Add support for variant_prepend properties in bp2build for cc library

Some properties in soong are marked "variant_prepend", which means
in bp2build output, variant properties(select ...) should come before
general properties.
Prepend property is added in StringListAttribute
stuct so that bp2build can handlle variant_prepend properly, if
Prepend is properly set in different module logics.
This change also coordinates cc library with Prepend.
Coordination with other module types will be in separate CLs.

Bug: 261644490
Test: TestCcLibraryHeadersSimple,
TestCcLibraryHeadersArchAndTargetExportSystemIncludes and TH

Change-Id: I3b61c491c54bbe91ba9aa2af9b4c84193c91ae7f

bazel/properties.go

@@ -1207,6 +1207,11 @@ type StringListAttribute struct {
 	// The configured attribute label list Values. Optional
 	// a map of independent configurability axes
 	ConfigurableValues configurableStringLists
+
+	// If a property has struct tag "variant_prepend", this value should
+	// be set to True, so that when bp2build generates BUILD.bazel, variant
+	// properties(select ...) come before general properties.
+	Prepend bool
 }
 
 // IsEmpty returns true if the attribute has no values under any configuration.
@@ -1273,6 +1278,9 @@ func (sla StringListAttribute) HasConfigurableValues() bool {
 // Append appends all values, including os and arch specific ones, from another
 // StringListAttribute to this StringListAttribute
 func (sla *StringListAttribute) Append(other StringListAttribute) *StringListAttribute {
+	if sla.Prepend != other.Prepend {
+		panic(fmt.Errorf("StringListAttribute could not be appended because it has different prepend value"))
+	}
 	sla.Value = append(sla.Value, other.Value...)
 	if sla.ConfigurableValues == nil {
 		sla.ConfigurableValues = make(configurableStringLists)

bp2build/cc_library_headers_conversion_test.go

@@ -107,15 +107,15 @@ cc_library_headers {
 }`,
 		ExpectedBazelTargets: []string{
 			MakeBazelTarget("cc_library_headers", "foo_headers", AttrNameToString{
-				"export_includes": `[
+				"export_includes": `select({
-        "dir-1",
-        "dir-2",
-    ] + select({
         "//build/bazel/platforms/arch:arm64": ["arch_arm64_exported_include_dir"],
         "//build/bazel/platforms/arch:x86": ["arch_x86_exported_include_dir"],
         "//build/bazel/platforms/arch:x86_64": ["arch_x86_64_exported_include_dir"],
         "//conditions:default": [],
-    })`,
+    }) + [
+        "dir-1",
+        "dir-2",
+    ]`,
 				"sdk_version":     `"current"`,
 				"min_sdk_version": `"29"`,
 			}),
@@ -340,16 +340,16 @@ func TestCcLibraryHeadersArchAndTargetExportSystemIncludes(t *testing.T) {
 }`,
 		ExpectedBazelTargets: []string{
 			MakeBazelTarget("cc_library_headers", "foo_headers", AttrNameToString{
-				"export_system_includes": `["shared_include_dir"] + select({
+				"export_system_includes": `select({
-        "//build/bazel/platforms/arch:arm": ["arm_include_dir"],
-        "//build/bazel/platforms/arch:x86_64": ["x86_64_include_dir"],
-        "//conditions:default": [],
-    }) + select({
         "//build/bazel/platforms/os:android": ["android_include_dir"],
         "//build/bazel/platforms/os:darwin": ["darwin_include_dir"],
         "//build/bazel/platforms/os:linux": ["linux_include_dir"],
         "//conditions:default": [],
-    })`,
+    }) + select({
+        "//build/bazel/platforms/arch:arm": ["arm_include_dir"],
+        "//build/bazel/platforms/arch:x86_64": ["x86_64_include_dir"],
+        "//conditions:default": [],
+    }) + ["shared_include_dir"]`,
 			}),
 		},
 	})

bp2build/configurability.go

@@ -37,10 +37,11 @@ func getStringValue(str bazel.StringAttribute) (reflect.Value, []selects) {
 	return value, []selects{ret}
 }
 
-func getStringListValues(list bazel.StringListAttribute) (reflect.Value, []selects) {
+func getStringListValues(list bazel.StringListAttribute) (reflect.Value, []selects, bool) {
 	value := reflect.ValueOf(list.Value)
+	prepend := reflect.ValueOf(list.Prepend).Bool()
 	if !list.HasConfigurableValues() {
-		return value, []selects{}
+		return value, []selects{}, prepend
 	}
 
 	var ret []selects
@@ -56,7 +57,7 @@ func getStringListValues(list bazel.StringListAttribute) (reflect.Value, []selec
 		}
 	}
 
-	return value, ret
+	return value, ret, prepend
 }
 
 func getLabelValue(label bazel.LabelAttribute) (reflect.Value, []selects) {
@@ -156,6 +157,7 @@ var (
 func prettyPrintAttribute(v bazel.Attribute, indent int) (string, error) {
 	var value reflect.Value
 	var configurableAttrs []selects
+	var prepend bool
 	var defaultSelectValue *string
 	var emitZeroValues bool
 	// If true, print the default attribute value, even if the attribute is zero.
@@ -168,7 +170,7 @@ func prettyPrintAttribute(v bazel.Attribute, indent int) (string, error) {
 		value, configurableAttrs = getStringValue(list)
 		defaultSelectValue = &bazelNone
 	case bazel.StringListAttribute:
-		value, configurableAttrs = getStringListValues(list)
+		value, configurableAttrs, prepend = getStringListValues(list)
 		defaultSelectValue = &emptyBazelList
 	case bazel.LabelListAttribute:
 		value, configurableAttrs = getLabelListValues(list)
@@ -203,22 +205,28 @@ func prettyPrintAttribute(v bazel.Attribute, indent int) (string, error) {
 
 		ret += s
 	}
-	// Convenience function to append selects components to an attribute value.
+	// Convenience function to prepend/append selects components to an attribute value.
-	appendSelects := func(selectsData selects, defaultValue *string, s string) (string, error) {
+	concatenateSelects := func(selectsData selects, defaultValue *string, s string, prepend bool) (string, error) {
 		selectMap, err := prettyPrintSelectMap(selectsData, defaultValue, indent, emitZeroValues)
 		if err != nil {
 			return "", err
 		}
-		if s != "" && selectMap != "" {
+		var left, right string
-			s += " + "
+		if prepend {
+			left, right = selectMap, s
+		} else {
+			left, right = s, selectMap
 		}
-		s += selectMap
+		if left != "" && right != "" {
+			left += " + "
+		}
+		left += right
 
-		return s, nil
+		return left, nil
 	}
 
 	for _, configurableAttr := range configurableAttrs {
-		ret, err = appendSelects(configurableAttr, defaultSelectValue, ret)
+		ret, err = concatenateSelects(configurableAttr, defaultSelectValue, ret, prepend)
 		if err != nil {
 			return "", err
 		}

cc/bp2build.go

@@ -1257,6 +1257,13 @@ func bp2BuildParseExportedIncludes(ctx android.BazelConversionPathContext, modul
 	} else {
 		exported = BazelIncludes{}
 	}
+
+	// cc library Export_include_dirs and Export_system_include_dirs are marked
+	// "variant_prepend" in struct tag, set their prepend property to true to make
+	// sure bp2build generates correct result.
+	exported.Includes.Prepend = true
+	exported.SystemIncludes.Prepend = true
+
 	bp2BuildPropParseHelper(ctx, module, &FlagExporterProperties{}, func(axis bazel.ConfigurationAxis, config string, props interface{}) {
 		if flagExporterProperties, ok := props.(*FlagExporterProperties); ok {
 			if len(flagExporterProperties.Export_include_dirs) > 0 {