Make the Rust implementation the only one: crate at the root, Go tree removed

src/config.rs

@@ -0,0 +1,75 @@
+//! User settings from a JSON file in the OS-specific user configuration
+//! directory. Knows nothing about rendering.
+
+use crate::brand;
+use serde::Deserialize;
+use std::collections::HashMap;
+use std::path::PathBuf;
+
+/// User preferences. Load starts from the defaults and overlays the file.
+#[derive(Clone, Debug, Deserialize)]
+#[serde(default)]
+pub struct Settings {
+    pub workers: String,         // conservative|balanced|aggressive|N
+    pub follow_symlinks: String, // none|same-filesystem|all
+    pub one_file_system: bool,
+    pub units: String,     // iec|si
+    pub size_mode: String, // allocated|logical
+    pub theme: String,
+    pub mouse: bool,
+    pub excludes: Vec<String>,
+    /// Maps an extension (without dot) to "#rrggbb".
+    pub extension_colors: HashMap<String, String>,
+    /// Maps a category name to "#rrggbb".
+    pub category_colors: HashMap<String, String>,
+    /// UI refresh rate while scanning.
+    pub refresh_hz: i64,
+}
+
+impl Default for Settings {
+    fn default() -> Self {
+        Settings {
+            workers: "balanced".into(),
+            follow_symlinks: "none".into(),
+            one_file_system: false,
+            units: "iec".into(),
+            size_mode: "allocated".into(),
+            theme: "default".into(),
+            mouse: true,
+            excludes: Vec::new(),
+            extension_colors: HashMap::new(),
+            category_colors: HashMap::new(),
+            refresh_hz: 10,
+        }
+    }
+}
+
+/// The config file location.
+pub fn path() -> Option<PathBuf> {
+    let env = |k: &str| std::env::var_os(k).filter(|v| !v.is_empty()).map(PathBuf::from);
+    let dir = if cfg!(target_os = "macos") {
+        env("HOME")?.join("Library/Application Support")
+    } else {
+        env("XDG_CONFIG_HOME").or_else(|| env("HOME").map(|h| h.join(".config")))?
+    };
+    Some(dir.join(brand::NAME).join("config.json"))
+}
+
+/// Reads the config file if present. A missing file is not an error.
+pub fn load() -> (Settings, Option<String>) {
+    let Some(p) = path() else { return (Settings::default(), None) };
+    let b = match std::fs::read(&p) {
+        Ok(b) => b,
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return (Settings::default(), None),
+        Err(e) => return (Settings::default(), Some(e.to_string())),
+    };
+    match serde_json::from_slice::<Settings>(&b) {
+        Ok(mut s) => {
+            if !(1..=60).contains(&s.refresh_hz) {
+                s.refresh_hz = 10;
+            }
+            (s, None)
+        }
+        Err(e) => (Settings::default(), Some(e.to_string())),
+    }
+}