config: deprecate macOS legacy platform configs

CHANGELOG.md

@@ -36,6 +36,10 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   [`templates.draft_commit_description`](docs/config.md#default-description),
   and/or [`templates.commit_trailers`](docs/config.md#commit-trailers).
 
+* On macOS, config.toml files in `~/Library/Application Support/jj` are
+  deprecated; one should instead use `$XDG_CONFIG_HOME/jj`
+  (defaults to `~/.config/jj`)
+
 ### New features
 
 * Color-words diff has gained [an option to compare conflict pairs without

cli/src/cli_util.rs

@@ -3873,7 +3873,7 @@ impl<'a> CliRunner<'a> {
                     "Did you update to a commit where the directory doesn't exist?",
                 )
             })?;
-        let mut config_env = ConfigEnv::from_environment();
+        let mut config_env = ConfigEnv::from_environment(ui);
         let mut last_config_migration_descriptions = Vec::new();
         let mut migrate_config = |config: &mut StackedConfig| -> Result<(), CommandError> {
             last_config_migration_descriptions =

cli/src/complete.rs

@@ -838,7 +838,7 @@ fn get_jj_command() -> Result<(JjBuilder, UserSettings), CommandError> {
         .and_then(dunce::canonicalize)
         .map_err(user_error)?;
     // No config migration for completion. Simply ignore deprecated variables.
-    let mut config_env = ConfigEnv::from_environment();
+    let mut config_env = ConfigEnv::from_environment(&ui);
     let maybe_cwd_workspace_loader = DefaultWorkspaceLoaderFactory.create(find_workspace_dir(&cwd));
     let _ = config_env.reload_user_config(&mut raw_config);
     if let Ok(loader) = &maybe_cwd_workspace_loader {

cli/src/config.rs

@@ -43,6 +43,7 @@ use crate::command_error::config_error;
 use crate::command_error::config_error_with_message;
 use crate::command_error::CommandError;
 use crate::text_util;
+use crate::ui::Ui;
 
 // TODO(#879): Consider generating entire schema dynamically vs. static file.
 pub const CONFIG_SCHEMA: &str = include_str!("config-schema.json");
@@ -192,7 +193,6 @@ impl ConfigPath {
     fn as_path(&self) -> &Path {
         &self.path
     }
-
     fn exists(&self) -> bool {
         match self.state {
             ConfigPathState::Exists => true,
@@ -218,13 +218,14 @@ fn create_dir_all(path: &Path) -> std::io::Result<()> {
 #[derive(Clone, Default, Debug)]
 struct UnresolvedConfigEnv {
     config_dir: Option<PathBuf>,
+    // TODO: remove after jj 0.35
     macos_legacy_config_dir: Option<PathBuf>,
     home_dir: Option<PathBuf>,
     jj_config: Option<String>,
 }
 
 impl UnresolvedConfigEnv {
-    fn resolve(self) -> Vec<ConfigPath> {
+    fn resolve(self, ui: &Ui) -> Vec<ConfigPath> {
         if let Some(paths) = self.jj_config {
             return split_paths(&paths)
                 .filter(|path| !path.as_os_str().is_empty())
@@ -283,17 +284,41 @@ impl UnresolvedConfigEnv {
 
         if let Some(path) = legacy_platform_config_path {
             if path.exists() {
+                Self::warn_for_deprecated_path(
+                    ui,
+                    path.as_path(),
+                    "~/Library/Application Support",
+                    "~/.config",
+                );
                 paths.push(path);
             }
         }
         if let Some(path) = legacy_platform_config_dir {
             if path.exists() {
+                Self::warn_for_deprecated_path(
+                    ui,
+                    path.as_path(),
+                    "~/Library/Application Support",
+                    "~/.config",
+                );
                 paths.push(path);
             }
         }
 
         paths
     }
+
+    fn warn_for_deprecated_path(ui: &Ui, path: &Path, old: &str, new: &str) {
+        let _ = indoc::writedoc!(
+            ui.warning_default(),
+            r"
+            Deprecated configuration file `{}`.
+            Configuration files in `{old}` are deprecated, and support will be removed in a future release.
+            Instead, move your configuration files to `{new}`.
+            ",
+            path.display(),
+        );
+    }
 }
 
 #[derive(Clone, Debug)]
@@ -307,7 +332,7 @@ pub struct ConfigEnv {
 
 impl ConfigEnv {
     /// Initializes configuration loader based on environment variables.
-    pub fn from_environment() -> Self {
+    pub fn from_environment(ui: &Ui) -> Self {
         let config_dir = etcetera::choose_base_strategy()
             .ok()
             .map(|s| s.config_dir());
@@ -341,7 +366,7 @@ impl ConfigEnv {
         ConfigEnv {
             home_dir,
             repo_path: None,
-            user_config_paths: env.resolve(),
+            user_config_paths: env.resolve(ui),
             repo_config_path: None,
             command: None,
         }
@@ -1727,7 +1752,7 @@ mod tests {
         ConfigEnv {
             home_dir,
             repo_path: None,
-            user_config_paths: env.resolve(),
+            user_config_paths: env.resolve(&Ui::null()),
             repo_config_path: None,
             command: None,
         }