platform_build_soong/starlark_import
Cole Faust c9508aac4c Load starlark files from soong
There are a number of instances where we are exporting information
from soong to bazel via soong_injection. This could be more bazel-centric
if the information was instead held in bzl files, and both bazel and
soong read it from there.

Add a starlark package that will run
//build/bazel/constants_exported_to_soong.bzl at initialization time,
and then results can be retreived with GetStarlarkValue.

Since changes to the starlark files mean that soong has to rerun,
add them as ninja deps.

Unfortunately, the starlark code has to be run at runtime rather than
pregenerating their results, because tests run from intellij wouldn't
go through any pregeneration steps. This means that starlark is run
multiple times during the build, once per test package and once per
primary builder invocation. (currently 3, could be reduced to 2 if we
made the symlink forest generation into its own standalone tool) The
starlark code we have so far in this cl is very fast, roughly half a
millisecond, so it's not a big deal for now, but something to keep an
eye on as we add more starlark constants.

Bug: 279095899
Test: go test
Change-Id: I1e7ca1df1d8d67333cbfc46e8396e229820e4476
2023-04-26 17:18:19 -07:00
..
Android.bp
README.md
starlark_import.go
starlark_import_test.go
unmarshal.go
unmarshal_test.go

starlark_import package

This allows soong to read constant information from starlark files. At package initialization time, soong will read build/bazel/constants_exported_to_soong.bzl, and then make the variables from that file available via starlark_import.GetStarlarkValue(). So to import a new variable, it must be added to constants_exported_to_soong.bzl and then it can be accessed by name.

Only constant information can be read, since this is not a full bazel execution but a standalone starlark interpreter. This means you can't use bazel contructs like rule, provider, select, glob, etc.

All starlark files that were loaded must be added as ninja deps that cause soong to rerun. The loaded files can be retrieved via starlark_import.GetNinjaDeps().