move supportsSplitEditor to editor input and let it return true by default

src/vs/workbench/browser/parts/editor/baseEditor.ts

@@ -131,14 +131,6 @@ export abstract class BaseEditor extends Panel implements IEditor {
 		return this._position;
 	}
 
-	/**
-	 * Controls if the editor shows an action to split the input of the editor to the side. Subclasses should override
-	 * if they are capable of showing the same editor input side by side.
-	 */
-	public supportsSplitEditor(): boolean {
-		return false;
-	}
-
 	public dispose(): void {
 		this._input = null;
 		this._options = null;

src/vs/workbench/browser/parts/editor/editorActions.ts

@@ -7,7 +7,6 @@
 import {TPromise} from 'vs/base/common/winjs.base';
 import nls = require('vs/nls');
 import {Action} from 'vs/base/common/actions';
-import {BaseEditor} from 'vs/workbench/browser/parts/editor/baseEditor';
 import {EditorInput, getUntitledOrFileResource, TextEditorOptions, EditorOptions, IEditorIdentifier} from 'vs/workbench/common/editor';
 import {QuickOpenEntryGroup} from 'vs/base/parts/quickopen/browser/quickOpenModel';
 import {EditorQuickOpenEntry, EditorQuickOpenEntryGroup, IEditorQuickOpenEntry, QuickOpenAction} from 'vs/workbench/browser/quickopen';
@@ -49,7 +48,7 @@ export class SplitEditorAction extends Action {
 		}
 
 		// Return if the editor to split does not support split editing
-		if (!(<BaseEditor>editorToSplit).supportsSplitEditor()) {
+		if (editorToSplit.input instanceof EditorInput && !(<EditorInput>editorToSplit.input).supportsSplitEditor()) {
 			return TPromise.as(true);
 		}
 
@@ -215,7 +214,7 @@ export abstract class BaseFocusSideGroupAction extends Action {
 		}
 
 		// Require the reference editor to be visible and supporting split editor
-		if (referenceEditor && (<BaseEditor>referenceEditor).supportsSplitEditor()) {
+		if (referenceEditor && (<EditorInput>referenceEditor.input).supportsSplitEditor()) {
 			return this.editorService.openEditor(referenceEditor.input, null, this.getTargetEditorSide());
 		}
 

src/vs/workbench/browser/parts/editor/iframeEditor.ts

@@ -261,10 +261,6 @@ export class IFrameEditor extends BaseEditor {
 		setTimeout(() => this.reload(true));
 	}
 
-	public supportsSplitEditor(): boolean {
-		return true;
-	}
-
 	/**
 	 * Reloads the contents of the iframe in this editor by reapplying the input.
 	 */

src/vs/workbench/browser/parts/editor/noTabsTitleControl.ts

@@ -10,9 +10,8 @@ import {prepareActions} from 'vs/workbench/browser/actionBarRegistry';
 import errors = require('vs/base/common/errors');
 import arrays = require('vs/base/common/arrays');
 import {Builder, $} from 'vs/base/browser/builder';
-import {IEditorGroup} from 'vs/workbench/common/editor';
+import {IEditorGroup, EditorInput} from 'vs/workbench/common/editor';
 import DOM = require('vs/base/browser/dom');
-import {BaseEditor} from 'vs/workbench/browser/parts/editor/baseEditor';
 import {ToolBar} from 'vs/base/browser/ui/toolbar/toolbar';
 import {IWorkbenchEditorService} from 'vs/workbench/services/editor/common/editorService';
 import {IContextMenuService} from 'vs/platform/contextview/browser/contextView';
@@ -153,8 +152,6 @@ export class NoTabsTitleControl extends TitleControl {
 
 		const isPinned = group.isPinned(group.activeEditor);
 		const isActive = this.stacks.isActive(group);
-		const position = this.stacks.positionOfGroup(group);
-		const control = this.editorService.getVisibleEditors()[position];
 
 		// Pinned state
 		if (isPinned) {
@@ -194,7 +191,7 @@ export class NoTabsTitleControl extends TitleControl {
 		// Update Editor Actions Toolbar
 		const editorActions = this.getEditorActions(group);
 		const primaryEditorActions = prepareActions(editorActions.primary);
-		if (isActive && control instanceof BaseEditor && control.supportsSplitEditor()) {
+		if (isActive && editor instanceof EditorInput && editor.supportsSplitEditor()) {
 			primaryEditorActions.push(this.splitEditorAction);
 		}
 		primaryEditorActions.push(this.closeEditorAction);

src/vs/workbench/browser/parts/editor/stringEditor.ts

@@ -162,10 +162,6 @@ export class StringEditor extends BaseTextEditor {
 		}
 	}
 
-	public supportsSplitEditor(): boolean {
-		return true;
-	}
-
 	public clearInput(): void {
 
 		// Keep editor view state in settings to restore when coming back

src/vs/workbench/browser/parts/editor/titleControl.ts

@@ -13,7 +13,7 @@ import errors = require('vs/base/common/errors');
 import {Builder} from 'vs/base/browser/builder';
 import {BaseEditor, IEditorInputActionContext} from 'vs/workbench/browser/parts/editor/baseEditor';
 import {RunOnceScheduler} from 'vs/base/common/async';
-import {IEditorStacksModel, IEditorGroup} from 'vs/workbench/common/editor';
+import {IEditorStacksModel, IEditorGroup, EditorInput} from 'vs/workbench/common/editor';
 import {EventType as BaseEventType} from 'vs/base/common/events';
 import {IActionItem, ActionsOrientation, Separator} from 'vs/base/browser/ui/actionbar/actionbar';
 import {ToolBar} from 'vs/base/browser/ui/toolbar/toolbar';
@@ -208,8 +208,7 @@ export abstract class TitleControl {
 	}
 
 	protected getGroupActions(group: IEditorGroup): IToolbarActions {
-		const position = this.stacks.positionOfGroup(group);
-		const editor = this.editorService.getVisibleEditors()[position];
+		const editor = group.activeEditor;
 		const primary: IAction[] = [];
 
 		const isOverflowing = group.count > 1;
@@ -241,7 +240,7 @@ export abstract class TitleControl {
 		}
 
 		// Splitting
-		if (editor && editor instanceof BaseEditor && editor.supportsSplitEditor()) {
+		if (editor instanceof EditorInput && editor.supportsSplitEditor()) {
 			primary.push(this.splitEditorAction);
 		}
 

src/vs/workbench/common/editor.ts

@@ -121,6 +121,13 @@ export abstract class EditorInput extends EventEmitter implements IEditorInput {
 		this.dispose();
 	}
 
+	/**
+	 * Subclasses can set this to false if it does not make sense to split the editor input.
+	 */
+	public supportsSplitEditor(): boolean {
+		return true;
+	}
+
 	/**
 	 * Returns true if this input is identical to the otherInput.
 	 */

src/vs/workbench/common/editor/diffEditorInput.ts

@@ -153,6 +153,10 @@ export class DiffEditorInput extends BaseDiffEditorInput {
 		});
 	}
 
+	public supportsSplitEditor(): boolean {
+		return false;
+	}
+
 	public matches(otherInput: any): boolean {
 		if (super.matches(otherInput) === true) {
 			return true;

src/vs/workbench/parts/files/browser/editors/binaryFileEditor.ts

@@ -27,8 +27,4 @@ export class BinaryFileEditor extends BaseBinaryResourceEditor {
 	public getTitle(): string {
 		return this.getInput() ? this.getInput().getName() : nls.localize('binaryFileEditor', "Binary File Viewer");
 	}
-
-	public supportsSplitEditor(): boolean {
-		return true; // yes, we can!
-	}
 }
\ No newline at end of file

src/vs/workbench/parts/files/browser/editors/textFileEditor.ts

@@ -272,10 +272,6 @@ export class TextFileEditor extends BaseTextEditor {
 		return options;
 	}
 
-	public supportsSplitEditor(): boolean {
-		return true; // yes, we can!
-	}
-
 	/**
 	 * Saves the text editor view state under the given key.
 	 */

src/vs/workbench/parts/html/browser/htmlPreviewPart.ts

@@ -68,10 +68,6 @@ export class HtmlPreviewPart extends BaseEditor {
 		super.dispose();
 	}
 
-	public supportsSplitEditor(): boolean {
-		return true;
-	}
-
 	public createEditor(parent: Builder): void {
 		this._container = document.createElement('div');
 		this._container.style.paddingLeft = '20px';