Code generation for extensions api

tools/json_schema_compiler/code.py

Index: tools/json_schema_compiler/code.py
diff --git a/tools/json_schema_compiler/code.py b/tools/json_schema_compiler/code.py
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+++ b/tools/json_schema_compiler/code.py
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+# Copyright (c) 2012 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+class Code(object):
+  """A convenience object for constructing code.
+
+  Logically each object should be a block of code. All methods except |render|

[Yoyo Zhou, 2012/01/19 02:19:40]

render and is_empty, apparently.

[calamity, 2012/01/20 01:10:25]

Done.

+  return self.
+  """
+  def __init__(self, indent_size=2, comment_length=80):
+    self.__code = []

[Yoyo Zhou, 2012/01/19 02:19:40]

I think one underscore is more typical.

[calamity, 2012/01/20 01:10:25]

Done.

+    self.__indent_level = 0
+    self.__indent_size = indent_size
+    self.__comment_length = comment_length

[Yoyo Zhou, 2012/01/19 02:19:40]

I feel like this variable should have "wrap" in its name.

Although, why wrap comments? I suppose I don't understand whether any human will
read the generated code.

[calamity, 2012/01/20 01:10:25]

Since the tool is standalone, it may be used to generate classes that aren't
necessarily side effects of a build. Also, this would be useful for debugging
(both code using the generated code and the generator itself) and checking
interface conformance. I don't think it hurts to make it readable.

[Yoyo Zhou, 2012/01/23 23:16:42]

Ah, I see. That seems fine then.

+
+  def append(self, line=''):

[Yoyo Zhou, 2012/01/19 02:19:40]

The Python style is to name things like Append and IsEmpty. See
http://www.chromium.org/developers/coding-style.

[calamity, 2012/01/20 01:10:25]

Ah, I was following 
http://google-styleguide.googlecode.com/svn/trunk/pyguide.html

[Yoyo Zhou, 2012/01/23 23:16:42]

Function names should start with a capital.

+    """Appends a line of code at the current indent level or just a newline if
+    line is not specified. Trailing whitespace is stripped.
+    """
+    self.__code.append(((' ' * self.__indent_level) + line).rstrip())
+    return self
+
+  def is_empty(self):
+    """Returns True if the Code object is empty.
+    """
+    return bool(self.__code)
+
+  def concat(self, obj):
+    """Concatenate another Code object onto this one. Trailing whitespace is
+    stripped.
+
+    Appends the code at the current indent level. Will fail if there are any
+    un-interpolated format specifiers eg %s, %(something)s which helps
+    isolate any strings that haven't been substituted.
+    """
+    if not isinstance(obj, Code):
+      raise TypeError()
+    assert self is not obj
+    for line in obj.__code:
+      # line % () will fail if any substitution tokens are left in line
+      self.__code.append(((' ' * self.__indent_level) + line % ()).rstrip())
+
+    return self
+
+  def sblock(self, line=''):
+    """Starts a code block.
+
+    Appends a line of code and then increases the indent level.
+    """
+    self.append(line)
+    self.__indent_level += self.__indent_size
+    return self
+
+  def eblock(self, line=''):
+    """Ends a code block by decreasing and then appending a line (or a blank
+    line if not given).
+    """
+    # TODO(calamity): Decide if type checking is necessary
+    #if not isinstance(line, basestring):
+    #  raise TypeError
+    self.__indent_level -= self.__indent_size
+    self.append(line)
+    return self
+
+  # TODO(calamity): Make comment its own class or something and render at
+  # self.render() time
+  def comment(self, comment):
+    """Adds the given string as a comment.
+
+    Will split the comment if it's too long. Use mainly for variable length
+    comments. Otherwise just use code.append('// ...') for comments.
+    """
+    comment_symbol = '// '
+    max_len = self.__comment_length - self.__indent_level - len(comment_symbol)
+    while len(comment) >= max_len:
+      line = comment[0:max_len]
+      last_space = line.rfind(' ')
+      if last_space != -1:
+        line = line[0:last_space]
+        comment = comment[last_space + 1:]
+      else:
+        comment = comment[max_len:]
+      self.append(comment_symbol + line)
+    self.append(comment_symbol + comment)
+    return self
+
+  def substitute(self, d):
+    """Goes through each line and interpolates using the given dict.
+
+    Raises type error if passed something that isn't a dict
+
+    Use for long pieces of code using interpolation with the same variables
+    repeatedly. This will reduce code and allow for named placeholders which
+    are more clear.
+    """
+    if not isinstance(d, dict):
+      raise TypeError('Passed argument is not a dictionary: ' + d)
+    for i, line in enumerate(self.__code):
+      # Only need to check %s because arg is a dict and python will allow
+      # '%s %(named)s' but just about nothing else
+      if '%s' in self.__code[i] or '%r' in self.__code[i]:
+        raise TypeError('%s or %r found in substitution.'
+            'Named arguments only. Use %%s to escape')

[Yoyo Zhou, 2012/01/19 02:19:40]

Indent to paren. Missing a space between the first 2 sentences, and a period at
the end. "%s" is confusing as a plural of "%" in this context, isn't it?

[calamity, 2012/01/20 01:10:25]

Done. Added quotes around %s and %r to be clearer.

+      self.__code[i] = line % d
+    return self
+
+  def render(self):
+    """Renders Code as a string.
+    """
+    return '\n'.join(self.__code)
+