fix: keep symlinked configuration and vocabulary in place

src/config.rs

@@ -127,22 +127,32 @@ impl Config {
     }
 
     pub fn save_to(&self, path: &Path) -> Result<()> {
-        if let Some(parent) = path.parent() {
-            fs::create_dir_all(parent)?;
-        }
-        let mut temporary = path.as_os_str().to_os_string();
-        temporary.push(format!(".{}.tmp", std::process::id()));
-        let temporary = PathBuf::from(temporary);
-        fs::write(&temporary, toml::to_string_pretty(self)?)?;
-        fs::rename(temporary, path)?;
-        Ok(())
+        paths::write_atomic(path, toml::to_string_pretty(self)?.as_bytes())
     }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    #[test]
+    fn saving_through_a_symlink_updates_the_link_target() {
+        let directory =
+            std::env::temp_dir().join(format!("whispers-config-symlink-{}", std::process::id()));
+        let _ = fs::remove_dir_all(&directory);
+        assert!(fs::create_dir_all(&directory).is_ok());
+        let target = directory.join("dotfiles-config.toml");
+        let link = directory.join("config.toml");
+        assert!(fs::write(&target, "version = 1\n").is_ok());
+        assert!(std::os::unix::fs::symlink(&target, &link).is_ok());
+
+        assert!(Config::default().save_to(&link).is_ok());
+
+        assert!(link.is_symlink());
+        assert!(fs::read_to_string(&target).is_ok_and(|text| text.contains("version = 2")));
+        let _ = fs::remove_dir_all(&directory);
+    }
+
     #[test]
     fn existing_unversioned_configuration_requires_migration() {
         let path = std::env::temp_dir().join(format!(

src/paths.rs

@@ -1,10 +1,41 @@
 use std::env;
-use std::path::PathBuf;
+use std::fs;
+use std::path::{Path, PathBuf};
 
 use crate::{Error, Result};
 
 pub const MANAGED_LLAMA_RUNTIME: &str = "runtimes/llama.cpp/b10258-vulkan";
 
+/// Writes `contents` to `path` through an atomic rename, following symbolic
+/// links so that dotfile-managed files stay links to their real location.
+pub(crate) fn write_atomic(path: &Path, contents: &[u8]) -> Result<()> {
+    let target = resolve_symlink(path);
+    if let Some(parent) = target.parent() {
+        fs::create_dir_all(parent)?;
+    }
+    let mut temporary = target.as_os_str().to_os_string();
+    temporary.push(format!(".{}.tmp", std::process::id()));
+    let temporary = PathBuf::from(temporary);
+    fs::write(&temporary, contents)?;
+    fs::rename(&temporary, &target)?;
+    Ok(())
+}
+
+fn resolve_symlink(path: &Path) -> PathBuf {
+    if !path.is_symlink() {
+        return path.to_path_buf();
+    }
+    if let Ok(canonical) = fs::canonicalize(path) {
+        return canonical;
+    }
+    let parent = path.parent().unwrap_or_else(|| Path::new("."));
+    match fs::read_link(path) {
+        Ok(link) if link.is_absolute() => link,
+        Ok(link) => parent.join(link),
+        Err(_) => path.to_path_buf(),
+    }
+}
+
 pub fn config_dir() -> Result<PathBuf> {
     xdg_path("XDG_CONFIG_HOME", ".config").map(|path| path.join("whispers"))
 }

src/vocabulary.rs

@@ -1,5 +1,5 @@
 use std::fs;
-use std::path::{Path, PathBuf};
+use std::path::Path;
 
 use serde::{Deserialize, Serialize};
 
@@ -57,13 +57,7 @@ impl Vocabulary {
     }
 
     pub fn save_to(&self, path: &Path) -> Result<()> {
-        if let Some(parent) = path.parent() {
-            fs::create_dir_all(parent)?;
-        }
-        let temporary = temporary_path(path);
-        fs::write(&temporary, toml::to_string_pretty(self)?)?;
-        fs::rename(temporary, path)?;
-        Ok(())
+        paths::write_atomic(path, toml::to_string_pretty(self)?.as_bytes())
     }
 
     pub fn add(&mut self, term: &str, aliases: Vec<String>) -> Result<()> {
@@ -185,16 +179,30 @@ fn word_character(character: char) -> bool {
     character.is_alphanumeric() || character == '_'
 }
 
-fn temporary_path(path: &Path) -> PathBuf {
-    let mut temporary = path.as_os_str().to_os_string();
-    temporary.push(format!(".{}.tmp", std::process::id()));
-    PathBuf::from(temporary)
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    #[test]
+    fn saving_through_a_symlink_updates_the_link_target() {
+        let directory = std::env::temp_dir().join(format!(
+            "whispers-vocabulary-symlink-{}",
+            std::process::id()
+        ));
+        let _ = fs::remove_dir_all(&directory);
+        assert!(fs::create_dir_all(&directory).is_ok());
+        let target = directory.join("dotfiles-vocabulary.toml");
+        let link = directory.join("vocabulary.toml");
+        assert!(fs::write(&target, "version = 0\n").is_ok());
+        assert!(std::os::unix::fs::symlink(&target, &link).is_ok());
+
+        assert!(Vocabulary::default().save_to(&link).is_ok());
+
+        assert!(link.is_symlink());
+        assert!(fs::read_to_string(&target).is_ok_and(|text| text.contains("version = 1")));
+        let _ = fs::remove_dir_all(&directory);
+    }
+
     #[test]
     fn replaces_aliases_at_word_boundaries() {
         let vocabulary = Vocabulary {