fix(conditionalPanel): Coerce condition result to boolean

NEWS.md

@@ -10,6 +10,8 @@
 
 * Fixed a bug introduced in v1.9.0 where the boundaries of hover/click/brush regions on plots were being incorrectly scaled when browser zoom was used. (#4111)
 
+* Fixed a bug in `conditionalPanel()` that would cause the panel to repeatedly show/hide itself when the provided condition was not boolean. (@kamilzyla, #4127)
+
 # shiny 1.9.0
 
 ## New busy indication feature

inst/www/shared/shiny.js

@@ -23917,7 +23917,7 @@
           }
           var nsPrefix = el.attr("data-ns-prefix");
           var nsScope = this._narrowScope(scope, nsPrefix);
-          var show3 = condFunc(nsScope);
+          var show3 = Boolean(condFunc(nsScope));
           var showing = el.css("display") !== "none";
           if (show3 !== showing) {
             if (show3) {

srcts/src/shiny/shinyapp.ts

@@ -614,7 +614,7 @@ class ShinyApp {
 
       const nsPrefix = el.attr("data-ns-prefix") as string;
       const nsScope = this._narrowScope(scope, nsPrefix);
-      const show = condFunc(nsScope);
+      const show = Boolean(condFunc(nsScope));
       const showing = el.css("display") !== "none";
 
       if (show !== showing) {

srcts/src/utils/index.ts

@@ -148,7 +148,7 @@ function pixelRatio(): number {
 //
 // When the function is executed, it will evaluate that expression using
 // "with" on the argument value, and return the result.
-function scopeExprToFunc(expr: string): (scope: unknown) => boolean {
+function scopeExprToFunc(expr: string): (scope: unknown) => unknown {
   /*jshint evil: true */
   const exprEscaped = expr
     .replace(/[\\"']/g, "\\$&")
@@ -159,7 +159,7 @@ function scopeExprToFunc(expr: string): (scope: unknown) => boolean {
     // \b has a special meaning; need [\b] to match backspace char.
     .replace(/[\b]/g, "\\b");
 
-  let func: () => boolean;
+  let func: () => unknown;
 
   try {
     // @ts-expect-error; Do not know how to type this _dangerous_ situation
@@ -178,7 +178,7 @@ function scopeExprToFunc(expr: string): (scope: unknown) => boolean {
     throw e;
   }
 
-  return function (scope: unknown): boolean {
+  return function (scope: unknown): unknown {
     return func.call(scope);
   };
 }

srcts/types/src/utils/index.d.ts

@@ -10,7 +10,7 @@ declare function parseDate(dateString: string): Date;
 declare function formatDateUTC(x: Date): string;
 declare function makeResizeFilter(el: HTMLElement, func: (width: HTMLElement["offsetWidth"], height: HTMLElement["offsetHeight"]) => void): () => void;
 declare function pixelRatio(): number;
-declare function scopeExprToFunc(expr: string): (scope: unknown) => boolean;
+declare function scopeExprToFunc(expr: string): (scope: unknown) => unknown;
 declare function asArray<T>(value: T | T[] | null | undefined): T[];
 declare function mergeSort<Item>(list: Item[], sortfunc: (a: Item, b: Item) => boolean | number): Item[];
 declare function $escape(val: undefined): undefined;