bp2build correctly handle empty soong_config_var

Previously in cases where a variable value was set but empty in a bp
file we ignored the value in bp2build; however, the correct behavior is
to take the empty value for each case. The tests for soong config vars
with empty_prop_for_string_var and unused_string_var:
https://cs.android.com/android/platform/superproject/+/master:build/soong/android/soong_config_modules_test.go;l=243-283;drc=72beb34609217f3c98623fb6795b6417c7f0fc65
highlight the difference in when conditions default should be used or
not.

Test: go test bp2build tests
Change-Id: I9768241f013a1a1bc8fa23657a066b5b3f52f09b

android/variable.go

@@ -702,124 +702,9 @@ func ProductVariableProperties(ctx BazelConversionPathContext) ProductConfigProp
 		}
 	}
 
-	productConfigProperties.zeroValuesForNamespacedVariables()
-
 	return productConfigProperties
 }
 
-// zeroValuesForNamespacedVariables ensures that selects that contain __only__
-// conditions default values have zero values set for the other non-default
-// values for that select statement.
-//
-// If the ProductConfigProperties map contains these items, as parsed from the .bp file:
-//
-//	library_linking_strategy: {
-//	    prefer_static: {
-//	        static_libs: [
-//	            "lib_a",
-//	            "lib_b",
-//	        ],
-//	    },
-//	    conditions_default: {
-//	        shared_libs: [
-//	            "lib_a",
-//	            "lib_b",
-//	        ],
-//	    },
-//	},
-//
-// Static_libs {Library_linking_strategy ANDROID prefer_static} [lib_a lib_b]
-// Shared_libs {Library_linking_strategy ANDROID conditions_default} [lib_a lib_b]
-//
-// We need to add this:
-//
-// Shared_libs {Library_linking_strategy ANDROID prefer_static} []
-//
-// so that the following gets generated for the "dynamic_deps" attribute,
-// instead of putting lib_a and lib_b directly into dynamic_deps without a
-// select:
-//
-//	dynamic_deps = select({
-//	    "//build/bazel/product_variables:android__library_linking_strategy__prefer_static": [],
-//	    "//conditions:default": [
-//	        "//foo/bar:lib_a",
-//	        "//foo/bar:lib_b",
-//	    ],
-//	}),
-func (props *ProductConfigProperties) zeroValuesForNamespacedVariables() {
-	// A map of product config properties to the zero values of their respective
-	// property value.
-	zeroValues := make(map[ProductConfigProperty]interface{})
-
-	// A map of prop names (e.g. cflags) to product config properties where the
-	// (prop name, ProductConfigProperty) tuple contains a non-conditions_default key.
-	//
-	// e.g.
-	//
-	// prefer_static: {
-	//     static_libs: [
-	//         "lib_a",
-	//         "lib_b",
-	//     ],
-	// },
-	// conditions_default: {
-	//     shared_libs: [
-	//         "lib_a",
-	//         "lib_b",
-	//     ],
-	// },
-	//
-	// The tuple of ("static_libs", prefer_static) would be in this map.
-	hasNonDefaultValue := make(map[string]map[ProductConfigProperty]bool)
-
-	// Iterate over all added soong config variables.
-	for propName, v := range *props {
-		for p, intf := range v {
-			if p.Namespace == "" {
-				// If there's no namespace, this isn't a soong config variable,
-				// i.e. this is a product variable. product variables have no
-				// conditions_defaults, so skip them.
-				continue
-			}
-			if p.FullConfig == bazel.ConditionsDefaultConfigKey {
-				// Skip conditions_defaults.
-				continue
-			}
-			if hasNonDefaultValue[propName] == nil {
-				hasNonDefaultValue[propName] = make(map[ProductConfigProperty]bool)
-				hasNonDefaultValue[propName][p] = false
-			}
-			// Create the zero value of the variable.
-			if _, exists := zeroValues[p]; !exists {
-				zeroValue := reflect.Zero(reflect.ValueOf(intf).Type()).Interface()
-				if zeroValue == nil {
-					panic(fmt.Errorf("Expected non-nil zero value for product/config variable %+v\n", intf))
-				}
-				zeroValues[p] = zeroValue
-			}
-			hasNonDefaultValue[propName][p] = true
-		}
-	}
-
-	for propName := range *props {
-		for p, zeroValue := range zeroValues {
-			// Ignore variables that already have a non-default value for that axis
-			if exists, _ := hasNonDefaultValue[propName][p]; !exists {
-				// fmt.Println(propName, p.Namespace, p.Name, p.FullConfig, zeroValue)
-				// Insert the zero value for this propname + product config value.
-				props.AddProductConfigProperty(
-					propName,
-					p.Namespace,
-					p.Name,
-					p.FullConfig,
-					zeroValue,
-					bazel.NoConfigAxis,
-				)
-			}
-		}
-	}
-}
-
 func (p *ProductConfigProperties) AddProductConfigProperty(
 	propertyName, namespace, productVariableName, config string, property interface{}, outerAxis bazel.ConfigurationAxis) {
 	if (*p)[propertyName] == nil {
@@ -945,14 +830,16 @@ func (productConfigProperties *ProductConfigProperties) AddProductConfigProperti
 
 		for j := 0; j < variableValue.NumField(); j++ {
 			property := variableValue.Field(j)
+			// e.g. Asflags, Cflags, Enabled, etc.
+			propertyName := variableValue.Type().Field(j).Name
+			// config can also be "conditions_default".
+			config := proptools.PropertyNameForField(propertyName)
+
 			// If the property wasn't set, no need to pass it along
 			if property.IsZero() {
 				continue
 			}
 
-			// e.g. Asflags, Cflags, Enabled, etc.
-			propertyName := variableValue.Type().Field(j).Name
-
 			if v, ok := maybeExtractConfigVarProp(property); ok {
 				// The field is a struct, which is used by:
 				// 1) soong_config_string_variables
@@ -972,13 +859,14 @@ func (productConfigProperties *ProductConfigProperties) AddProductConfigProperti
 				//     static_libs: ...
 				// }
 				field := v
+				// Iterate over fields of this struct prop.
 				for k := 0; k < field.NumField(); k++ {
-					// Iterate over fields of this struct prop.
+					// For product variables, zero values are irrelevant; however, for soong config variables,
-					if field.Field(k).IsZero() {
+					// empty values are relevant because there can also be a conditions default which is not
+					// applied for empty variables.
+					if field.Field(k).IsZero() && namespace == "" {
 						continue
 					}
-					// config can also be "conditions_default".
-					config := proptools.PropertyNameForField(propertyName)
 					actualPropertyName := field.Type().Field(k).Name
 
 					productConfigProperties.AddProductConfigProperty(

bazel/properties.go

@@ -1367,6 +1367,9 @@ func (sla *StringListAttribute) DeduplicateAxesFromBase() {
 // TryVariableSubstitution, replace string substitution formatting within each string in slice with
 // Starlark string.format compatible tag for productVariable.
 func TryVariableSubstitutions(slice []string, productVariable string) ([]string, bool) {
+	if len(slice) == 0 {
+		return slice, false
+	}
 	ret := make([]string, 0, len(slice))
 	changesMade := false
 	for _, s := range slice {

bp2build/soong_config_module_type_conversion_test.go

@@ -192,6 +192,7 @@ custom_cc_library_static {
     copts = select({
         "//build/bazel/product_variables:acme__board__soc_a": ["-DSOC_A"],
         "//build/bazel/product_variables:acme__board__soc_b": ["-DSOC_B"],
+        "//build/bazel/product_variables:acme__board__soc_c": [],
         "//conditions:default": ["-DSOC_DEFAULT"],
     }),
     local_includes = ["."],
@@ -210,7 +211,7 @@ soong_config_bool_variable {
 
 soong_config_string_variable {
 	name: "board",
-	values: ["soc_a", "soc_b", "soc_c"],
+	values: ["soc_a", "soc_b", "soc_c", "soc_d"],
 }
 
 soong_config_module_type {
@@ -263,6 +264,7 @@ custom_cc_library_static {
     copts = select({
         "//build/bazel/product_variables:acme__board__soc_a": ["-DSOC_A"],
         "//build/bazel/product_variables:acme__board__soc_b": ["-DSOC_B"],
+        "//build/bazel/product_variables:acme__board__soc_c": [],
         "//conditions:default": ["-DSOC_DEFAULT"],
     }) + select({
         "//build/bazel/product_variables:acme__feature1": ["-DFEATURE1"],
@@ -279,7 +281,7 @@ func TestSoongConfigModuleType_StringVar_LabelListDeps(t *testing.T) {
 	bp := `
 soong_config_string_variable {
 	name: "board",
-	values: ["soc_a", "soc_b", "soc_c"],
+	values: ["soc_a", "soc_b", "soc_c", "soc_d"],
 }
 
 soong_config_module_type {
@@ -332,11 +334,13 @@ cc_library_static { name: "soc_default_static_dep", bazel_module: { bp2build_ava
     copts = select({
         "//build/bazel/product_variables:acme__board__soc_a": ["-DSOC_A"],
         "//build/bazel/product_variables:acme__board__soc_b": ["-DSOC_B"],
+        "//build/bazel/product_variables:acme__board__soc_c": [],
         "//conditions:default": ["-DSOC_DEFAULT"],
     }),
     implementation_deps = select({
         "//build/bazel/product_variables:acme__board__soc_a": ["//foo/bar:soc_a_dep"],
         "//build/bazel/product_variables:acme__board__soc_b": ["//foo/bar:soc_b_dep"],
+        "//build/bazel/product_variables:acme__board__soc_c": [],
         "//conditions:default": ["//foo/bar:soc_default_static_dep"],
     }),
     local_includes = ["."],
@@ -604,6 +608,90 @@ cc_library_static {
 )`}})
 }
 
+func TestSoongConfigModuleType_UnsetConditions(t *testing.T) {
+	bp := `
+soong_config_string_variable {
+    name: "library_linking_strategy",
+    values: [
+        "prefer_static",
+    ],
+}
+
+soong_config_module_type {
+    name: "library_linking_strategy_cc_defaults",
+    module_type: "cc_defaults",
+    config_namespace: "ANDROID",
+    variables: ["library_linking_strategy"],
+    properties: [
+        "shared_libs",
+        "static_libs",
+    ],
+}
+
+library_linking_strategy_cc_defaults {
+    name: "library_linking_strategy_lib_a_defaults",
+    soong_config_variables: {
+        library_linking_strategy: {
+            prefer_static: {},
+            conditions_default: {
+                shared_libs: [
+                    "lib_a",
+                ],
+            },
+        },
+    },
+}
+
+library_linking_strategy_cc_defaults {
+    name: "library_linking_strategy_merged_defaults",
+    defaults: ["library_linking_strategy_lib_a_defaults"],
+    host_supported: true,
+    soong_config_variables: {
+        library_linking_strategy: {
+            prefer_static: {},
+            conditions_default: {
+                shared_libs: [
+                    "lib_b",
+                ],
+            },
+        },
+    },
+}
+
+cc_binary {
+    name: "library_linking_strategy_sample_binary",
+    srcs: ["library_linking_strategy.cc"],
+    defaults: ["library_linking_strategy_merged_defaults"],
+    include_build_directory: false,
+}`
+
+	otherDeps := `
+cc_library { name: "lib_a", bazel_module: { bp2build_available: false } }
+cc_library { name: "lib_b", bazel_module: { bp2build_available: false } }
+cc_library { name: "lib_default", bazel_module: { bp2build_available: false } }
+`
+
+	runSoongConfigModuleTypeTest(t, Bp2buildTestCase{
+		Description:                "soong config variables - generates selects for library_linking_strategy",
+		ModuleTypeUnderTest:        "cc_binary",
+		ModuleTypeUnderTestFactory: cc.BinaryFactory,
+		Blueprint:                  bp,
+		Filesystem: map[string]string{
+			"foo/bar/Android.bp": otherDeps,
+		},
+		ExpectedBazelTargets: []string{`cc_binary(
+    name = "library_linking_strategy_sample_binary",
+    dynamic_deps = select({
+        "//build/bazel/product_variables:android__library_linking_strategy__prefer_static": [],
+        "//conditions:default": [
+            "//foo/bar:lib_b",
+            "//foo/bar:lib_a",
+        ],
+    }),
+    srcs = ["library_linking_strategy.cc"],
+)`}})
+}
+
 func TestSoongConfigModuleType_Defaults(t *testing.T) {
 	bp := `
 soong_config_string_variable {