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// Copyright 2018 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.actions;
import java.util.function.Consumer;
/** An interface for an object that customizes how it is expanded into a command line. */
public interface CommandLineItem {
/**
* A map function that allows caller customization how a type is expanded into the command line.
*/
interface MapFn<T> {
MapFn<Object> DEFAULT =
(Object object, Consumer<String> args) ->
args.accept(CommandLineItem.expandToCommandLine(object));
void expandToCommandLine(T object, Consumer<String> args);
}
/**
* Use this map function when parametrizing over a limited set of values.
*
* <p>The user promises that the number of distinct instances constructed is closer to O(rule
* class count) than O(rule count).
*
* <p>Without this, {@link
* com.google.devtools.build.lib.collect.nestedset.NestedSetFingerprintCache} will refuse to cache
* your {@link MapFn} computations.
*/
abstract class ParametrizedMapFn<T> implements MapFn<T> {
@Override
public abstract boolean equals(Object obj);
@Override
public abstract int hashCode();
/**
* This method controls the max number of distinct instances allowed. If the system sees any
* more than this, it will throw.
*
* <p>Override and set this to something low. You want this to represent the small number of
* preallocated static instances used in this blaze instance. 3 is an OK number, 100 is a bad
* number.
*/
public abstract int maxInstancesAllowed();
}
/**
* Use this map function when your map function needs to capture per-rule information.
*
* <p>Use of this class prevents sharing sub-computations over shared NestedSets, since the map
* function is per-target. This will make your action key computations become O(N^2). Please avoid
* if possible.
*/
interface CapturingMapFn<T> extends MapFn<T> {}
/** Expands the object into the command line as a string. */
String expandToCommandLine();
/**
* The default method of expanding types.
*
* <p>If the object is a {@link CommandLineItem} we use its {@link
* CommandLineItem#expandToCommandLine} method, else we call {@link Object#toString()}.
*/
static String expandToCommandLine(Object object) {
// TODO(bazel-team): The fallback on toString() isn't great. Particularly so for
// SkylarkCustomCommandLine, since toString() does not necessarily give the same results as
// Skylark's str() or repr().
//
// The ideal refactoring is to make SkylarkValue implement CommandLineItem (or a slimmer version
// thereof). Then the default behavior can be that SkylarkValue#expandToCommandLine calls
// SkylarkPrintable#str. This default behavior is inefficient but rare; Artifacts and the like
// would continue to override expandToCommandLine to take the fast code path that doesn't
// involve a Printer.
//
// Since SkylarkValue should be moved out of Bazel, this refactoring would be blocked on making
// a BuildSkylarkValue subinterface for Bazel-specific Skylark types. It would then be
// BuildSkylarkValue, rather than SkylarkValue, that extends CommandLineItem.
if (object instanceof CommandLineItem) {
return ((CommandLineItem) object).expandToCommandLine();
} else {
return object.toString();
}
}
}
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