A global style setup and usage bug via FormatCode, FormatFile[dev branch only]

Short Description: If you would like to set up default style globally, you’re getting back DEFAULT_STYLE_FACTORY that was defined as Pep8 (this is the reason why Pep8 style works well) for all possible pre-defined styles(google, chromium and etc…)

Long Description: I hack on one project that uses yapf and caught one interesting bug in last development version.

This function sets up a configuration of global style SetGlobalStyle(). It is being used by FormatCode ( FormatFile uses it implicitly via FormatCode call )

I found some tests that are using a global style’s setting from the previous test or setting up own style:

1. https://github.com/google/yapf/blob/master/yapftests/yapf_test.py#L229
2. https://github.com/google/yapf/blob/master/yapftests/yapf_test.py#L238
3. https://github.com/google/yapf/blob/master/yapftests/yapf_test.py#L1130

In Format Code we have next string: Check yapf_api.py - https://github.com/google/yapf/blob/master/yapf/yapflib/yapf_api.py#L120

 style.SetGlobalStyle(style.CreateStyleFromConfig(style_config))

The style_config parameter defined like a string or None: https://github.com/google/yapf/blob/master/yapf/yapflib/yapf_api.py#L23 . It has three options:

1. pre-defined style by name: ‘pep8’, ‘google’ and etc
2. path to a file with style
3. None, use a DEFAULT_STYLE_FACTORY

And how it was ( https://github.com/google/yapf/blob/7e088293e4ea05bfd479258ae7748cd57e84a218/yapf/yapflib/style.py#L316 ):

 if style_config is None:
    return DEFAULT_STYLE_FACTORY()

Ok, but in last changes we got this :

Check: style.py - https://github.com/google/yapf/blob/master/yapf/yapflib/style.py#L320

styles = (CreatePEP8Style(), CreateGoogleStyle(),
             CreateFacebookStyle(), CreateChromiumStyle())
  def_style = False
  if style_config is None:
    for style in styles:
      if _style == style:
        def_style = True
        break
    if not def_style:
        return _style
    return DEFAULT_STYLE_FACTORY()
  style_factory = _STYLE_NAME_TO_FACTORY.get(style_config.lower())

Check DEFAULT_STYLE_FACTORY: https://github.com/google/yapf/blob/master/yapf/yapflib/style.py#L419

# The default style - used if yapf is not invoked without specifically
# requesting a formatting style.
DEFAULT_STYLE = 'pep8'
DEFAULT_STYLE_FACTORY = CreatePEP8Style

(test for this part has number 3 This code, has next steps:

1. firstly, does check style_config is None, Ok, we got None(remember we set up style globally, it will None always, )
2. Is the globally defined style in the list of default styles?
3. Nope, we’ve defined our own style and returned a _style that references to our style. (def_style = False)

in first look all is good but it does not:

# what if I do something like this
 style.SetGlobalStyle(style.CreateChromiumStyle())
yapf_api.FormatCode(<input_unformatted_code_here>, style_config=None)

# or like in the given test

yapf_api.FormatCode(<input_unformatted_code_here>, style_config= style.SetGlobalStyle(style.CreateChromiumStyle()))

both calls are equivalent to each other, but we get a DEFAULT_STYLE_FACTORY back!!!

(but first is much more readable and clear, because setter always returns None and It sets the global state, and we do not confuse a caller about the callee’s arguments contract).

We get this because when we check _style(a global style) it assigns to def_style a True value and breaking out from the loop. The second condition would be ignored and DEFAULT_STYLE_FACTORY is being returned back as a result of a callee.

# caller calls the method:
#yapf_api.FormatCode(<input_unformatted_code_here>, 
#                                    style_config= style.SetGlobalStyle(style.CreateChromiumStyle()))

styles = (CreatePEP8Style(), CreateGoogleStyle(),
             CreateFacebookStyle(), CreateChromiumStyle())
  def_style = False
  if style_config is None:   # style_config = None, but _style = CreateChromiumStyle()
    for style in styles:
      if _style == style: # ok we got this as the last element, it is really default style
        def_style = True 
        break # get out from the loop
    if not def_style: # def_style = True, but `not def_style` is a False
        return _style # skip this step, our condition gets false
    return DEFAULT_STYLE_FACTORY() # yeah, method returns DEFAULT_STYLE_FACTORY that's equal al CreatePEP8Style by default
  style_factory = _STYLE_NAME_TO_FACTORY.get(style_config.lower())

In General, this code raises some questions like:

• Have tests been relevant for the current piece of code?
• Why was KISS principle ignored? ( excerpt was copy-pasted from ipython console)

In [3]:  styles = (style.CreatePEP8Style(), style.CreateGoogleStyle(),
             style.CreateFacebookStyle(), style.CreateChromiumStyle())

In [4]: style._style in styles
Out[4]: True

In [5]: if style._style in styles: print('true')
true

In [6]: style.SetGlobalStyle(style.CreateChromiumStyle())

In [7]: style._style == style.CreateChromiumStyle()
Out[7]: True

In [8]: style._style in styles
Out[8]: True

In [9]: if style._style in styles: print('true')
true

In [10]: 

I rewrote this part in my fork and changed the behavior and callee’s contract. if style_config equals None it returns a global style( _style). On start _style equals a DEFAULT_STYLE_FACTORY. After that, we must apply next convention that appears as a caller-callee contract: either use a style_config or use a global style(via SetGlobalStyle) and style_config keep None.

This approach has a positive and negative effects:

1. I implemented a global getter because we have a global setter by the module level.
2. A global getter is breaking an encapsulation of a global style, but it has broken already - you can change the global _style externally that is a global state change. And Yeah I’ve been reading eliben’s todo and I absolutely agree with that.

[bwendling]

From what I can see, it looks like we should be returning _style here instead of DEFAULT_STYLE_FACTORY(). Does this seem correct?

diff --git a/yapf/yapflib/style.py b/yapf/yapflib/style.py
index cebbc27..3ee6395 100644
--- a/yapf/yapflib/style.py
+++ b/yapf/yapflib/style.py
@@ -327,7 +327,7 @@ def CreateStyleFromConfig(style_config):
         break
     if not def_style:
         return _style
-    return DEFAULT_STYLE_FACTORY()
+    return _style
   style_factory = _STYLE_NAME_TO_FACTORY.get(style_config.lower())
   if style_factory is not None:
     return style_factory()

[rojaster]

@gwelymernans I commented your commit.