bpo-694339: IDLE: Dedenting with shift+tab

Author: mlouielu

Lib/idlelib/config-keys.def

@@ -47,6 +47,7 @@ goto-line=<Alt-Key-g> <Meta-Key-g> <Alt-Key-G> <Meta-Key-G>
 smart-backspace=<Key-BackSpace>
 newline-and-indent=<Key-Return> <Key-KP_Enter>
 smart-indent=<Key-Tab>
+smart-dedent=<Shift-Key-Tab>
 indent-region=<Control-Key-bracketright>
 dedent-region=<Control-Key-bracketleft>
 comment-region=<Alt-Key-3> <Meta-Key-3>
@@ -98,6 +99,7 @@ goto-line=<Alt-Key-g> <Meta-Key-g>
 smart-backspace=<Key-BackSpace>
 newline-and-indent=<Key-Return> <Key-KP_Enter>
 smart-indent=<Key-Tab>
+smart-dedent=<Shift-ISO_Left_Tab>
 indent-region=<Control-Key-bracketright>
 dedent-region=<Control-Key-bracketleft>
 comment-region=<Alt-Key-3>
@@ -149,6 +151,7 @@ goto-line = <Control-Key-g>
 smart-backspace = <Key-BackSpace>
 newline-and-indent = <Key-Return> <Key-KP_Enter>
 smart-indent = <Key-Tab>
+smart-dedent = <Shift-ISO_Left_Tab>
 indent-region = <Control-Key-bracketright>
 dedent-region = <Control-Key-bracketleft>
 comment-region = <Control-Key-d>
@@ -200,6 +203,7 @@ goto-line=<Command-Key-j>
 smart-backspace=<Key-BackSpace>
 newline-and-indent=<Key-Return> <Key-KP_Enter>
 smart-indent=<Key-Tab>
+smart-dedent=<Shift-Key-Tab>
 indent-region=<Command-Key-bracketright>
 dedent-region=<Command-Key-bracketleft>
 comment-region=<Control-Key-3>
@@ -239,6 +243,7 @@ smart-backspace = <Key-BackSpace>
 change-indentwidth = <Control-Key-u>
 do-nothing = <Control-Key-F12>
 smart-indent = <Key-Tab>
+smart-dedent = <Shift-Key-Tab>
 center-insert = <Control-Key-l>
 history-next = <Control-Key-n>
 del-word-right = <Option-Key-Delete>

Lib/idlelib/config.py

@@ -649,6 +649,7 @@ def GetCoreKeys(self, keySetName=None):
             '<<smart-backspace>>': ['<Key-BackSpace>'],
             '<<newline-and-indent>>': ['<Key-Return>', '<Key-KP_Enter>'],
             '<<smart-indent>>': ['<Key-Tab>'],
+            '<<smart-dedent>>': ['<Shift-ISO_Left_Tab>', '<Shift-Key-Tab>'],
             '<<indent-region>>': ['<Control-Key-bracketright>'],
             '<<dedent-region>>': ['<Control-Key-bracketleft>'],
             '<<comment-region>>': ['<Alt-Key-3>'],

Lib/idlelib/editor.py

@@ -160,6 +160,7 @@ def __init__(self, flist=None, filename=None, key=None, root=None):
         text.bind("<<smart-backspace>>",self.smart_backspace_event)
         text.bind("<<newline-and-indent>>",self.newline_and_indent_event)
         text.bind("<<smart-indent>>",self.smart_indent_event)
+        text.bind("<<smart-dedent>>", self.smart_dedent_event)
         text.bind("<<indent-region>>",self.indent_region_event)
         text.bind("<<dedent-region>>",self.dedent_region_event)
         text.bind("<<comment-region>>",self.comment_region_event)
@@ -1216,6 +1217,27 @@ def smart_indent_event(self, event):
         finally:
             text.undo_block_stop()
 
+    def smart_dedent_event(self, event):
+        # if selection:
+        #     do dedent-region
+        # elif only whitespace to the left:
+        #      dedent one level
+        first, last = self.get_selection_indices()
+        self.text.undo_block_start()
+        try:
+            if first and last:
+                if index2line(first) != index2line(last):
+                    return self.dedent_region_event(event)
+            prefix = self.text.get('insert linestart', 'insert')
+            raw, effective = classifyws(prefix, self.tabwidth)
+            if raw == len(prefix):
+                # Only whitespace to the left
+                self.reindent_to(effective - self.indentwidth)
+            self.text.see('insert')
+            return 'break'
+        finally:
+            self.text.undo_block_stop()
+
     def newline_and_indent_event(self, event):
         text = self.text
         first, last = self.get_selection_indices()