cli: git push: optionally describe commits that would fail push

cli/src/commands/git/push.rs

@@ -140,6 +140,9 @@ pub struct GitPushArgs {
     /// Only display what will change on the remote
     #[arg(long)]
     dry_run: bool,
+    /// Display per-commit reasons for failed pushes
+    #[arg(long)]
+    explain_denied: bool,
 }
 
 fn make_bookmark_term(bookmark_names: &[impl fmt::Display]) -> String {
@@ -402,15 +405,33 @@ fn validate_commits_ready_to_push(
         if commit.has_conflict()? {
             reasons.push("it has conflicts");
         }
+        let mut exposition = vec![];
         if !args.allow_private && is_private(commit.id())? {
             reasons.push("it is private");
+
+            if args.explain_denied {
+                exposition.push(format!(
+                    "commit {}, description: '{}'",
+                    short_commit_hash(commit.id()),
+                    commit
+                        .description()
+                        .lines()
+                        .next()
+                        .expect("commit should have at least one line with private description")
+                ));
+            }
         }
         if !reasons.is_empty() {
-            return Err(user_error(format!(
+            let mut message = format!(
                 "Won't push commit {} since {}",
                 short_commit_hash(commit.id()),
                 reasons.join(" and ")
-            )));
+            );
+            if args.explain_denied {
+                message.push('\n');
+                message.push_str(&exposition.join("\n"));
+            }
+            return Err(user_error(message));
         }
     }
     Ok(())

cli/tests/test_git_private_commits.rs

@@ -104,6 +104,25 @@ fn test_git_private_commits_block_pushing() {
     "#);
 }
 
+#[test]
+fn test_git_private_commits_block_pushing_with_explanation() {
+    let (test_env, workspace_root) = set_up();
+
+    test_env.jj_cmd_ok(&workspace_root, &["new", "main", "-m=private 1"]);
+    test_env.jj_cmd_ok(&workspace_root, &["bookmark", "set", "main"]);
+
+    // Will not push when a pushed commit is contained in git.private-commits
+    test_env.add_config(r#"git.private-commits = "description(glob:'private*')""#);
+    let stderr = test_env.jj_cmd_failure(
+        &workspace_root,
+        &["git", "push", "--all", "--explain-failed"],
+    );
+    insta::assert_snapshot!(stderr, @r###"
+    Error: Won't push commit aa3058ff8663 since it is private
+    commit aa3058ff8663, description: 'private 1'
+    "###);
+}
+
 #[test]
 fn test_git_private_commits_can_be_overridden() {
     let (test_env, workspace_root) = set_up();