settings: add helper to turn ConfigError::NotFound into Option

Now we have 4 callers, I concluded this is common enough to add an
extension method. Still I think it's preferred to define config items in
src/config/*.toml if possible. It will catch typo of config keys.

lib/src/settings.rs

@@ -198,3 +198,17 @@ impl JJRng {
         }
     }
 }
+
+pub trait ConfigResultExt<T> {
+    fn optional(self) -> Result<Option<T>, config::ConfigError>;
+}
+
+impl<T> ConfigResultExt<T> for Result<T, config::ConfigError> {
+    fn optional(self) -> Result<Option<T>, config::ConfigError> {
+        match self {
+            Ok(value) => Ok(Some(value)),
+            Err(config::ConfigError::NotFound(_)) => Ok(None),
+            Err(err) => Err(err),
+        }
+    }
+}

src/commands/git.rs

@@ -7,14 +7,13 @@ use std::sync::Mutex;
 use std::time::Instant;
 
 use clap::{ArgGroup, Subcommand};
-use config::ConfigError;
 use itertools::Itertools;
 use jujutsu_lib::backend::ObjectId;
 use jujutsu_lib::git::{self, GitFetchError, GitPushError, GitRefUpdate};
 use jujutsu_lib::op_store::{BranchTarget, RefTarget};
 use jujutsu_lib::refs::{classify_branch_push_action, BranchPushAction, BranchPushUpdate};
 use jujutsu_lib::repo::Repo;
-use jujutsu_lib::settings::UserSettings;
+use jujutsu_lib::settings::{ConfigResultExt as _, UserSettings};
 use jujutsu_lib::store::Store;
 use jujutsu_lib::view::View;
 use jujutsu_lib::workspace::Workspace;
@@ -341,27 +340,22 @@ fn get_default_fetch_remotes(
 ) -> Result<Vec<String>, CommandError> {
     const KEY: &str = "git.fetch";
     let config = command.settings().config();
-
-    match config
-        .get(KEY)
-        .or_else(|_| config.get_string(KEY).map(|r| vec![r]))
-    {
+    if let Ok(remotes) = config.get(KEY) {
+        Ok(remotes)
+    } else if let Some(remote) = config.get_string(KEY).optional()? {
+        Ok(vec![remote])
+    } else if let Some(remote) = get_single_remote(git_repo)? {
         // if nothing was explicitly configured, try to guess
-        Err(ConfigError::NotFound(_)) => {
-            if let Some(remote) = get_single_remote(git_repo)? {
-                if remote != DEFAULT_REMOTE {
-                    writeln!(
-                        ui.hint(),
-                        "Fetching from the only existing remote: {}",
-                        remote
-                    )?;
-                }
-                Ok(vec![remote])
-            } else {
-                Ok(vec![DEFAULT_REMOTE.to_owned()])
-            }
+        if remote != DEFAULT_REMOTE {
+            writeln!(
+                ui.hint(),
+                "Fetching from the only existing remote: {}",
+                remote
+            )?;
         }
-        r => Ok(r?),
+        Ok(vec![remote])
+    } else {
+        Ok(vec![DEFAULT_REMOTE.to_owned()])
     }
 }
 
@@ -928,19 +922,17 @@ fn get_default_push_remote(
     command: &CommandHelper,
     git_repo: &git2::Repository,
 ) -> Result<String, CommandError> {
-    match command.settings().config().get_string("git.push") {
+    let config = command.settings().config();
+    if let Some(remote) = config.get_string("git.push").optional()? {
+        Ok(remote)
+    } else if let Some(remote) = get_single_remote(git_repo)? {
         // similar to get_default_fetch_remotes
-        Err(ConfigError::NotFound(_)) => {
-            if let Some(remote) = get_single_remote(git_repo)? {
-                if remote != DEFAULT_REMOTE {
-                    writeln!(ui.hint(), "Pushing to the only existing remote: {}", remote)?;
-                }
-                Ok(remote)
-            } else {
-                Ok(DEFAULT_REMOTE.to_owned())
-            }
+        if remote != DEFAULT_REMOTE {
+            writeln!(ui.hint(), "Pushing to the only existing remote: {}", remote)?;
         }
-        r => Ok(r?),
+        Ok(remote)
+    } else {
+        Ok(DEFAULT_REMOTE.to_owned())
     }
 }
 

src/config.rs

@@ -20,6 +20,7 @@ use std::{env, fmt};
 
 use config::Source;
 use itertools::Itertools;
+use jujutsu_lib::settings::ConfigResultExt as _;
 use thiserror::Error;
 
 #[derive(Error, Debug)]
@@ -144,10 +145,13 @@ impl LayeredConfigs {
         };
         for (source, config) in self.sources() {
             let top_value = match prefix_key {
-                Some(ref key) => match config.get(key) {
-                    Err(config::ConfigError::NotFound { .. }) => continue,
-                    val => val?,
-                },
+                Some(ref key) => {
+                    if let Some(val) = config.get(key).optional()? {
+                        val
+                    } else {
+                        continue;
+                    }
+                }
                 None => config.collect()?.into(),
             };
             let mut config_stack: Vec<(Vec<&str>, &config::Value)> =

src/merge_tools.rs

@@ -29,7 +29,7 @@ use jujutsu_lib::conflicts::{
 use jujutsu_lib::gitignore::GitIgnoreFile;
 use jujutsu_lib::matchers::EverythingMatcher;
 use jujutsu_lib::repo_path::RepoPath;
-use jujutsu_lib::settings::UserSettings;
+use jujutsu_lib::settings::{ConfigResultExt as _, UserSettings};
 use jujutsu_lib::store::Store;
 use jujutsu_lib::tree::Tree;
 use jujutsu_lib::working_copy::{CheckoutError, SnapshotError, TreeState};
@@ -507,17 +507,15 @@ fn editor_args_from_settings(
 ) -> Result<CommandNameAndArgs, ExternalToolError> {
     // TODO: Make this configuration have a table of possible editors and detect the
     // best one here.
-    match settings.config().get::<CommandNameAndArgs>(key) {
-        Ok(args) => Ok(args),
-        Err(config::ConfigError::NotFound(_)) => {
-            let default_editor = "meld";
-            writeln!(
-                ui.hint(),
-                "Using default editor '{default_editor}'; you can change this by setting {key}"
-            )?;
-            Ok(default_editor.into())
-        }
-        Err(err) => Err(err.into()),
+    if let Some(args) = settings.config().get(key).optional()? {
+        Ok(args)
+    } else {
+        let default_editor = "meld";
+        writeln!(
+            ui.hint(),
+            "Using default editor '{default_editor}'; you can change this by setting {key}"
+        )?;
+        Ok(default_editor.into())
     }
 }