bug #19127 [Form] Add exception to FormRenderer about non-unique bloc…

…k names (enumag)

This PR was merged into the 2.7 branch.

Discussion
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[Form] Add exception to FormRenderer about non-unique block names

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #17874
| License       | MIT
| Doc PR        |

Commits
-------

c6db6f3 [Form] Add exception to FormRenderer about non-unique block names

src/Symfony/Component/Form/FormRenderer.php

@@ -253,10 +253,11 @@ public function searchAndRenderBlock(FormView $view, $blockNameSuffix, array $va
 
         // Escape if no resource exists for this block
         if (!$resource) {
-            throw new LogicException(sprintf(
-                'Unable to render the form as none of the following blocks exist: "%s".',
-                implode('", "', array_reverse($blockNameHierarchy))
-            ));
+            if (count($blockNameHierarchy) !== count(array_unique($blockNameHierarchy))) {
+                throw new LogicException(sprintf('Unable to render the form because the block names array contains duplicates: "%s".', implode('", "', array_reverse($blockNameHierarchy))));
+            }
+
+            throw new LogicException(sprintf('Unable to render the form as none of the following blocks exist: "%s".', implode('", "', array_reverse($blockNameHierarchy))));
         }
 
         // Merge the passed with the existing attributes