src/vs/workbench/browser/parts/editor/textDiffEditor.ts/TextDiffEditor/getConfigurationOverrides
class TextDiffEditor:	protected override getConfigurationOverrides(): IDiffEditorOptions {
		const readOnly = this.input instanceof DiffEditorInput && this.input.modified.hasCapability(EditorInputCapabilities.Readonly);

		return {
			...super.getConfigurationOverrides(),
			readOnly,
			originalEditable: this.input instanceof DiffEditorInput && !this.input.original.hasCapability(EditorInputCapabilities.Readonly),
			lineDecorationsWidth: '2ch'
		};
	}