Move INDENT value to the postponed prefix

This makes blib2to3's tree output valid again (which was broken by the previous
fiddling with INDENT and DEDENT nodes).

Fixes #334

README.md

@@ -830,6 +830,9 @@ More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
 
   * they now correctly work across function/class boundaries (#335)
 
+  * they now work when an indentation block starts with empty lines or misaligned
+    comments (#334)
+
 * fixed improper formatting of f-strings with quotes inside interpolated
   expressions (#322)
 

blib2to3/pgen2/driver.py

@@ -70,24 +70,19 @@ def parse_tokens(self, tokens, debug=False):
             if debug:
                 self.logger.debug("%s %r (prefix=%r)",
                                   token.tok_name[type], value, prefix)
-            if type in {token.INDENT, token.DEDENT}:
-                _prefix = prefix
+            if type == token.INDENT:
+                indent_columns.append(len(value))
+                _prefix = prefix + value
                 prefix = ""
-            if type == token.DEDENT:
+                value = ""
+            elif type == token.DEDENT:
                 _indent_col = indent_columns.pop()
-                prefix, _prefix = self._partially_consume_prefix(_prefix, _indent_col)
+                prefix, _prefix = self._partially_consume_prefix(prefix, _indent_col)
             if p.addtoken(type, value, (prefix, start)):
                 if debug:
                     self.logger.debug("Stop.")
                 break
             prefix = ""
-            if type == token.INDENT:
-                indent_columns.append(len(value))
-                if _prefix.startswith(value):
-                    # Don't double-indent.  Since we're delaying the prefix that
-                    # would normally belong to INDENT, we need to put the value
-                    # at the end versus at the beginning.
-                    _prefix = _prefix[len(value):] + value
             if type in {token.INDENT, token.DEDENT}:
                 prefix = _prefix
             lineno, column = end

tests/data/debug_visitor.out

@@ -36,10 +36,11 @@ file_input
         NEWLINE
  '\n'
         INDENT
- '    '
+ ''
         simple_stmt
           expr_stmt
             NAME
+ '    '
  'tree_depth'
             annassign
               COLON
@@ -109,10 +110,11 @@ file_input
             NEWLINE
  '\n'
             INDENT
- '        '
+ ''
             simple_stmt
               expr_stmt
                 NAME
+ '        '
  'indent'
                 EQUAL
  ' '
@@ -184,10 +186,11 @@ file_input
                 NEWLINE
  '\n'
                 INDENT
- '            '
+ ''
                 simple_stmt
                   expr_stmt
                     NAME
+ '            '
  '_type'
                     EQUAL
  ' '
@@ -297,10 +300,11 @@ file_input
                     NEWLINE
  '\n'
                     INDENT
- '                '
+ ''
                     simple_stmt
                       yield_expr
                         NAME
+ '                '
  'yield'
                         yield_arg
                           NAME
@@ -410,10 +414,11 @@ file_input
                 NEWLINE
  '\n'
                 INDENT
- '            '
+ ''
                 simple_stmt
                   expr_stmt
                     NAME
+ '            '
  '_type'
                     EQUAL
  ' '
@@ -542,11 +547,11 @@ file_input
                     NEWLINE
  '\n'
                     INDENT
- '                '
+ ''
                     simple_stmt
                       power
                         NAME
- "# We don't have to handle prefixes for `Node` objects since\n                # that delegates to the first child anyway.\n                "
+ "                # We don't have to handle prefixes for `Node` objects since\n                # that delegates to the first child anyway.\n                "
  'out'
                         trailer
                           LPAR
@@ -699,9 +704,10 @@ file_input
               NEWLINE
  '\n'
               INDENT
- '        '
+ ''
               simple_stmt
                 STRING
+ '        '
  '"""Pretty-prints a given string of `code`.\n\n        Convenience method for debugging.\n        """'
                 NEWLINE
  '\n'

tests/data/fmtonoff2.py

@@ -19,8 +19,17 @@ def test_fader(test):
     pass
 
 def check_fader(test):
+
     pass
 
+def verify_fader(test):
+  # misaligned comment
+    pass
+
+def verify_fader(test):
+    """Hey, ho."""
+    assert test.passed()
+
 def test_calculate_fades():
     calcs = [
         # one is zero/none