Make loading of cached assets closer in performance to integrated assets

Using BufReader makes sense for large files, but assets are never large enough
to require buffering. It is significantly faster to load the file contents in
one go, so let's do that instead.

Closes #1753

CHANGELOG.md

@@ -8,6 +8,8 @@
 
 ## Other
 
+- Load cached assets as fast as integrated assets, see #1753 (@Enselic)
+
 
 ## Syntaxes
 

src/assets.rs

@@ -1,7 +1,6 @@
 use std::collections::BTreeMap;
 use std::ffi::OsStr;
-use std::fs::{self, File};
-use std::io::BufReader;
+use std::fs;
 use std::path::Path;
 
 use syntect::dumps::{dump_to_file, from_binary, from_reader};
@@ -298,15 +297,14 @@ fn asset_to_cache<T: serde::Serialize>(asset: &T, path: &Path, description: &str
 }
 
 fn asset_from_cache<T: serde::de::DeserializeOwned>(path: &Path, description: &str) -> Result<T> {
-    let asset_file = File::open(&path).chain_err(|| {
+    let contents = fs::read(path).chain_err(|| {
         format!(
             "Could not load cached {} '{}'",
             description,
             path.to_string_lossy()
         )
     })?;
-    from_reader(BufReader::new(asset_file))
-        .chain_err(|| format!("Could not parse cached {}", description))
+    from_reader(&contents[..]).chain_err(|| format!("Could not parse cached {}", description))
 }
 
 #[cfg(test)]
@@ -316,7 +314,7 @@ mod tests {
     use std::ffi::OsStr;
 
     use std::fs::File;
-    use std::io::Write;
+    use std::io::{BufReader, Write};
     use tempfile::TempDir;
 
     use crate::input::Input;