Add functionality to diff specific Git commits

In this commit, functionality is added to generate diffs of specific Git commits for a given project. The Git diffing function is modified to generate strings of diffs in addition to its existing behavior, and an additional function is added to the application to perform diffing based on specified Git commit ids.

Main changes:
- Added the `git_commit_diff` function which takes a project id and commit id, retrieves the corresponding Git repository, finds the specific commit, and generates a diff against its parent commit. 
- The resulting diff is converted to a string using the existing `diff_hunks_to_string` function.
- The `diff_hunks_to_string` function is updated to be a standalone function as it is now utilized in two places.
- Added the `getCommitDiff` function to the front-end, which invokes the newly added `git_commit_diff`.
- The `git_commit_diff` function is added to the main function, ensuring it can be executed in the application

src-tauri/src/app.rs

@@ -352,8 +352,35 @@ impl App {
             &diff::Options { context_lines },
         )
         .context("failed to diff")?;
+        let diff = Self::diff_hunks_to_string(diff);
+        Ok(diff)
+    }
+    pub fn git_commit_diff(
+        &self,
+        project_id: &str,
+        commit_id: &str,
+    ) -> Result<HashMap<path::PathBuf, String>> {
+        let project = self.gb_project(project_id)?;
+        let project_repository = project_repository::Repository::open(&project)
+            .context("failed to open project repository")?;
 
-        let diff = diff
+        let commit = project_repository
+            .git_repository
+            .find_commit(git2::Oid::from_str(commit_id).unwrap())?;
+
+        let parent = commit.parent(0).context("failed to get parent commit")?;
+        let commit_tree = commit.tree().context("failed to get commit tree")?;
+        let parent_tree = parent.tree().context("failed to get parent tree")?;
+        let diff = diff::trees(&project_repository, &parent_tree, &commit_tree)?;
+
+        let diff = Self::diff_hunks_to_string(diff);
+        Ok(diff)
+    }
+
+    fn diff_hunks_to_string(
+        diff: HashMap<path::PathBuf, Vec<project_repository::diff::Hunk>>,
+    ) -> HashMap<path::PathBuf, String> {
+        return diff
             .into_iter()
             .map(|(file_path, hunks)| {
                 (
@@ -366,8 +393,6 @@ impl App {
                 )
             })
             .collect::<HashMap<_, _>>();
-
-        Ok(diff)
     }
 
     pub fn git_match_paths(&self, project_id: &str, pattern: &str) -> Result<Vec<String>> {

src-tauri/src/main.rs

@@ -288,6 +288,25 @@ async fn git_wd_diff(
     Ok(diff)
 }
 
+#[tauri::command(async)]
+#[instrument(name = "git_commit_diff", skip(handle))]
+async fn git_commit_diff(
+    handle: tauri::AppHandle,
+    project_id: &str,
+    commit_id: &str,
+) -> Result<HashMap<path::PathBuf, String>, Error> {
+    let app = handle.state::<app::App>();
+    let diff = app
+        .git_commit_diff(project_id, commit_id)
+        .with_context(|| {
+            format!(
+                "failed to get git diff for project {} and commit {}",
+                project_id, commit_id
+            )
+        })?;
+    Ok(diff)
+}
+
 #[tauri::command(async)]
 #[instrument(name = "git_match_paths", skip(handle))]
 async fn git_match_paths(
@@ -708,6 +727,7 @@ async fn main() {
             git_stage,
             git_unstage,
             git_wd_diff,
+            git_commit_diff,
             delete_all_data,
             get_logs_archive_path,
             get_project_archive_path,

src/lib/api/git/diffs.ts

@@ -11,6 +11,10 @@ const list = (params: { projectId: string; contextLines?: number }) =>
 
 const stores: Record<string, WritableLoadable<Record<string, string>>> = {};
 
+export function getCommitDiff(params: { projectId: string; commitId: string }) {
+	return invoke<Record<string, string>>('git_commit_diff', params);
+}
+
 export function getDiffsStore(params: { projectId: string }) {
 	if (stores[params.projectId]) return stores[params.projectId];
 	const store = asyncWritable([], () => list(params));

src/routes/repo/[projectId]/BaseBranchPeek.svelte

@@ -5,6 +5,7 @@
 	import type { BranchController } from '$lib/vbranches/branchController';
 	import Scrollbar from '$lib/components/Scrollbar.svelte';
 	import { projectMergeUpstreamWarningDismissed } from '$lib/config/config';
+	// import { getCommitDiff } from '$lib/api/git/diffs';
 
 	export let base: BaseBranch;
 	export let branchController: BranchController;
@@ -72,6 +73,16 @@
 			<div class="flex flex-col gap-y-2">
 				{#each base.recentCommits as commit}
 					<CommitCard url={base.commitUrl(commit.id)} {commit} />
+					<!-- <button
+						on:click={() => {
+							getCommitDiff({ projectId: branchController.projectId, commitId: commit.id }).then(
+								(result) => {
+									console.log(result);
+								}
+							);
+						}}
+						class="w-full bg-red-400">{commit.id}</button
+					> -->
 				{/each}
 			</div>
 		</div>