com.google.devtools.build.lib.syntax.SkylarkCallbackFunction.java Source code

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Here is the source code for com.google.devtools.build.lib.syntax.SkylarkCallbackFunction.java

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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.syntax;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableList.Builder;

/**
 * A helper class for calling Skylark functions from Java.
 */
public class SkylarkCallbackFunction {

    private final BaseFunction callback;
    private final FuncallExpression ast;
    private final Environment funcallEnv;

    public SkylarkCallbackFunction(BaseFunction callback, FuncallExpression ast, Environment funcallEnv) {
        this.callback = callback;
        this.ast = ast;
        this.funcallEnv = funcallEnv;
    }

    public ImmutableList<String> getParameterNames() {
        return callback.signature.getSignature().getNames();
    }

    public Object call(ClassObject ctx, Object... arguments) throws EvalException, InterruptedException {
        try (Mutability mutability = Mutability.create("callback %s", callback)) {
            Environment env = Environment.builder(mutability).setEventHandler(funcallEnv.getEventHandler())
                    .setGlobals(funcallEnv.getGlobals()).build();
            return callback.call(buildArgumentList(ctx, arguments), null, ast, env);
        } catch (ClassCastException | IllegalArgumentException e) {
            throw new EvalException(ast.getLocation(), e.getMessage());
        }
    }

    /**
     * Creates a list of actual arguments that contains the given arguments and all attribute values
     * required from the specified context.
     */
    private ImmutableList<Object> buildArgumentList(ClassObject ctx, Object... arguments) {
        Builder<Object> builder = ImmutableList.<Object>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 = ctx.getValue(name);
            if (value == null) {
                throw new IllegalArgumentException(ctx.errorMessage(name));
            }
            builder.add(value);
        }
        return builder.add(arguments).build();
    }
}