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Add MergeResponseInspector functionality to Java API
Provides a simple API to collect information that is necessary for content-aware merges. The base for that information is already available via the `Conflict`s returned in a `MergeResponse`. The approach is based on information from the merge-request and merge-response. It collects the conflicting contents from the _merge-base_ using a Nessie-API "get-contents" call and then uses Nessie's diff-operations to identify and filter the conflicting contents from the diffs of _merge-base_-to-_merge-source_ and _merge-base_-to-_merge-target_. The content information is aggregated ("grouped" by content-ID) and returned as a Java `Stream` via the introduced API. This change does not implement any content-aware merge operation. This is a pure Nessie-Java-API/client change, no REST API change.
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‎api/client/src/main/java/org/projectnessie/client/api/MergeReferenceBuilder.java‎

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@@ -62,5 +62,12 @@ default MergeReferenceBuilder fromRef(Reference fromRef) {
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return fromRefName(fromRef.getName()).fromHash(fromRef.getHash());
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}
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/** Perform the merge operation. */
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MergeResponse merge() throws NessieNotFoundException, NessieConflictException;
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/**
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* Perform the merge operation and allows to optionally inspect merge conflicts using the content
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* state of the conflicting contents on the merge-base, merge-source and merge-target.
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*/
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MergeResponseInspector mergeInspect() throws NessieNotFoundException, NessieConflictException;
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}

‎api/client/src/main/java/org/projectnessie/client/api/MergeResponseInspector.java‎

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/*
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* Copyright (C) 2023 Dremio
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.projectnessie.client.api;
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import java.util.stream.Stream;
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import javax.annotation.Nullable;
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import org.immutables.value.Value;
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import org.projectnessie.api.v2.params.Merge;
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import org.projectnessie.error.NessieNotFoundException;
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import org.projectnessie.model.Conflict;
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import org.projectnessie.model.Conflict.ConflictType;
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import org.projectnessie.model.Content;
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import org.projectnessie.model.ContentKey;
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import org.projectnessie.model.MergeBehavior;
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import org.projectnessie.model.MergeKeyBehavior;
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import org.projectnessie.model.MergeResponse;
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/**
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* Allows inspection of merge results, to resolve {@link ConflictType#VALUE_DIFFERS content related}
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* merge {@link Conflict conflicts} indicated in the {@link #getResponse() merge response}.
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*/
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public interface MergeResponseInspector {
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/** The merge request sent to Nessie. */
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Merge getRequest();
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/** The merge response received from Nessie. */
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MergeResponse getResponse();
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/**
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* Provides details about the conflicts that happened during a merge operation.
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*
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* <p>The returned stream contains one {@link MergeConflictDetails element} for each conflict.
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* Non-conflicting contents are not included.
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*
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* <p>Each {@link MergeConflictDetails conflict details object} allows callers to resolve
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* conflicts based on that information, also known as "content aware merge".
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*
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* <p>Once conflicts have been either resolved, or alternatively specific keys declared to "use
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* the {@link MergeBehavior#DROP left/from} or {@link MergeBehavior#FORCE right/target} side",
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* another {@link MergeReferenceBuilder merge operation} cna be performed, providing a {@link
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* MergeKeyBehavior#getResolvedContent() resolved content} for a content key.
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*
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* <p>Keep in mind that calling this function triggers API calls against nessie to retrieve the
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* relevant content objects on the merge-base and and the content keys and content objects on the
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* merge-from (source) and merge-target.
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*/
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Stream<MergeConflictDetails> collectMergeConflictDetails() throws NessieNotFoundException;
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@Value.Immutable
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interface MergeConflictDetails {
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/** The content ID of the conflicting content. */
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default String getContentId() {
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return contentOnMergeBase().getId();
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}
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/** Key of the content on the {@link MergeResponse#getCommonAncestor() merge-base commit}. */
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ContentKey keyOnMergeBase();
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/** Key of the content on the {@link MergeReferenceBuilder#fromRef merge-from reference}. */
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@Nullable
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@jakarta.annotation.Nullable
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ContentKey keyOnSource();
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/**
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* Key of the content on the {@link MergeResponse#getEffectiveTargetHash() merge-target
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* reference}.
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*/
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@Nullable
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@jakarta.annotation.Nullable
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ContentKey keyOnTarget();
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/** Content object on the {@link MergeResponse#getCommonAncestor() merge-base commit}. */
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// TODO this can also be null, if the same key was added on source + target but is not present
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// on merge-base.
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Content contentOnMergeBase();
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/**
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* Content on the {@link MergeReferenceBuilder#fromRef merge-from reference}, or {@code null} if
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* not present on the merge-from.
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*/
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@Nullable
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@jakarta.annotation.Nullable
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Content contentOnSource();
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/**
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* Content on the {@link MergeResponse#getEffectiveTargetHash() merge-target reference}, or
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* {@code null} if not present on the merge-target.
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*/
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@Nullable
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@jakarta.annotation.Nullable
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Content contentOnTarget();
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/**
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* Contains {@link Conflict#conflictType() machine interpretable} and {@link Conflict#message()
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* human.readable information} about the conflict.
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*/
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// TODO this can also be null, if the same key was added on source + target but is not present
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// on merge-base.
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Conflict conflict();
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}
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}

‎api/client/src/main/java/org/projectnessie/client/api/impl/BaseMergeResponseInspector.java‎

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/*
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* Copyright (C) 2023 Dremio
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.projectnessie.client.api.impl;
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import static java.util.Collections.emptyList;
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import static java.util.Objects.requireNonNull;
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import static org.projectnessie.client.api.impl.MapEntry.mapEntry;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.Map;
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import java.util.Objects;
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import java.util.Set;
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import java.util.function.Function;
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import java.util.stream.Collectors;
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import java.util.stream.Stream;
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import org.projectnessie.client.api.ImmutableMergeConflictDetails;
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import org.projectnessie.client.api.MergeResponseInspector;
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import org.projectnessie.error.NessieNotFoundException;
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import org.projectnessie.model.Conflict;
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import org.projectnessie.model.Content;
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import org.projectnessie.model.ContentKey;
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import org.projectnessie.model.Detached;
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import org.projectnessie.model.DiffResponse;
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import org.projectnessie.model.GetMultipleContentsResponse;
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import org.projectnessie.model.MergeResponse;
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/** Base class used for testing and production code, because testing does not use the Nessie API. */
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public abstract class BaseMergeResponseInspector implements MergeResponseInspector {
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@Override
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public Stream<MergeConflictDetails> collectMergeConflictDetails() throws NessieNotFoundException {
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// Note: The API exposes a `Stream` so we can optimize this implementation later to reduce
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// runtime or heap pressure.
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return mergeConflictDetails().stream();
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}
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protected List<MergeConflictDetails> mergeConflictDetails() throws NessieNotFoundException {
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Map<ContentKey, Conflict> conflictMap = conflictMap();
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Map<ContentKey, Content> mergeBaseContentByKey = mergeBaseContentByKey();
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if (mergeBaseContentByKey.isEmpty()) {
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return emptyList();
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}
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Map<String, List<DiffResponse.DiffEntry>> sourceDiff = sourceDiff();
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Map<String, List<DiffResponse.DiffEntry>> targetDiff = targetDiff();
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List<MergeConflictDetails> details = new ArrayList<>(mergeBaseContentByKey.size());
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for (Map.Entry<ContentKey, Content> base : mergeBaseContentByKey.entrySet()) {
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ContentKey baseKey = base.getKey();
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Content baseContent = base.getValue();
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Map.Entry<ContentKey, Content> source = keyAndContent(baseKey, baseContent, sourceDiff);
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Map.Entry<ContentKey, Content> target = keyAndContent(baseKey, baseContent, targetDiff);
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MergeConflictDetails detail =
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ImmutableMergeConflictDetails.builder()
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.conflict(conflictMap.get(baseKey))
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.keyOnMergeBase(baseKey)
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.keyOnSource(source.getKey())
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.keyOnTarget(target.getKey())
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.contentOnMergeBase(baseContent)
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.contentOnSource(source.getValue())
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.contentOnTarget(target.getValue())
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.build();
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details.add(detail);
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}
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return details;
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}
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protected Map<ContentKey, Conflict> conflictMap() {
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return getResponse().getDetails().stream()
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.map(MergeResponse.ContentKeyDetails::getConflict)
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.filter(Objects::nonNull)
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.collect(Collectors.toMap(Conflict::key, Function.identity()));
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}
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protected Set<String> mergeBaseContentIds() throws NessieNotFoundException {
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return mergeBaseContents().stream()
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.map(GetMultipleContentsResponse.ContentWithKey::getContent)
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.map(Content::getId)
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.filter(Objects::nonNull)
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.collect(Collectors.toSet());
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}
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protected Map<ContentKey, Content> mergeBaseContentByKey() throws NessieNotFoundException {
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return mergeBaseContents().stream()
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.collect(
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Collectors.toMap(
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GetMultipleContentsResponse.ContentWithKey::getKey,
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GetMultipleContentsResponse.ContentWithKey::getContent));
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}
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protected Map<String, List<DiffResponse.DiffEntry>> sourceDiff() throws NessieNotFoundException {
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// TODO it would help to have the effective from-hash in the response, in case the merge-request
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// did not contain it. If we have that merge, we can use 'DETACHED' here.
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String hash = getRequest().getFromHash();
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String ref = hash != null ? Detached.REF_NAME : getRequest().getFromRefName();
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return diffByContentId(ref, hash);
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}
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protected Map<String, List<DiffResponse.DiffEntry>> targetDiff() throws NessieNotFoundException {
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return diffByContentId(Detached.REF_NAME, getResponse().getEffectiveTargetHash());
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}
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protected abstract List<GetMultipleContentsResponse.ContentWithKey> mergeBaseContents()
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throws NessieNotFoundException;
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protected abstract Map<String, List<DiffResponse.DiffEntry>> diffByContentId(
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String ref, String hash) throws NessieNotFoundException;
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static String contentIdFromDiffEntry(DiffResponse.DiffEntry e) {
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Content from = e.getFrom();
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return requireNonNull(from != null ? from.getId() : requireNonNull(e.getTo()).getId());
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}
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static Map.Entry<ContentKey, Content> keyAndContent(
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ContentKey baseKey, Content baseContent, Map<String, List<DiffResponse.DiffEntry>> diff) {
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List<DiffResponse.DiffEntry> diffs = diff.get(baseContent.getId());
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if (diffs != null) {
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int size = diffs.size();
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DiffResponse.DiffEntry last = diffs.get(size - 1);
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return mapEntry(last.getKey(), last.getTo());
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}
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return mapEntry(baseKey, baseContent);
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}
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}

‎api/client/src/main/java/org/projectnessie/client/api/impl/MapEntry.java‎

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/*
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* Copyright (C) 2023 Dremio
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.projectnessie.client.api.impl;
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import java.util.Map;
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import javax.annotation.Nullable;
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import org.immutables.value.Value;
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/**
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* A helper that implements {@link Map.Entry}, because the code is built for Java 8 and Guava's not
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* a dependency.
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*/
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@Value.Immutable
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abstract class MapEntry<K, V> implements Map.Entry<K, V> {
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private static final MapEntry<?, ?> EMPTY_ENTRY = (MapEntry<?, ?>) MapEntry.mapEntry(null, null);
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@SuppressWarnings("unchecked")
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static <K, V> Map.Entry<K, V> emptyEntry() {
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return (Map.Entry<K, V>) EMPTY_ENTRY;
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}
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static <K, V> Map.Entry<K, V> mapEntry(K key, V value) {
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return ImmutableMapEntry.of(key, value);
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}
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@Override
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@Value.Parameter(order = 1)
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@Nullable
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public abstract K getKey();
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@Override
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@Value.Parameter(order = 2)
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@Nullable
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public abstract V getValue();
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@Override
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public V setValue(V value) {
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throw new UnsupportedOperationException();
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}
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}

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