Create a "current_product" named platform.

This enables output paths of product agnostic targets (e.g. mainline
apex) to be identical when switching between target products, since the
product name is no longer embedded in:

1) the output path prefix in bazel-out
2) the PlatformOptions contribution to the configuration hash as part of a transition

Test: treehugger
Change-Id: I3fd0f7134209aa7eede3ed98412a1c5482689b57
diff --git a/bp2build/bp2build_product_config.go b/bp2build/bp2build_product_config.go
index 3abef9d..66d0cc5 100644
--- a/bp2build/bp2build_product_config.go
+++ b/bp2build/bp2build_product_config.go
@@ -68,6 +68,14 @@
 	"@//build/bazel/product_config:__subpackages__",
 	"@soong_injection//product_config_platforms:__subpackages__",
 ])
+
+load("//{PRODUCT_FOLDER}:soong.variables.bzl", _soong_variables = "variables")
+load("@//build/bazel/product_config:android_product.bzl", "android_product")
+
+android_product(
+    name = "current_product-{VARIANT}",
+    soong_variables = _soong_variables,
+)
 `)),
 		newFile(
 			"product_config_platforms",
@@ -78,6 +86,7 @@
 # TODO: When we start generating the platforms for more than just the
 # currently lunched product, they should all be listed here
 product_labels = [
+  "@soong_injection//product_config_platforms:current_product-{VARIANT}",
   "@soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}"
 ]
 `)),
@@ -85,25 +94,30 @@
 			"product_config_platforms",
 			"common.bazelrc",
 			productReplacer.Replace(`
-build --platforms @soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}_linux_x86_64
+# current_product refers to the current TARGET_PRODUCT set, usually through
+# 'lunch' or 'banchan'.  Every build will have a primary TARGET_PRODUCT, but
+# bazel supports using other products in tests or configuration transitions. The
+# other products can be found in
+# @soong_injection//product_config_platforms/products/...
+build --platforms @soong_injection//product_config_platforms:current_product-{VARIANT}_linux_x86_64
 
-build:android --platforms=@soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}
-build:linux_x86_64 --platforms=@soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}_linux_x86_64
-build:linux_bionic_x86_64 --platforms=@soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}_linux_bionic_x86_64
-build:linux_musl_x86 --platforms=@soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}_linux_musl_x86
-build:linux_musl_x86_64 --platforms=@soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}_linux_musl_x86_64
+build:android --platforms=@soong_injection//product_config_platforms:current_product-{VARIANT}
+build:linux_x86_64 --platforms=@soong_injection//product_config_platforms:current_product-{VARIANT}_linux_x86_64
+build:linux_bionic_x86_64 --platforms=@soong_injection//product_config_platforms:current_product-{VARIANT}_linux_bionic_x86_64
+build:linux_musl_x86 --platforms=@soong_injection//product_config_platforms:current_product-{VARIANT}_linux_musl_x86
+build:linux_musl_x86_64 --platforms=@soong_injection//product_config_platforms:current_product-{VARIANT}_linux_musl_x86_64
 `)),
 		newFile(
 			"product_config_platforms",
 			"linux.bazelrc",
 			productReplacer.Replace(`
-build --host_platform @soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}_linux_x86_64
+build --host_platform @soong_injection//product_config_platforms:current_product-{VARIANT}_linux_x86_64
 `)),
 		newFile(
 			"product_config_platforms",
 			"darwin.bazelrc",
 			productReplacer.Replace(`
-build --host_platform @soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}_darwin_x86_64
+build --host_platform product_config_platforms:current_product-{VARIANT}_darwin_x86_64
 `)),
 		newFile(
 			"product_config_platforms",
@@ -111,7 +125,7 @@
 			productReplacer.Replace(`
 flags:
   --cpu=k8
-    @soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}
+	@soong_injection//product_config_platforms:current_product-{VARIANT}
 `)),
 	}