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Allow V2 console rules to use colors #7689

merged 4 commits into from May 9, 2019


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commented May 9, 2019


To improve the UX of V2 rules, there are certain times that we would like to use colors in the output, just as we do in V1.

However, we also need some way to respect the global flag --no-colors / --colors.


Add safe color methods to the Console and MockConsole classes. These take a parameter for whether colors may be used, which in the former case get initialized by the global options.

Console rule users would then use colors like this: console.write_stdout("Pretty colors!")).

Alternative API considered: stripping output

Instead of defining color methods on the Console class, we could have left the callers to use the colors library normally, then changed Console.write_stderr() et al. to call colors.strip_colors() on the payload.

This reduces the risk of people in the current approach accidentally directly using colors rather than the console methods. It also allows us to keep the definition of Console a bit smaller.

However, the idea of first adding color codes then intentionally stripping them away is awkward and it was decided that this was not worth it.


Colors can now be safely used in V2, which unblocks #7676.

The v2 test rule was also updated to print in red "Tests failed" upon any failures.

Screen Shot 2019-05-09 at 8 53 41 AM

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Looks reasonable to me, but this definitely isn't my area of expertise.

Show resolved Hide resolved tests/python/pants_test/engine/ Outdated

@illicitonion illicitonion requested a review from blorente May 9, 2019


stuhood approved these changes May 9, 2019

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I expect that MockConsole and Console can actually be merged at some point, but just keeping them shaped the same way is fine for now.

@@ -145,9 +147,10 @@ def remove_locations_from_traceback(trace):
class MockConsole(object):
"""An implementation of pants.engine.console.Console which captures output."""

def __init__(self):
def __init__(self, use_colors=True):

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stuhood May 9, 2019


Maybe for a followup: defaulting this to false (or using false explicitly in tests) would avoid needing to strip things in most cases.

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Eric-Arellano May 9, 2019

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Ack. Realized it was important parametrize this and to not hardcode for exactly that reason.

I'm thinking that we'll want callers of this to explicitly say that they don't want colors—to opt out, rather than opt in.

Usually for unit tests, we will want to check that colors are being rendered properly (iirc we do this for V1 in some places), so I think it's good to default to this here.

@Eric-Arellano Eric-Arellano merged commit fd3ff0c into pantsbuild:master May 9, 2019

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@Eric-Arellano Eric-Arellano deleted the Eric-Arellano:v2-colors branch May 9, 2019

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