refactor Bazel variable export

Most of the variable export code for cc modules can be re-used for
exporting variables for java modules. Refactor this code into a more
composable structure for reuse.

Test: build/bazel/bp2build.sh
Test: manual comparison of
  out/soong/soong_injection/cc_toolchain/constants.bzl
  with previous output
Change-Id: Ie5a6fee08cc888b7dc69c3e324e5c3f8aa269a8f
diff --git a/android/Android.bp b/android/Android.bp
index c072ac2..49d5b91 100644
--- a/android/Android.bp
+++ b/android/Android.bp
@@ -36,6 +36,7 @@
         "bazel_handler.go",
         "bazel_paths.go",
         "config.go",
+        "config_bp2build.go",
         "csuite_config.go",
         "deapexer.go",
         "defaults.go",
@@ -96,6 +97,7 @@
         "bazel_handler_test.go",
         "bazel_test.go",
         "config_test.go",
+        "config_bp2build_test.go",
         "csuite_config_test.go",
         "defaults_test.go",
         "depset_test.go",
diff --git a/android/api_levels.go b/android/api_levels.go
index 27a3b7f..8163894 100644
--- a/android/api_levels.go
+++ b/android/api_levels.go
@@ -19,6 +19,7 @@
 	"fmt"
 	"strconv"
 
+	"android/soong/bazel"
 	"android/soong/starlark_fmt"
 )
 
@@ -393,10 +394,10 @@
 }
 
 func StarlarkApiLevelConfigs(config Config) string {
-	return fmt.Sprintf(`# GENERATED FOR BAZEL FROM SOONG. DO NOT EDIT.
+	return fmt.Sprintf(bazel.GeneratedBazelFileWarning+`
 _api_levels = %s
 
 api_levels = _api_levels
 `, printApiLevelsStarlarkDict(config),
 	)
-}
\ No newline at end of file
+}
diff --git a/android/config_bp2build.go b/android/config_bp2build.go
new file mode 100644
index 0000000..80b09fc
--- /dev/null
+++ b/android/config_bp2build.go
@@ -0,0 +1,435 @@
+// Copyright 2021 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package android
+
+import (
+	"fmt"
+	"reflect"
+	"regexp"
+	"sort"
+	"strings"
+
+	"android/soong/bazel"
+	"android/soong/starlark_fmt"
+
+	"github.com/google/blueprint"
+)
+
+// BazelVarExporter is a collection of configuration variables that can be exported for use in Bazel rules
+type BazelVarExporter interface {
+	// asBazel expands strings of configuration variables into their concrete values
+	asBazel(Config, ExportedStringVariables, ExportedStringListVariables, ExportedConfigDependingVariables) []bazelConstant
+}
+
+// ExportedVariables is a collection of interdependent configuration variables
+type ExportedVariables struct {
+	// Maps containing toolchain variables that are independent of the
+	// environment variables of the build.
+	exportedStringVars         ExportedStringVariables
+	exportedStringListVars     ExportedStringListVariables
+	exportedStringListDictVars ExportedStringListDictVariables
+
+	exportedVariableReferenceDictVars ExportedVariableReferenceDictVariables
+
+	/// Maps containing variables that are dependent on the build config.
+	exportedConfigDependingVars ExportedConfigDependingVariables
+
+	pctx PackageContext
+}
+
+// NewExportedVariables creats an empty ExportedVariables struct with non-nil maps
+func NewExportedVariables(pctx PackageContext) ExportedVariables {
+	return ExportedVariables{
+		exportedStringVars:                ExportedStringVariables{},
+		exportedStringListVars:            ExportedStringListVariables{},
+		exportedStringListDictVars:        ExportedStringListDictVariables{},
+		exportedVariableReferenceDictVars: ExportedVariableReferenceDictVariables{},
+		exportedConfigDependingVars:       ExportedConfigDependingVariables{},
+		pctx:                              pctx,
+	}
+}
+
+func (ev ExportedVariables) asBazel(config Config,
+	stringVars ExportedStringVariables, stringListVars ExportedStringListVariables, cfgDepVars ExportedConfigDependingVariables) []bazelConstant {
+	ret := []bazelConstant{}
+	ret = append(ret, ev.exportedStringVars.asBazel(config, stringVars, stringListVars, cfgDepVars)...)
+	ret = append(ret, ev.exportedStringListVars.asBazel(config, stringVars, stringListVars, cfgDepVars)...)
+	ret = append(ret, ev.exportedStringListDictVars.asBazel(config, stringVars, stringListVars, cfgDepVars)...)
+	// Note: ExportedVariableReferenceDictVars collections can only contain references to other variables and must be printed last
+	ret = append(ret, ev.exportedVariableReferenceDictVars.asBazel(config, stringVars, stringListVars, cfgDepVars)...)
+	return ret
+}
+
+// ExportStringStaticVariable declares a static string variable and exports it to
+// Bazel's toolchain.
+func (ev ExportedVariables) ExportStringStaticVariable(name string, value string) {
+	ev.pctx.StaticVariable(name, value)
+	ev.exportedStringVars.set(name, value)
+}
+
+// ExportStringListStaticVariable declares a static variable and exports it to
+// Bazel's toolchain.
+func (ev ExportedVariables) ExportStringListStaticVariable(name string, value []string) {
+	ev.pctx.StaticVariable(name, strings.Join(value, " "))
+	ev.exportedStringListVars.set(name, value)
+}
+
+// ExportVariableConfigMethod declares a variable whose value is evaluated at
+// runtime via a function with access to the Config and exports it to Bazel's
+// toolchain.
+func (ev ExportedVariables) ExportVariableConfigMethod(name string, method interface{}) blueprint.Variable {
+	ev.exportedConfigDependingVars.set(name, method)
+	return ev.pctx.VariableConfigMethod(name, method)
+}
+
+// ExportSourcePathVariable declares a static "source path" variable and exports
+// it to Bazel's toolchain.
+func (ev ExportedVariables) ExportSourcePathVariable(name string, value string) {
+	ev.pctx.SourcePathVariable(name, value)
+	ev.exportedStringVars.set(name, value)
+}
+
+// ExportString only exports a variable to Bazel, but does not declare it in Soong
+func (ev ExportedVariables) ExportString(name string, value string) {
+	ev.exportedStringVars.set(name, value)
+}
+
+// ExportStringList only exports a variable to Bazel, but does not declare it in Soong
+func (ev ExportedVariables) ExportStringList(name string, value []string) {
+	ev.exportedStringListVars.set(name, value)
+}
+
+// ExportStringListDict only exports a variable to Bazel, but does not declare it in Soong
+func (ev ExportedVariables) ExportStringListDict(name string, value map[string][]string) {
+	ev.exportedStringListDictVars.set(name, value)
+}
+
+// ExportVariableReferenceDict only exports a variable to Bazel, but does not declare it in Soong
+func (ev ExportedVariables) ExportVariableReferenceDict(name string, value map[string]string) {
+	ev.exportedVariableReferenceDictVars.set(name, value)
+}
+
+// ExportedConfigDependingVariables is a mapping of variable names to functions
+// of type func(config Config) string which return the runtime-evaluated string
+// value of a particular variable
+type ExportedConfigDependingVariables map[string]interface{}
+
+func (m ExportedConfigDependingVariables) set(k string, v interface{}) {
+	m[k] = v
+}
+
+// Ensure that string s has no invalid characters to be generated into the bzl file.
+func validateCharacters(s string) string {
+	for _, c := range []string{`\n`, `"`, `\`} {
+		if strings.Contains(s, c) {
+			panic(fmt.Errorf("%s contains illegal character %s", s, c))
+		}
+	}
+	return s
+}
+
+type bazelConstant struct {
+	variableName       string
+	internalDefinition string
+	sortLast           bool
+}
+
+// ExportedStringVariables is a mapping of variable names to string values
+type ExportedStringVariables map[string]string
+
+func (m ExportedStringVariables) set(k string, v string) {
+	m[k] = v
+}
+
+func (m ExportedStringVariables) asBazel(config Config,
+	stringVars ExportedStringVariables, stringListVars ExportedStringListVariables, cfgDepVars ExportedConfigDependingVariables) []bazelConstant {
+	ret := make([]bazelConstant, 0, len(m))
+	for k, variableValue := range m {
+		expandedVar, err := expandVar(config, variableValue, stringVars, stringListVars, cfgDepVars)
+		if err != nil {
+			panic(fmt.Errorf("error expanding config variable %s: %s", k, err))
+		}
+		if len(expandedVar) > 1 {
+			panic(fmt.Errorf("%s expands to more than one string value: %s", variableValue, expandedVar))
+		}
+		ret = append(ret, bazelConstant{
+			variableName:       k,
+			internalDefinition: fmt.Sprintf(`"%s"`, validateCharacters(expandedVar[0])),
+		})
+	}
+	return ret
+}
+
+// ExportedStringListVariables is a mapping of variable names to a list of strings
+type ExportedStringListVariables map[string][]string
+
+func (m ExportedStringListVariables) set(k string, v []string) {
+	m[k] = v
+}
+
+func (m ExportedStringListVariables) asBazel(config Config,
+	stringScope ExportedStringVariables, stringListScope ExportedStringListVariables,
+	exportedVars ExportedConfigDependingVariables) []bazelConstant {
+	ret := make([]bazelConstant, 0, len(m))
+	// For each exported variable, recursively expand elements in the variableValue
+	// list to ensure that interpolated variables are expanded according to their values
+	// in the variable scope.
+	for k, variableValue := range m {
+		var expandedVars []string
+		for _, v := range variableValue {
+			expandedVar, err := expandVar(config, v, stringScope, stringListScope, exportedVars)
+			if err != nil {
+				panic(fmt.Errorf("Error expanding config variable %s=%s: %s", k, v, err))
+			}
+			expandedVars = append(expandedVars, expandedVar...)
+		}
+		// Assign the list as a bzl-private variable; this variable will be exported
+		// out through a constants struct later.
+		ret = append(ret, bazelConstant{
+			variableName:       k,
+			internalDefinition: starlark_fmt.PrintStringList(expandedVars, 0),
+		})
+	}
+	return ret
+}
+
+// ExportedStringListDictVariables is a mapping from variable names to a
+// dictionary which maps keys to lists of strings
+type ExportedStringListDictVariables map[string]map[string][]string
+
+func (m ExportedStringListDictVariables) set(k string, v map[string][]string) {
+	m[k] = v
+}
+
+// Since dictionaries are not supported in Ninja, we do not expand variables for dictionaries
+func (m ExportedStringListDictVariables) asBazel(_ Config, _ ExportedStringVariables,
+	_ ExportedStringListVariables, _ ExportedConfigDependingVariables) []bazelConstant {
+	ret := make([]bazelConstant, 0, len(m))
+	for k, dict := range m {
+		ret = append(ret, bazelConstant{
+			variableName:       k,
+			internalDefinition: starlark_fmt.PrintStringListDict(dict, 0),
+		})
+	}
+	return ret
+}
+
+// ExportedVariableReferenceDictVariables is a mapping from variable names to a
+// dictionary which references previously defined variables. This is used to
+// create a Starlark output such as:
+// 		string_var1 = "string1
+// 		var_ref_dict_var1 = {
+// 			"key1": string_var1
+// 		}
+// This type of variable collection must be expanded last so that it recognizes
+// previously defined variables.
+type ExportedVariableReferenceDictVariables map[string]map[string]string
+
+func (m ExportedVariableReferenceDictVariables) set(k string, v map[string]string) {
+	m[k] = v
+}
+
+func (m ExportedVariableReferenceDictVariables) asBazel(_ Config, _ ExportedStringVariables,
+	_ ExportedStringListVariables, _ ExportedConfigDependingVariables) []bazelConstant {
+	ret := make([]bazelConstant, 0, len(m))
+	for n, dict := range m {
+		for k, v := range dict {
+			matches, err := variableReference(v)
+			if err != nil {
+				panic(err)
+			} else if !matches.matches {
+				panic(fmt.Errorf("Expected a variable reference, got %q", v))
+			} else if len(matches.fullVariableReference) != len(v) {
+				panic(fmt.Errorf("Expected only a variable reference, got %q", v))
+			}
+			dict[k] = "_" + matches.variable
+		}
+		ret = append(ret, bazelConstant{
+			variableName:       n,
+			internalDefinition: starlark_fmt.PrintDict(dict, 0),
+			sortLast:           true,
+		})
+	}
+	return ret
+}
+
+// BazelToolchainVars expands an ExportedVariables collection and returns a string
+// of formatted Starlark variable definitions
+func BazelToolchainVars(config Config, exportedVars ExportedVariables) string {
+	results := exportedVars.asBazel(
+		config,
+		exportedVars.exportedStringVars,
+		exportedVars.exportedStringListVars,
+		exportedVars.exportedConfigDependingVars,
+	)
+
+	sort.Slice(results, func(i, j int) bool {
+		if results[i].sortLast != results[j].sortLast {
+			return !results[i].sortLast
+		}
+		return results[i].variableName < results[j].variableName
+	})
+
+	definitions := make([]string, 0, len(results))
+	constants := make([]string, 0, len(results))
+	for _, b := range results {
+		definitions = append(definitions,
+			fmt.Sprintf("_%s = %s", b.variableName, b.internalDefinition))
+		constants = append(constants,
+			fmt.Sprintf("%[1]s%[2]s = _%[2]s,", starlark_fmt.Indention(1), b.variableName))
+	}
+
+	// Build the exported constants struct.
+	ret := bazel.GeneratedBazelFileWarning
+	ret += "\n\n"
+	ret += strings.Join(definitions, "\n\n")
+	ret += "\n\n"
+	ret += "constants = struct(\n"
+	ret += strings.Join(constants, "\n")
+	ret += "\n)"
+
+	return ret
+}
+
+type match struct {
+	matches               bool
+	fullVariableReference string
+	variable              string
+}
+
+func variableReference(input string) (match, error) {
+	// e.g. "${ExternalCflags}"
+	r := regexp.MustCompile(`\${(?:config\.)?([a-zA-Z0-9_]+)}`)
+
+	matches := r.FindStringSubmatch(input)
+	if len(matches) == 0 {
+		return match{}, nil
+	}
+	if len(matches) != 2 {
+		return match{}, fmt.Errorf("Expected to only match 1 subexpression in %s, got %d", input, len(matches)-1)
+	}
+	return match{
+		matches:               true,
+		fullVariableReference: matches[0],
+		// Index 1 of FindStringSubmatch contains the subexpression match
+		// (variable name) of the capture group.
+		variable: matches[1],
+	}, nil
+}
+
+// expandVar recursively expand interpolated variables in the exportedVars scope.
+//
+// We're using a string slice to track the seen variables to avoid
+// stackoverflow errors with infinite recursion. it's simpler to use a
+// string slice than to handle a pass-by-referenced map, which would make it
+// quite complex to track depth-first interpolations. It's also unlikely the
+// interpolation stacks are deep (n > 1).
+func expandVar(config Config, toExpand string, stringScope ExportedStringVariables,
+	stringListScope ExportedStringListVariables, exportedVars ExportedConfigDependingVariables) ([]string, error) {
+
+	// Internal recursive function.
+	var expandVarInternal func(string, map[string]bool) (string, error)
+	expandVarInternal = func(toExpand string, seenVars map[string]bool) (string, error) {
+		var ret string
+		remainingString := toExpand
+		for len(remainingString) > 0 {
+			matches, err := variableReference(remainingString)
+			if err != nil {
+				panic(err)
+			}
+			if !matches.matches {
+				return ret + remainingString, nil
+			}
+			matchIndex := strings.Index(remainingString, matches.fullVariableReference)
+			ret += remainingString[:matchIndex]
+			remainingString = remainingString[matchIndex+len(matches.fullVariableReference):]
+
+			variable := matches.variable
+			// toExpand contains a variable.
+			if _, ok := seenVars[variable]; ok {
+				return ret, fmt.Errorf(
+					"Unbounded recursive interpolation of variable: %s", variable)
+			}
+			// A map is passed-by-reference. Create a new map for
+			// this scope to prevent variables seen in one depth-first expansion
+			// to be also treated as "seen" in other depth-first traversals.
+			newSeenVars := map[string]bool{}
+			for k := range seenVars {
+				newSeenVars[k] = true
+			}
+			newSeenVars[variable] = true
+			if unexpandedVars, ok := stringListScope[variable]; ok {
+				expandedVars := []string{}
+				for _, unexpandedVar := range unexpandedVars {
+					expandedVar, err := expandVarInternal(unexpandedVar, newSeenVars)
+					if err != nil {
+						return ret, err
+					}
+					expandedVars = append(expandedVars, expandedVar)
+				}
+				ret += strings.Join(expandedVars, " ")
+			} else if unexpandedVar, ok := stringScope[variable]; ok {
+				expandedVar, err := expandVarInternal(unexpandedVar, newSeenVars)
+				if err != nil {
+					return ret, err
+				}
+				ret += expandedVar
+			} else if unevaluatedVar, ok := exportedVars[variable]; ok {
+				evalFunc := reflect.ValueOf(unevaluatedVar)
+				validateVariableMethod(variable, evalFunc)
+				evaluatedResult := evalFunc.Call([]reflect.Value{reflect.ValueOf(config)})
+				evaluatedValue := evaluatedResult[0].Interface().(string)
+				expandedVar, err := expandVarInternal(evaluatedValue, newSeenVars)
+				if err != nil {
+					return ret, err
+				}
+				ret += expandedVar
+			} else {
+				return "", fmt.Errorf("Unbound config variable %s", variable)
+			}
+		}
+		return ret, nil
+	}
+	var ret []string
+	for _, v := range strings.Split(toExpand, " ") {
+		val, err := expandVarInternal(v, map[string]bool{})
+		if err != nil {
+			return ret, err
+		}
+		ret = append(ret, val)
+	}
+
+	return ret, nil
+}
+
+func validateVariableMethod(name string, methodValue reflect.Value) {
+	methodType := methodValue.Type()
+	if methodType.Kind() != reflect.Func {
+		panic(fmt.Errorf("method given for variable %s is not a function",
+			name))
+	}
+	if n := methodType.NumIn(); n != 1 {
+		panic(fmt.Errorf("method for variable %s has %d inputs (should be 1)",
+			name, n))
+	}
+	if n := methodType.NumOut(); n != 1 {
+		panic(fmt.Errorf("method for variable %s has %d outputs (should be 1)",
+			name, n))
+	}
+	if kind := methodType.Out(0).Kind(); kind != reflect.String {
+		panic(fmt.Errorf("method for variable %s does not return a string",
+			name))
+	}
+}
diff --git a/cc/config/bp2build_test.go b/android/config_bp2build_test.go
similarity index 68%
rename from cc/config/bp2build_test.go
rename to android/config_bp2build_test.go
index 9a8178a..05a1798 100644
--- a/cc/config/bp2build_test.go
+++ b/android/config_bp2build_test.go
@@ -12,25 +12,24 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package config
+package android
 
 import (
+	"android/soong/bazel"
 	"testing"
-
-	"android/soong/android"
 )
 
 func TestExpandVars(t *testing.T) {
-	android_arm64_config := android.TestConfig("out", nil, "", nil)
-	android_arm64_config.BuildOS = android.Android
-	android_arm64_config.BuildArch = android.Arm64
+	android_arm64_config := TestConfig("out", nil, "", nil)
+	android_arm64_config.BuildOS = Android
+	android_arm64_config.BuildArch = Arm64
 
 	testCases := []struct {
 		description     string
-		config          android.Config
-		stringScope     exportedStringVariables
-		stringListScope exportedStringListVariables
-		configVars      exportedConfigDependingVariables
+		config          Config
+		stringScope     ExportedStringVariables
+		stringListScope ExportedStringListVariables
+		configVars      ExportedConfigDependingVariables
 		toExpand        string
 		expectedValues  []string
 	}{
@@ -41,7 +40,7 @@
 		},
 		{
 			description: "single level expansion for string var",
-			stringScope: exportedStringVariables{
+			stringScope: ExportedStringVariables{
 				"foo": "bar",
 			},
 			toExpand:       "${foo}",
@@ -49,7 +48,7 @@
 		},
 		{
 			description: "single level expansion with short-name for string var",
-			stringScope: exportedStringVariables{
+			stringScope: ExportedStringVariables{
 				"foo": "bar",
 			},
 			toExpand:       "${config.foo}",
@@ -57,7 +56,7 @@
 		},
 		{
 			description: "single level expansion string list var",
-			stringListScope: exportedStringListVariables{
+			stringListScope: ExportedStringListVariables{
 				"foo": []string{"bar"},
 			},
 			toExpand:       "${foo}",
@@ -65,11 +64,11 @@
 		},
 		{
 			description: "mixed level expansion for string list var",
-			stringScope: exportedStringVariables{
+			stringScope: ExportedStringVariables{
 				"foo": "${bar}",
 				"qux": "hello",
 			},
-			stringListScope: exportedStringListVariables{
+			stringListScope: ExportedStringListVariables{
 				"bar": []string{"baz", "${qux}"},
 			},
 			toExpand:       "${foo}",
@@ -77,7 +76,7 @@
 		},
 		{
 			description: "double level expansion",
-			stringListScope: exportedStringListVariables{
+			stringListScope: ExportedStringListVariables{
 				"foo": []string{"${bar}"},
 				"bar": []string{"baz"},
 			},
@@ -86,7 +85,7 @@
 		},
 		{
 			description: "double level expansion with a literal",
-			stringListScope: exportedStringListVariables{
+			stringListScope: ExportedStringListVariables{
 				"a": []string{"${b}", "c"},
 				"b": []string{"d"},
 			},
@@ -95,7 +94,7 @@
 		},
 		{
 			description: "double level expansion, with two variables in a string",
-			stringListScope: exportedStringListVariables{
+			stringListScope: ExportedStringListVariables{
 				"a": []string{"${b} ${c}"},
 				"b": []string{"d"},
 				"c": []string{"e"},
@@ -105,7 +104,7 @@
 		},
 		{
 			description: "triple level expansion with two variables in a string",
-			stringListScope: exportedStringListVariables{
+			stringListScope: ExportedStringListVariables{
 				"a": []string{"${b} ${c}"},
 				"b": []string{"${c}", "${d}"},
 				"c": []string{"${d}"},
@@ -116,9 +115,9 @@
 		},
 		{
 			description: "expansion with config depending vars",
-			configVars: exportedConfigDependingVariables{
-				"a": func(c android.Config) string { return c.BuildOS.String() },
-				"b": func(c android.Config) string { return c.BuildArch.String() },
+			configVars: ExportedConfigDependingVariables{
+				"a": func(c Config) string { return c.BuildOS.String() },
+				"b": func(c Config) string { return c.BuildArch.String() },
 			},
 			config:         android_arm64_config,
 			toExpand:       "${a}-${b}",
@@ -126,14 +125,14 @@
 		},
 		{
 			description: "double level multi type expansion",
-			stringListScope: exportedStringListVariables{
+			stringListScope: ExportedStringListVariables{
 				"platform": []string{"${os}-${arch}"},
 				"const":    []string{"const"},
 			},
-			configVars: exportedConfigDependingVariables{
-				"os":   func(c android.Config) string { return c.BuildOS.String() },
-				"arch": func(c android.Config) string { return c.BuildArch.String() },
-				"foo":  func(c android.Config) string { return "foo" },
+			configVars: ExportedConfigDependingVariables{
+				"os":   func(c Config) string { return c.BuildOS.String() },
+				"arch": func(c Config) string { return c.BuildArch.String() },
+				"foo":  func(c Config) string { return "foo" },
 			},
 			config:         android_arm64_config,
 			toExpand:       "${const}/${platform}/${foo}",
@@ -160,19 +159,19 @@
 func TestBazelToolchainVars(t *testing.T) {
 	testCases := []struct {
 		name        string
-		config      android.Config
-		vars        []bazelVarExporter
+		config      Config
+		vars        ExportedVariables
 		expectedOut string
 	}{
 		{
 			name: "exports strings",
-			vars: []bazelVarExporter{
-				exportedStringVariables{
+			vars: ExportedVariables{
+				exportedStringVars: ExportedStringVariables{
 					"a": "b",
 					"c": "d",
 				},
 			},
-			expectedOut: `# GENERATED FOR BAZEL FROM SOONG. DO NOT EDIT.
+			expectedOut: bazel.GeneratedBazelFileWarning + `
 
 _a = "b"
 
@@ -185,13 +184,13 @@
 		},
 		{
 			name: "exports string lists",
-			vars: []bazelVarExporter{
-				exportedStringListVariables{
+			vars: ExportedVariables{
+				exportedStringListVars: ExportedStringListVariables{
 					"a": []string{"b1", "b2"},
 					"c": []string{"d1", "d2"},
 				},
 			},
-			expectedOut: `# GENERATED FOR BAZEL FROM SOONG. DO NOT EDIT.
+			expectedOut: bazel.GeneratedBazelFileWarning + `
 
 _a = [
     "b1",
@@ -210,13 +209,13 @@
 		},
 		{
 			name: "exports string lists dicts",
-			vars: []bazelVarExporter{
-				exportedStringListDictVariables{
-					"a": map[string][]string{"b1": []string{"b2"}},
-					"c": map[string][]string{"d1": []string{"d2"}},
+			vars: ExportedVariables{
+				exportedStringListDictVars: ExportedStringListDictVariables{
+					"a": map[string][]string{"b1": {"b2"}},
+					"c": map[string][]string{"d1": {"d2"}},
 				},
 			},
-			expectedOut: `# GENERATED FOR BAZEL FROM SOONG. DO NOT EDIT.
+			expectedOut: bazel.GeneratedBazelFileWarning + `
 
 _a = {
     "b1": ["b2"],
@@ -233,13 +232,13 @@
 		},
 		{
 			name: "exports dict with var refs",
-			vars: []bazelVarExporter{
-				exportedVariableReferenceDictVariables{
+			vars: ExportedVariables{
+				exportedVariableReferenceDictVars: ExportedVariableReferenceDictVariables{
 					"a": map[string]string{"b1": "${b2}"},
 					"c": map[string]string{"d1": "${config.d2}"},
 				},
 			},
-			expectedOut: `# GENERATED FOR BAZEL FROM SOONG. DO NOT EDIT.
+			expectedOut: bazel.GeneratedBazelFileWarning + `
 
 _a = {
     "b1": _b2,
@@ -256,25 +255,25 @@
 		},
 		{
 			name: "sorts across types with variable references last",
-			vars: []bazelVarExporter{
-				exportedStringVariables{
+			vars: ExportedVariables{
+				exportedStringVars: ExportedStringVariables{
 					"b": "b-val",
 					"d": "d-val",
 				},
-				exportedStringListVariables{
+				exportedStringListVars: ExportedStringListVariables{
 					"c": []string{"c-val"},
 					"e": []string{"e-val"},
 				},
-				exportedStringListDictVariables{
-					"a": map[string][]string{"a1": []string{"a2"}},
-					"f": map[string][]string{"f1": []string{"f2"}},
+				exportedStringListDictVars: ExportedStringListDictVariables{
+					"a": map[string][]string{"a1": {"a2"}},
+					"f": map[string][]string{"f1": {"f2"}},
 				},
-				exportedVariableReferenceDictVariables{
+				exportedVariableReferenceDictVars: ExportedVariableReferenceDictVariables{
 					"aa": map[string]string{"b1": "${b}"},
 					"cc": map[string]string{"d1": "${config.d}"},
 				},
 			},
-			expectedOut: `# GENERATED FOR BAZEL FROM SOONG. DO NOT EDIT.
+			expectedOut: bazel.GeneratedBazelFileWarning + `
 
 _a = {
     "a1": ["a2"],
@@ -315,7 +314,7 @@
 
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
-			out := bazelToolchainVars(tc.config, tc.vars...)
+			out := BazelToolchainVars(tc.config, tc.vars)
 			if out != tc.expectedOut {
 				t.Errorf("Expected \n%s, got \n%s", tc.expectedOut, out)
 			}
diff --git a/bazel/constants.go b/bazel/constants.go
index 6beb496..b10f256 100644
--- a/bazel/constants.go
+++ b/bazel/constants.go
@@ -21,7 +21,7 @@
 
 	SoongInjectionDirName = "soong_injection"
 
-	GeneratedBazelFileWarning = "# GENERATED FOR BAZEL FROM SOONG. DO NOT EDIT"
+	GeneratedBazelFileWarning = "# GENERATED FOR BAZEL FROM SOONG. DO NOT EDIT."
 )
 
 // String returns the name of the run.
diff --git a/cc/config/Android.bp b/cc/config/Android.bp
index e1b0605..1a21c13 100644
--- a/cc/config/Android.bp
+++ b/cc/config/Android.bp
@@ -11,7 +11,6 @@
         "soong-starlark-format",
     ],
     srcs: [
-        "bp2build.go",
         "clang.go",
         "global.go",
         "tidy.go",
@@ -33,7 +32,6 @@
         "arm64_linux_host.go",
     ],
     testSrcs: [
-        "bp2build_test.go",
         "tidy_test.go",
     ],
 }
diff --git a/cc/config/arm64_device.go b/cc/config/arm64_device.go
index 4d0ae1a..dfe143f 100644
--- a/cc/config/arm64_device.go
+++ b/cc/config/arm64_device.go
@@ -98,28 +98,28 @@
 	pctx.SourcePathVariable("Arm64GccRoot",
 		"prebuilts/gcc/${HostPrebuiltTag}/aarch64/aarch64-linux-android-${arm64GccVersion}")
 
-	exportStringListStaticVariable("Arm64Ldflags", arm64Ldflags)
-	exportStringListStaticVariable("Arm64Lldflags", arm64Lldflags)
+	exportedVars.ExportStringListStaticVariable("Arm64Ldflags", arm64Ldflags)
+	exportedVars.ExportStringListStaticVariable("Arm64Lldflags", arm64Lldflags)
 
-	exportStringListStaticVariable("Arm64Cflags", arm64Cflags)
-	exportStringListStaticVariable("Arm64Cppflags", arm64Cppflags)
+	exportedVars.ExportStringListStaticVariable("Arm64Cflags", arm64Cflags)
+	exportedVars.ExportStringListStaticVariable("Arm64Cppflags", arm64Cppflags)
 
-	exportedVariableReferenceDictVars.Set("Arm64ArchVariantCflags", arm64ArchVariantCflagsVar)
-	exportedVariableReferenceDictVars.Set("Arm64CpuVariantCflags", arm64CpuVariantCflagsVar)
-	exportedVariableReferenceDictVars.Set("Arm64CpuVariantLdflags", arm64CpuVariantLdflags)
+	exportedVars.ExportVariableReferenceDict("Arm64ArchVariantCflags", arm64ArchVariantCflagsVar)
+	exportedVars.ExportVariableReferenceDict("Arm64CpuVariantCflags", arm64CpuVariantCflagsVar)
+	exportedVars.ExportVariableReferenceDict("Arm64CpuVariantLdflags", arm64CpuVariantLdflags)
 
-	exportStringListStaticVariable("Arm64Armv8ACflags", arm64ArchVariantCflags["armv8-a"])
-	exportStringListStaticVariable("Arm64Armv8ABranchProtCflags", arm64ArchVariantCflags["armv8-a-branchprot"])
-	exportStringListStaticVariable("Arm64Armv82ACflags", arm64ArchVariantCflags["armv8-2a"])
-	exportStringListStaticVariable("Arm64Armv82ADotprodCflags", arm64ArchVariantCflags["armv8-2a-dotprod"])
+	exportedVars.ExportStringListStaticVariable("Arm64Armv8ACflags", arm64ArchVariantCflags["armv8-a"])
+	exportedVars.ExportStringListStaticVariable("Arm64Armv8ABranchProtCflags", arm64ArchVariantCflags["armv8-a-branchprot"])
+	exportedVars.ExportStringListStaticVariable("Arm64Armv82ACflags", arm64ArchVariantCflags["armv8-2a"])
+	exportedVars.ExportStringListStaticVariable("Arm64Armv82ADotprodCflags", arm64ArchVariantCflags["armv8-2a-dotprod"])
 
-	exportStringListStaticVariable("Arm64CortexA53Cflags", arm64CpuVariantCflags["cortex-a53"])
-	exportStringListStaticVariable("Arm64CortexA55Cflags", arm64CpuVariantCflags["cortex-a55"])
-	exportStringListStaticVariable("Arm64KryoCflags", arm64CpuVariantCflags["kryo"])
-	exportStringListStaticVariable("Arm64ExynosM1Cflags", arm64CpuVariantCflags["exynos-m1"])
-	exportStringListStaticVariable("Arm64ExynosM2Cflags", arm64CpuVariantCflags["exynos-m2"])
+	exportedVars.ExportStringListStaticVariable("Arm64CortexA53Cflags", arm64CpuVariantCflags["cortex-a53"])
+	exportedVars.ExportStringListStaticVariable("Arm64CortexA55Cflags", arm64CpuVariantCflags["cortex-a55"])
+	exportedVars.ExportStringListStaticVariable("Arm64KryoCflags", arm64CpuVariantCflags["kryo"])
+	exportedVars.ExportStringListStaticVariable("Arm64ExynosM1Cflags", arm64CpuVariantCflags["exynos-m1"])
+	exportedVars.ExportStringListStaticVariable("Arm64ExynosM2Cflags", arm64CpuVariantCflags["exynos-m2"])
 
-	exportStringListStaticVariable("Arm64FixCortexA53Ldflags", []string{"-Wl,--fix-cortex-a53-843419"})
+	exportedVars.ExportStringListStaticVariable("Arm64FixCortexA53Ldflags", []string{"-Wl,--fix-cortex-a53-843419"})
 }
 
 var (
diff --git a/cc/config/arm_device.go b/cc/config/arm_device.go
index 4466632..d702c61 100644
--- a/cc/config/arm_device.go
+++ b/cc/config/arm_device.go
@@ -178,41 +178,41 @@
 	pctx.SourcePathVariable("ArmGccRoot", "prebuilts/gcc/${HostPrebuiltTag}/arm/arm-linux-androideabi-${armGccVersion}")
 
 	// Just exported. Not created as a Ninja static variable.
-	exportedStringVars.Set("ArmClangTriple", clangTriple)
+	exportedVars.ExportString("ArmClangTriple", clangTriple)
 
-	exportStringListStaticVariable("ArmLdflags", armLdflags)
-	exportStringListStaticVariable("ArmLldflags", armLldflags)
+	exportedVars.ExportStringListStaticVariable("ArmLdflags", armLdflags)
+	exportedVars.ExportStringListStaticVariable("ArmLldflags", armLldflags)
 
-	exportStringListStaticVariable("ArmFixCortexA8LdFlags", armFixCortexA8LdFlags)
-	exportStringListStaticVariable("ArmNoFixCortexA8LdFlags", armNoFixCortexA8LdFlags)
+	exportedVars.ExportStringListStaticVariable("ArmFixCortexA8LdFlags", armFixCortexA8LdFlags)
+	exportedVars.ExportStringListStaticVariable("ArmNoFixCortexA8LdFlags", armNoFixCortexA8LdFlags)
 
 	// Clang cflags
-	exportStringListStaticVariable("ArmToolchainCflags", armToolchainCflags)
-	exportStringListStaticVariable("ArmCflags", armCflags)
-	exportStringListStaticVariable("ArmCppflags", armCppflags)
+	exportedVars.ExportStringListStaticVariable("ArmToolchainCflags", armToolchainCflags)
+	exportedVars.ExportStringListStaticVariable("ArmCflags", armCflags)
+	exportedVars.ExportStringListStaticVariable("ArmCppflags", armCppflags)
 
 	// Clang ARM vs. Thumb instruction set cflags
-	exportStringListStaticVariable("ArmArmCflags", armArmCflags)
-	exportStringListStaticVariable("ArmThumbCflags", armThumbCflags)
+	exportedVars.ExportStringListStaticVariable("ArmArmCflags", armArmCflags)
+	exportedVars.ExportStringListStaticVariable("ArmThumbCflags", armThumbCflags)
 
-	exportedVariableReferenceDictVars.Set("ArmArchVariantCflags", armArchVariantCflagsVar)
-	exportedVariableReferenceDictVars.Set("ArmCpuVariantCflags", armCpuVariantCflagsVar)
+	exportedVars.ExportVariableReferenceDict("ArmArchVariantCflags", armArchVariantCflagsVar)
+	exportedVars.ExportVariableReferenceDict("ArmCpuVariantCflags", armCpuVariantCflagsVar)
 
 	// Clang arch variant cflags
-	exportStringListStaticVariable("ArmArmv7ACflags", armArchVariantCflags["armv7-a"])
-	exportStringListStaticVariable("ArmArmv7ANeonCflags", armArchVariantCflags["armv7-a-neon"])
-	exportStringListStaticVariable("ArmArmv8ACflags", armArchVariantCflags["armv8-a"])
-	exportStringListStaticVariable("ArmArmv82ACflags", armArchVariantCflags["armv8-2a"])
+	exportedVars.ExportStringListStaticVariable("ArmArmv7ACflags", armArchVariantCflags["armv7-a"])
+	exportedVars.ExportStringListStaticVariable("ArmArmv7ANeonCflags", armArchVariantCflags["armv7-a-neon"])
+	exportedVars.ExportStringListStaticVariable("ArmArmv8ACflags", armArchVariantCflags["armv8-a"])
+	exportedVars.ExportStringListStaticVariable("ArmArmv82ACflags", armArchVariantCflags["armv8-2a"])
 
 	// Clang cpu variant cflags
-	exportStringListStaticVariable("ArmGenericCflags", armCpuVariantCflags[""])
-	exportStringListStaticVariable("ArmCortexA7Cflags", armCpuVariantCflags["cortex-a7"])
-	exportStringListStaticVariable("ArmCortexA8Cflags", armCpuVariantCflags["cortex-a8"])
-	exportStringListStaticVariable("ArmCortexA15Cflags", armCpuVariantCflags["cortex-a15"])
-	exportStringListStaticVariable("ArmCortexA53Cflags", armCpuVariantCflags["cortex-a53"])
-	exportStringListStaticVariable("ArmCortexA55Cflags", armCpuVariantCflags["cortex-a55"])
-	exportStringListStaticVariable("ArmKraitCflags", armCpuVariantCflags["krait"])
-	exportStringListStaticVariable("ArmKryoCflags", armCpuVariantCflags["kryo"])
+	exportedVars.ExportStringListStaticVariable("ArmGenericCflags", armCpuVariantCflags[""])
+	exportedVars.ExportStringListStaticVariable("ArmCortexA7Cflags", armCpuVariantCflags["cortex-a7"])
+	exportedVars.ExportStringListStaticVariable("ArmCortexA8Cflags", armCpuVariantCflags["cortex-a8"])
+	exportedVars.ExportStringListStaticVariable("ArmCortexA15Cflags", armCpuVariantCflags["cortex-a15"])
+	exportedVars.ExportStringListStaticVariable("ArmCortexA53Cflags", armCpuVariantCflags["cortex-a53"])
+	exportedVars.ExportStringListStaticVariable("ArmCortexA55Cflags", armCpuVariantCflags["cortex-a55"])
+	exportedVars.ExportStringListStaticVariable("ArmKraitCflags", armCpuVariantCflags["krait"])
+	exportedVars.ExportStringListStaticVariable("ArmKryoCflags", armCpuVariantCflags["kryo"])
 }
 
 var (
diff --git a/cc/config/bp2build.go b/cc/config/bp2build.go
deleted file mode 100644
index 73f65f5..0000000
--- a/cc/config/bp2build.go
+++ /dev/null
@@ -1,378 +0,0 @@
-// Copyright 2021 Google Inc. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package config
-
-import (
-	"fmt"
-	"reflect"
-	"regexp"
-	"sort"
-	"strings"
-
-	"android/soong/android"
-	"android/soong/starlark_fmt"
-
-	"github.com/google/blueprint"
-)
-
-type bazelVarExporter interface {
-	asBazel(android.Config, exportedStringVariables, exportedStringListVariables, exportedConfigDependingVariables) []bazelConstant
-}
-
-// Helpers for exporting cc configuration information to Bazel.
-var (
-	// Maps containing toolchain variables that are independent of the
-	// environment variables of the build.
-	exportedStringListVars     = exportedStringListVariables{}
-	exportedStringVars         = exportedStringVariables{}
-	exportedStringListDictVars = exportedStringListDictVariables{}
-	// Note: these can only contain references to other variables and must be printed last
-	exportedVariableReferenceDictVars = exportedVariableReferenceDictVariables{}
-
-	/// Maps containing variables that are dependent on the build config.
-	exportedConfigDependingVars = exportedConfigDependingVariables{}
-)
-
-type exportedConfigDependingVariables map[string]interface{}
-
-func (m exportedConfigDependingVariables) Set(k string, v interface{}) {
-	m[k] = v
-}
-
-// Ensure that string s has no invalid characters to be generated into the bzl file.
-func validateCharacters(s string) string {
-	for _, c := range []string{`\n`, `"`, `\`} {
-		if strings.Contains(s, c) {
-			panic(fmt.Errorf("%s contains illegal character %s", s, c))
-		}
-	}
-	return s
-}
-
-type bazelConstant struct {
-	variableName       string
-	internalDefinition string
-	sortLast           bool
-}
-
-type exportedStringVariables map[string]string
-
-func (m exportedStringVariables) Set(k string, v string) {
-	m[k] = v
-}
-
-func (m exportedStringVariables) asBazel(config android.Config,
-	stringVars exportedStringVariables, stringListVars exportedStringListVariables, cfgDepVars exportedConfigDependingVariables) []bazelConstant {
-	ret := make([]bazelConstant, 0, len(m))
-	for k, variableValue := range m {
-		expandedVar, err := expandVar(config, variableValue, stringVars, stringListVars, cfgDepVars)
-		if err != nil {
-			panic(fmt.Errorf("error expanding config variable %s: %s", k, err))
-		}
-		if len(expandedVar) > 1 {
-			panic(fmt.Errorf("%s expands to more than one string value: %s", variableValue, expandedVar))
-		}
-		ret = append(ret, bazelConstant{
-			variableName:       k,
-			internalDefinition: fmt.Sprintf(`"%s"`, validateCharacters(expandedVar[0])),
-		})
-	}
-	return ret
-}
-
-// Convenience function to declare a static variable and export it to Bazel's cc_toolchain.
-func exportStringStaticVariable(name string, value string) {
-	pctx.StaticVariable(name, value)
-	exportedStringVars.Set(name, value)
-}
-
-type exportedStringListVariables map[string][]string
-
-func (m exportedStringListVariables) Set(k string, v []string) {
-	m[k] = v
-}
-
-func (m exportedStringListVariables) asBazel(config android.Config,
-	stringScope exportedStringVariables, stringListScope exportedStringListVariables,
-	exportedVars exportedConfigDependingVariables) []bazelConstant {
-	ret := make([]bazelConstant, 0, len(m))
-	// For each exported variable, recursively expand elements in the variableValue
-	// list to ensure that interpolated variables are expanded according to their values
-	// in the variable scope.
-	for k, variableValue := range m {
-		var expandedVars []string
-		for _, v := range variableValue {
-			expandedVar, err := expandVar(config, v, stringScope, stringListScope, exportedVars)
-			if err != nil {
-				panic(fmt.Errorf("Error expanding config variable %s=%s: %s", k, v, err))
-			}
-			expandedVars = append(expandedVars, expandedVar...)
-		}
-		// Assign the list as a bzl-private variable; this variable will be exported
-		// out through a constants struct later.
-		ret = append(ret, bazelConstant{
-			variableName:       k,
-			internalDefinition: starlark_fmt.PrintStringList(expandedVars, 0),
-		})
-	}
-	return ret
-}
-
-// Convenience function to declare a static "source path" variable and export it to Bazel's cc_toolchain.
-func exportVariableConfigMethod(name string, method interface{}) blueprint.Variable {
-	exportedConfigDependingVars.Set(name, method)
-	return pctx.VariableConfigMethod(name, method)
-}
-
-// Convenience function to declare a static "source path" variable and export it to Bazel's cc_toolchain.
-func exportSourcePathVariable(name string, value string) {
-	pctx.SourcePathVariable(name, value)
-	exportedStringVars.Set(name, value)
-}
-
-// Convenience function to declare a static variable and export it to Bazel's cc_toolchain.
-func exportStringListStaticVariable(name string, value []string) {
-	pctx.StaticVariable(name, strings.Join(value, " "))
-	exportedStringListVars.Set(name, value)
-}
-
-func ExportStringList(name string, value []string) {
-	exportedStringListVars.Set(name, value)
-}
-
-type exportedStringListDictVariables map[string]map[string][]string
-
-func (m exportedStringListDictVariables) Set(k string, v map[string][]string) {
-	m[k] = v
-}
-
-// Since dictionaries are not supported in Ninja, we do not expand variables for dictionaries
-func (m exportedStringListDictVariables) asBazel(_ android.Config, _ exportedStringVariables,
-	_ exportedStringListVariables, _ exportedConfigDependingVariables) []bazelConstant {
-	ret := make([]bazelConstant, 0, len(m))
-	for k, dict := range m {
-		ret = append(ret, bazelConstant{
-			variableName:       k,
-			internalDefinition: starlark_fmt.PrintStringListDict(dict, 0),
-		})
-	}
-	return ret
-}
-
-type exportedVariableReferenceDictVariables map[string]map[string]string
-
-func (m exportedVariableReferenceDictVariables) Set(k string, v map[string]string) {
-	m[k] = v
-}
-
-func (m exportedVariableReferenceDictVariables) asBazel(_ android.Config, _ exportedStringVariables,
-	_ exportedStringListVariables, _ exportedConfigDependingVariables) []bazelConstant {
-	ret := make([]bazelConstant, 0, len(m))
-	for n, dict := range m {
-		for k, v := range dict {
-			matches, err := variableReference(v)
-			if err != nil {
-				panic(err)
-			} else if !matches.matches {
-				panic(fmt.Errorf("Expected a variable reference, got %q", v))
-			} else if len(matches.fullVariableReference) != len(v) {
-				panic(fmt.Errorf("Expected only a variable reference, got %q", v))
-			}
-			dict[k] = "_" + matches.variable
-		}
-		ret = append(ret, bazelConstant{
-			variableName:       n,
-			internalDefinition: starlark_fmt.PrintDict(dict, 0),
-			sortLast:           true,
-		})
-	}
-	return ret
-}
-
-// BazelCcToolchainVars generates bzl file content containing variables for
-// Bazel's cc_toolchain configuration.
-func BazelCcToolchainVars(config android.Config) string {
-	return bazelToolchainVars(
-		config,
-		exportedStringListDictVars,
-		exportedStringListVars,
-		exportedStringVars,
-		exportedVariableReferenceDictVars)
-}
-
-func bazelToolchainVars(config android.Config, vars ...bazelVarExporter) string {
-	ret := "# GENERATED FOR BAZEL FROM SOONG. DO NOT EDIT.\n\n"
-
-	results := []bazelConstant{}
-	for _, v := range vars {
-		results = append(results, v.asBazel(config, exportedStringVars, exportedStringListVars, exportedConfigDependingVars)...)
-	}
-
-	sort.Slice(results, func(i, j int) bool {
-		if results[i].sortLast != results[j].sortLast {
-			return !results[i].sortLast
-		}
-		return results[i].variableName < results[j].variableName
-	})
-
-	definitions := make([]string, 0, len(results))
-	constants := make([]string, 0, len(results))
-	for _, b := range results {
-		definitions = append(definitions,
-			fmt.Sprintf("_%s = %s", b.variableName, b.internalDefinition))
-		constants = append(constants,
-			fmt.Sprintf("%[1]s%[2]s = _%[2]s,", starlark_fmt.Indention(1), b.variableName))
-	}
-
-	// Build the exported constants struct.
-	ret += strings.Join(definitions, "\n\n")
-	ret += "\n\n"
-	ret += "constants = struct(\n"
-	ret += strings.Join(constants, "\n")
-	ret += "\n)"
-
-	return ret
-}
-
-type match struct {
-	matches               bool
-	fullVariableReference string
-	variable              string
-}
-
-func variableReference(input string) (match, error) {
-	// e.g. "${ExternalCflags}"
-	r := regexp.MustCompile(`\${(?:config\.)?([a-zA-Z0-9_]+)}`)
-
-	matches := r.FindStringSubmatch(input)
-	if len(matches) == 0 {
-		return match{}, nil
-	}
-	if len(matches) != 2 {
-		return match{}, fmt.Errorf("Expected to only match 1 subexpression in %s, got %d", input, len(matches)-1)
-	}
-	return match{
-		matches:               true,
-		fullVariableReference: matches[0],
-		// Index 1 of FindStringSubmatch contains the subexpression match
-		// (variable name) of the capture group.
-		variable: matches[1],
-	}, nil
-}
-
-// expandVar recursively expand interpolated variables in the exportedVars scope.
-//
-// We're using a string slice to track the seen variables to avoid
-// stackoverflow errors with infinite recursion. it's simpler to use a
-// string slice than to handle a pass-by-referenced map, which would make it
-// quite complex to track depth-first interpolations. It's also unlikely the
-// interpolation stacks are deep (n > 1).
-func expandVar(config android.Config, toExpand string, stringScope exportedStringVariables,
-	stringListScope exportedStringListVariables, exportedVars exportedConfigDependingVariables) ([]string, error) {
-
-	// Internal recursive function.
-	var expandVarInternal func(string, map[string]bool) (string, error)
-	expandVarInternal = func(toExpand string, seenVars map[string]bool) (string, error) {
-		var ret string
-		remainingString := toExpand
-		for len(remainingString) > 0 {
-			matches, err := variableReference(remainingString)
-			if err != nil {
-				panic(err)
-			}
-			if !matches.matches {
-				return ret + remainingString, nil
-			}
-			matchIndex := strings.Index(remainingString, matches.fullVariableReference)
-			ret += remainingString[:matchIndex]
-			remainingString = remainingString[matchIndex+len(matches.fullVariableReference):]
-
-			variable := matches.variable
-			// toExpand contains a variable.
-			if _, ok := seenVars[variable]; ok {
-				return ret, fmt.Errorf(
-					"Unbounded recursive interpolation of variable: %s", variable)
-			}
-			// A map is passed-by-reference. Create a new map for
-			// this scope to prevent variables seen in one depth-first expansion
-			// to be also treated as "seen" in other depth-first traversals.
-			newSeenVars := map[string]bool{}
-			for k := range seenVars {
-				newSeenVars[k] = true
-			}
-			newSeenVars[variable] = true
-			if unexpandedVars, ok := stringListScope[variable]; ok {
-				expandedVars := []string{}
-				for _, unexpandedVar := range unexpandedVars {
-					expandedVar, err := expandVarInternal(unexpandedVar, newSeenVars)
-					if err != nil {
-						return ret, err
-					}
-					expandedVars = append(expandedVars, expandedVar)
-				}
-				ret += strings.Join(expandedVars, " ")
-			} else if unexpandedVar, ok := stringScope[variable]; ok {
-				expandedVar, err := expandVarInternal(unexpandedVar, newSeenVars)
-				if err != nil {
-					return ret, err
-				}
-				ret += expandedVar
-			} else if unevaluatedVar, ok := exportedVars[variable]; ok {
-				evalFunc := reflect.ValueOf(unevaluatedVar)
-				validateVariableMethod(variable, evalFunc)
-				evaluatedResult := evalFunc.Call([]reflect.Value{reflect.ValueOf(config)})
-				evaluatedValue := evaluatedResult[0].Interface().(string)
-				expandedVar, err := expandVarInternal(evaluatedValue, newSeenVars)
-				if err != nil {
-					return ret, err
-				}
-				ret += expandedVar
-			} else {
-				return "", fmt.Errorf("Unbound config variable %s", variable)
-			}
-		}
-		return ret, nil
-	}
-	var ret []string
-	for _, v := range strings.Split(toExpand, " ") {
-		val, err := expandVarInternal(v, map[string]bool{})
-		if err != nil {
-			return ret, err
-		}
-		ret = append(ret, val)
-	}
-
-	return ret, nil
-}
-
-func validateVariableMethod(name string, methodValue reflect.Value) {
-	methodType := methodValue.Type()
-	if methodType.Kind() != reflect.Func {
-		panic(fmt.Errorf("method given for variable %s is not a function",
-			name))
-	}
-	if n := methodType.NumIn(); n != 1 {
-		panic(fmt.Errorf("method for variable %s has %d inputs (should be 1)",
-			name, n))
-	}
-	if n := methodType.NumOut(); n != 1 {
-		panic(fmt.Errorf("method for variable %s has %d outputs (should be 1)",
-			name, n))
-	}
-	if kind := methodType.Out(0).Kind(); kind != reflect.String {
-		panic(fmt.Errorf("method for variable %s does not return a string",
-			name))
-	}
-}
diff --git a/cc/config/global.go b/cc/config/global.go
index fad675a..f5b8f3c 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -23,6 +23,9 @@
 )
 
 var (
+	pctx         = android.NewPackageContext("android/soong/cc/config")
+	exportedVars = android.NewExportedVariables(pctx)
+
 	// Flags used by lots of devices.  Putting them in package static variables
 	// will save bytes in build.ninja so they aren't repeated for every file
 	commonGlobalCflags = []string{
@@ -299,20 +302,28 @@
 	WarningAllowedOldProjects = []string{}
 )
 
-var pctx = android.NewPackageContext("android/soong/cc/config")
+// BazelCcToolchainVars generates bzl file content containing variables for
+// Bazel's cc_toolchain configuration.
+func BazelCcToolchainVars(config android.Config) string {
+	return android.BazelToolchainVars(config, exportedVars)
+}
+
+func ExportStringList(name string, value []string) {
+	exportedVars.ExportStringList(name, value)
+}
 
 func init() {
 	if runtime.GOOS == "linux" {
 		commonGlobalCflags = append(commonGlobalCflags, "-fdebug-prefix-map=/proc/self/cwd=")
 	}
 
-	exportStringListStaticVariable("CommonGlobalConlyflags", commonGlobalConlyflags)
-	exportStringListStaticVariable("DeviceGlobalCppflags", deviceGlobalCppflags)
-	exportStringListStaticVariable("DeviceGlobalLdflags", deviceGlobalLdflags)
-	exportStringListStaticVariable("DeviceGlobalLldflags", deviceGlobalLldflags)
-	exportStringListStaticVariable("HostGlobalCppflags", hostGlobalCppflags)
-	exportStringListStaticVariable("HostGlobalLdflags", hostGlobalLdflags)
-	exportStringListStaticVariable("HostGlobalLldflags", hostGlobalLldflags)
+	exportedVars.ExportStringListStaticVariable("CommonGlobalConlyflags", commonGlobalConlyflags)
+	exportedVars.ExportStringListStaticVariable("DeviceGlobalCppflags", deviceGlobalCppflags)
+	exportedVars.ExportStringListStaticVariable("DeviceGlobalLdflags", deviceGlobalLdflags)
+	exportedVars.ExportStringListStaticVariable("DeviceGlobalLldflags", deviceGlobalLldflags)
+	exportedVars.ExportStringListStaticVariable("HostGlobalCppflags", hostGlobalCppflags)
+	exportedVars.ExportStringListStaticVariable("HostGlobalLdflags", hostGlobalLdflags)
+	exportedVars.ExportStringListStaticVariable("HostGlobalLldflags", hostGlobalLldflags)
 
 	// Export the static default CommonGlobalCflags to Bazel.
 	// TODO(187086342): handle cflags that are set in VariableFuncs.
@@ -323,7 +334,7 @@
 			"-ftrivial-auto-var-init=zero",
 			"-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang",
 		}...)
-	exportedStringListVars.Set("CommonGlobalCflags", bazelCommonGlobalCflags)
+	exportedVars.ExportStringList("CommonGlobalCflags", bazelCommonGlobalCflags)
 
 	pctx.VariableFunc("CommonGlobalCflags", func(ctx android.PackageVarContext) string {
 		flags := commonGlobalCflags
@@ -352,17 +363,17 @@
 
 	// Export the static default DeviceGlobalCflags to Bazel.
 	// TODO(187086342): handle cflags that are set in VariableFuncs.
-	exportedStringListVars.Set("DeviceGlobalCflags", deviceGlobalCflags)
+	exportedVars.ExportStringList("DeviceGlobalCflags", deviceGlobalCflags)
 
 	pctx.VariableFunc("DeviceGlobalCflags", func(ctx android.PackageVarContext) string {
 		return strings.Join(deviceGlobalCflags, " ")
 	})
 
-	exportStringListStaticVariable("HostGlobalCflags", hostGlobalCflags)
-	exportStringListStaticVariable("NoOverrideGlobalCflags", noOverrideGlobalCflags)
-	exportStringListStaticVariable("NoOverrideExternalGlobalCflags", noOverrideExternalGlobalCflags)
-	exportStringListStaticVariable("CommonGlobalCppflags", commonGlobalCppflags)
-	exportStringListStaticVariable("ExternalCflags", extraExternalCflags)
+	exportedVars.ExportStringListStaticVariable("HostGlobalCflags", hostGlobalCflags)
+	exportedVars.ExportStringListStaticVariable("NoOverrideGlobalCflags", noOverrideGlobalCflags)
+	exportedVars.ExportStringListStaticVariable("NoOverrideExternalGlobalCflags", noOverrideExternalGlobalCflags)
+	exportedVars.ExportStringListStaticVariable("CommonGlobalCppflags", commonGlobalCppflags)
+	exportedVars.ExportStringListStaticVariable("ExternalCflags", extraExternalCflags)
 
 	// Everything in these lists is a crime against abstraction and dependency tracking.
 	// Do not add anything to this list.
@@ -377,11 +388,11 @@
 		"frameworks/native/opengl/include",
 		"frameworks/av/include",
 	}
-	exportedStringListVars.Set("CommonGlobalIncludes", commonGlobalIncludes)
+	exportedVars.ExportStringList("CommonGlobalIncludes", commonGlobalIncludes)
 	pctx.PrefixedExistentPathsForSourcesVariable("CommonGlobalIncludes", "-I", commonGlobalIncludes)
 
-	exportStringStaticVariable("CLANG_DEFAULT_VERSION", ClangDefaultVersion)
-	exportStringStaticVariable("CLANG_DEFAULT_SHORT_VERSION", ClangDefaultShortVersion)
+	exportedVars.ExportStringStaticVariable("CLANG_DEFAULT_VERSION", ClangDefaultVersion)
+	exportedVars.ExportStringStaticVariable("CLANG_DEFAULT_SHORT_VERSION", ClangDefaultShortVersion)
 
 	pctx.StaticVariableWithEnvOverride("ClangBase", "LLVM_PREBUILTS_BASE", ClangDefaultBase)
 	pctx.StaticVariableWithEnvOverride("ClangVersion", "LLVM_PREBUILTS_VERSION", ClangDefaultVersion)
@@ -421,7 +432,7 @@
 	pctx.StaticVariableWithEnvOverride("REAbiLinkerExecStrategy", "RBE_ABI_LINKER_EXEC_STRATEGY", remoteexec.LocalExecStrategy)
 }
 
-var HostPrebuiltTag = exportVariableConfigMethod("HostPrebuiltTag", android.Config.PrebuiltOS)
+var HostPrebuiltTag = exportedVars.ExportVariableConfigMethod("HostPrebuiltTag", android.Config.PrebuiltOS)
 
 func ClangPath(ctx android.PathContext, file string) android.SourcePath {
 	type clangToolKey string
diff --git a/cc/config/x86_64_device.go b/cc/config/x86_64_device.go
index 164e7a6..aebda0b 100644
--- a/cc/config/x86_64_device.go
+++ b/cc/config/x86_64_device.go
@@ -91,26 +91,26 @@
 	pctx.SourcePathVariable("X86_64GccRoot",
 		"prebuilts/gcc/${HostPrebuiltTag}/x86/x86_64-linux-android-${x86_64GccVersion}")
 
-	exportStringListStaticVariable("X86_64ToolchainCflags", []string{"-m64"})
-	exportStringListStaticVariable("X86_64ToolchainLdflags", []string{"-m64"})
+	exportedVars.ExportStringListStaticVariable("X86_64ToolchainCflags", []string{"-m64"})
+	exportedVars.ExportStringListStaticVariable("X86_64ToolchainLdflags", []string{"-m64"})
 
-	exportStringListStaticVariable("X86_64Ldflags", x86_64Ldflags)
-	exportStringListStaticVariable("X86_64Lldflags", x86_64Ldflags)
+	exportedVars.ExportStringListStaticVariable("X86_64Ldflags", x86_64Ldflags)
+	exportedVars.ExportStringListStaticVariable("X86_64Lldflags", x86_64Ldflags)
 
 	// Clang cflags
-	exportStringListStaticVariable("X86_64Cflags", x86_64Cflags)
-	exportStringListStaticVariable("X86_64Cppflags", x86_64Cppflags)
+	exportedVars.ExportStringListStaticVariable("X86_64Cflags", x86_64Cflags)
+	exportedVars.ExportStringListStaticVariable("X86_64Cppflags", x86_64Cppflags)
 
 	// Yasm flags
-	exportStringListStaticVariable("X86_64YasmFlags", []string{
+	exportedVars.ExportStringListStaticVariable("X86_64YasmFlags", []string{
 		"-f elf64",
 		"-m amd64",
 	})
 
 	// Extended cflags
 
-	exportedStringListDictVars.Set("X86_64ArchVariantCflags", x86_64ArchVariantCflags)
-	exportedStringListDictVars.Set("X86_64ArchFeatureCflags", x86_64ArchFeatureCflags)
+	exportedVars.ExportStringListDict("X86_64ArchVariantCflags", x86_64ArchVariantCflags)
+	exportedVars.ExportStringListDict("X86_64ArchFeatureCflags", x86_64ArchFeatureCflags)
 
 	// Architecture variant cflags
 	for variant, cflags := range x86_64ArchVariantCflags {
diff --git a/cc/config/x86_device.go b/cc/config/x86_device.go
index e32e1bd..421b083 100644
--- a/cc/config/x86_device.go
+++ b/cc/config/x86_device.go
@@ -98,25 +98,25 @@
 	pctx.SourcePathVariable("X86GccRoot",
 		"prebuilts/gcc/${HostPrebuiltTag}/x86/x86_64-linux-android-${x86GccVersion}")
 
-	exportStringListStaticVariable("X86ToolchainCflags", []string{"-m32"})
-	exportStringListStaticVariable("X86ToolchainLdflags", []string{"-m32"})
+	exportedVars.ExportStringListStaticVariable("X86ToolchainCflags", []string{"-m32"})
+	exportedVars.ExportStringListStaticVariable("X86ToolchainLdflags", []string{"-m32"})
 
-	exportStringListStaticVariable("X86Ldflags", x86Ldflags)
-	exportStringListStaticVariable("X86Lldflags", x86Ldflags)
+	exportedVars.ExportStringListStaticVariable("X86Ldflags", x86Ldflags)
+	exportedVars.ExportStringListStaticVariable("X86Lldflags", x86Ldflags)
 
 	// Clang cflags
-	exportStringListStaticVariable("X86Cflags", x86Cflags)
-	exportStringListStaticVariable("X86Cppflags", x86Cppflags)
+	exportedVars.ExportStringListStaticVariable("X86Cflags", x86Cflags)
+	exportedVars.ExportStringListStaticVariable("X86Cppflags", x86Cppflags)
 
 	// Yasm flags
-	exportStringListStaticVariable("X86YasmFlags", []string{
+	exportedVars.ExportStringListStaticVariable("X86YasmFlags", []string{
 		"-f elf32",
 		"-m x86",
 	})
 
 	// Extended cflags
-	exportedStringListDictVars.Set("X86ArchVariantCflags", x86ArchVariantCflags)
-	exportedStringListDictVars.Set("X86ArchFeatureCflags", x86ArchFeatureCflags)
+	exportedVars.ExportStringListDict("X86ArchVariantCflags", x86ArchVariantCflags)
+	exportedVars.ExportStringListDict("X86ArchFeatureCflags", x86ArchFeatureCflags)
 
 	// Architecture variant cflags
 	for variant, cflags := range x86ArchVariantCflags {
diff --git a/cc/config/x86_linux_host.go b/cc/config/x86_linux_host.go
index e1659d3..4e8fd77 100644
--- a/cc/config/x86_linux_host.go
+++ b/cc/config/x86_linux_host.go
@@ -121,40 +121,40 @@
 )
 
 func init() {
-	exportStringStaticVariable("LinuxGccVersion", linuxGccVersion)
-	exportStringStaticVariable("LinuxGlibcVersion", linuxGlibcVersion)
+	exportedVars.ExportStringStaticVariable("LinuxGccVersion", linuxGccVersion)
+	exportedVars.ExportStringStaticVariable("LinuxGlibcVersion", linuxGlibcVersion)
 
 	// Most places use the full GCC version. A few only use up to the first two numbers.
 	if p := strings.Split(linuxGccVersion, "."); len(p) > 2 {
-		exportStringStaticVariable("ShortLinuxGccVersion", strings.Join(p[:2], "."))
+		exportedVars.ExportStringStaticVariable("ShortLinuxGccVersion", strings.Join(p[:2], "."))
 	} else {
-		exportStringStaticVariable("ShortLinuxGccVersion", linuxGccVersion)
+		exportedVars.ExportStringStaticVariable("ShortLinuxGccVersion", linuxGccVersion)
 	}
 
-	exportSourcePathVariable("LinuxGccRoot",
+	exportedVars.ExportSourcePathVariable("LinuxGccRoot",
 		"prebuilts/gcc/linux-x86/host/x86_64-linux-glibc${LinuxGlibcVersion}-${ShortLinuxGccVersion}")
 
-	exportStringListStaticVariable("LinuxGccTriple", []string{"x86_64-linux"})
+	exportedVars.ExportStringListStaticVariable("LinuxGccTriple", []string{"x86_64-linux"})
 
-	exportStringListStaticVariable("LinuxCflags", linuxCflags)
-	exportStringListStaticVariable("LinuxLdflags", linuxLdflags)
-	exportStringListStaticVariable("LinuxLldflags", linuxLdflags)
-	exportStringListStaticVariable("LinuxGlibcCflags", linuxGlibcCflags)
-	exportStringListStaticVariable("LinuxGlibcLdflags", linuxGlibcLdflags)
-	exportStringListStaticVariable("LinuxGlibcLldflags", linuxGlibcLdflags)
-	exportStringListStaticVariable("LinuxMuslCflags", linuxMuslCflags)
-	exportStringListStaticVariable("LinuxMuslLdflags", linuxMuslLdflags)
-	exportStringListStaticVariable("LinuxMuslLldflags", linuxMuslLdflags)
+	exportedVars.ExportStringListStaticVariable("LinuxCflags", linuxCflags)
+	exportedVars.ExportStringListStaticVariable("LinuxLdflags", linuxLdflags)
+	exportedVars.ExportStringListStaticVariable("LinuxLldflags", linuxLdflags)
+	exportedVars.ExportStringListStaticVariable("LinuxGlibcCflags", linuxGlibcCflags)
+	exportedVars.ExportStringListStaticVariable("LinuxGlibcLdflags", linuxGlibcLdflags)
+	exportedVars.ExportStringListStaticVariable("LinuxGlibcLldflags", linuxGlibcLdflags)
+	exportedVars.ExportStringListStaticVariable("LinuxMuslCflags", linuxMuslCflags)
+	exportedVars.ExportStringListStaticVariable("LinuxMuslLdflags", linuxMuslLdflags)
+	exportedVars.ExportStringListStaticVariable("LinuxMuslLldflags", linuxMuslLdflags)
 
-	exportStringListStaticVariable("LinuxX86Cflags", linuxX86Cflags)
-	exportStringListStaticVariable("LinuxX8664Cflags", linuxX8664Cflags)
-	exportStringListStaticVariable("LinuxX86Ldflags", linuxX86Ldflags)
-	exportStringListStaticVariable("LinuxX86Lldflags", linuxX86Ldflags)
-	exportStringListStaticVariable("LinuxX8664Ldflags", linuxX8664Ldflags)
-	exportStringListStaticVariable("LinuxX8664Lldflags", linuxX8664Ldflags)
+	exportedVars.ExportStringListStaticVariable("LinuxX86Cflags", linuxX86Cflags)
+	exportedVars.ExportStringListStaticVariable("LinuxX8664Cflags", linuxX8664Cflags)
+	exportedVars.ExportStringListStaticVariable("LinuxX86Ldflags", linuxX86Ldflags)
+	exportedVars.ExportStringListStaticVariable("LinuxX86Lldflags", linuxX86Ldflags)
+	exportedVars.ExportStringListStaticVariable("LinuxX8664Ldflags", linuxX8664Ldflags)
+	exportedVars.ExportStringListStaticVariable("LinuxX8664Lldflags", linuxX8664Ldflags)
 	// Yasm flags
-	exportStringListStaticVariable("LinuxX86YasmFlags", []string{"-f elf32 -m x86"})
-	exportStringListStaticVariable("LinuxX8664YasmFlags", []string{"-f elf64 -m amd64"})
+	exportedVars.ExportStringListStaticVariable("LinuxX86YasmFlags", []string{"-f elf32 -m x86"})
+	exportedVars.ExportStringListStaticVariable("LinuxX8664YasmFlags", []string{"-f elf64 -m amd64"})
 }
 
 type toolchainLinux struct {