make match() on Enum into a top-level function in meta.py

[cosmicexplorer]

Problem

Importing via from pants.util.collections import Enum induces an indirection which isn't necessary for most users of Enum (the ones that don't use the .match() function).

Solution

• Use the normal stdlib enum type.
• Make match into a top-level function in meta.py.
• Migrate the codebase.

Result

An awkward import is resolved, and a new import is born! Complete credit for the solution goes to @jsirois in the #engine channel on our Slack.

[Eric-Arellano]

Awesome! Thank you Danny and John!

[jsirois]

I guess, but it seems much more straight forward to say:

class Platform(Enum):
  darwin = ("darwin", "DYLD_LIBRARY_PATH")
  linux = ("linux", "LD_LIBRARY_PATH")

  def __new__(cls, value, runtime_lib_path_env_var) -> 'Platform':
    instance = super().__new__(cls, value)
    instance._runtime_lib_path_env_var = runtime_lib_path_env_var
    return instance

  @property
  def runtime_lib_path_env_var(self):
    return self._runtime_lib_path_env_var

Or even:

@dataclass(frozen=True)
class PlatformInfo:
  name: str
  runtime_lib_path_env_var: str


class Platform(Enum):
  darwin = PlatformInfo("darwin", "DYLD_LIBRARY_PATH")
  linux = PlatformInfo("linux", "LD_LIBRARY_PATH")
  
  # Optional for less code ripple, but arguably you'd just kill and have users say:
  # `platform_instance.value.runtime_lib_path_env_var` themselves.
  @property
  def runtime_lib_path_env_var(self):
    return self.value.runtime_lib_path_env_var

IOW if the enum value passed to match is self, that seems like a smell that the enum value should be a struct instead of a single value. If you agree I'd definitely follow up and not scope creep this PR.

[cosmicexplorer]

I agree and will move to a followup PR!

[Eric-Arellano]

Yay! Thanks!

[Eric-Arellano]

Hello, was this previously blocked by the broken master CI? Would love to see this land :)

[blorente]

Very neat solution, thanks!

[Eric-Arellano]

Yay! Thank you for finishing this out.

Nit: consider from pants.util.enums import match and using match directly. This fits with the codebase style better.

[Eric-Arellano]

Awesome! Thanks Danny!