Allow testing.TestEnvironment / TestEnvironmentInfo to be read from Starlark

[rickeylev]

Description of the bug:

Given a target that returns the testing.TestEnvironment / TestEnvironmentInfo, that provider cannot be read from the target.

This makes it impossible to easily test that the rule constructs an appropriate TestEnvironmentInfo object.

What's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

def _provides_info(ctx):
  return [testing.TestEnvironment({})]

provides_info = rule(implementation = _provides_info)

def _reads_info(ctx):
  print(ctx.attr.target[testing.TestEnvironment])

reads_info = rule(implementation=_reads_info, attrs={"target": attr.label()})

provides_info(name="provides")
reads_info(name="reads", target=":provides")

Actual behavior:

An error like below occurs:

Error: Type Target only supports indexing by object constructors, got builtin_function_or_method instead

Expected behavior:

The TestEnvironmentInfo provider instance is returned.

Which operating system are you running Bazel on?

Linux

What is the output of bazel info release?

google build

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

Google build

What's the output of git remote get-url origin; git rev-parse master; git rev-parse HEAD ?

n/a

Have you found anything relevant by searching the web?

None found

Any other information, logs, or outputs that you want to share?

No response

[brandjon]

At a glance, it looks like this provider is consumed natively but indeed not accessible from Starlark. The above example fails because the testing.TestEnvironment object is a builtin factory function that produces TestEnvironment instances, yet not itself the actual provider object.