Hide textarea and show error for old version.

src/app/formalVerification.js

@@ -6,17 +6,26 @@ function FormalVerification (outputElement, renderer) {
 }
 
 FormalVerification.prototype.compiling = function () {
-  $('#formalVerificationInput', this.outputElement).val('');
+  $('#formalVerificationInput', this.outputElement)
+    .val('')
+    .hide();
   $('#formalVerificationErrors').empty();
 };
 
 FormalVerification.prototype.compilationFinished = function (compilationResult) {
-  if (compilationResult.formal !== undefined) {
+  if (compilationResult.formal === undefined) {
+    this.renderer.error(
+      'Formal verification not supported by this compiler version.',
+      $('#formalVerificationErrors'),
+      true
+    );
+  } else {
     if (compilationResult.formal['why3'] !== undefined) {
       $('#formalVerificationInput', this.outputElement).val(
         '(* copy this to http://why3.lri.fr/try/ *)' +
         compilationResult.formal['why3']
-      );
+      )
+      .show();
     }
     if (compilationResult.formal.errors !== undefined) {
       var errors = compilationResult.formal.errors;