cli: when export to git fails, report failed branches

This adds a warning whenever export to the backing Git repo fails,
whether it's by an explicit `jj git export` or an automatic export. It
might be too spammy to print the message after every failed command in
the colocated case, but let's try it and see.

CHANGELOG.md

@@ -71,6 +71,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   some additional insight into what is happening behind the scenes. 
   Note: This is not comprehensively supported by all operations yet.
 
+* (#493) When exporting branches to Git, we used to fail if some branches could
+  not be exported (e.g. because Git doesn't allow a branch called `main` and
+  another branch called `main/sub`). We now print a warning about these branches
+  instead.
+
 ### Fixed bugs
 
 * (#463) A bug in the export of branches to Git caused spurious conflicted

src/cli_util.rs

@@ -839,7 +839,8 @@ impl WorkspaceCommandHelper {
         if self.working_copy_shared_with_git {
             self.export_head_to_git(mut_repo)?;
             let git_repo = self.repo.store().git_repo().unwrap();
-            git::export_refs(mut_repo, &git_repo)?;
+            let failed_branches = git::export_refs(mut_repo, &git_repo)?;
+            print_failed_git_export(ui, &failed_branches)?;
         }
         let maybe_old_commit = tx
             .base_repo()
@@ -883,6 +884,22 @@ pub fn print_checkout_stats(ui: &mut Ui, stats: CheckoutStats) -> Result<(), std
     Ok(())
 }
 
+pub fn print_failed_git_export(
+    ui: &mut Ui,
+    failed_branches: &[String],
+) -> Result<(), std::io::Error> {
+    if !failed_branches.is_empty() {
+        ui.write_warn("Failed to export some branches:\n")?;
+        let mut formatter = ui.stderr_formatter();
+        for branch_name in failed_branches {
+            formatter.write_str("  ")?;
+            formatter.with_label("branch", |formatter| formatter.write_str(branch_name))?;
+            formatter.write_str("\n")?;
+        }
+    }
+    Ok(())
+}
+
 /// Expands "~/" to "$HOME/" as Git seems to do for e.g. core.excludesFile.
 fn expand_git_path(path_str: String) -> PathBuf {
     if let Some(remainder) = path_str.strip_prefix("~/") {

src/commands.rs

@@ -53,9 +53,9 @@ use maplit::{hashmap, hashset};
 use pest::Parser;
 
 use crate::cli_util::{
-    print_checkout_stats, resolve_base_revs, short_commit_description, short_commit_hash,
-    user_error, user_error_with_hint, write_commit_summary, Args, CommandError, CommandHelper,
-    WorkspaceCommandHelper,
+    print_checkout_stats, print_failed_git_export, resolve_base_revs, short_commit_description,
+    short_commit_hash, user_error, user_error_with_hint, write_commit_summary, Args, CommandError,
+    CommandHelper, WorkspaceCommandHelper,
 };
 use crate::formatter::{Formatter, PlainTextFormatter};
 use crate::graphlog::{AsciiGraphDrawer, Edge};
@@ -4542,8 +4542,9 @@ fn cmd_git_export(
     let repo = workspace_command.repo();
     let git_repo = get_git_repo(repo.store())?;
     let mut tx = workspace_command.start_transaction("export git refs");
-    git::export_refs(tx.mut_repo(), &git_repo)?;
+    let failed_branches = git::export_refs(tx.mut_repo(), &git_repo)?;
     workspace_command.finish_transaction(ui, tx)?;
+    print_failed_git_export(ui, &failed_branches)?;
     Ok(())
 }
 

tests/test_git_colocated.rs

@@ -16,7 +16,7 @@ use std::path::Path;
 
 use git2::Oid;
 
-use crate::common::TestEnvironment;
+use crate::common::{get_stderr_string, TestEnvironment};
 
 pub mod common;
 
@@ -178,6 +178,42 @@ fn test_git_colocated_branches() {
     "###);
 }
 
+#[test]
+fn test_git_colocated_conflicting_git_refs() {
+    let test_env = TestEnvironment::default();
+    let workspace_root = test_env.env_root().join("repo");
+    git2::Repository::init(&workspace_root).unwrap();
+    test_env.jj_cmd_success(&workspace_root, &["init", "--git-repo", "."]);
+    let assert = test_env
+        .jj_cmd(&workspace_root, &["branch", "create", ""])
+        .assert()
+        .success()
+        .stdout("");
+    insta::assert_snapshot!(get_stderr_string(&assert), @r###"
+    Failed to export some branches:
+      
+    "###);
+    let assert = test_env
+        .jj_cmd(&workspace_root, &["branch", "create", "main"])
+        .assert()
+        .success()
+        .stdout("");
+    insta::assert_snapshot!(get_stderr_string(&assert), @r###"
+    Failed to export some branches:
+      
+    "###);
+    let assert = test_env
+        .jj_cmd(&workspace_root, &["branch", "create", "main/sub"])
+        .assert()
+        .success()
+        .stdout("");
+    insta::assert_snapshot!(get_stderr_string(&assert), @r###"
+    Failed to export some branches:
+      
+      main/sub
+    "###);
+}
+
 fn get_log_output(test_env: &TestEnvironment, workspace_root: &Path) -> String {
     test_env.jj_cmd_success(workspace_root, &["log", "-T", "commit_id \" \" branches"])
 }

tests/test_git_export.rs

@@ -0,0 +1,39 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use crate::common::{get_stderr_string, TestEnvironment};
+
+pub mod common;
+
+#[test]
+fn test_git_export_conflicting_git_refs() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    // TODO: Make it an error to try to create a branch with an empty name
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", ""]);
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", "main"]);
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", "main/sub"]);
+    let assert = test_env
+        .jj_cmd(&repo_path, &["git", "export"])
+        .assert()
+        .success()
+        .stdout("");
+    insta::assert_snapshot!(get_stderr_string(&assert), @r###"
+    Failed to export some branches:
+      
+      main/sub
+    "###);
+}