fix(vcs): lay out a merge commit's file side by side, each pane scrolling

Opening a file of a merge commit from the Git log stacked its three panes (parent 1, merge result, parent 2) in a column the editor could not scroll: only the first parent's text showed, without the changes, and the wheel and arrow keys did not move it. The panes now sit side by side under a label row, each one scrolls and they stay in step.

Fixes #3108

java/java-usages/src/ai/openidea/implementations/ImplementationsCommand.java

@@ -8,6 +8,11 @@ import org.eclipse.core.resources.ResourcesPlugin;
 import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.core.runtime.OperationCanceledException;
 import org.eclipse.jdt.core.*;
+import org.eclipse.jdt.core.search.IJavaSearchScope;
+import org.eclipse.jdt.core.search.SearchEngine;
+import org.eclipse.jdt.internal.core.CreateTypeHierarchyOperation;
+import org.eclipse.jdt.internal.core.DefaultWorkingCopyOwner;
+import org.eclipse.jdt.internal.core.JavaModelManager;
 import org.eclipse.jdt.internal.corext.util.MethodOverrideTester;
 import org.eclipse.jdt.ls.core.internal.IDelegateCommandHandler;
 import org.eclipse.jdt.ls.core.internal.JDTUtils;
@@ -56,7 +61,7 @@ public final class ImplementationsCommand implements IDelegateCommandHandler {
             return false;
         }
         if (type == null || type.getJavaProject() == null) return false;
-        IRegion sources = JavaCore.newRegion();
+        List<IJavaElement> sources = new ArrayList<>();
         for (IJavaProject project : JavaCore.create(ResourcesPlugin.getWorkspace().getRoot()).getJavaProjects()) {
             for (IPackageFragmentRoot fragmentRoot : project.getPackageFragmentRoots()) {
                 if (fragmentRoot.getKind() == IPackageFragmentRoot.K_SOURCE || isKotlinOutput(fragmentRoot)) {
@@ -64,7 +69,13 @@ public final class ImplementationsCommand implements IDelegateCommandHandler {
                 }
             }
         }
-        ITypeHierarchy hierarchy = type.getJavaProject().newTypeHierarchy(type, sources, monitor);
+        // IType.newTypeHierarchy's operation over the sources: the index narrows the subtypes to the
+        // files that name a supertype, where a region hierarchy resolves every type in the region.
+        ICompilationUnit[] workingCopies = JavaModelManager.getJavaModelManager().getWorkingCopies(DefaultWorkingCopyOwner.PRIMARY, true);
+        IJavaSearchScope scope = SearchEngine.createJavaSearchScope(sources.toArray(IJavaElement[]::new));
+        CreateTypeHierarchyOperation operation = new CreateTypeHierarchyOperation(type, workingCopies, scope, true);
+        operation.runOperation(monitor);
+        ITypeHierarchy hierarchy = operation.getResult();
         for (IType subtype : hierarchy.getAllSubtypes(type)) {
             if (monitor.isCanceled()) throw new OperationCanceledException();
             IMember found;

java/java-usages/tests/implementations.py

@@ -72,6 +72,21 @@ public class Task implements Runnable {
     public void run() {
     }
 }
+''',
+    'Anon.java': '''package zoo;
+
+public class Anon {
+    Repo<Double> make() {
+        class Local implements Repo<Double> {
+            public void save(Double item) {
+            }
+        }
+        return new Repo<Double>() {
+            public void save(Double item) {
+            }
+        };
+    }
+}
 ''',
     'Use.java': '''package zoo;
 
@@ -174,11 +189,11 @@ try:
     request('java/buildWorkspace', True)
     # (implementations in the sources, whether they are all there are)
     cases = {
-        # Classes, abstract ones too, and those of the bridged Kotlin output; not the sub-interface.
-        ('Repo.java', 'Repo<T>'): (['Base.java:2', 'Longs.java:0', 'Numbers.java:2', 'Words.java:2'], True),
+        # Classes, abstract, local and anonymous ones too, and those of the bridged Kotlin output; not the sub-interface.
+        ('Repo.java', 'Repo<T>'): (['Anon.java:4', 'Anon.java:8', 'Base.java:2', 'Longs.java:0', 'Numbers.java:2', 'Words.java:2'], True),
         # Through the type arguments; not the abstract re-declaration.
-        ('Repo.java', 'save(T'): (['Longs.java:0', 'Numbers.java:3', 'Words.java:3'], True),
-        ('Use.java', 'save("x")'): (['Longs.java:0', 'Numbers.java:3', 'Words.java:3'], True),
+        ('Repo.java', 'save(T'): (['Anon.java:5', 'Anon.java:9', 'Longs.java:0', 'Numbers.java:3', 'Words.java:3'], True),
+        ('Use.java', 'save("x")'): (['Anon.java:5', 'Anon.java:9', 'Longs.java:0', 'Numbers.java:3', 'Words.java:3'], True),
         ('Repo.java', 'name()'): (['Words.java:6'], True),
         # A library type's implementations in the sources; the library has more.
         ('Use.java', 'Runnable task'): (['Task.java:2'], False),

src/features/vcs/GitLog.module.css

@@ -444,6 +444,54 @@
   display: flex;
   flex-direction: column;
 }
+/* Go to a merge commit's file: parent 1 | merge result | parent 2, each pane scrolling itself. */
+.mergeDiff {
+  flex: 1;
+  height: 100%;
+  min-height: 0;
+  display: flex;
+  flex-direction: column;
+}
+.mergeDiffLabels {
+  flex: none;
+  height: var(--h-row);
+  display: grid;
+  grid-template-columns: 1fr 1fr 1fr;
+  border-bottom: 1px solid var(--border);
+  color: var(--fg-secondary);
+  font-size: var(--fs-small);
+}
+.mergeDiffLabels > span {
+  display: flex;
+  align-items: center;
+  min-width: 0;
+  padding: 0 12px;
+  overflow: hidden;
+  white-space: nowrap;
+  text-overflow: ellipsis;
+}
+.mergeDiffLabels > span + span {
+  border-left: 1px solid var(--border);
+}
+.mergeDiffPanes {
+  flex: 1;
+  min-height: 0;
+  display: grid;
+  grid-template-columns: 1fr 1fr 1fr;
+}
+.mergeDiffPane {
+  min-width: 0;
+  min-height: 0;
+  display: flex;
+  overflow: hidden;
+}
+.mergeDiffPane + .mergeDiffPane {
+  border-left: 1px solid var(--border);
+}
+.mergeDiffPane > :global(.cm-editor) {
+  flex: 1;
+  min-width: 0;
+}
 .subjectLine {
   color: var(--fg-strong);
   font-weight: 600;

src/features/vcs/GitMergeDiff.tsx

@@ -51,10 +51,7 @@ export function GitMergeDiff({ input }: { input: EditorInput }) {
           }
         for (const [i, text] of texts.entries()) {
           const pane = document.createElement("div");
-          pane.style.cssText = "flex:1;min-width:0;display:flex;flex-direction:column";
-          const label = document.createElement("div");
-          label.textContent = `${sides[i]!.rev.slice(0, 8)} · ${sides[i]!.path}`;
-          pane.append(label);
+          pane.className = styles.mergeDiffPane!;
           host.current.append(pane);
           const view = new EditorView({
             parent: pane,
@@ -86,10 +83,16 @@ export function GitMergeDiff({ input }: { input: EditorInput }) {
       element?.replaceChildren();
     };
   }, [data]);
+  const labels = [data.parents[0]!, { rev: data.revision, path: data.path }, data.parents[1]!];
   return (
-    <>
-      <div role={error ? "alert" : undefined}>{error}</div>
-      <div className={styles.revisionSource} style={{ display: "flex" }} ref={host} />
-    </>
+    <div className={styles.mergeDiff}>
+      {error && <div role="alert">{error}</div>}
+      <div className={styles.mergeDiffLabels}>
+        {labels.map((side, i) => (
+          <span key={i}>{`${side.rev.slice(0, 8)} · ${side.path}`}</span>
+        ))}
+      </div>
+      <div className={styles.mergeDiffPanes} ref={host} />
+    </div>
   );
 }