Add option for very accurate dirty flag

Set the `fastdirty` option flag to off if you really want accurate
reporting on whether the buffer is modified. This is more resource
intensive but it can be useful for people who don't mind.

Closes #787
Closes #467

cmd/micro/settings.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"crypto/md5"
 	"encoding/json"
 	"errors"
 	"io/ioutil"
@@ -198,10 +199,13 @@ func DefaultGlobalSettings() map[string]interface{} {
 		"colorscheme":    "default",
 		"cursorline":     true,
 		"eofnewline":     false,
-		"rmtrailingws":   false,
+		"fastdirty":      true,
+		"fileformat":     "unix",
 		"ignorecase":     false,
 		"indentchar":     " ",
 		"infobar":        true,
+		"mouse":          true,
+		"rmtrailingws":   false,
 		"ruler":          true,
 		"savecursor":     false,
 		"saveundo":       false,
@@ -221,8 +225,6 @@ func DefaultGlobalSettings() map[string]interface{} {
 		},
 		"pluginrepos": []string{},
 		"useprimary":  true,
-		"fileformat":  "unix",
-		"mouse":       true,
 	}
 }
 
@@ -236,10 +238,13 @@ func DefaultLocalSettings() map[string]interface{} {
 		"colorcolumn":    float64(0),
 		"cursorline":     true,
 		"eofnewline":     false,
-		"rmtrailingws":   false,
+		"fastdirty":      true,
+		"fileformat":     "unix",
 		"filetype":       "Unknown",
 		"ignorecase":     false,
 		"indentchar":     " ",
+		"mouse":          true,
+		"rmtrailingws":   false,
 		"ruler":          true,
 		"savecursor":     false,
 		"saveundo":       false,
@@ -254,8 +259,6 @@ func DefaultLocalSettings() map[string]interface{} {
 		"tabsize":        float64(4),
 		"tabstospaces":   false,
 		"useprimary":     true,
-		"fileformat":     "unix",
-		"mouse":          true,
 	}
 }
 
@@ -358,6 +361,26 @@ func SetLocalOption(option, value string, view *View) error {
 		return err
 	}
 
+	if option == "fastdirty" {
+		// If it is being turned off, we have to hash every open buffer
+		var empty [16]byte
+		for _, tab := range tabs {
+			for _, v := range tab.views {
+				if !nativeValue.(bool) {
+					if v.Buf.origHash == empty {
+						data, err := ioutil.ReadFile(v.Buf.AbsPath)
+						if err != nil {
+							data = []byte{}
+						}
+						v.Buf.origHash = md5.Sum(data)
+					}
+				} else {
+					v.Buf.IsModified = v.Buf.Modified()
+				}
+			}
+		}
+	}
+
 	buf.Settings[option] = nativeValue
 
 	if option == "statusline" {