Fix things being committed even when nothing was written

Committing nothing is fine and not the problem here. The issue is that we only have exclusive access to git if we have a writing scope. Otherwise, we get issues with multiple threads trying to commit at the same time, this errors even though they're committing nothing.

Author: TheEpicBlock

platform_api/src/main/java/net/modfest/platform/git/GitScopeManager.java

@@ -11,6 +11,14 @@ public class GitScopeManager {
 	private final Git git;
 	private final GitConfig config;
 	private final ThreadLocal<GitScope> gitScopes = new ThreadLocal<>();
+	/**
+	 * Helps manage which scope is the current "write" scope. Many threads can set
+	 * a scope, but once the scope is actually used¹ the thread that owns the scope will
+	 * retrieve this lock. The thread that owns the locks owns the writing scope.
+	 *
+	 * ¹ Often a scope will be set but nothing will actually be written and no locking is needed.
+	 *   For example, each request sets a scope.
+	 */
 	private final ReentrantLock scopeLock = new ReentrantLock();
 
 	public GitScopeManager(Git git, GitConfig config) {
@@ -27,12 +35,20 @@ public void closeScope() {
 		this.gitScopes.remove();
 	}
 
+	/**
+	 * Sets the git commit message for any writes that may or may not be
+	 * done during the provided runnable. All writes will be batched into a
+	 * single commit.
+	 */
 	public void runWithScope(GitScope scope, Runnable r) {
 		setScope(scope);
 		r.run();
 		closeScope();
 	}
 
+	/**
+	 * Activates the current scope to be used for writing
+	 */
 	void runWithScopedGit(GitFunction r) {
 		var threadScope = gitScopes.get();
 		try {
@@ -60,19 +76,20 @@ Git getGitUnscoped() {
 	}
 
 	private void finalizeScope(GitScope scope) {
-		try {
-			this.git.commit()
-				.setAuthor(config.getUser(), config.getEmail())
-				.setMessage(scope.commitMessage())
-				.setAllowEmpty(false)
-				.setSign(false)
-				.call();
-		} catch (EmptyCommitException ignored) {
-			// If nothing changed we simply do not commit anything
-		} catch (GitAPIException e) {
-			throw new RuntimeException(e);
-		} finally {
-			if (this.scopeLock.isHeldByCurrentThread()) {
+		// We only need to commit if the scope was locked for use in writing
+		if (this.scopeLock.isHeldByCurrentThread()) {
+			try {
+				this.git.commit()
+					.setAuthor(config.getUser(), config.getEmail())
+					.setMessage(scope.commitMessage())
+					.setAllowEmpty(false)
+					.setSign(false)
+					.call();
+			} catch (EmptyCommitException ignored) {
+				// If nothing changed we simply do not commit anything
+			} catch (GitAPIException e) {
+				throw new RuntimeException(e);
+			} finally {
 				this.scopeLock.unlock();
 			}
 		}