Auto merge of #25217 - pshaughn:fix25150, r=jdm

hidden field named _charset_ now appears in FormData as UTF-8

<!-- Please describe your changes on the following line: -->
HTMLInputElement now has special case logic for putting a hidden field named `_charset_` in an entry set. To support this, the encoding used when constructing a form dataset is now being passed further down the callchain than it was before.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #25150

<!-- Either: -->
- [X] There are tests for these changes

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

1 files changed, 15 insertions, 5 deletions

diff --git a/components/script/dom/htmlformelement.rs b/components/script/dom/htmlformelement.rs
index 913f5f8530a..f4135ac3e0a 100755
--- a/components/script/dom/htmlformelement.rs
+++ b/components/script/dom/htmlformelement.rs
@@ -357,7 +357,7 @@ impl HTMLFormElement {
         let encoding = self.pick_encoding();
 
         // Step 9
-        let mut form_data = match self.get_form_dataset(Some(submitter)) {
+        let mut form_data = match self.get_form_dataset(Some(submitter), Some(encoding)) {
             Some(form_data) => form_data,
             None => return,
         };
@@ -645,8 +645,14 @@ impl HTMLFormElement {
     }
 
     /// <https://html.spec.whatwg.org/multipage/#constructing-the-form-data-set>
+    /// terminology note:  "form data set" = "entry list"
     /// Steps range from 3 to 5
-    fn get_unclean_dataset(&self, submitter: Option<FormSubmitter>) -> Vec<FormDatum> {
+    /// 5.x substeps are mostly handled inside element-specific methods
+    fn get_unclean_dataset(
+        &self,
+        submitter: Option<FormSubmitter>,
+        encoding: Option<&'static Encoding>,
+    ) -> Vec<FormDatum> {
         let controls = self.controls.borrow();
         let mut data_set = Vec::new();
         for child in controls.iter() {
@@ -668,7 +674,7 @@ impl HTMLFormElement {
                     HTMLElementTypeId::HTMLInputElement => {
                         let input = child.downcast::<HTMLInputElement>().unwrap();
 
-                        data_set.append(&mut input.form_datums(submitter));
+                        data_set.append(&mut input.form_datums(submitter, encoding));
                     },
                     HTMLElementTypeId::HTMLButtonElement => {
                         let button = child.downcast::<HTMLButtonElement>().unwrap();
@@ -705,7 +711,11 @@ impl HTMLFormElement {
     }
 
     /// <https://html.spec.whatwg.org/multipage/#constructing-the-form-data-set>
-    pub fn get_form_dataset(&self, submitter: Option<FormSubmitter>) -> Option<Vec<FormDatum>> {
+    pub fn get_form_dataset(
+        &self,
+        submitter: Option<FormSubmitter>,
+        encoding: Option<&'static Encoding>,
+    ) -> Option<Vec<FormDatum>> {
         fn clean_crlf(s: &str) -> DOMString {
             // Step 4
             let mut buf = "".to_owned();
@@ -746,7 +756,7 @@ impl HTMLFormElement {
         self.constructing_entry_list.set(true);
 
         // Step 3-6
-        let mut ret = self.get_unclean_dataset(submitter);
+        let mut ret = self.get_unclean_dataset(submitter, encoding);
         for datum in &mut ret {
             match &*datum.ty {
                 "file" | "textarea" => (), // TODO