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/*
* Copyright 2016 Google Inc. 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.turbine.binder.env;
import com.google.common.base.Joiner;
import com.google.common.collect.ImmutableMap;
import com.google.turbine.binder.sym.Symbol;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import org.jspecify.nullness.Nullable;
/**
* An env that permits an analysis pass to access information about symbols from the current pass,
* recursively. Cycles are detected, and result in an {@link LazyBindingError} being thrown.
*
* <p>This is used primarily for resolving the supertype hierarchy in {@code HierarchyBinder}. The
* supertype hierarchy forms a directed acyclic graph, and {@code HierarchyBinder} needs to process
* classes in a topological sort order of that graph. Unfortuntately, we can't produce a suitable
* sort order until the graph exists.
*
* @param <T> the interface type of the bound node {@link V}, shared by any underlying environments.
* @param <V> a specific implementation of {@code T}. For example, during hierarchy binding {@code
* SourceHeaderBoundClass} nodes are being completed from the sources being compiled, and the
* analysis of a given symbol may require looking up {@code HeaderBoundClass} nodes that will
* either be backed by other {@code SourceHeaderBoundClass} nodes or {@code BytecodeBoundClass}
* nodes. So the phase uses an {@code LazyEnv<HeaderBoundClass, SourceHeaderBoundClass>}.
*/
public class LazyEnv<S extends Symbol, T, V extends T> implements Env<S, V> {
/** The list of symbols that are currently being processed, used to check for cycles. */
private final LinkedHashSet<S> seen = new LinkedHashSet<>();
/** Lazy value providers for the symbols in the environment. */
private final ImmutableMap<S, Completer<S, T, V>> completers;
/** Values that have already been computed. */
private final Map<S, @Nullable V> cache = new LinkedHashMap<>();
/** An underlying env of already-computed {@code T}s that can be queried during completion. */
private final Env<S, T> rec;
public LazyEnv(ImmutableMap<S, Completer<S, T, V>> completers, Env<S, ? extends T> base) {
this.completers = completers;
this.rec = CompoundEnv.<S, T>of(base).append(this);
}
@Override
public @Nullable V get(S sym) {
V v = cache.get(sym);
if (v != null) {
return v;
}
Completer<S, T, V> completer = completers.get(sym);
if (completer != null) {
if (!seen.add(sym)) {
throw new LazyBindingError(Joiner.on(" -> ").join(seen) + " -> " + sym);
}
v = completer.complete(rec, sym);
seen.remove(sym);
cache.put(sym, v);
return v;
}
return null;
}
/** A lazy value provider which is given access to the current environment. */
public interface Completer<S extends Symbol, T, V extends T> {
/** Provides the value for the given symbol in the current environment. */
@Nullable
V complete(Env<S, T> env, S k);
}
/** Indicates that a completer tried to complete itself, possibly transitively. */
public static class LazyBindingError extends Error {
public LazyBindingError(String message) {
super(message);
}
}
}
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