| // Copyright 2019 The Bazel Authors. 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 com.google.devtools.build.lib.rules.python; |
| |
| import static com.google.devtools.build.lib.packages.Type.STRING; |
| |
| import com.google.devtools.build.lib.analysis.config.transitions.ConfigurationTransition; |
| import com.google.devtools.build.lib.analysis.config.transitions.NoTransition; |
| import com.google.devtools.build.lib.analysis.config.transitions.TransitionFactory; |
| import com.google.devtools.build.lib.packages.AttributeTransitionData; |
| import com.google.devtools.build.lib.skylarkbuildapi.python.PyStarlarkTransitionsApi; |
| import com.google.devtools.build.lib.syntax.Printer; |
| import com.google.devtools.build.lib.syntax.StarlarkValue; |
| |
| /** |
| * Exposes a native transition to Starlark for changing the Python version. |
| * |
| * <p>This is not intended to be a stable API. It is only available when {@code |
| * --experimental_google_legacy_api} is enabled. For production code, users should generally use a |
| * Starlark-defined transition (SBC) based on {@code //command_line_option:python_version}. |
| * |
| * <p>The only reason to expose the native transition here is that it performs better; |
| * Starlark-based transitions cannot yet collapse equivalent configurations together due to |
| * differences in the output root. Most builds should not need this level of optimization. For the |
| * ones that do, this transition can unblock PY2 -> PY3 migration. |
| * |
| * <p>See also internal bugs b/137574156 and b/140565289. |
| */ |
| public final class PyStarlarkTransitions implements PyStarlarkTransitionsApi { |
| |
| /** Singleton instance of {@link PySkylarkTransitions}. */ |
| public static final PyStarlarkTransitions INSTANCE = new PyStarlarkTransitions(); |
| |
| @Override |
| public StarlarkValue getTransition() { |
| return StarlarkVersionTransition.INSTANCE; |
| } |
| |
| private static class StarlarkVersionTransition |
| implements TransitionFactory<AttributeTransitionData>, StarlarkValue { |
| |
| private static final StarlarkVersionTransition INSTANCE = new StarlarkVersionTransition(); |
| |
| @Override |
| public ConfigurationTransition create(AttributeTransitionData data) { |
| if (!data.attributes().has("python_version")) { |
| return NoTransition.INSTANCE; |
| } |
| String version = data.attributes().get("python_version", STRING); |
| if ("DEFAULT".equals(version)) { |
| return PythonVersionTransition.toDefault(); |
| } else if (PythonVersion.TARGET_STRINGS.contains(version)) { |
| return PythonVersionTransition.toConstant(PythonVersion.parseTargetValue(version)); |
| } else { |
| return NoTransition.INSTANCE; |
| } |
| } |
| |
| @Override |
| public void repr(Printer printer) { |
| printer.append("<py_transitions.cfg>"); |
| } |
| } |
| } |