src/vs/workbench/browser/parts/editor/textDiffEditor.ts/TextDiffEditor/getConfigurationOverrides
class TextDiffEditor:	protected override getConfigurationOverrides(): ICodeEditorOptions {
		const options: IDiffEditorOptions = super.getConfigurationOverrides();

		options.readOnly = this.input instanceof DiffEditorInput && this.input.modifiedInput.hasCapability(EditorInputCapabilities.Readonly);
		options.originalEditable = this.input instanceof DiffEditorInput && !this.input.originalInput.hasCapability(EditorInputCapabilities.Readonly);
		options.lineDecorationsWidth = '2ch';

		return options;
	}