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// Copyright 2014 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.packages;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.devtools.build.lib.events.Event;
import com.google.devtools.build.lib.events.EventHandler;
import net.starlark.java.eval.EvalException;
import net.starlark.java.eval.Mutability;
import net.starlark.java.eval.Starlark;
import net.starlark.java.eval.StarlarkFunction;
import net.starlark.java.eval.StarlarkSemantics;
import net.starlark.java.eval.StarlarkThread;
import net.starlark.java.eval.Structure;
/**
* A helper class for calling Starlark functions from Java, where the argument values are supplied
* by the fields of a Structure, as in the case of computed attribute defaults and computed implicit
* outputs.
*/
// TODO(brandjon): Consider eliminating this class by executing the callback in the same thread as
// the caller, i.e. in the thread evaluating a BUILD file. This might not be possible for implicit
// outputs without some refactoring to cache the result of the computation (currently RuleContext
// seems to reinvoke the callback).
public final class StarlarkCallbackHelper {
private final StarlarkFunction callback;
// These fields, parts of the state of the loading-phase
// thread that instantiated a rule, must be propagated to
// the child threads (implicit outputs, attribute defaults).
// This includes any other thread-local state, such as
// PackageFactory.PackageContext.
// TODO(adonovan): it would be cleaner and less error prone to
// perform these callbacks in the actual loading-phase thread,
// at the end of BUILD file execution.
// Alternatively (or additionally), we could put PackageContext
// into BazelStarlarkContext so there's only a single blob of state.
private final StarlarkSemantics starlarkSemantics;
public StarlarkCallbackHelper(StarlarkFunction callback, StarlarkSemantics starlarkSemantics) {
this.callback = callback;
this.starlarkSemantics = starlarkSemantics;
}
public ImmutableList<String> getParameterNames() {
return callback.getParameterNames();
}
// TODO(adonovan): opt: all current callers are forced to construct a temporary Structure.
// Instead, make them supply a map.
public Object call(EventHandler eventHandler, Structure struct, Object... arguments)
throws EvalException, InterruptedException {
try (Mutability mu = Mutability.create("callback", callback)) {
StarlarkThread thread = new StarlarkThread(mu, starlarkSemantics);
thread.setPrintHandler(Event.makeDebugPrintHandler(eventHandler));
new BazelStarlarkContext(
BazelStarlarkContext.Phase.LOADING,
// TODO(brandjon): In principle, if we're creating a new symbol generator here, we
// should have a unique owner object to associate it with for distinguishing
// reference-equality objects. But I don't think implicit outputs or computed defaults
// care about identity.
new SymbolGenerator<>(new Object()))
.storeInThread(thread);
return Starlark.call(
thread, callback, buildArgumentList(struct, arguments), /*kwargs=*/ ImmutableMap.of());
} catch (ClassCastException | IllegalArgumentException e) { // TODO(adonovan): investigate
throw new EvalException(e);
}
}
/**
* Creates a list of actual arguments that contains the given arguments and all attribute values
* required from the specified structure.
*/
private ImmutableList<Object> buildArgumentList(Structure struct, Object... arguments)
throws EvalException {
ImmutableList.Builder<Object> builder = ImmutableList.builder();
ImmutableList<String> names = getParameterNames();
int requiredParameters = names.size() - arguments.length;
for (int pos = 0; pos < requiredParameters; ++pos) {
String name = names.get(pos);
Object value = struct.getValue(name);
if (value == null) {
throw new IllegalArgumentException(struct.getErrorMessageForUnknownField(name));
}
builder.add(value);
}
return builder.add(arguments).build();
}
}