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/android/bazel_handler.go b/android/bazel_handler.go
index 47dd161..d71eca2 100644
--- a/android/bazel_handler.go
+++ b/android/bazel_handler.go
@@ -674,6 +674,18 @@
 		// We don't need to set --host_platforms because it's set in bazelrc files
 		// that the bazel shell script wrapper passes
 
+		// Optimize Ninja rebuilds by ensuring Bazel write into product-agnostic
+		// output paths for the configured targets that shouldn't be affected by
+		// TARGET_PRODUCT. Otherwise product agnostic modules will be rebuilt by
+		// Ninja when the product changes, unconditionally.
+		//
+		// For example, Mainline APEXes should be identical regardless of the
+		// product (modulo arch/cpu).
+		//
+		// This flag forcibly disables the platform prefix in the intermediate
+		// outputs during a mixed build.
+		"--noexperimental_platform_in_output_dir",
+
 		// Suppress noise
 		"--ui_event_filters=-INFO",
 		"--noshow_progress",
@@ -719,9 +731,9 @@
 #####################################################
 def _config_node_transition_impl(settings, attr):
     if attr.os == "android" and attr.arch == "target":
-        target = "{PRODUCT}-{VARIANT}"
+        target = "current_product-{VARIANT}"
     else:
-        target = "{PRODUCT}-{VARIANT}_%s_%s" % (attr.os, attr.arch)
+        target = "current_product-{VARIANT}_%s_%s" % (attr.os, attr.arch)
     apex_name = ""
     if attr.within_apex:
         # //build/bazel/rules/apex:apex_name has to be set to a non_empty value,
@@ -732,7 +744,7 @@
         # value here.
         apex_name = "dcla_apex"
     outputs = {
-        "//command_line_option:platforms": "@soong_injection//product_config_platforms/products/{PRODUCT}-{VARIANT}:%s" % target,
+        "//command_line_option:platforms": "@soong_injection//product_config_platforms:%s" % target,
         "@//build/bazel/rules/apex:within_apex": attr.within_apex,
         "@//build/bazel/rules/apex:min_sdk_version": attr.apex_sdk_version,
         "@//build/bazel/rules/apex:apex_name": apex_name,
@@ -958,9 +970,9 @@
   platform_name = platforms[0].name
   if platform_name == "host":
     return "HOST"
-  if not platform_name.startswith("{TARGET_PRODUCT}-{TARGET_BUILD_VARIANT}"):
-    fail("expected platform name of the form '{TARGET_PRODUCT}-{TARGET_BUILD_VARIANT}_android_<arch>' or '{TARGET_PRODUCT}-{TARGET_BUILD_VARIANT}_linux_<arch>', but was " + str(platforms))
-  platform_name = platform_name.removeprefix("{TARGET_PRODUCT}-{TARGET_BUILD_VARIANT}").removeprefix("_")
+  if not platform_name.startswith("current_product-{TARGET_BUILD_VARIANT}"):
+    fail("expected platform name of the form 'current_product-{TARGET_BUILD_VARIANT}_android_<arch>' or 'current_product-{TARGET_BUILD_VARIANT}_linux_<arch>', but was " + str(platforms))
+  platform_name = platform_name.removeprefix("current_product-{TARGET_BUILD_VARIANT}").removeprefix("_")
   config_key = ""
   if not platform_name:
     config_key = "target|android"
@@ -969,7 +981,7 @@
   elif platform_name.startswith("linux_"):
     config_key = platform_name.removeprefix("linux_") + "|linux"
   else:
-    fail("expected platform name of the form '{TARGET_PRODUCT}-{TARGET_BUILD_VARIANT}_android_<arch>' or '{TARGET_PRODUCT}-{TARGET_BUILD_VARIANT}_linux_<arch>', but was " + str(platforms))
+    fail("expected platform name of the form 'current_product-{TARGET_BUILD_VARIANT}_android_<arch>' or 'current_product-{TARGET_BUILD_VARIANT}_linux_<arch>', but was " + str(platforms))
 
   within_apex = buildoptions.get("//build/bazel/rules/apex:within_apex")
   apex_sdk_version = buildoptions.get("//build/bazel/rules/apex:min_sdk_version")
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}
 `)),
 	}