEAD is missing")?];
+
+    if let Ok(head_ref) = run_command(&["git", "symbolic-ref", "--quiet", "HEAD"])
+        && let Some(path) = get_git_path(head_ref.trim())?
+    {
+        paths.push(path);
+    }
+
+    if let Some(path) = get_git_path("packed-refs")? {
+        paths.push(path);
+    }
+
+    Ok(paths)
+}
+
+/// Get the absolute path to a Git file when it exists.
+fn get_git_path(path: &str) -> Result<Option<PathBuf>> {
+    let path = run_command(&["git", "rev-parse", "--path-format=absolute", "--git-path", path])?;
+    let path = PathBuf::from(path.trim());
+    Ok(path.exists().then_some(path))
+}
+
 fn run_command(program_and_args: &[&str]) -> Result<String> {
     let mut command = Command::new(program_and_args[0]);
     command.args(&program_and_args[1..]);

source/rust_verify/build.rs

@@ -1,6 +1,6 @@
 use std::process::Command;
 
-use cargo_verus_toolchains::versions::get_verus_version;
+use cargo_verus_toolchains::versions::{get_git_head_paths, get_verus_version};
 
 fn main() {
     let (default_version, default_sha) = get_verus_version(true).expect("version info");
@@ -12,7 +12,9 @@ fn main() {
         run_command(&["rustup", "show", "active-toolchain"]).expect("active toolchain")
     });
 
-    println!("cargo::rerun-if-changed=../.git/HEAD");
+    for path in get_git_head_paths().expect("Git HEAD paths") {
+        println!("cargo::rerun-if-changed={}", path.display());
+    }
     println!("cargo::rerun-if-env-changed=VARGO_BUILD_PROFILE");
     println!("cargo::rerun-if-env-changed=VARGO_BUILD_VERSION");
     println!("cargo::rerun-if-env-changed=VARGO_BUILD_SHA");