cli: respect Git's core.excludesFile config (#87)

It probably doesn't make sense to respect Git's `core.excludesFile`
config when not running in a Git-backed repo, but we also already
respect `.gitignore` files in the working copy regardless of backend,
so at least it's consistent with that. We can revisit it when the
native backend becomes a reasonable choice.

Closes #87.

docs/git-compatibility.md

@@ -15,9 +15,11 @@ The following list describes which Git features Jujutsu is compatible with. For
 a comparison with Git, including how workflows are different, see the
 [Git-comparison doc](git-comparison.md).
 
-* **Configuration: No.** The only configuration from Git (e.g. in
-  `~/.gitconfig`) that's respected is the configuration of remotes. Feel free
-  to file a bug if you miss any particular configuration options.
+* **Configuration: Partial.** The only configuration from Git (e.g. in
+  `~/.gitconfig`) that's respected is the following. Feel free to file a bug if
+  you miss any particular configuration options.
+  * The configuration of remotes (`[remote "<name>"]`).
+  * `core.exludesFile`
 * **Authentication: Partial.** Only `ssh-agent` or a password-less key file at
   `~/.ssh/id_rsa` (and only at exactly that path).
 * **Branches: Yes.** You can read more about

src/commands.rs

@@ -382,13 +382,23 @@ impl WorkspaceCommandHelper {
         self.working_copy_shared_with_git
     }
 
+    fn git_config(&self) -> Result<git2::Config, git2::Error> {
+        if let Some(git_repo) = self.repo.store().git_repo() {
+            git_repo.config()
+        } else {
+            git2::Config::open_default()
+        }
+    }
+
     fn base_ignores(&self) -> Arc<GitIgnoreFile> {
         let mut git_ignores = GitIgnoreFile::empty();
-        if let Ok(home_dir) = std::env::var("HOME") {
-            let home_dir_path = PathBuf::from(home_dir);
-            // TODO: Look up the name of the file in the core.excludesFile config instead of
-            // hard-coding its name like this.
-            git_ignores = git_ignores.chain_with_file("", home_dir_path.join(".gitignore"));
+        if let Ok(excludes_file_str) = self
+            .git_config()
+            .and_then(|git_config| git_config.get_string("core.excludesFile"))
+        {
+            let excludes_file_path =
+                std::fs::canonicalize(PathBuf::from(excludes_file_str)).unwrap();
+            git_ignores = git_ignores.chain_with_file("", excludes_file_path);
         }
         if let Some(git_repo) = self.repo.store().git_repo() {
             git_ignores =

tests/test_gitignores.rs

@@ -26,21 +26,47 @@ fn test_gitignores() {
         .assert()
         .success();
 
-    // Say in .git/info/exclude that we don't want file1 and file2
+    // Say in core.excludesFiles that we don't want file1, file2, or file3
+    let mut file = std::fs::OpenOptions::new()
+        .append(true)
+        .open(workspace_root.join(".git").join("config"))
+        .unwrap();
+    let excludes_file_path = test_env
+        .env_root()
+        .join("my-ignores")
+        .to_str()
+        .unwrap()
+        .to_string();
+    file.write_all(
+        format!(
+            "[core]\nexcludesFile=\"{}\"",
+            excludes_file_path
+                .replace('\\', "\\\\")
+                .replace('\"', "\\\"")
+        )
+        .as_bytes(),
+    )
+    .unwrap();
+    drop(file);
+    std::fs::write(excludes_file_path, "file1\nfile2\nfile3").unwrap();
+
+    // Say in .git/info/exclude that we actually do want file2 and file3
     let mut file = std::fs::OpenOptions::new()
         .append(true)
         .open(workspace_root.join(".git").join("info").join("exclude"))
         .unwrap();
-    file.write_all(b"file1\nfile2").unwrap();
+    file.write_all(b"!file2\n!file3").unwrap();
     drop(file);
 
-    // Say in .gitignore (in the working copy) that we actually do want file2
-    std::fs::write(workspace_root.join(".gitignore"), "!file2").unwrap();
+    // Say in .gitignore (in the working copy) that we actually do not want file2
+    // (again)
+    std::fs::write(workspace_root.join(".gitignore"), "file2").unwrap();
 
     // Writes some files to the working copy
     std::fs::write(workspace_root.join("file0"), "contents").unwrap();
     std::fs::write(workspace_root.join("file1"), "contents").unwrap();
     std::fs::write(workspace_root.join("file2"), "contents").unwrap();
+    std::fs::write(workspace_root.join("file3"), "contents").unwrap();
 
     let assert = test_env
         .jj_cmd(&workspace_root, &["diff", "-s"])
@@ -49,6 +75,6 @@ fn test_gitignores() {
     insta::assert_snapshot!(get_stdout_string(&assert), @r###"
     A .gitignore
     A file0
-    A file2
+    A file3
     "###);
 }