bp2build: export some cc toolchain flags into Starlark.
This CL exports common/global/device/host clang/ld/ldd flags
from their Ninja variable initialization locations in
cc/config/global.go and cc/config/clang.go to make Bazel's cc_toolchain
and Soong's cc actions more consistent with each other.
This does not handle env-dependent or arch-specific toolchain flags
yet (logic in compiler.go and linker.go).
Test: TH
Bug: 187086342
Bug: 187084737
Bug: 186628704
Bug: 187857770
Change-Id: Ie403d7cd23f35160897b9dd902c799cbf1bd7f0c
diff --git a/cc/config/bp2build.go b/cc/config/bp2build.go
new file mode 100644
index 0000000..16892e6
--- /dev/null
+++ b/cc/config/bp2build.go
@@ -0,0 +1,148 @@
+// 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 (
+ "android/soong/android"
+ "fmt"
+ "regexp"
+ "strings"
+)
+
+// Helpers for exporting cc configuration information to Bazel.
+
+var (
+ // Map containing toolchain variables that are independent of the
+ // environment variables of the build.
+ exportedVars = exportedVariablesMap{}
+)
+
+// variableValue is a string slice because the exported variables are all lists
+// of string, and it's simpler to manipulate string lists before joining them
+// into their final string representation.
+type variableValue []string
+
+// envDependentVariable is a toolchain variable computed based on an environment variable.
+type exportedVariablesMap map[string]variableValue
+
+func (m exportedVariablesMap) Set(k string, v variableValue) {
+ m[k] = v
+}
+
+// Convenience function to declare a static variable and export it to Bazel's cc_toolchain.
+func staticVariableExportedToBazel(name string, value []string) {
+ pctx.StaticVariable(name, strings.Join(value, " "))
+ exportedVars.Set(name, variableValue(value))
+}
+
+// BazelCcToolchainVars generates bzl file content containing variables for
+// Bazel's cc_toolchain configuration.
+func BazelCcToolchainVars() string {
+ ret := "# GENERATED FOR BAZEL FROM SOONG. DO NOT EDIT.\n\n"
+
+ // Ensure that string s has no invalid characters to be generated into the bzl file.
+ validateCharacters := func(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
+ }
+
+ // For each exported variable, recursively expand elements in the variableValue
+ // list to ensure that interpolated variables are expanded according to their values
+ // in the exportedVars scope.
+ for _, k := range android.SortedStringKeys(exportedVars) {
+ variableValue := exportedVars[k]
+ var expandedVars []string
+ for _, v := range variableValue {
+ expandedVars = append(expandedVars, expandVar(v, exportedVars)...)
+ }
+ // Build the list for this variable.
+ list := "["
+ for _, flag := range expandedVars {
+ list += fmt.Sprintf("\n \"%s\",", validateCharacters(flag))
+ }
+ list += "\n]"
+ // Assign the list as a bzl-private variable; this variable will be exported
+ // out through a constants struct later.
+ ret += fmt.Sprintf("_%s = %s\n", k, list)
+ ret += "\n"
+ }
+
+ // Build the exported constants struct.
+ ret += "constants = struct(\n"
+ for _, k := range android.SortedStringKeys(exportedVars) {
+ ret += fmt.Sprintf(" %s = _%s,\n", k, k)
+ }
+ ret += ")"
+ return ret
+}
+
+// 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(toExpand string, exportedVars map[string]variableValue) []string {
+ // e.g. "${ClangExternalCflags}"
+ r := regexp.MustCompile(`\${([a-zA-Z0-9_]+)}`)
+
+ // Internal recursive function.
+ var expandVarInternal func(string, map[string]bool) []string
+ expandVarInternal = func(toExpand string, seenVars map[string]bool) []string {
+ var ret []string
+ for _, v := range strings.Split(toExpand, " ") {
+ matches := r.FindStringSubmatch(v)
+ if len(matches) == 0 {
+ return []string{v}
+ }
+
+ if len(matches) != 2 {
+ panic(fmt.Errorf(
+ "Expected to only match 1 subexpression in %s, got %d",
+ v,
+ len(matches)-1))
+ }
+
+ // Index 1 of FindStringSubmatch contains the subexpression match
+ // (variable name) of the capture group.
+ variable := matches[1]
+ // toExpand contains a variable.
+ if _, ok := seenVars[variable]; ok {
+ panic(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
+ unexpandedVars := exportedVars[variable]
+ for _, unexpandedVar := range unexpandedVars {
+ ret = append(ret, expandVarInternal(unexpandedVar, newSeenVars)...)
+ }
+ }
+ return ret
+ }
+
+ return expandVarInternal(toExpand, map[string]bool{})
+}