cli: add jj config unset

Allow unsetting config values similar to `git config unset`.

```bash
$ jj config set --user some-key some-val
$ jj config get some-key
some-val
$ jj config unset --user some-key
$ jj config get some-key
Config error: configuration property "some-key" not found
For help, see https://martinvonz.github.io/jj/latest/config/.
```

Unsetting a key, which is part of a table, might leave that table empty.
For now we do not delete such empty tables, as there may be cases where
an empty table is semantically meaningful
(#4458 (comment)).

For example:

```toml
[table]
key = "value"

[another-table]
key = "value"
```

Running `jj config unset --user table.key` will leave us with `table`
being empty:
```toml
[table]

[another-table]
key = "value"
```

CHANGELOG.md

@@ -78,6 +78,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 * Add a new template alias `bultin_log_compact_full_description()`.
 
+* New command `jj config unset` that unsets config values. For example,
+  `jj config unset --user user.name`.
+
 ### Fixed bugs
 
 * Error on `trunk()` revset resolution is now handled gracefully.

cli/src/commands/config/mod.rs

@@ -17,6 +17,7 @@ mod get;
 mod list;
 mod path;
 mod set;
+mod unset;
 
 use tracing::instrument;
 
@@ -30,6 +31,8 @@ use self::path::cmd_config_path;
 use self::path::ConfigPathArgs;
 use self::set::cmd_config_set;
 use self::set::ConfigSetArgs;
+use self::unset::cmd_config_unset;
+use self::unset::ConfigUnsetArgs;
 use crate::cli_util::CommandHelper;
 use crate::command_error::CommandError;
 use crate::config::ConfigSource;
@@ -82,6 +85,8 @@ pub(crate) enum ConfigCommand {
     Path(ConfigPathArgs),
     #[command(visible_alias("s"))]
     Set(ConfigSetArgs),
+    #[command(visible_alias("u"))]
+    Unset(ConfigUnsetArgs),
 }
 
 #[instrument(skip_all)]
@@ -96,5 +101,6 @@ pub(crate) fn cmd_config(
         ConfigCommand::List(args) => cmd_config_list(ui, command, args),
         ConfigCommand::Path(args) => cmd_config_path(ui, command, args),
         ConfigCommand::Set(args) => cmd_config_set(ui, command, args),
+        ConfigCommand::Unset(args) => cmd_config_unset(ui, command, args),
     }
 }

cli/src/commands/config/unset.rs

@@ -0,0 +1,50 @@
+// Copyright 2024 The Jujutsu Authors
+//
+// 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 tracing::instrument;
+
+use super::ConfigLevelArgs;
+use crate::cli_util::get_new_config_file_path;
+use crate::cli_util::CommandHelper;
+use crate::command_error::user_error;
+use crate::command_error::CommandError;
+use crate::config::remove_config_value_from_file;
+use crate::config::ConfigNamePathBuf;
+use crate::ui::Ui;
+
+/// Update config file to unset the given option.
+#[derive(clap::Args, Clone, Debug)]
+pub struct ConfigUnsetArgs {
+    #[arg(required = true)]
+    name: ConfigNamePathBuf,
+    #[command(flatten)]
+    level: ConfigLevelArgs,
+}
+
+#[instrument(skip_all)]
+pub fn cmd_config_unset(
+    _ui: &mut Ui,
+    command: &CommandHelper,
+    args: &ConfigUnsetArgs,
+) -> Result<(), CommandError> {
+    let config_path = get_new_config_file_path(&args.level.expect_source_kind(), command)?;
+    if config_path.is_dir() {
+        return Err(user_error(format!(
+            "Can't set config in path {path} (dirs not supported)",
+            path = config_path.display()
+        )));
+    }
+
+    remove_config_value_from_file(&args.name, &config_path)
+}

cli/src/config.rs

@@ -648,6 +648,34 @@ pub fn write_config_value_to_file(
     write_config(path, &doc)
 }
 
+pub fn remove_config_value_from_file(
+    key: &ConfigNamePathBuf,
+    path: &Path,
+) -> Result<(), CommandError> {
+    let mut doc = read_config(path)?;
+
+    // Find target table
+    let mut key_iter = key.components();
+    let last_key = key_iter.next_back().expect("key must not be empty");
+    let target_table = key_iter.try_fold(doc.as_table_mut(), |table, key| {
+        table
+            .get_mut(key)
+            .ok_or_else(|| config::ConfigError::NotFound(key.to_string()))
+            .and_then(|table| {
+                table.as_table_mut().ok_or_else(|| {
+                    config::ConfigError::Message(format!(r#""{key}" is not a table"#))
+                })
+            })
+    })?;
+
+    // Remove config value
+    target_table
+        .remove(last_key)
+        .ok_or_else(|| config::ConfigError::NotFound(key.to_string()))?;
+
+    write_config(path, &doc)
+}
+
 /// Command name and arguments specified by config.
 #[derive(Clone, Debug, Eq, PartialEq, serde::Deserialize)]
 #[serde(untagged)]

cli/tests/cli-reference@.md.snap

@@ -30,6 +30,7 @@ This document contains the help content for the `jj` command-line program.
 * [`jj config list`↴](#jj-config-list)
 * [`jj config path`↴](#jj-config-path)
 * [`jj config set`↴](#jj-config-set)
+* [`jj config unset`↴](#jj-config-unset)
 * [`jj describe`↴](#jj-describe)
 * [`jj diff`↴](#jj-diff)
 * [`jj diffedit`↴](#jj-diffedit)
@@ -479,6 +480,7 @@ For file locations, supported config options, and other details about jj config,
 * `list` — List variables set in config file, along with their values
 * `path` — Print the path to the config file
 * `set` — Update config file to set the given option to a given value
+* `unset` — Update config file to unset the given option
 
 
 
@@ -580,6 +582,23 @@ Update config file to set the given option to a given value
 
 
 
+## `jj config unset`
+
+Update config file to unset the given option
+
+**Usage:** `jj config unset <--user|--repo> <NAME>`
+
+###### **Arguments:**
+
+* `<NAME>`
+
+###### **Options:**
+
+* `--user` — Target the user-level config
+* `--repo` — Target the repo-level config
+
+
+
 ## `jj describe`
 
 Update the change description or other metadata

cli/tests/test_config_command.rs

@@ -602,6 +602,93 @@ fn test_config_set_nontable_parent() {
     "###);
 }
 
+#[test]
+fn test_config_unset_non_existent_key() {
+    let mut test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
+    // Point to a config file since `config set` can't handle directories.
+    let user_config_path = test_env.config_path().join("config.toml");
+    test_env.set_config_path(user_config_path);
+    let repo_path = test_env.env_root().join("repo");
+
+    let stderr = test_env.jj_cmd_failure(&repo_path, &["config", "unset", "--user", "nonexistent"]);
+    insta::assert_snapshot!(stderr, @r###"
+    Config error: configuration property "nonexistent" not found
+    For help, see https://martinvonz.github.io/jj/latest/config/.
+    "###);
+}
+
+#[test]
+fn test_config_unset_inline_table_key() {
+    let mut test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
+    // Point to a config file since `config set` can't handle directories.
+    let user_config_path = test_env.config_path().join("config.toml");
+    test_env.set_config_path(user_config_path.clone());
+    let repo_path = test_env.env_root().join("repo");
+
+    test_env.jj_cmd_ok(
+        &repo_path,
+        &["config", "set", "--user", "inline-table", "{ foo = true }"],
+    );
+    let stderr = test_env.jj_cmd_failure(
+        &repo_path,
+        &["config", "unset", "--user", "inline-table.foo"],
+    );
+
+    insta::assert_snapshot!(stderr, @r###"
+    Config error: "inline-table" is not a table
+    For help, see https://martinvonz.github.io/jj/latest/config/.
+    "###);
+}
+
+#[test]
+fn test_config_unset_for_user() {
+    let mut test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
+    // Point to a config file since `config set` can't handle directories.
+    let user_config_path = test_env.config_path().join("config.toml");
+    test_env.set_config_path(user_config_path.clone());
+    let repo_path = test_env.env_root().join("repo");
+
+    test_env.jj_cmd_ok(&repo_path, &["config", "set", "--user", "foo", "true"]);
+    test_env.jj_cmd_ok(&repo_path, &["config", "unset", "--user", "foo"]);
+
+    test_env.jj_cmd_ok(
+        &repo_path,
+        &["config", "set", "--user", "table.foo", "true"],
+    );
+    test_env.jj_cmd_ok(&repo_path, &["config", "unset", "--user", "table.foo"]);
+
+    test_env.jj_cmd_ok(
+        &repo_path,
+        &["config", "set", "--user", "table.inline", "{ foo = true }"],
+    );
+    test_env.jj_cmd_ok(&repo_path, &["config", "unset", "--user", "table.inline"]);
+
+    let user_config_toml = std::fs::read_to_string(&user_config_path).unwrap();
+    insta::assert_snapshot!(user_config_toml, @r#"
+        [table]
+        "#);
+}
+
+#[test]
+fn test_config_unset_for_repo() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    test_env.jj_cmd_ok(
+        &repo_path,
+        &["config", "set", "--repo", "test-key", "test-val"],
+    );
+    test_env.jj_cmd_ok(&repo_path, &["config", "unset", "--repo", "test-key"]);
+
+    let repo_config_path = repo_path.join(".jj/repo/config.toml");
+    let repo_config_toml = std::fs::read_to_string(&repo_config_path).unwrap();
+    insta::assert_snapshot!(repo_config_toml, @"");
+}
+
 #[test]
 fn test_config_edit_missing_opt() {
     let test_env = TestEnvironment::default();