feat: show ecc2 selected worktree diff summaries

ecc2/src/worktree/mod.rs

@@ -87,6 +87,56 @@ pub fn list() -> Result<Vec<String>> {
     Ok(worktrees)
 }
 
+pub fn diff_summary(worktree: &WorktreeInfo) -> Result<Option<String>> {
+    let base_ref = format!("{}...HEAD", worktree.base_branch);
+    let committed = git_diff_shortstat(&worktree.path, &[&base_ref])?;
+    let working = git_diff_shortstat(&worktree.path, &[])?;
+
+    let mut parts = Vec::new();
+    if let Some(committed) = committed {
+        parts.push(format!("Branch {committed}"));
+    }
+    if let Some(working) = working {
+        parts.push(format!("Working tree {working}"));
+    }
+
+    if parts.is_empty() {
+        Ok(Some(format!("Clean relative to {}", worktree.base_branch)))
+    } else {
+        Ok(Some(parts.join(" | ")))
+    }
+}
+
+fn git_diff_shortstat(worktree_path: &Path, extra_args: &[&str]) -> Result<Option<String>> {
+    let mut command = Command::new("git");
+    command
+        .arg("-C")
+        .arg(worktree_path)
+        .arg("diff")
+        .arg("--shortstat");
+    command.args(extra_args);
+
+    let output = command
+        .output()
+        .context("Failed to generate worktree diff summary")?;
+
+    if !output.status.success() {
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        tracing::warn!(
+            "Worktree diff summary warning for {}: {stderr}",
+            worktree_path.display()
+        );
+        return Ok(None);
+    }
+
+    let summary = String::from_utf8_lossy(&output.stdout).trim().to_string();
+    if summary.is_empty() {
+        Ok(None)
+    } else {
+        Ok(Some(summary))
+    }
+}
+
 fn get_current_branch(repo_root: &Path) -> Result<String> {
     let output = Command::new("git")
         .arg("-C")
@@ -97,3 +147,69 @@ fn get_current_branch(repo_root: &Path) -> Result<String> {
 
     Ok(String::from_utf8_lossy(&output.stdout).trim().to_string())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use anyhow::Result;
+    use std::fs;
+    use std::process::Command;
+    use uuid::Uuid;
+
+    fn run_git(repo: &Path, args: &[&str]) -> Result<()> {
+        let output = Command::new("git").arg("-C").arg(repo).args(args).output()?;
+        if !output.status.success() {
+            anyhow::bail!("{}", String::from_utf8_lossy(&output.stderr));
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn diff_summary_reports_clean_and_dirty_worktrees() -> Result<()> {
+        let root = std::env::temp_dir().join(format!("ecc2-worktree-{}", Uuid::new_v4()));
+        let repo = root.join("repo");
+        fs::create_dir_all(&repo)?;
+
+        run_git(&repo, &["init", "-b", "main"])?;
+        run_git(&repo, &["config", "user.email", "ecc@example.com"])?;
+        run_git(&repo, &["config", "user.name", "ECC"])?;
+        fs::write(repo.join("README.md"), "hello\n")?;
+        run_git(&repo, &["add", "README.md"])?;
+        run_git(&repo, &["commit", "-m", "init"])?;
+
+        let worktree_dir = root.join("wt-1");
+        run_git(
+            &repo,
+            &[
+                "worktree",
+                "add",
+                "-b",
+                "ecc/test",
+                worktree_dir.to_str().expect("utf8 path"),
+                "HEAD",
+            ],
+        )?;
+
+        let info = WorktreeInfo {
+            path: worktree_dir.clone(),
+            branch: "ecc/test".to_string(),
+            base_branch: "main".to_string(),
+        };
+
+        assert_eq!(diff_summary(&info)?, Some("Clean relative to main".to_string()));
+
+        fs::write(worktree_dir.join("README.md"), "hello\nmore\n")?;
+        let dirty = diff_summary(&info)?.expect("dirty summary");
+        assert!(dirty.contains("Working tree"));
+        assert!(dirty.contains("file changed"));
+
+        let _ = Command::new("git")
+            .arg("-C")
+            .arg(&repo)
+            .args(["worktree", "remove", "--force"])
+            .arg(&worktree_dir)
+            .output();
+        let _ = fs::remove_dir_all(root);
+        Ok(())
+    }
+}