fix: fix tab-space mix with tab indenation and continuation_align_style=SPACE

[spaceone]

Fixes #967

Let's see what the tests say about this?

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[spaceone]

@googlebot I signed it!

[bwendling]

I'm sorry to get to this so late. Could you update the CHANGELOG please? Also, please add a test case derived from the original issue.

[spaceone]

I'm sorry to get to this so late. Could you update the CHANGELOG please? Also, please add a test case derived from the original issue.

OK, I created a changelog entry.
Is a new test case necessary? As I adjusted a current one, which already tests this.

[bwendling]

I would prefer the testcase just so we have a concrete example of what we're fixing, so that if something goes wrong we won't mess it up.

[dhouck]

(To clarify: Iʼm a member of the general public, not Google)

I think what you want is best solved with just using CONTINUATION_ALIGN_STYLE=FIXED; changing what CONTINUATION_ALIGN_STYLE=SPACE does will break things.

The point of using spaces for alignment is so that something like

def foo_function(arg1, arg2,
                 arg3):
»   return [
»           'hello',
»           'world',
»   ]

looks good (ie. the arg3 right under the arg1 and the strings right after the [) even when viewed with a different tab width. However, as you see in #967, if it canʼt figure out how to line up continuation lines, itʼll just fall back to four spaces, which isnʼt ideal.

Maybe a better simple option would be to have the default CONTINUATION_ALIGN_STYLE be SPACE when USE_TABS is false, and FIXED when itʼs true? It looks like itʼd take a bigger refactor to add a fourth CONTINUATION_ALIGN_STYLE that uses tabs for generic continuations and spaces if it can actually align things, I think?

[spaceone]

Since Python3 mixing tabs with spaces is a SyntaxError - so when USE_TABS=True we must make sure that spaces are never used for indentation.

[dhouck]

Putting spaces before a tab is an error. Putting spaces after a tab is not, and even if it were this only uses spaces for continuation lines, not technically indentation, where it definitely isnʼt an error. I just tested with my example code and with

def foo2():
»   print("Unconditional")
»   if foo_function(1,2,3):
»       print("Conditional")

which uses tabs and then spaces for indentation, not just the alignment yapf generates, and both work in python 3.9.7.

And if it were an error, then this PR wouldnʼt help, because not all indentations are a multiple of tab_width; youʼd need one of the other two (already existing) options for CONTINUATION_ALIGN_STYLE.