More efficient loading for default syntax files

This change introduces header files for syntax files. The header
files only contain the filetype and detection info and can be
parsed much faster than parsing a full yaml file. To determine
which filetype a file is, only scanning the headers is necessary
and afterwards only one yaml file needs to be parsed. Use the
make_headers.go file to generate the header files. Micro expects
that all default syntax files will have header files and that
custom user syntax files may or may not have them. Resolving
includes within syntax has not yet been implemented. This
optimization improves startup time.

Ref #1427

pkg/highlight/parser.go

@@ -1,6 +1,7 @@
 package highlight
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"regexp"
@@ -41,6 +42,14 @@ type Header struct {
 	FtDetect [2]*regexp.Regexp
 }
 
+type HeaderYaml struct {
+	FileType string `yaml:"filetype"`
+	Detect   struct {
+		FNameRgx  string `yaml:"filename"`
+		HeaderRgx string `yaml:"header"`
+	} `yaml:"detect"`
+}
+
 type File struct {
 	FileType string
 
@@ -82,52 +91,67 @@ func init() {
 	Groups = make(map[string]Group)
 }
 
-func ParseFtDetect(file *File) (r [2]*regexp.Regexp, err error) {
-	defer func() {
-		if r := recover(); r != nil {
-			var ok bool
-			err, ok = r.(error)
-			if !ok {
-				err = fmt.Errorf("pkg: %v", r)
-			}
-		}
-	}()
+// MakeHeader takes a header (.hdr file) file and parses the header
+// Header files make parsing more efficient when you only want to compute
+// on the headers of syntax files
+// A yaml file might take ~400us to parse while a header file only takes ~20us
+func MakeHeader(data []byte) (*Header, error) {
+	lines := bytes.Split(data, []byte{'\n'})
+	if len(lines) < 3 {
+		return nil, errors.New("Header file has incorrect format")
+	}
+	header := new(Header)
+	var err error
+	header.FileType = string(lines[0])
+	fnameRgx := string(lines[1])
+	headerRgx := string(lines[2])
 
-	rules := file.yamlSrc
-
-	loaded := 0
-	for k, v := range rules {
-		if k == "detect" {
-			ftdetect := v.(map[interface{}]interface{})
-			if len(ftdetect) >= 1 {
-				syntax, err := regexp.Compile(ftdetect["filename"].(string))
-				if err != nil {
-					return r, err
-				}
-
-				r[0] = syntax
-			}
-			if len(ftdetect) >= 2 {
-				header, err := regexp.Compile(ftdetect["header"].(string))
-				if err != nil {
-					return r, err
-				}
-
-				r[1] = header
-			}
-			loaded++
-		}
-
-		if loaded >= 2 {
-			break
-		}
+	if fnameRgx == "" && headerRgx == "" {
+		return nil, errors.New("Syntax file must include at least one detection regex")
 	}
 
-	if loaded == 0 {
-		return r, errors.New("No detect regexes found")
+	if fnameRgx != "" {
+		header.FtDetect[0], err = regexp.Compile(fnameRgx)
+	}
+	if headerRgx != "" {
+		header.FtDetect[1], err = regexp.Compile(headerRgx)
 	}
 
-	return r, err
+	if err != nil {
+		return nil, err
+	}
+
+	return header, nil
+}
+
+// MakeHeaderYaml takes a yaml spec for a syntax file and parses the
+// header
+func MakeHeaderYaml(data []byte) (*Header, error) {
+	var hdrYaml HeaderYaml
+	err := yaml.Unmarshal(data, &hdrYaml)
+	if err != nil {
+		return nil, err
+	}
+
+	header := new(Header)
+	header.FileType = hdrYaml.FileType
+
+	if hdrYaml.Detect.FNameRgx == "" && hdrYaml.Detect.HeaderRgx == "" {
+		return nil, errors.New("Syntax file must include at least one detection regex")
+	}
+
+	if hdrYaml.Detect.FNameRgx != "" {
+		header.FtDetect[0], err = regexp.Compile(hdrYaml.Detect.FNameRgx)
+	}
+	if hdrYaml.Detect.HeaderRgx != "" {
+		header.FtDetect[1], err = regexp.Compile(hdrYaml.Detect.HeaderRgx)
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	return header, nil
 }
 
 func ParseFile(input []byte) (f *File, err error) {