Make ProjectCache#get return an Optional<ProjectState>

This refactoring forces callers to think about how to handle projects
that do not exist explicitly. As a general guidance, API handlers will
want to throw a BadRequestException and components in the inner works of
Gerrit where content should have been pre-validated should throw an
IllegalStateException.

But overall, it's a case-by-case decision.

In a follow-up commit, we will remove #checkedGet and move callers to
get instead.

Change-Id: I95bbc22ad5f3279e6f40f1d05c8d7235d601e32d

java/com/google/gerrit/server/query/change/ChangeData.java

@@ -14,6 +14,7 @@
 
 package com.google.gerrit.server.query.change;
 
+import static com.google.gerrit.server.project.ProjectCache.illegalState;
 import static java.util.Objects.requireNonNull;
 import static java.util.stream.Collectors.toList;
 import static java.util.stream.Collectors.toMap;
@@ -915,7 +916,9 @@ public class ChangeData {
             return false;
           }
           String mergeStrategy =
-              mergeUtilFactory.create(projectCache.get(project())).mergeStrategyName();
+              mergeUtilFactory
+                  .create(projectCache.get(project()).orElseThrow(illegalState(project())))
+                  .mergeStrategyName();
           mergeable =
               mergeabilityCache.get(ps.commitId(), ref, str.type, mergeStrategy, c.getDest(), repo);
         } catch (IOException e) {

java/com/google/gerrit/server/query/change/ConflictsPredicate.java

@@ -16,6 +16,7 @@ package com.google.gerrit.server.query.change;
 
 import static com.google.common.base.MoreObjects.firstNonNull;
 import static com.google.common.flogger.LazyArgs.lazy;
+import static com.google.gerrit.server.project.ProjectCache.noSuchProject;
 import static java.util.concurrent.TimeUnit.MINUTES;
 
 import com.google.common.flogger.FluentLogger;
@@ -218,10 +219,7 @@ public class ConflictsPredicate {
 
     ProjectState getProjectState() throws NoSuchProjectException {
       if (projectState == null) {
-        projectState = projectCache.get(cd.project());
-        if (projectState == null) {
-          throw new NoSuchProjectException(cd.project());
-        }
+        projectState = projectCache.get(cd.project()).orElseThrow(noSuchProject(cd.project()));
       }
       return projectState;
     }

java/com/google/gerrit/server/query/change/EqualsLabelPredicate.java

@@ -29,6 +29,7 @@ import com.google.gerrit.server.permissions.PermissionBackendException;
 import com.google.gerrit.server.project.ProjectCache;
 import com.google.gerrit.server.project.ProjectState;
 import java.io.IOException;
+import java.util.Optional;
 
 public class EqualsLabelPredicate extends ChangeIndexPredicate {
   protected final ProjectCache projectCache;
@@ -60,14 +61,14 @@ public class EqualsLabelPredicate extends ChangeIndexPredicate {
       return false;
     }
 
-    ProjectState project = projectCache.get(c.getDest().project());
-    if (project == null) {
+    Optional<ProjectState> project = projectCache.get(c.getDest().project());
+    if (!project.isPresent()) {
       // The project has disappeared.
       //
       return false;
     }
 
-    LabelType labelType = type(project.getLabelTypes(), label);
+    LabelType labelType = type(project.get().getLabelTypes(), label);
     if (labelType == null) {
       return false; // Label is not defined by this project.
     }

java/com/google/gerrit/server/query/change/ParentProjectPredicate.java

@@ -26,6 +26,7 @@ import com.google.gerrit.server.project.ProjectState;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Optional;
 
 public class ParentProjectPredicate extends OrPredicate<ChangeData> {
   private static final FluentLogger logger = FluentLogger.forEnclosingClass();
@@ -40,15 +41,15 @@ public class ParentProjectPredicate extends OrPredicate<ChangeData> {
 
   protected static List<Predicate<ChangeData>> predicates(
       ProjectCache projectCache, ChildProjects childProjects, String value) {
-    ProjectState projectState = projectCache.get(Project.nameKey(value));
-    if (projectState == null) {
+    Optional<ProjectState> projectState = projectCache.get(Project.nameKey(value));
+    if (!projectState.isPresent()) {
       return Collections.emptyList();
     }
 
     List<Predicate<ChangeData>> r = new ArrayList<>();
-    r.add(new ProjectPredicate(projectState.getName()));
+    r.add(new ProjectPredicate(projectState.get().getName()));
     try {
-      for (ProjectInfo p : childProjects.list(projectState.getNameKey())) {
+      for (ProjectInfo p : childProjects.list(projectState.get().getNameKey())) {
         r.add(new ProjectPredicate(p.name));
       }
     } catch (PermissionBackendException e) {