doc: update CHANGELOG.md

setting default values for optional keys in malli coercion

CHANGELOG.md

@@ -17,6 +17,7 @@ We use [Break Versioning][breakver]. The version numbers follow a `<major>.<mino
 * Allow multimethods as handlers when validating [#755](https://github.com/metosin/reitit/pull/755)
 * Improve error reporting when generating OpenAPI fails [#754](https://github.com/metosin/reitit/pull/754)
 * Allow middleware registry to be used when defining middleware in `ring-handler`. See [docs](./doc/ring/middleware_registry.md). [#739](https://github.com/metosin/reitit/pull/739)
+* Allow passing options (eg. `:malli.transform/add-optional-keys`) to malli's `default-value-transformer`. See [docs](./doc/coercion/malli_coercion.md). [#756](https://github.com/metosin/reitit/pull/756)
 
 ## 0.9.1 (2025-05-27)
 

doc/coercion/malli_coercion.md

@@ -73,9 +73,10 @@ Using `create` with options to create the coercion instead of `coercion`:
   {:transformers {:body {:default reitit.coercion.malli/default-transformer-provider
                          :formats {"application/json" reitit.coercion.malli/json-transformer-provider}}
                   :string {:default reitit.coercion.malli/string-transformer-provider}
-                  :response {:default reitit.coercion.malli/default-transformer-provider}}
+                  :response {:default reitit.coercion.malli/default-transformer-provider
+                             :formats {"application/json" reitit.coercion.malli/json-transformer-provider}}}
    ;; set of keys to include in error messages
-   :error-keys #{:type :coercion :in :schema :value :errors :humanized #_:transformed}
+   :error-keys #{:type :coercion :in #_:schema :value #_:errors :humanized #_:transformed}
    ;; support lite syntax?
    :lite true
    ;; schema identity function (default: close all map schemas)
@@ -87,7 +88,11 @@ Using `create` with options to create the coercion instead of `coercion`:
    ;; strip-extra-keys (affects only predefined transformers)
    :strip-extra-keys true
    ;; add/set default values
+   ;; Can be false, true or a map of options to pass to malli.transform/default-value-transformer,
+   ;; for example {:malli.transform/add-optional-keys true}
    :default-values true
+   ;; encode-error
+   :encode-error nil
    ;; malli options
    :options nil})
 ```

modules/reitit-malli/src/reitit/coercion/malli.cljc

@@ -9,8 +9,7 @@
             [malli.swagger :as swagger]
             [malli.transform :as mt]
             [malli.util :as mu]
-            [reitit.coercion :as coercion]
+            [reitit.coercion :as coercion]))
-            [clojure.string :as string]))
 
 ;;
 ;; coercion
@@ -31,7 +30,7 @@
       (mt/transformer
        (if strip-extra-keys (mt/strip-extra-keys-transformer))
        transformer
-       (if default-values (mt/default-value-transformer))))))
+       (if default-values (mt/default-value-transformer (if (map? default-values) default-values {})))))))
 
 (def string-transformer-provider (-provider (mt/string-transformer)))
 (def json-transformer-provider (-provider (mt/json-transformer)))
@@ -116,7 +115,9 @@
    :enabled true
    ;; strip-extra-keys (affects only predefined transformers)
    :strip-extra-keys true
-   ;; add/set default values
+   ;; add/set default values.
+   ;; Can be false, true or a map of options to pass to malli.transform/default-value-transformer,
+   ;; for example {:malli.transform/add-optional-keys true}
    :default-values true
    ;; encode-error
    :encode-error nil

test/cljc/reitit/coercion_test.cljc

@@ -140,6 +140,36 @@
         (let [m (r/match-by-path r "/none/kikka/abba")]
           (is (= nil (coercion/coerce! m))))))))
 
+(deftest malli-query-parameter-coercion-test
+  (let [router (fn [coercion]
+                 (r/router ["/test"
+                            {:coercion coercion
+                             :parameters {:query [:map
+                                                  [:a [:string {:default "a"}]]
+                                                  [:x {:optional true} [:keyword {:default :a}]]]}}]
+                           {:compile coercion/compile-request-coercers}))]
+    (testing "default values for :optional query keys do not get added"
+      (is (= {:query {:a "a"}}
+             (-> (r/match-by-path (router reitit.coercion.malli/coercion) "/test")
+                 (assoc :query-params {})
+                 (coercion/coerce!)))))
+    (testing "default values for :optional query keys get added when :malli.transform/add-optional-keys is set"
+      (is (= {:query {:a "a" :x :a}}
+             (-> (r/match-by-path (router (reitit.coercion.malli/create
+                                           (assoc reitit.coercion.malli/default-options
+                                                  :default-values {:malli.transform/add-optional-keys true}))) "/test")
+                 (assoc :query-params {})
+                 (coercion/coerce!)))))
+    (testing "default values can be disabled"
+      (is (thrown-with-msg?
+           ExceptionInfo
+           #"Request coercion failed"
+           (-> (r/match-by-path (router (reitit.coercion.malli/create
+                                         (assoc reitit.coercion.malli/default-options
+                                                :default-values false))) "/test")
+               (assoc :query-params {})
+               (coercion/coerce!)))))))
+
 (defn match-by-path-and-coerce! [router path]
   (if-let [match (r/match-by-path router path)]
     (assoc match :parameters (coercion/coerce! match))))