docs: note about Get() being slow due to file matching

Fixes #714

Author: alecthomas

lexers/lexers.go

@@ -30,6 +30,9 @@ func Names(withAliases bool) []string {
 }
 
 // Get a Lexer by name, alias or file extension.
+//
+// Note that this if there isn't an exact match on name or alias, this will
+// call Match(), so it is not efficient.
 func Get(name string) chroma.Lexer {
 	return GlobalLexerRegistry.Get(name)
 }
@@ -40,6 +43,9 @@ func MatchMimeType(mimeType string) chroma.Lexer {
 }
 
 // Match returns the first lexer matching filename.
+//
+// Note that this iterates over all file patterns in all lexers, so it's not
+// particularly efficient.
 func Match(filename string) chroma.Lexer {
 	return GlobalLexerRegistry.Match(filename)
 }

lexers/lexers_test.go

@@ -179,7 +179,6 @@ func FileTestAnalysis(t *testing.T, lexer chroma.Lexer, actualFilepath, expected
 				assert.NoError(t, err)
 				assert.NoError(t, f.Close())
 			} else {
-				// fail via an assertion of string comparison for nicer diff output
 				assert.Equal(t, string(expectedData), actualData.String())
 			}
 		}

registry.go

@@ -97,6 +97,8 @@ func (l *LexerRegistry) MatchMimeType(mimeType string) Lexer {
 }
 
 // Match returns the first lexer matching filename.
+//
+// Note that this iterates over all file patterns in all lexers, so is not fast.
 func (l *LexerRegistry) Match(filename string) Lexer {
 	filename = filepath.Base(filename)
 	matched := PrioritisedLexers{}