Remove rescue block and add test for error bubbling in InputSchema validation

Author: tylerrowsell

lib/mcp/tool/input_schema.rb

@@ -38,18 +38,14 @@ def validate_arguments(arguments)
 
       def validate_schema!
         schema = to_h
-        begin
-          schema_reader = JSON::Schema::Reader.new(
-            accept_uri: false,
-            accept_file: ->(path) { path.to_s.start_with?(Gem.loaded_specs["json-schema"].full_gem_path) },
-          )
-          metaschema = JSON::Validator.validator_for_name("draft4").metaschema
-          errors = JSON::Validator.fully_validate(metaschema, schema, schema_reader: schema_reader)
-          if errors.any?
-            raise ArgumentError, "Invalid JSON Schema: #{errors.join(", ")}"
-          end
-        rescue StandardError => e
-          raise ArgumentError, "Invalid JSON Schema: #{e.message}"
+        schema_reader = JSON::Schema::Reader.new(
+          accept_uri: false,
+          accept_file: ->(path) { path.to_s.start_with?(Gem.loaded_specs["json-schema"].full_gem_path) },
+        )
+        metaschema = JSON::Validator.validator_for_name("draft4").metaschema
+        errors = JSON::Validator.fully_validate(metaschema, schema, schema_reader: schema_reader)
+        if errors.any?
+          raise ArgumentError, "Invalid JSON Schema: #{errors.join(", ")}"
         end
       end
     end

test/mcp/tool/input_schema_test.rb

@@ -51,6 +51,16 @@ class InputSchemaTest < ActiveSupport::TestCase
           schema.validate_arguments({ foo: 123 })
         end
       end
+
+      test "unexpected errors bubble up from validate_arguments" do
+        schema = InputSchema.new(properties: { foo: { type: "string" } }, required: [:foo])
+
+        JSON::Validator.stub(:fully_validate, ->(*) { raise "unexpected error" }) do
+          assert_raises(RuntimeError) do
+            schema.validate_arguments({ foo: "bar" })
+          end
+        end
+      end
     end
   end
 end