Revert "Merge pull request #1810 from meanphil/mappings-slow-exception"

This reverts commit b6ae67d, reversing
changes made to 0ef4a58.

This caused custom inputs to not load properly on non-eager load
environments like dev/test, because those constants may not have been
defined yet.

The previous code would try to constantize them and force-load the
lazily-loaded files/constants, the new code breaks that behavior, so
we're reverting.

Closes #1824, see for more info.

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## Unreleased
 
+* Revert "Speed up input mapping lookup by avoiding rescuing exceptions" from v5.3.0, it caused a regression on dev/test environments with custom inputs.
 * Add support to Ruby 3.3. (no changes required.)
 
 ## 5.3.0

lib/simple_form/form_builder.rb

@@ -673,7 +673,11 @@ def mapping_override(klass)
     def attempt_mapping(mapping, at)
       return if SimpleForm.inputs_discovery == false && at == Object
 
-      at.const_get(mapping) if at.const_defined?(mapping)
+      begin
+        at.const_get(mapping)
+      rescue NameError => e
+        raise if e.message !~ /#{mapping}$/
+      end
     end
 
     def attempt_mapping_with_custom_namespace(input_name)