options: Add capability to define the line count parsed for the signature check

internal/buffer/buffer.go

@@ -766,9 +766,15 @@ func (b *Buffer) UpdateRules() {
 		if length > 0 {
 			signatureMatch := false
 			if length > 1 {
+				detectlimit := util.IntOpt(b.Settings["detectlimit"])
+				lineCount := len(b.lines)
+				limit := lineCount
+				if detectlimit > 0 && lineCount > detectlimit {
+					limit = detectlimit
+				}
 				for i := 0; i < length && !signatureMatch; i++ {
 					if syntaxFiles[i].header.HasFileSignature() {
-						for j := 0; j < 100 && !signatureMatch; j++ {
+						for j := 0; j < limit && !signatureMatch; j++ {
 							if syntaxFiles[i].header.MatchFileSignature(b.lines[j].data) {
 								syntaxFile = syntaxFiles[i].fileName
 								b.SyntaxDef = syntaxFiles[i].syntaxDef

internal/config/settings.go

@@ -44,6 +44,7 @@ func init() {
 var optionValidators = map[string]optionValidator{
 	"autosave":     validateNonNegativeValue,
 	"clipboard":    validateClipboard,
+	"detectlimit":  validateNonNegativeValue,
 	"tabsize":      validatePositiveValue,
 	"scrollmargin": validateNonNegativeValue,
 	"scrollspeed":  validateNonNegativeValue,
@@ -280,6 +281,7 @@ var defaultCommonSettings = map[string]interface{}{
 	"basename":       false,
 	"colorcolumn":    float64(0),
 	"cursorline":     true,
+	"detectlimit":    float64(100),
 	"diffgutter":     false,
 	"encoding":       "utf-8",
 	"eofnewline":     true,