completion: teach config about keys

There are two known limitations right now:

- Only statically known keys are suggested.

- Keys that the user did not set are still suggested for `jj config get`.
  Running that suggestion may result in an error. The error message will be
  appropriate though and there is some value in letting the user know that
  this config value theoretically exists. Some users may try to explore what
  configurations are available via the completions.

cli/Cargo.toml

@@ -80,6 +80,7 @@ rpassword = { workspace = true }
 sapling-renderdag = { workspace = true }
 scm-record = { workspace = true }
 serde = { workspace = true }
+serde_json = { workspace = true }
 slab = { workspace = true }
 strsim = { workspace = true }
 tempfile = { workspace = true }

cli/src/commands/config/get.rs

@@ -14,11 +14,13 @@
 
 use std::io::Write as _;
 
+use clap_complete::ArgValueCandidates;
 use tracing::instrument;
 
 use crate::cli_util::CommandHelper;
 use crate::command_error::config_error;
 use crate::command_error::CommandError;
+use crate::complete;
 use crate::config::ConfigNamePathBuf;
 use crate::ui::Ui;
 
@@ -34,7 +36,7 @@ use crate::ui::Ui;
 #[derive(clap::Args, Clone, Debug)]
 #[command(verbatim_doc_comment)]
 pub struct ConfigGetArgs {
-    #[arg(required = true)]
+    #[arg(required = true, add = ArgValueCandidates::new(complete::leaf_config_keys))]
     name: ConfigNamePathBuf,
 }
 

cli/src/commands/config/list.rs

@@ -12,11 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use clap_complete::ArgValueCandidates;
 use tracing::instrument;
 
 use super::ConfigLevelArgs;
 use crate::cli_util::CommandHelper;
 use crate::command_error::CommandError;
+use crate::complete;
 use crate::config::to_toml_value;
 use crate::config::AnnotatedValue;
 use crate::config::ConfigNamePathBuf;
@@ -31,6 +33,7 @@ use crate::ui::Ui;
 #[command(mut_group("config_level", |g| g.required(false)))]
 pub struct ConfigListArgs {
     /// An optional name of a specific config option to look up.
+    #[arg(add = ArgValueCandidates::new(complete::config_keys))]
     pub name: Option<ConfigNamePathBuf>,
     /// Whether to explicitly include built-in default values in the list.
     #[arg(long, conflicts_with = "config_level")]

cli/src/commands/config/set.rs

@@ -14,6 +14,7 @@
 
 use std::io;
 
+use clap_complete::ArgValueCandidates;
 use jj_lib::commit::Commit;
 use jj_lib::repo::Repo;
 use tracing::instrument;
@@ -24,6 +25,7 @@ use crate::cli_util::CommandHelper;
 use crate::cli_util::WorkspaceCommandHelper;
 use crate::command_error::user_error;
 use crate::command_error::CommandError;
+use crate::complete;
 use crate::config::parse_toml_value_or_bare_string;
 use crate::config::write_config_value_to_file;
 use crate::config::ConfigNamePathBuf;
@@ -32,7 +34,7 @@ use crate::ui::Ui;
 /// Update config file to set the given option to a given value.
 #[derive(clap::Args, Clone, Debug)]
 pub struct ConfigSetArgs {
-    #[arg(required = true)]
+    #[arg(required = true, add = ArgValueCandidates::new(complete::leaf_config_keys))]
     name: ConfigNamePathBuf,
     #[arg(required = true)]
     value: String,

cli/src/commands/config/unset.rs

@@ -12,21 +12,23 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use clap_complete::ArgValueCandidates;
 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::complete;
 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)]
+    #[arg(required = true, add = ArgValueCandidates::new(complete::leaf_config_keys))]
     name: ConfigNamePathBuf,
     #[command(flatten)]
     level: ConfigLevelArgs,

cli/src/commands/util/config_schema.rs

@@ -16,6 +16,7 @@ use std::io::Write as _;
 
 use crate::cli_util::CommandHelper;
 use crate::command_error::CommandError;
+use crate::config::CONFIG_SCHEMA;
 use crate::ui::Ui;
 
 /// Print the JSON schema for the jj TOML config format.
@@ -27,8 +28,6 @@ pub fn cmd_util_config_schema(
     _command: &CommandHelper,
     _args: &UtilConfigSchemaArgs,
 ) -> Result<(), CommandError> {
-    // TODO(#879): Consider generating entire schema dynamically vs. static file.
-    let buf = include_bytes!("../../config-schema.json");
-    ui.stdout().write_all(buf)?;
+    ui.stdout().write_all(CONFIG_SCHEMA.as_bytes())?;
     Ok(())
 }

cli/src/complete.rs

@@ -26,7 +26,9 @@ use crate::cli_util::GlobalArgs;
 use crate::command_error::user_error;
 use crate::command_error::CommandError;
 use crate::config::default_config;
+use crate::config::ConfigNamePathBuf;
 use crate::config::LayeredConfigs;
+use crate::config::CONFIG_SCHEMA;
 use crate::ui::Ui;
 
 const BOOKMARK_HELP_TEMPLATE: &str = r#"
@@ -292,6 +294,66 @@ pub fn workspaces() -> Vec<CompletionCandidate> {
     })
 }
 
+fn config_keys_rec(
+    prefix: ConfigNamePathBuf,
+    properties: &serde_json::Map<String, serde_json::Value>,
+    acc: &mut Vec<CompletionCandidate>,
+    only_leaves: bool,
+) {
+    for (key, value) in properties {
+        let mut prefix = prefix.clone();
+        prefix.push(key);
+
+        let value = value.as_object().unwrap();
+        match value.get("type").and_then(|v| v.as_str()) {
+            Some("object") => {
+                if !only_leaves {
+                    let help = value
+                        .get("description")
+                        .map(|desc| desc.as_str().unwrap().to_string().into());
+                    let escaped_key = prefix.to_string();
+                    acc.push(CompletionCandidate::new(escaped_key).help(help));
+                }
+                let Some(properties) = value.get("properties") else {
+                    continue;
+                };
+                let properties = properties.as_object().unwrap();
+                config_keys_rec(prefix, properties, acc, only_leaves);
+            }
+            _ => {
+                let help = value
+                    .get("description")
+                    .map(|desc| desc.as_str().unwrap().to_string().into());
+                let escaped_key = prefix.to_string();
+                acc.push(CompletionCandidate::new(escaped_key).help(help));
+            }
+        }
+    }
+}
+
+fn config_keys_impl(only_leaves: bool) -> Vec<CompletionCandidate> {
+    let schema: serde_json::Value = serde_json::from_str(CONFIG_SCHEMA).unwrap();
+    let schema = schema.as_object().unwrap();
+    let properties = schema["properties"].as_object().unwrap();
+
+    let mut candidates = Vec::new();
+    config_keys_rec(
+        ConfigNamePathBuf::root(),
+        properties,
+        &mut candidates,
+        only_leaves,
+    );
+    candidates
+}
+
+pub fn config_keys() -> Vec<CompletionCandidate> {
+    config_keys_impl(false)
+}
+
+pub fn leaf_config_keys() -> Vec<CompletionCandidate> {
+    config_keys_impl(true)
+}
+
 /// Shell out to jj during dynamic completion generation
 ///
 /// In case of errors, print them and early return an empty vector.
@@ -402,3 +464,14 @@ fn get_jj_command() -> Result<(std::process::Command, Config), CommandError> {
 
     Ok((cmd, config))
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_config_keys() {
+        // Just make sure the schema is parsed without failure.
+        let _ = config_keys();
+    }
+}

cli/src/config.rs

@@ -35,6 +35,9 @@ use crate::command_error::user_error;
 use crate::command_error::user_error_with_message;
 use crate::command_error::CommandError;
 
+// TODO(#879): Consider generating entire schema dynamically vs. static file.
+pub const CONFIG_SCHEMA: &str = include_str!("config-schema.json");
+
 /// Parses a TOML value expression. Interprets the given value as string if it
 /// can't be parsed.
 pub fn parse_toml_value_or_bare_string(value_str: &str) -> toml_edit::Value {

cli/tests/test_completion.rs

@@ -472,3 +472,25 @@ fn test_workspaces() {
     default	initial
     ");
 }
+
+#[test]
+fn test_config() {
+    let mut test_env = TestEnvironment::default();
+    test_env.add_env_var("COMPLETE", "fish");
+    let dir = test_env.env_root();
+
+    let stdout = test_env.jj_cmd_success(dir, &["--", "jj", "config", "get", "c"]);
+    insta::assert_snapshot!(stdout, @r"
+    core.fsmonitor	Whether to use an external filesystem monitor, useful for large repos
+    core.watchman.register_snapshot_trigger	Whether to use triggers to monitor for changes in the background.
+    ");
+
+    let stdout = test_env.jj_cmd_success(dir, &["--", "jj", "config", "list", "c"]);
+    insta::assert_snapshot!(stdout, @r"
+    colors	Mapping from jj formatter labels to colors
+    core
+    core.fsmonitor	Whether to use an external filesystem monitor, useful for large repos
+    core.watchman
+    core.watchman.register_snapshot_trigger	Whether to use triggers to monitor for changes in the background.
+    ");
+}