Add <alt-:> for ensuring selections are forward (cursor >= anchor)

Not very useful interactively, but that feature can make macros much
more robust.

README.asciidoc

@@ -195,6 +195,7 @@ Basic Movement
 
  * +;+: reduce selections to their cursor
  * +alt-;+: flip the selections direction
+ * +alt-:+: ensure selections are in forward direction (cursor after anchor)
 
 
 A word is a sequence of alphanumeric characters or underscore, a WORD is a

src/normal.cc

@@ -1373,6 +1373,11 @@ void flip_selections(Context& context, NormalParams)
     flip_selections(context.selections());
 }
 
+void ensure_forward(Context& context, NormalParams)
+{
+    ensure_forward(context.selections());
+}
+
 static NormalCmdDesc cmds[] =
 {
     { 'h', "move left", move<CharCount, Backward> },
@@ -1434,6 +1439,7 @@ static NormalCmdDesc cmds[] =
     { alt(' '), "remove main selection", remove_selection },
     { ';', "reduce selections to their cursor", clear_selections },
     { alt(';'), "swap selections cursor and anchor", flip_selections },
+    { alt(':'), "ensure selection cursor is after anchor", ensure_forward },
 
     { 'w', "select to next word start", repeated<&select<SelectMode::Replace, select_to_next_word<Word>>> },
     { 'e', "select to next word end", repeated<select<SelectMode::Replace, select_to_next_word_end<Word>>> },

src/selectors.hh

@@ -28,13 +28,24 @@ inline void flip_selections(SelectionList& selections)
 {
     for (auto& sel : selections)
     {
-        ByteCoord tmp = sel.anchor();
+        const ByteCoord tmp = sel.anchor();
         sel.anchor() = sel.cursor();
         sel.cursor() = tmp;
     }
     selections.check_invariant();
 }
 
+inline void ensure_forward(SelectionList& selections)
+{
+    for (auto& sel : selections)
+    {
+        const ByteCoord min = sel.min(), max = sel.max();
+        sel.anchor() = min;
+        sel.cursor() = max;
+    }
+    selections.check_invariant();
+}
+
 inline void keep_selection(SelectionList& selections, int index)
 {
     if (index < selections.size())