Platform mapping-based product config

This allows us to set product variables as build settings instead
of loading them from a target's provider, which further allows us
to read product config variables in transitions.

Bug: 287539062
Bug: 269577299
Test: Presubmits
Change-Id: I8497703f706162572ceb3486240e1eb02a37f5f6
diff --git a/bp2build/bp2build_product_config.go b/bp2build/bp2build_product_config.go
index 7224496..8d5c99c 100644
--- a/bp2build/bp2build_product_config.go
+++ b/bp2build/bp2build_product_config.go
@@ -1,14 +1,20 @@
 package bp2build
 
 import (
+	"android/soong/android"
+	"android/soong/starlark_import"
+	"encoding/json"
 	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
+
+	"github.com/google/blueprint/proptools"
+	"go.starlark.net/starlark"
 )
 
 func CreateProductConfigFiles(
-	ctx *CodegenContext) ([]BazelFile, error) {
+	ctx *CodegenContext) ([]BazelFile, []BazelFile, error) {
 	cfg := &ctx.config
 	targetProduct := "unknown"
 	if cfg.HasDeviceProduct() {
@@ -25,9 +31,14 @@
 	if !strings.HasPrefix(productVariablesFileName, "/") {
 		productVariablesFileName = filepath.Join(ctx.topDir, productVariablesFileName)
 	}
-	bytes, err := os.ReadFile(productVariablesFileName)
+	productVariablesBytes, err := os.ReadFile(productVariablesFileName)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
+	}
+	productVariables := android.ProductVariables{}
+	err = json.Unmarshal(productVariablesBytes, &productVariables)
+	if err != nil {
+		return nil, nil, err
 	}
 
 	// TODO(b/249685973): the name is product_config_platforms because product_config
@@ -39,11 +50,16 @@
 		"{VARIANT}", targetBuildVariant,
 		"{PRODUCT_FOLDER}", currentProductFolder)
 
-	result := []BazelFile{
+	platformMappingContent, err := platformMappingContent(productReplacer.Replace("@soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}"), &productVariables)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	injectionDirFiles := []BazelFile{
 		newFile(
 			currentProductFolder,
 			"soong.variables.bzl",
-			`variables = json.decode("""`+strings.ReplaceAll(string(bytes), "\\", "\\\\")+`""")`),
+			`variables = json.decode("""`+strings.ReplaceAll(string(productVariablesBytes), "\\", "\\\\")+`""")`),
 		newFile(
 			currentProductFolder,
 			"BUILD",
@@ -99,6 +115,7 @@
 			"product_config_platforms",
 			"common.bazelrc",
 			productReplacer.Replace(`
+build --platform_mappings=platform_mappings
 build --platforms @soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}_linux_x86_64
 
 build:android --platforms=@soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}
@@ -120,6 +137,48 @@
 build --host_platform @soong_injection//{PRODUCT_FOLDER}:{PRODUCT}-{VARIANT}_darwin_x86_64
 `)),
 	}
+	bp2buildDirFiles := []BazelFile{
+		newFile(
+			"",
+			"platform_mappings",
+			platformMappingContent),
+	}
+	return injectionDirFiles, bp2buildDirFiles, nil
+}
 
+func platformMappingContent(mainProductLabel string, mainProductVariables *android.ProductVariables) (string, error) {
+	productsForTesting, err := starlark_import.GetStarlarkValue[map[string]map[string]starlark.Value]("products_for_testing")
+	if err != nil {
+		return "", err
+	}
+	result := "platforms:\n"
+	result += platformMappingSingleProduct(mainProductLabel, mainProductVariables)
+	for product, productVariablesStarlark := range productsForTesting {
+		productVariables, err := starlarkMapToProductVariables(productVariablesStarlark)
+		if err != nil {
+			return "", err
+		}
+		result += platformMappingSingleProduct("@//build/bazel/tests/products:"+product, &productVariables)
+	}
+	return result, nil
+}
+
+func platformMappingSingleProduct(label string, productVariables *android.ProductVariables) string {
+	buildSettings := ""
+	buildSettings += fmt.Sprintf("    --//build/bazel/product_config:apex_global_min_sdk_version_override=%s\n", proptools.String(productVariables.ApexGlobalMinSdkVersionOverride))
+	result := ""
+	for _, extension := range []string{"", "_linux_x86_64", "_linux_bionic_x86_64", "_linux_musl_x86", "_linux_musl_x86_64"} {
+		result += "  " + label + extension + "\n" + buildSettings
+	}
+	return result
+}
+
+func starlarkMapToProductVariables(in map[string]starlark.Value) (android.ProductVariables, error) {
+	var err error
+	result := android.ProductVariables{}
+	result.ApexGlobalMinSdkVersionOverride, err = starlark_import.NoneableString(in["ApexGlobalMinSdkVersionOverride"])
+	if err != nil {
+		return result, err
+	}
 	return result, nil
 }