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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.base.Joiner;
import com.google.common.base.Preconditions;
import com.google.common.base.Predicates;
import com.google.common.base.Verify;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Iterables;
import com.google.devtools.build.lib.analysis.config.ConfigMatchingProvider;
import com.google.devtools.build.lib.cmdline.Label;
import com.google.devtools.build.lib.packages.BuildType.Selector;
import com.google.devtools.build.lib.packages.BuildType.SelectorList;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import javax.annotation.Nullable;
/**
* {@link AttributeMap} implementation that binds a rule's attribute as follows:
*
* <ol>
* <li>If the attribute is selectable (i.e. its BUILD declaration is of the form
* "attr = { config1: "value1", "config2: "value2", ... }", returns the subset of values
* chosen by the current configuration in accordance with Bazel's documented policy on
* configurable attribute selection.
* <li>If the attribute is not selectable (i.e. its value is static), returns that value with
* no additional processing.
* </ol>
*
* <p>Example usage:
* <pre>
* Label fooLabel = ConfiguredAttributeMapper.of(ruleConfiguredTarget).get("foo", Type.LABEL);
* </pre>
*/
public class ConfiguredAttributeMapper extends AbstractAttributeMapper {
private final Map<Label, ConfigMatchingProvider> configConditions;
private final String configHash;
private ConfiguredAttributeMapper(
Rule rule, ImmutableMap<Label, ConfigMatchingProvider> configConditions, String configHash) {
super(Preconditions.checkNotNull(rule));
this.configConditions = configConditions;
this.configHash = configHash;
}
/**
* "Manual" constructor that requires the caller to pass the set of configurability conditions
* that trigger this rule's configurable attributes.
*
* <p>If you don't know how to do this, you really want to use one of the "do-it-all"
* constructors.
*/
public static ConfiguredAttributeMapper of(
Rule rule, ImmutableMap<Label, ConfigMatchingProvider> configConditions, String configHash) {
return new ConfiguredAttributeMapper(rule, configConditions, configHash);
}
/**
* Checks that all attributes can be mapped to their configured values. This is useful for
* checking that the configuration space in a configured attribute doesn't contain unresolvable
* contradictions.
*
* @throws ValidationException if any attribute's value can't be resolved under this mapper
*/
public void validateAttributes() throws ValidationException {
for (String attrName : getAttributeNames()) {
getAndValidate(attrName, getAttributeType(attrName));
}
}
/** ValidationException indicates an error during attribute validation. */
public static final class ValidationException extends Exception {
private ValidationException(String message) {
super(message);
}
}
/**
* Variation of {@link #get} that throws an informative exception if the attribute can't be
* resolved due to intrinsic contradictions in the configuration.
*/
private <T> T getAndValidate(String attributeName, Type<T> type) throws ValidationException {
SelectorList<T> selectorList = getSelectorList(attributeName, type);
if (selectorList == null) {
// This is a normal attribute.
return super.get(attributeName, type);
}
List<T> resolvedList = new ArrayList<>();
for (Selector<T> selector : selectorList.getSelectors()) {
ConfigKeyAndValue<T> resolvedPath = resolveSelector(attributeName, selector);
if (!selector.isValueSet(resolvedPath.configKey)) {
// Use the default. We don't have access to the rule here, so pass null to
// Attribute.getValue(). This has the result of making attributes with condition
// predicates ineligible for "None" values. But no user-facing attributes should
// do that anyway, so that isn't a loss.
Attribute attr = getAttributeDefinition(attributeName);
if (attr.isMandatory()) {
throw new ValidationException(
String.format(
"Mandatory attribute '%s' resolved to 'None' after evaluating 'select'"
+ " expression",
attributeName));
}
Verify.verify(attr.getCondition() == Predicates.<AttributeMap>alwaysTrue());
@SuppressWarnings("unchecked")
T defaultValue = (T) attr.getDefaultValue(null);
resolvedList.add(defaultValue);
} else {
resolvedList.add(resolvedPath.value);
}
}
return resolvedList.size() == 1 ? resolvedList.get(0) : type.concat(resolvedList);
}
private static class ConfigKeyAndValue<T> {
final Label configKey;
final T value;
/** If null, this means the default condition (doesn't correspond to a config_setting). * */
@Nullable final ConfigMatchingProvider provider;
ConfigKeyAndValue(Label key, T value, @Nullable ConfigMatchingProvider provider) {
this.configKey = key;
this.value = value;
this.provider = provider;
}
}
private <T> ConfigKeyAndValue<T> resolveSelector(String attributeName, Selector<T> selector)
throws ValidationException {
Map<Label, ConfigKeyAndValue<T>> matchingConditions = new LinkedHashMap<>();
// Use a LinkedHashSet to guarantee deterministic error message ordering. We use a LinkedHashSet
// vs. a more general SortedSet because the latter supports insertion-order, which should more
// closely match how users see select() structures in BUILD files.
LinkedHashSet<Label> conditionLabels = new LinkedHashSet<>();
ConfigKeyAndValue<T> matchingResult = null;
// Find the matching condition and record its value (checking for duplicates).
for (Map.Entry<Label, T> entry : selector.getEntries().entrySet()) {
Label selectorKey = entry.getKey();
if (BuildType.Selector.isReservedLabel(selectorKey)) {
continue;
}
ConfigMatchingProvider curCondition =
configConditions.get(getLabel().resolveRepositoryRelative(selectorKey));
if (curCondition == null) {
// This can happen if the rule is in error
continue;
}
conditionLabels.add(selectorKey);
if (curCondition.matches()) {
// We keep track of all matches which are more precise than any we have found so far.
// Therefore, we remove any previous matches which are strictly less precise than this
// one, and only add this one if none of the previous matches are more precise.
// It is an error if we do not end up with only one most-precise match.
boolean suppressed = false;
Iterator<Map.Entry<Label, ConfigKeyAndValue<T>>> it =
matchingConditions.entrySet().iterator();
while (it.hasNext()) {
ConfigMatchingProvider existingMatch = it.next().getValue().provider;
if (curCondition.refines(existingMatch)) {
it.remove();
} else if (existingMatch.refines(curCondition)) {
suppressed = true;
break;
}
}
if (!suppressed) {
matchingConditions.put(
selectorKey, new ConfigKeyAndValue<>(selectorKey, entry.getValue(), curCondition));
}
}
}
if (matchingConditions.size() > 1) {
throw new ValidationException(
"Illegal ambiguous match on configurable attribute \""
+ attributeName
+ "\" in "
+ getLabel()
+ ":\n"
+ Joiner.on("\n").join(matchingConditions.keySet())
+ "\nMultiple matches are not allowed unless one is unambiguously more specialized.");
} else if (matchingConditions.size() == 1) {
matchingResult = Iterables.getOnlyElement(matchingConditions.values());
}
// If nothing matched, choose the default condition.
if (matchingResult == null) {
if (!selector.hasDefault()) {
throw new ValidationException(
noMatchError(
attributeName,
selector.getNoMatchError(),
conditionLabels,
getLabel(),
configHash));
}
matchingResult =
selector.hasDefault()
? new ConfigKeyAndValue<>(
Selector.DEFAULT_CONDITION_LABEL, selector.getDefault(), null)
: null;
}
return matchingResult;
}
/**
* Constructs a <a href="https://bazel.build/designs/2016/05/23/beautiful-error-messages.html">
* beautiful error</a> for when no conditions in a configurable attribute match.
*/
private static String noMatchError(
String attribute,
String customNoMatchError,
LinkedHashSet<Label> conditionLabels,
Label targetLabel,
String configHash) {
String error =
String.format(
"configurable attribute \"%s\" in %s doesn't match this configuration",
attribute, targetLabel);
if (!customNoMatchError.isEmpty()) {
error += String.format(": %s\n", customNoMatchError);
} else {
error +=
". Would a default condition help?\n\n"
+ "Conditions checked:\n "
+ Joiner.on("\n ").join(conditionLabels)
+ "\n\n"
+ "To see a condition's definition, run: bazel query --output=build "
+ "<condition label>.\n";
}
// See ConfiguredTargetQueryEnvironment#shortID for the substring rationale.
String configShortHash = configHash.substring(0, 7);
error +=
String.format(
"\nThis instance of %s has configuration identifier %s. "
+ "To inspect its configuration, run: bazel config %s.\n",
targetLabel, configShortHash, configShortHash);
error +=
"\n"
+ "For more help, see"
+ " https://docs.bazel.build/configurable-attributes.html#why-doesnt-my-select-choose-what-i-expect.\n\n";
return error;
}
@Override
public <T> T get(String attributeName, Type<T> type) {
try {
return getAndValidate(attributeName, type);
} catch (ValidationException e) {
// Callers that reach this branch should explicitly validate the attribute through an
// appropriate call and handle the exception directly. This method assumes
// pre-validated attributes.
throw new IllegalStateException(
"lookup failed on attribute " + attributeName + ": " + e.getMessage());
}
}
@Override
public boolean isAttributeValueExplicitlySpecified(String attributeName) {
SelectorList<?> selectorList = getSelectorList(attributeName, getAttributeType(attributeName));
if (selectorList == null) {
// This is a normal attribute.
return super.isAttributeValueExplicitlySpecified(attributeName);
}
for (Selector<?> selector : selectorList.getSelectors()) {
try {
ConfigKeyAndValue<?> resolvedPath = resolveSelector(attributeName, selector);
if (selector.isValueSet(resolvedPath.configKey)) {
return true;
}
} catch (ValidationException unused) {
// This will trigger an error via any other call, so the actual return doesn't matter much.
return true;
}
}
return false; // Every select() in this list chooses a path with value "None".
}
}