Extract rerun-if logic to separate fn

mullvad-version/build.rs

@@ -75,6 +75,27 @@ fn get_dev_suffix(target: Target, product_version: &str) -> Option<String> {
         Target::Desktop => product_version.to_owned(),
     };
 
+    rerun_if_git_ref_changed(&release_tag)?;
+
+    // Get the git commit hashes for the latest release and current HEAD
+    // Return `None` if unable to find the hash for HEAD.
+    let head_commit_hash = git_rev_parse_commit_hash("HEAD")?;
+    let product_version_commit_hash = git_rev_parse_commit_hash(&release_tag);
+
+    // If we are currently building the release tag, there is no dev suffix
+    if Some(&head_commit_hash) == product_version_commit_hash.as_ref() {
+        return None;
+    }
+    Some(format!(
+        "-dev-{}",
+        &head_commit_hash[..GIT_HASH_DEV_SUFFIX_LEN]
+    ))
+}
+
+/// Trigger rebuild of `mullvad-version` on changing branch (`.git/HEAD`), on changes to the ref of
+/// the current branch (`.git/refs/heads/$current_branch`) and on changes to the ref of the current
+/// release tag (`.git/refs/tags/$current_release_tag`).
+fn rerun_if_git_ref_changed(release_tag: &String) -> Option<()> {
     let git_dir = Path::new("..").join(".git");
 
     // If we build our output on information about HEAD we need to re-run if HEAD moves
@@ -83,14 +104,14 @@ fn get_dev_suffix(target: Target, product_version: &str) -> Option<String> {
         println!("cargo:rerun-if-changed={}", head_path.display());
     }
 
+    // If we build our output on information about the ref of the current branch, we need to re-run
+    // on changes to it
     let output = Command::new("git")
         .arg("branch")
         .arg("--show-current")
         .output()
         .ok()?;
     let current_branch = String::from_utf8(output.stdout).unwrap();
-    // If we build our output on information about a git reference, we need to re-run
-    // if it moves. Instead of trying to be smart, just re-run if any git reference moves.
     let git_current_branch_ref = git_dir
         .join("refs")
         .join("heads")
@@ -101,27 +122,14 @@ fn get_dev_suffix(target: Target, product_version: &str) -> Option<String> {
             git_current_branch_ref.display()
         );
     }
-    let git_current_branch_ref = git_dir.join("refs").join("tags").join(&release_tag);
-    if git_current_branch_ref.exists() {
-        println!(
-            "cargo:rerun-if-changed={}",
-            git_current_branch_ref.display()
-        );
-    }
-
-    // Get the git commit hashes for the latest release and current HEAD
-    // Return `None` if unable to find the hash for HEAD.
-    let head_commit_hash = git_rev_parse_commit_hash("HEAD")?;
-    let product_version_commit_hash = git_rev_parse_commit_hash(&release_tag);
 
-    // If we are currently building the release tag, there is no dev suffix
-    if Some(&head_commit_hash) == product_version_commit_hash.as_ref() {
-        return None;
-    }
-    Some(format!(
-        "-dev-{}",
-        &head_commit_hash[..GIT_HASH_DEV_SUFFIX_LEN]
-    ))
+    // To rebuild in the case where the release tag moves to the current commit, we need to track
+    // changes to it
+    let git_release_tag_ref = git_dir.join("refs").join("tags").join(release_tag);
+    if git_release_tag_ref.exists() {
+        println!("cargo:rerun-if-changed={}", git_release_tag_ref.display());
+    };
+    Some(())
 }
 
 /// Returns the commit hash for the commit that `git_ref` is pointing to.