Implement retab command

Ref #919

cmd/micro/actions.go

@@ -542,6 +542,40 @@ func (v *View) ParagraphNext(usePlugin bool) bool {
 	return true
 }
 
+func (v *View) Retab(usePlugin bool) bool {
+	if usePlugin && !PreActionCall("Retab", v) {
+		return false
+	}
+
+	toSpaces := v.Buf.Settings["tabstospaces"].(bool)
+	tabsize := int(v.Buf.Settings["tabsize"].(float64))
+	dirty := false
+
+	for i := 0; i < v.Buf.NumLines; i++ {
+		l := v.Buf.Line(i)
+
+		ws := GetLeadingWhitespace(l)
+		if ws != "" {
+			if toSpaces {
+				ws = strings.Replace(ws, "\t", Spaces(tabsize), -1)
+			} else {
+				ws = strings.Replace(ws, Spaces(tabsize), "\t", -1)
+			}
+		}
+
+		l = strings.TrimLeft(l, " \t")
+		v.Buf.lines[i].data = []byte(ws + l)
+		dirty = true
+	}
+
+	v.Buf.IsModified = dirty
+
+	if usePlugin {
+		return PostActionCall("Retab", v)
+	}
+	return true
+}
+
 // CursorStart moves the cursor to the start of the buffer
 func (v *View) CursorStart(usePlugin bool) bool {
 	if usePlugin && !PreActionCall("CursorStart", v) {

cmd/micro/command.go

@@ -55,6 +55,7 @@ func init() {
 		"Open":       Open,
 		"TabSwitch":  TabSwitch,
 		"MemUsage":   MemUsage,
+		"Retab":      Retab,
 	}
 }
 
@@ -110,6 +111,7 @@ func DefaultCommands() map[string]StrCommand {
 		"open":       {"Open", []Completion{FileCompletion}},
 		"tabswitch":  {"TabSwitch", []Completion{NoCompletion}},
 		"memusage":   {"MemUsage", []Completion{NoCompletion}},
+		"retab":      {"Retab", []Completion{NoCompletion}},
 	}
 }
 
@@ -196,6 +198,10 @@ func PluginCmd(args []string) {
 	}
 }
 
+func Retab(args []string) {
+	CurView().Retab(true)
+}
+
 // TabSwitch switches to a given tab either by name or by number
 func TabSwitch(args []string) {
 	if len(args) > 0 {

runtime/help/commands.md

@@ -76,6 +76,9 @@ Here are the possible commands that you can use.
 
 * `open filename`: Open a file in the current buffer.
 
+* `retab`: Replaces all leading tabs with spaces or leading spaces with tabs
+   depending on the value of `tabstospaces`.
+
 ---
 
 The following commands are provided by the default plugins: