Using generics for the providers API allows a type to be associated
with a ProviderKey, resulting in a type-safe API without that doesn't
require runtime type assertions by every caller.
Unfortunately, Go does not allow generic types in methods, only in
functions [1]. This prevents a type-safe API on ModuleContext, and
requires moving the API to be functions that take a ModuleContext as
a parameter.
[1] https://go.googlesource.com/proposal/+/refs/heads/master/design/43651-type-parameters.md#no-parameterized-methods)
Bug: 316410648
Test: provider_test.go
Change-Id: Ide91de9f2a2a7d075b05e287c7cc86b395db0edb
This was the only one in the source tree.
Side cleanup: remove some dead code that I assume comes from the time
where Blueprint files had to specify what subdirectories other Blueprint
files are in.
Test: Presubmits.
Change-Id: If84c4e85bc5516f30da97c1be29b56e50dddb3c4
Providers are a new concept for Blueprint, based on providers in Bazel:
https://docs.bazel.build/versions/master/skylark/rules.html#providers
Providers aim to simplify the interaction between modules by replacing
type asserting to arbitrary interfaces with requesting optional data
objects from modules. This will also move Blueprint closer to supporting
incremental analysis by serializing the providers and only rerunning
the analysis phase on modules whose inputs have changed.
Change-Id: I39f5f78b372412a7dbf151ceccb3f917f6c874bf
