feat!: Use Into<FormBuilder> as return type in the form closure

src/builder.rs

@@ -1483,15 +1483,14 @@ where
     ///     }
     /// );
     /// ```
-    pub fn form<F>(mut self, f: F) -> Self
+    pub fn form<F, R>(mut self, f: F) -> Self
     where
-        F: FnOnce(
-            FormBuilder<Other, (), <Other::Form as Extendable>::Empty>,
-        ) -> FormBuilder<Other, String, Other::Form>,
+        F: FnOnce(FormBuilder<Other, (), <Other::Form as Extendable>::Empty>) -> R,
+        R: Into<FormBuilder<Other, String, Other::Form>>,
     {
         self.forms
             .get_or_insert_with(Default::default)
-            .push(f(FormBuilder::new()));
+            .push(f(FormBuilder::new()).into());
         self
     }
 }
@@ -3977,6 +3976,40 @@ mod tests {
         );
     }
 
+    #[test]
+    fn simple_into_form() {
+        struct FormBuilderEx<Other: ExtendableThing, Href, OtherForm>(
+            FormBuilder<Other, Href, OtherForm>,
+        );
+        impl<Other: ExtendableThing, Href, OtherForm> From<FormBuilderEx<Other, Href, OtherForm>>
+            for FormBuilder<Other, Href, OtherForm>
+        {
+            fn from(value: FormBuilderEx<Other, Href, OtherForm>) -> Self {
+                value.0
+            }
+        }
+
+        let thing = ThingBuilder::<Nil, _>::new("MyLampThing")
+            .finish_extend()
+            .form(|form| FormBuilderEx(form.href("href").op(FormOperation::ReadAllProperties)))
+            .build()
+            .unwrap();
+
+        assert_eq!(
+            thing,
+            Thing {
+                context: TD_CONTEXT_11.into(),
+                title: "MyLampThing".to_string(),
+                forms: Some(vec![Form {
+                    op: DefaultedFormOperations::Custom(vec![FormOperation::ReadAllProperties]),
+                    href: "href".to_string(),
+                    ..Default::default()
+                }]),
+                ..Default::default()
+            }
+        );
+    }
+
     #[test]
     fn simple_form_with_uri_variables() {
         let thing = ThingBuilder::<Nil, _>::new("MyLampThing")

src/builder/affordance.rs

@@ -94,11 +94,10 @@ pub trait BuildableInteractionAffordance<Other: ExtendableThing> {
     ///     })
     /// );
     /// ```
-    fn form<F>(self, f: F) -> Self
+    fn form<F, R>(self, f: F) -> Self
     where
-        F: FnOnce(
-            FormBuilder<Other, (), <Other::Form as Extendable>::Empty>,
-        ) -> FormBuilder<Other, String, Other::Form>,
+        F: FnOnce(FormBuilder<Other, (), <Other::Form as Extendable>::Empty>) -> R,
+        R: Into<FormBuilder<Other, String, Other::Form>>,
         Other::Form: Extendable;
 
     /// Adds a new _URI variable_.
@@ -311,13 +310,12 @@ where
     Other: ExtendableThing,
     Other::Form: Extendable,
 {
-    fn form<F>(mut self, f: F) -> Self
+    fn form<F, R>(mut self, f: F) -> Self
     where
-        F: FnOnce(
-            FormBuilder<Other, (), <Other::Form as Extendable>::Empty>,
-        ) -> FormBuilder<Other, String, Other::Form>,
+        F: FnOnce(FormBuilder<Other, (), <Other::Form as Extendable>::Empty>) -> R,
+        R: Into<FormBuilder<Other, String, Other::Form>>,
     {
-        self.forms.push(f(FormBuilder::new()));
+        self.forms.push(f(FormBuilder::new()).into());
         self
     }
 
@@ -349,9 +347,10 @@ macro_rules! impl_buildable_interaction_affordance {
             where
                 Other::Form: Extendable
             {
-                fn form<F>(mut self, f: F) -> Self
+                fn form<F, R>(mut self, f: F) -> Self
                 where
-                    F: FnOnce(FormBuilder<Other, (), <Other::Form as Extendable>::Empty>) -> FormBuilder<Other, String, Other::Form>,
+                    F: FnOnce(FormBuilder<Other, (), <Other::Form as Extendable>::Empty>) -> R,
+                    R: Into<FormBuilder<Other, String, Other::Form>>,
                     Other::Form: Extendable,
                 {
                     self.$($interaction_path).* = self.$($interaction_path).*.form(f);