Add metadata information to cached assets

When saving/reading user-provided syntaxes or themes, `bat` will now maintain a
`metadata.yaml` file which includes information about the `bat` version which was
used to create the cached files. When loading cached files, we now print an error
if they have been created with an incompatible version

closes #882

src/bin/bat/assets.rs

@@ -1,18 +1,12 @@
 use std::borrow::Cow;
 use std::fs;
-use std::path::PathBuf;
+
+use clap::crate_version;
 
 use crate::directories::PROJECT_DIRS;
 
-use bat::HighlightingAssets;
-
-fn theme_set_path() -> PathBuf {
-    PROJECT_DIRS.cache_dir().join("themes.bin")
-}
-
-fn syntax_set_path() -> PathBuf {
-    PROJECT_DIRS.cache_dir().join("syntaxes.bin")
-}
+use bat::errors::*;
+use bat::{AssetsMetadata, HighlightingAssets};
 
 pub fn config_dir() -> Cow<'static, str> {
     PROJECT_DIRS.config_dir().to_string_lossy()
@@ -23,16 +17,40 @@ pub fn cache_dir() -> Cow<'static, str> {
 }
 
 pub fn clear_assets() {
+    let theme_set_path = PROJECT_DIRS.cache_dir().join("themes.bin");
+    let syntax_set_path = PROJECT_DIRS.cache_dir().join("syntaxes.bin");
+    let metadata_file = PROJECT_DIRS.cache_dir().join("metadata.yaml");
+
     print!("Clearing theme set cache ... ");
-    fs::remove_file(theme_set_path()).ok();
+    fs::remove_file(theme_set_path).ok();
     println!("okay");
 
     print!("Clearing syntax set cache ... ");
-    fs::remove_file(syntax_set_path()).ok();
+    fs::remove_file(syntax_set_path).ok();
+    println!("okay");
+
+    print!("Clearing metadata file ... ");
+    fs::remove_file(metadata_file).ok();
     println!("okay");
 }
 
-pub fn assets_from_cache_or_binary() -> HighlightingAssets {
-    HighlightingAssets::from_cache(&theme_set_path(), &syntax_set_path())
-        .unwrap_or(HighlightingAssets::from_binary())
+pub fn assets_from_cache_or_binary() -> Result<HighlightingAssets> {
+    let cache_dir = PROJECT_DIRS.cache_dir();
+    if let Some(metadata) = AssetsMetadata::load_from_folder(&cache_dir)? {
+        if !metadata.is_compatible() {
+            return Err(format!(
+                "The binary caches for the user-customized syntaxes and themes \
+                 in '{}' are not compatible with this version of bat ({}). To solve this, \
+                 either rebuild the cache (bat cache --build) or remove \
+                 the custom syntaxes/themes (bat cache --clear).\n\
+                 For more information, see:\n\n  \
+                 https://github.com/sharkdp/bat#adding-new-syntaxes--language-definitions",
+                cache_dir.to_string_lossy(),
+                crate_version!()
+            )
+            .into());
+        }
+    }
+
+    Ok(HighlightingAssets::from_cache(&cache_dir).unwrap_or(HighlightingAssets::from_binary()))
 }

src/bin/bat/main.rs

@@ -54,7 +54,7 @@ fn run_cache_subcommand(matches: &clap::ArgMatches) -> Result<()> {
 }
 
 pub fn list_languages(config: &Config) -> Result<()> {
-    let assets = assets_from_cache_or_binary();
+    let assets = assets_from_cache_or_binary()?;
     let mut languages = assets
         .syntaxes()
         .iter()
@@ -116,7 +116,7 @@ pub fn list_languages(config: &Config) -> Result<()> {
 }
 
 pub fn list_themes(cfg: &Config) -> Result<()> {
-    let assets = assets_from_cache_or_binary();
+    let assets = assets_from_cache_or_binary()?;
     let mut config = cfg.clone();
     let mut style = HashSet::new();
     style.insert(StyleComponent::Plain);
@@ -147,7 +147,7 @@ pub fn list_themes(cfg: &Config) -> Result<()> {
 }
 
 fn run_controller(config: &Config) -> Result<bool> {
-    let assets = assets_from_cache_or_binary();
+    let assets = assets_from_cache_or_binary()?;
     let controller = Controller::new(&config, &assets);
     controller.run()
 }