Replace unicase dependency

It was unnecessary, as comparisons were always done against ASCII
strings. The string comparison was also refactored to guard against this
invariant being violated in the future.

Cargo.toml

@@ -17,7 +17,6 @@ coveralls = { repository = "Ortham/esplugin" }
 encoding = "0.2.33"
 memmap = "0.7.0"
 nom = "5.0.0"
-unicase = "2.0.0"
 flate2 = { version = "1.0.1", optional = true }
 
 [dev-dependencies]

src/lib.rs

@@ -20,7 +20,6 @@
 extern crate encoding;
 extern crate memmap;
 extern crate nom;
-extern crate unicase;
 
 #[cfg(feature = "compressed-fields")]
 extern crate flate2;

src/plugin.rs

@@ -19,7 +19,6 @@
 
 use std::fs::File;
 use std::io::{BufReader, Read};
-use std::ops::Deref;
 use std::path::{Path, PathBuf};
 use std::str;
 
@@ -30,8 +29,6 @@ use nom::{self, IResult};
 
 use memmap::Mmap;
 
-use unicase::eq;
-
 use error::Error;
 use form_id::HashedFormId;
 use game_id::GameId;
@@ -42,6 +39,36 @@ use record_id::{NamespacedId, RecordId};
 // 1 MB is around the file size at which memory-mapping becomes more performant.
 const MIN_MMAP_FILE_SIZE: u64 = 1_000_000;
 
+#[derive(Copy, Clone, PartialEq, Eq)]
+enum FileExtension {
+    ESM,
+    ESL,
+}
+
+impl PartialEq<&std::borrow::Cow<'_, str>> for FileExtension {
+    fn eq(&self, other: &&std::borrow::Cow<'_, str>) -> bool {
+        const ESM: &str = "esm";
+        const ESL: &str = "esl";
+
+        // Lowercasing strings isn't generally a good way to compare them, but
+        // here the strings are of the correct length and they're being compared
+        // against ASCII literals.
+        match self {
+            FileExtension::ESM => other.len() == ESM.len() && other.to_lowercase() == ESM,
+            FileExtension::ESL => other.len() == ESL.len() && other.to_lowercase() == ESL,
+        }
+    }
+}
+
+fn is_ghost_file_extension(extension: &std::borrow::Cow<'_, str>) -> bool {
+    const GHOST: &str = "ghost";
+
+    // Generally not a good idea to lowercase strings for case-insensitive
+    // comparison, but this is ASCII, and we're checking that the string is of
+    // the correct length first, so lowercasing won't be expensive.
+    extension.len() == GHOST.len() && extension.to_lowercase() == GHOST
+}
+
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 enum RecordIds {
     None,
@@ -157,23 +184,21 @@ impl Plugin {
         masters(&self.data.header_record)
     }
 
-    fn has_extension(&self, extension: &str) -> bool {
-        if extension.is_empty() {
-            return false;
-        }
-
-        match self.path.extension() {
-            Some(x) if eq(x.to_string_lossy().deref(), &extension[1..]) => true,
-            Some(x) if eq(x.to_string_lossy().deref(), "ghost") => {
-                let file_stem = self
+    fn has_extension(&self, extension: FileExtension) -> bool {
+        let path_extension = self.path.extension().map(|e| e.to_string_lossy());
+        match path_extension {
+            Some(ref e) if extension == e => true,
+            Some(ref e) if is_ghost_file_extension(e) => {
+                let path_extension = self
                     .path
                     .file_stem()
-                    .and_then(std::ffi::OsStr::to_str)
-                    .map(str::to_lowercase);
+                    .map(Path::new)
+                    .and_then(|p| p.extension())
+                    .map(|e| e.to_string_lossy());
 
-                match file_stem {
-                    Some(file_stem) => file_stem.ends_with(extension),
-                    None => false,
+                match path_extension {
+                    Some(ref e) if extension == e => true,
+                    _ => false,
                 }
             }
             _ => false,
@@ -182,11 +207,11 @@ impl Plugin {
 
     pub fn is_master_file(&self) -> bool {
         match self.game_id {
-            GameId::Morrowind => self.has_extension(".esm"),
+            GameId::Morrowind => self.has_extension(FileExtension::ESM),
             GameId::Fallout4 | GameId::SkyrimSE => {
                 self.is_master_flag_set()
-                    || self.has_extension(".esm")
-                    || self.has_extension(".esl")
+                    || self.has_extension(FileExtension::ESM)
+                    || self.has_extension(FileExtension::ESL)
             }
             _ => self.is_master_flag_set(),
         }
@@ -195,7 +220,7 @@ impl Plugin {
     pub fn is_light_master_file(&self) -> bool {
         match self.game_id {
             GameId::Fallout4 | GameId::SkyrimSE => {
-                self.is_light_master_flag_set() || self.has_extension(".esl")
+                self.is_light_master_flag_set() || self.has_extension(FileExtension::ESL)
             }
             _ => false,
         }
@@ -245,7 +270,6 @@ impl Plugin {
             _ => 4,
         };
 
-
         self.data
             .header_record
             .subrecords()
@@ -1219,16 +1243,6 @@ mod tests {
         assert_eq!("Blank.esp.ghost", plugin.filename().unwrap());
     }
 
-    #[test]
-    fn has_extension_should_be_false_if_passed_an_empty_string() {
-        let plugin = Plugin::new(
-            GameId::Skyrim,
-            Path::new("testing-plugins/Skyrim/Data/Blank.esm"),
-        );
-
-        assert!(!plugin.has_extension(""));
-    }
-
     #[test]
     fn masters_should_be_empty_for_a_plugin_with_no_masters() {
         let mut plugin = Plugin::new(