feat: config file with defaults and unknown-key warnings

src/config.rs

@@ -0,0 +1,161 @@
+use std::path::{Path, PathBuf};
+
+use anyhow::{Context, Result};
+use serde::Deserialize;
+
+use crate::error::HintExt;
+
+#[derive(Debug, Clone, PartialEq, Deserialize, Default)]
+#[serde(default)]
+pub struct Config {
+    pub save: Save,
+    pub capture: Capture,
+}
+
+#[derive(Debug, Clone, PartialEq, Deserialize)]
+#[serde(default)]
+pub struct Save {
+    pub directory: String,
+    pub filename: String,
+    pub copy_to_clipboard: bool,
+}
+
+#[derive(Debug, Clone, PartialEq, Deserialize, Default)]
+#[serde(default)]
+pub struct Capture {
+    pub show_cursor: bool,
+}
+
+impl Default for Save {
+    fn default() -> Self {
+        Self {
+            directory: "~/Pictures/Screenshots".into(),
+            filename: "Screenshot %Y-%m-%d at %H.%M.%S.png".into(),
+            copy_to_clipboard: true,
+        }
+    }
+}
+
+impl Config {
+    /// The save directory with `~` and `$HOME` expanded.
+    pub fn save_dir(&self) -> PathBuf {
+        expand_home(&self.save.directory, &home())
+    }
+}
+
+pub fn home() -> PathBuf {
+    std::env::var_os("HOME")
+        .map(PathBuf::from)
+        .unwrap_or_else(|| "/".into())
+}
+
+/// `$XDG_CONFIG_HOME/valw/config.toml`, falling back to `~/.config`.
+pub fn default_path() -> PathBuf {
+    std::env::var_os("XDG_CONFIG_HOME")
+        .map(PathBuf::from)
+        .unwrap_or_else(|| home().join(".config"))
+        .join("valw/config.toml")
+}
+
+/// Loads the config. A missing file means defaults.
+pub fn load(path: &Path) -> Result<Config> {
+    let text = match std::fs::read_to_string(path) {
+        Ok(text) => text,
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(Config::default()),
+        Err(e) => return Err(e).with_context(|| format!("could not read {}", path.display())),
+    };
+    let (config, unknown) = parse(&text)
+        .with_context(|| format!("invalid config file {}", path.display()))
+        .hint("fix the file or delete it to use the defaults")?;
+    for key in unknown {
+        tracing::warn!("ignoring unknown config key `{key}` in {}", path.display());
+    }
+    Ok(config)
+}
+
+/// Parses config text. Returns the config and the keys valw doesn't know.
+pub fn parse(text: &str) -> Result<(Config, Vec<String>)> {
+    let de = toml::Deserializer::parse(text)?;
+    let mut unknown = Vec::new();
+    let config = serde_ignored::deserialize(de, |path| unknown.push(path.to_string()))?;
+    Ok((config, unknown))
+}
+
+pub fn expand_home(path: &str, home: &Path) -> PathBuf {
+    if path == "~" || path == "$HOME" {
+        return home.to_path_buf();
+    }
+    for prefix in ["~/", "$HOME/"] {
+        if let Some(rest) = path.strip_prefix(prefix) {
+            return home.join(rest);
+        }
+    }
+    PathBuf::from(path)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn empty_file_gives_defaults() {
+        let (config, unknown) = parse("").unwrap();
+        assert_eq!(config, Config::default());
+        assert!(unknown.is_empty());
+    }
+
+    #[test]
+    fn partial_file_keeps_other_defaults() {
+        let (config, _) = parse("[save]\ncopy_to_clipboard = false\n").unwrap();
+        assert!(!config.save.copy_to_clipboard);
+        assert_eq!(config.save.directory, "~/Pictures/Screenshots");
+        assert!(!config.capture.show_cursor);
+    }
+
+    #[test]
+    fn unknown_keys_are_reported_not_rejected() {
+        let text = "[preview]\nenabled = true\n\n[save]\nfolder = \"x\"\n";
+        let (config, unknown) = parse(text).unwrap();
+        assert_eq!(config, Config::default());
+        assert_eq!(
+            unknown,
+            vec!["preview".to_string(), "save.folder".to_string()]
+        );
+    }
+
+    #[test]
+    fn invalid_toml_names_the_line() {
+        let err = parse("[save]\ndirectory = \n").unwrap_err();
+        assert!(format!("{err:#}").contains("line 2"), "{err:#}");
+    }
+
+    #[test]
+    fn wrong_type_is_an_error() {
+        assert!(parse("[capture]\nshow_cursor = \"yes\"\n").is_err());
+    }
+
+    #[test]
+    fn missing_file_gives_defaults() {
+        let dir = tempfile::tempdir().unwrap();
+        assert_eq!(
+            load(&dir.path().join("nope.toml")).unwrap(),
+            Config::default()
+        );
+    }
+
+    #[test]
+    fn expands_home() {
+        let home = Path::new("/home/u");
+        assert_eq!(
+            expand_home("~/Pictures", home),
+            Path::new("/home/u/Pictures")
+        );
+        assert_eq!(
+            expand_home("$HOME/Pictures", home),
+            Path::new("/home/u/Pictures")
+        );
+        assert_eq!(expand_home("~", home), Path::new("/home/u"));
+        assert_eq!(expand_home("/srv/shots", home), Path::new("/srv/shots"));
+        assert_eq!(expand_home("~other/x", home), Path::new("~other/x"));
+    }
+}

src/main.rs

@@ -1,6 +1,7 @@
 // Modules land before the CLI uses them; Task 11 removes this.
 #![allow(dead_code)]
 
+mod config;
 mod error;
 
 use clap::Parser;