Config variables reader

Fixes: 182330871
Test: go test config_variables_test.go
Change-Id: I89240fb0f1900172cb4d62057c86907bb9a1f58f

mk2rbc/config_variables.go

@@ -0,0 +1,67 @@
+// Copyright 2021 Google LLC
+//
+// 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 mk2rbc
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"strings"
+
+	mkparser "android/soong/androidmk/parser"
+)
+
+// Extracts the list of product config variables from a file, calling
+// given registrar for each variable.
+func FindConfigVariables(mkFile string, vr variableRegistrar) error {
+	mkContents, err := ioutil.ReadFile(mkFile)
+	if err != nil {
+		return err
+	}
+	parser := mkparser.NewParser(mkFile, bytes.NewBuffer(mkContents))
+	nodes, errs := parser.Parse()
+	if len(errs) > 0 {
+		for _, e := range errs {
+			fmt.Fprintln(os.Stderr, "ERROR:", e)
+		}
+		return fmt.Errorf("cannot parse %s", mkFile)
+	}
+	for _, node := range nodes {
+		asgn, ok := node.(*mkparser.Assignment)
+		if !ok {
+			continue
+		}
+		// We are looking for a variable called '_product_list_vars'
+		// or '_product_single_value_vars'.
+		if !asgn.Name.Const() {
+			continue
+		}
+		varName := asgn.Name.Strings[0]
+		var starType starlarkType
+		if varName == "_product_list_vars" {
+			starType = starlarkTypeList
+		} else if varName == "_product_single_value_vars" {
+			starType = starlarkTypeUnknown
+		} else {
+			continue
+		}
+		for _, name := range strings.Fields(asgn.Value.Dump()) {
+			vr.NewVariable(name, VarClassConfig, starType)
+		}
+
+	}
+	return nil
+}