Always pass commit message to git::create_derived_commit

This function used to take an `Option<&str>` as commit message and provided a default. However, there was only one place where we passed `None`, so it's cleaner to just always pass the message.
We used to trim the message and append a new line at the end. However, `git2` provides a function to clean up a commit message, which is used here now.

Test Plan: `cargo build` and use the fresh build to submit this Pull Request

Reviewers: jozef-mokry

Reviewed By: jozef-mokry

Pull Request: #32

src/commands/diff.rs

@@ -320,11 +320,11 @@ async fn diff_impl(
 
             Some(git.create_derived_commit(
                 local_commit.parent_oid,
-                Some(if pull_request.is_some() {
+                if pull_request.is_some() {
                     "[𝘀𝗽𝗿] 𝘤𝘩𝘢𝘯𝘨𝘦𝘴 𝘪𝘯𝘵𝘳𝘰𝘥𝘶𝘤𝘦𝘥 𝘵𝘩𝘳𝘰𝘶𝘨𝘩 𝘳𝘦𝘣𝘢𝘴𝘦\n\n[skip ci]"
                 } else {
                     "[𝘀𝗽𝗿] 𝘤𝘩𝘢𝘯𝘨𝘦𝘴 𝘵𝘰 𝘮𝘢𝘴𝘵𝘦𝘳 𝘵𝘩𝘪𝘴 𝘤𝘰𝘮𝘮𝘪𝘵 𝘪𝘴 𝘣𝘢𝘴𝘦𝘥 𝘰𝘯\n\n[skip ci]"
-                }),
+                },
                 parent_tree_oid,
                 &parents[..],
             )?)
@@ -377,7 +377,10 @@ async fn diff_impl(
     // Create the new commit
     let pr_commit = git.create_derived_commit(
         local_commit.oid,
-        github_commit_message.as_ref().map(|s| &s[..]),
+        github_commit_message
+            .as_ref()
+            .map(|s| &s[..])
+            .unwrap_or("[𝘀𝗽𝗿] 𝘪𝘯𝘪𝘵𝘪𝘢𝘭 𝘷𝘦𝘳𝘴𝘪𝘰𝘯"),
         cherrypicked_tree.unwrap_or(tree_oid),
         &pr_commit_parents[..],
     )?;

src/commands/land.rs

@@ -102,7 +102,7 @@ pub async fn land(
     // what we want.
     let final_commit = git.create_derived_commit(
         prepared_commit.oid,
-        Some("[𝘀𝗽𝗿] 𝘭𝘢𝘯𝘥𝘦𝘥 𝘷𝘦𝘳𝘴𝘪𝘰𝘯\n\n[skip ci]"),
+        "[𝘀𝗽𝗿] 𝘭𝘢𝘯𝘥𝘦𝘥 𝘷𝘦𝘳𝘴𝘪𝘰𝘯\n\n[skip ci]",
         our_tree_oid,
         &[pull_request.head_oid, current_master],
     )?;

src/commands/patch.rs

@@ -67,7 +67,7 @@ pub async fn patch(
 
                 parent_oid = git.create_derived_commit(
                     pr.base_oid,
-                    Some(&format!("[𝘀𝗽𝗿] Base of Pull Request #{}", pr.number)),
+                    &format!("[𝘀𝗽𝗿] Base of Pull Request #{}", pr.number),
                     pr_base_tree,
                     &[parent_oid],
                 )?;
@@ -79,7 +79,7 @@ pub async fn patch(
         // the commit we created above to prepare the base of this commit.
         git.create_derived_commit(
             pr.head_oid,
-            Some(&build_commit_message(&pr.sections)),
+            &build_commit_message(&pr.sections),
             git.get_tree_oid_for_commit(pr.head_oid)?,
             &[parent_oid],
         )?

src/git.rs

@@ -362,7 +362,7 @@ impl Git {
     pub fn create_derived_commit(
         &self,
         original_commit_oid: Oid,
-        message: Option<&str>,
+        message: &str,
         tree_oid: Oid,
         parent_oids: &[Oid],
     ) -> Result<Oid> {
@@ -373,11 +373,7 @@ impl Git {
             .map(|oid| self.repo.find_commit(*oid))
             .collect::<std::result::Result<Vec<_>, _>>()?;
         let parent_refs = parents.iter().collect::<Vec<_>>();
-        let message = if let Some(text) = message {
-            format!("{}\n", text.trim())
-        } else {
-            "[𝘀𝗽𝗿] 𝘪𝘯𝘪𝘵𝘪𝘢𝘭 𝘷𝘦𝘳𝘴𝘪𝘰𝘯\n".into()
-        };
+        let message = git2::message_prettify(message, None)?;
 
         // The committer signature should be the default signature (i.e. the
         // current user - as configured in Git as `user.name` and `user.email` -