Improve performance of lexers.Get function (#351)

* Benchmark test for lexers.Get function

* Improve performance of lexers.Get function

Look for a lexer by file extension only when it failed to find a
lexer by name

lexers/internal/api.go

@@ -37,19 +37,20 @@ func Names(withAliases bool) []string {
 
 // Get a Lexer by name, alias or file extension.
 func Get(name string) chroma.Lexer {
-	candidates := chroma.PrioritisedLexers{}
 	if lexer := Registry.byName[name]; lexer != nil {
-		candidates = append(candidates, lexer)
+		return lexer
 	}
 	if lexer := Registry.byAlias[name]; lexer != nil {
-		candidates = append(candidates, lexer)
+		return lexer
 	}
 	if lexer := Registry.byName[strings.ToLower(name)]; lexer != nil {
-		candidates = append(candidates, lexer)
+		return lexer
 	}
 	if lexer := Registry.byAlias[strings.ToLower(name)]; lexer != nil {
-		candidates = append(candidates, lexer)
+		return lexer
 	}
+
+	candidates := chroma.PrioritisedLexers{}
 	// Try file extension.
 	if lexer := Match("filename." + name); lexer != nil {
 		candidates = append(candidates, lexer)

lexers/lexers_test.go

@@ -38,6 +38,12 @@ func TestGet(t *testing.T) {
 	})
 }
 
+func BenchmarkGet(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		lexers.Get("go")
+	}
+}
+
 // Test source files are in the form <key>.<key> and validation data is in the form <key>.<key>.expected.
 func TestLexers(t *testing.T) {
 	files, err := ioutil.ReadDir("testdata")