Decorate tabs for BUILD files with package name

Since BUILD files all have the same name it's hard
to distinguish them, so we can use EditorTabTitleProvider
to write full label in the editor tab title

base/src/META-INF/blaze-base.xml

@@ -462,6 +462,7 @@
     <completion.confidence language="BUILD" implementationClass="com.google.idea.blaze.base.lang.buildfile.completion.BuildFileCompletionConfidence"/>
     <spellchecker.support language="BUILD" implementationClass="com.google.idea.blaze.base.lang.buildfile.validation.BuildSpellcheckingStrategy"/>
     <highlightVisitor implementation="com.google.idea.blaze.base.editor.HighlightingStatsCollector"/>
+    <editorTabTitleProvider implementation="com.google.idea.blaze.base.editor.BazelEditorTabTitleProvider"/>
    <formattingService implementation="com.google.idea.blaze.base.buildmodifier.BuildifierFormattingService"/>
   </extensions>
 

base/src/com/google/idea/blaze/base/editor/BazelEditorTabTitleProvider.java

@@ -0,0 +1,31 @@
+package com.google.idea.blaze.base.editor;
+
+import com.google.idea.blaze.base.lang.buildfile.psi.BuildFile;
+import com.google.idea.blaze.base.settings.Blaze;
+import com.intellij.openapi.fileEditor.impl.EditorTabTitleProvider;
+import com.intellij.openapi.project.Project;
+import com.intellij.openapi.vfs.VirtualFile;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class BazelEditorTabTitleProvider implements EditorTabTitleProvider {
+  private static boolean requiresDecoration(Project project, String fileName) {
+    return Blaze.getBuildSystemProvider(project).possibleBuildFileNames().contains(fileName);
+  }
+  @Override
+  public @Nullable String getEditorTabTitle(@NotNull Project project,
+      @NotNull VirtualFile virtualFile) {
+    var fileName = virtualFile.getName();
+    if (!requiresDecoration(project, fileName)) {
+      return null;
+    }
+
+    return BuildFile.getBuildFileString(project, virtualFile.getPath());
+  }
+
+  @Override
+  public @Nullable String getEditorTabTooltipText(@NotNull Project project,
+      @NotNull VirtualFile virtualFile) {
+    return EditorTabTitleProvider.super.getEditorTabTooltipText(project, virtualFile);
+  }
+}