Make using python 2 an error

Except if BUILD_BROKEN_USES_SOONG_PYTHON2_MODULES is set, and except for
some core py2 modules that can't be removed until python2 is fully gone.

Bug: 203436762
Test: m nothing
Change-Id: I62ccb6f5687eab1e79c372ffc234a90ca5b566ac

android/config.go

@@ -1759,6 +1759,10 @@ func (c *deviceConfig) BuildBrokenTrebleSyspropNeverallow() bool {
 	return c.config.productVariables.BuildBrokenTrebleSyspropNeverallow
 }
 
+func (c *deviceConfig) BuildBrokenUsesSoongPython2Modules() bool {
+	return c.config.productVariables.BuildBrokenUsesSoongPython2Modules
+}
+
 func (c *deviceConfig) BuildDebugfsRestrictionsEnabled() bool {
 	return c.config.productVariables.BuildDebugfsRestrictionsEnabled
 }

android/variable.go

@@ -442,6 +442,7 @@ type productVariables struct {
 	BuildBrokenDepfile                 *bool    `json:",omitempty"`
 	BuildBrokenEnforceSyspropOwner     bool     `json:",omitempty"`
 	BuildBrokenTrebleSyspropNeverallow bool     `json:",omitempty"`
+	BuildBrokenUsesSoongPython2Modules bool     `json:",omitempty"`
 	BuildBrokenVendorPropertyNamespace bool     `json:",omitempty"`
 	BuildBrokenInputDirModules         []string `json:",omitempty"`
 

python/python.go

@@ -263,6 +263,12 @@ func versionSplitMutator() func(android.BottomUpMutatorContext) {
 				versionProps = append(versionProps, props.Version.Py3)
 			}
 			if proptools.BoolDefault(props.Version.Py2.Enabled, false) {
+				if !mctx.DeviceConfig().BuildBrokenUsesSoongPython2Modules() &&
+					mctx.ModuleName() != "par_test" &&
+					mctx.ModuleName() != "py2-cmd" &&
+					mctx.ModuleName() != "py2-stdlib" {
+					mctx.PropertyErrorf("version.py2.enabled", "Python 2 is no longer supported, please convert to python 3. This error can be temporarily overridden by setting BUILD_BROKEN_USES_SOONG_PYTHON2_MODULES := true in the product configuration")
+				}
 				versionNames = append(versionNames, pyVersion2)
 				versionProps = append(versionProps, props.Version.Py2)
 			}