Only include syntax layers specified by build tags; lazy-load syntax layers

README.md

@@ -23,6 +23,8 @@ Be sure to point your code to the correct path of `syntax_files`.
 Below is a simple example for highlighting a string (a Go snippet in this case).
 It uses `github.com/fatih/color` to actually colorize the output to the console.
 
+It must be built with `-tags=stxGo` to include the Go syntax layer.
+
 ```go
 package main
 
@@ -46,12 +48,8 @@ func helloWorld() {
     fmt.Println("Hello world")
 }`
 
-    // Load the go syntax file
-    // Make sure that the syntax_files directory is in the current directory
-    syntaxFile := syntax.GetGo()
-
-    // Parse it into a `*highlight.Def`
-    syntaxDef, err := highlight.ParseDef(syntaxFile)
+    // Load and parse the go syntax layer into a `*highlight.Def`
+    syntaxDef, err := highlight.ParseDef(syntax.Get("go"))
     if err != nil {
         fmt.Println(err)
         return
@@ -59,6 +57,7 @@ func helloWorld() {
 
     // Make a new highlighter from the definition
     h := highlight.NewHighlighter(syntaxDef)
+
     // Highlight the string
     // Matches is an array of maps which point to groups
     // matches[lineNum][colNum] will give you the change in group at that line and column number
@@ -84,8 +83,6 @@ func helloWorld() {
 				    color.Set(color.FgHiBlue)
 
 			    case highlight.Groups["preproc"]:
-				    //fallthrough
-				    //case highlight.Groups["high.red"]:
 				    color.Set(color.FgHiRed)
 
 			    case highlight.Groups["special"]:

syntax/1entry.go

@@ -0,0 +1,25 @@
+package syntax
+
+import "sync"
+
+var syntaxMap = make(map[string]*lazySyntax)
+
+type lazySyntax struct {
+	once        sync.Once
+	syntaxLayer []byte
+	init        func() []byte
+}
+
+func (ls *lazySyntax) get() []byte {
+	ls.once.Do(func() {
+		ls.syntaxLayer = ls.init()
+	})
+	return ls.syntaxLayer
+}
+
+func Get(id string) []byte {
+	if syntax, exists := syntaxMap[id]; exists {
+		return syntax.get()
+	}
+	return nil
+}

syntax/stxGo.go

@@ -1,7 +1,10 @@
+//go:build stxGo
+
 package syntax
 
-func GetGo() []byte {
-	return []byte(`filetype: go
+func init() {
+	syntaxMap["go"] = &lazySyntax{init: func() []byte {
+		return []byte(`filetype: go
 
 detect:
     filename: "\\.go$"
@@ -67,4 +70,5 @@ rules:
         rules:
             - todo: "(TODO|XXX|FIXME):?"
 `)
+	}}
 }