perf: using FxHashMap instead of HashMap (#83)

Cargo.toml

@@ -33,6 +33,7 @@ scroll = { version = "0.10.1", features = ["derive"], optional = true }
 data-encoding = "2.3.3"
 debugid = {version = "0.8.0", features = ["serde"] }
 base64-simd = { version = "0.7" }
+rustc-hash = "1.1.0"
 
 [build-dependencies]
 rustc_version = "0.2.3"

src/builder.rs

@@ -1,13 +1,13 @@
 #![cfg_attr(not(any(unix, windows, target_os = "redox")), allow(unused_imports))]
 
-use std::collections::HashMap;
 use std::convert::AsRef;
 use std::env;
 use std::fs;
 use std::io::Read;
 use std::path::{Path, PathBuf};
 
 use debugid::DebugId;
+use rustc_hash::FxHashMap;
 use url::Url;
 
 use crate::errors::Result;
@@ -20,10 +20,10 @@ use crate::types::{RawToken, SourceMap, Token};
 /// type can help.
 pub struct SourceMapBuilder {
     file: Option<String>,
-    name_map: HashMap<String, u32>,
+    name_map: FxHashMap<String, u32>,
     names: Vec<String>,
     tokens: Vec<RawToken>,
-    source_map: HashMap<String, u32>,
+    source_map: FxHashMap<String, u32>,
     source_root: Option<String>,
     sources: Vec<String>,
     source_contents: Vec<Option<String>>,
@@ -53,10 +53,10 @@ impl SourceMapBuilder {
     pub fn new(file: Option<&str>) -> SourceMapBuilder {
         SourceMapBuilder {
             file: file.map(str::to_owned),
-            name_map: HashMap::new(),
+            name_map: FxHashMap::default(),
             names: vec![],
             tokens: vec![],
-            source_map: HashMap::new(),
+            source_map: FxHashMap::default(),
             source_root: None,
             sources: vec![],
             source_contents: vec![],