IDEA-125372 diff: fix NPE

we can't provide correct 'canNavigate' because then we'll navigate to the corresponding temporal file, that is not a desired behaviour

platform/platform-api/src/com/intellij/openapi/fileEditor/FileEditorManager.java

@@ -30,7 +30,7 @@ public abstract class FileEditorManager {
 
   public static final Key<Boolean> USE_CURRENT_WINDOW = Key.create("OpenFile.searchForOpen");
 
-  public static FileEditorManager getInstance(Project project) {
+  public static FileEditorManager getInstance(@NotNull Project project) {
     return project.getComponent(FileEditorManager.class);
   }
 

platform/platform-impl/src/com/intellij/openapi/diff/ex/DiffPanelOptions.java

@@ -23,6 +23,8 @@ import com.intellij.openapi.fileEditor.OpenFileDescriptor;
 import com.intellij.openapi.ui.DialogWrapper;
 import com.intellij.openapi.ui.DialogWrapperDialog;
 import com.intellij.openapi.util.Disposer;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.awt.*;
 
@@ -56,25 +58,26 @@ public class DiffPanelOptions {
     myShowSourcePolicy = showSourcePolicy;
   }
 
-  public void showSource(OpenFileDescriptor descriptor) {
+  public void showSource(@Nullable OpenFileDescriptor descriptor) {
+    if (descriptor == null || myDiffPanel.getProject() == null) return;
     myShowSourcePolicy.showSource(descriptor, myDiffPanel);
   }
 
   public interface ShowSourcePolicy {
-    void showSource(OpenFileDescriptor descriptor, DiffPanelImpl diffPanel);
+    void showSource(@NotNull OpenFileDescriptor descriptor, @NotNull DiffPanelImpl diffPanel);
 
     ShowSourcePolicy DONT_SHOW = new ShowSourcePolicy() {
-      public void showSource(OpenFileDescriptor descriptor, DiffPanelImpl diffPanel) {}
+      public void showSource(@NotNull OpenFileDescriptor descriptor, @NotNull DiffPanelImpl diffPanel) {}
     };
 
     ShowSourcePolicy OPEN_EDITOR = new ShowSourcePolicy() {
-      public void showSource(OpenFileDescriptor descriptor, DiffPanelImpl diffPanel) {
+      public void showSource(@NotNull OpenFileDescriptor descriptor, @NotNull DiffPanelImpl diffPanel) {
         FileEditorManager.getInstance(diffPanel.getProject()).openTextEditor(descriptor, true);
       }
     };
 
     ShowSourcePolicy OPEN_EDITOR_AND_CLOSE_DIFF = new ShowSourcePolicy() {
-      public void showSource(OpenFileDescriptor descriptor, DiffPanelImpl diffPanel) {
+      public void showSource(@NotNull OpenFileDescriptor descriptor, @NotNull DiffPanelImpl diffPanel) {
         OPEN_EDITOR.showSource(descriptor, diffPanel);
         if (diffPanel.getOwnerWindow() == null) return;
         Disposer.dispose(diffPanel);
@@ -97,7 +100,7 @@ public class DiffPanelOptions {
     };
 
     ShowSourcePolicy DEFAULT = new ShowSourcePolicy() {
-      public void showSource(OpenFileDescriptor descriptor, DiffPanelImpl diffPanel) {
+      public void showSource(@NotNull OpenFileDescriptor descriptor, @NotNull DiffPanelImpl diffPanel) {
         Window window = diffPanel.getOwnerWindow();
         if (window == null) return;
         else if (window instanceof Frame) OPEN_EDITOR.showSource(descriptor, diffPanel);

platform/platform-impl/src/com/intellij/openapi/diff/impl/DiffPanelImpl.java

@@ -612,7 +612,7 @@ public class DiffPanelImpl implements DiffPanelEx, ContentChangeListener, TwoSid
     return myData.getProject();
   }
 
-  public void showSource(OpenFileDescriptor descriptor) {
+  public void showSource(@Nullable OpenFileDescriptor descriptor) {
     myOptions.showSource(descriptor);
   }
 
@@ -1009,10 +1009,7 @@ public class DiffPanelImpl implements DiffPanelEx, ContentChangeListener, TwoSid
 
     @Override
     public void navigate(boolean requestFocus) {
-      final OpenFileDescriptor descriptor = mySide.getCurrentOpenFileDescriptor();
-      if (descriptor != null) {
-        showSource(descriptor);
-      }
+      showSource(mySide.getCurrentOpenFileDescriptor());
     }
   }
 }