HTML: Partially implement HTMLInputElement's selection{Start,End}

Now that the implementation is in FormAssociatedElement, the
implementation in HTMLInputElement is effectively just a passthrough,
with some minor differences to handle small behavioural quirks between
the two (such as the difference in nullability of types).

Tests/LibWeb/Text/expected/input-selection-start-selection-end.txt

@@ -0,0 +1,7 @@
+Well hello friends    text selectionStart: 0
+text selectionEnd: 0
+date selectionStart: null
+date selectionEnd: null
+text selectionStart: 18
+text selectionEnd: 18
+date input setting selectionStart error: InvalidStateError: setSelectionStart does not apply to this input type

Tests/LibWeb/Text/input/input-selection-start-selection-end.html

@@ -0,0 +1,24 @@
+<input type="text" id="ladybird-text-input"></input>
+<input type="date" id="ladybird-date-input"></input>
+<script src="include.js"></script>
+<script>
+    test(() => {
+        let textInput = document.getElementById("ladybird-text-input");
+        let dateInput = document.getElementById("ladybird-date-input");
+
+        println(`text selectionStart: ${textInput.selectionStart}`);
+        println(`text selectionEnd: ${textInput.selectionEnd}`);
+        println(`date selectionStart: ${dateInput.selectionStart}`);
+        println(`date selectionEnd: ${dateInput.selectionEnd}`);
+
+        textInput.value = "Well hello friends";
+        println(`text selectionStart: ${textInput.selectionStart}`);
+        println(`text selectionEnd: ${textInput.selectionEnd}`);
+
+        try {
+            dateInput.selectionStart = 0;
+        } catch (e) {
+            println(`date input setting selectionStart error: ${e}`);
+        }
+    });
+</script>

Userland/Libraries/LibWeb/HTML/FormAssociatedElement.cpp

@@ -155,7 +155,8 @@ void FormAssociatedElement::reset_form_owner()
 // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#dom-textarea/input-selectionstart
 WebIDL::UnsignedLong FormAssociatedElement::selection_start() const
 {
-    // FIXME: 1. If this element is an input element, and selectionStart does not apply to this element, return null.
+    // 1. If this element is an input element, and selectionStart does not apply to this element, return null.
+    // NOTE: This is done by HTMLInputElement before calling this function
 
     // 2. If there is no selection, return the code unit offset within the relevant value to the character that
     //    immediately follows the text entry cursor.
@@ -170,10 +171,11 @@ WebIDL::UnsignedLong FormAssociatedElement::selection_start() const
 }
 
 // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#textFieldSelection:dom-textarea/input-selectionstart-2
-WebIDL::ExceptionOr<void> FormAssociatedElement::set_selection_start(WebIDL::UnsignedLong)
+WebIDL::ExceptionOr<void> FormAssociatedElement::set_selection_start(Optional<WebIDL::UnsignedLong> const&)
 {
-    // FIXME: 1. If this element is an input element, and selectionStart does not apply to this element, throw an
+    // 1. If this element is an input element, and selectionStart does not apply to this element, throw an
     //    "InvalidStateError" DOMException.
+    // NOTE: This is done by HTMLInputElement before calling this function
 
     // FIXME: 2. Let end be the value of this element's selectionEnd attribute.
     // FIXME: 3. If end is less than the given value, set end to the given value.
@@ -184,7 +186,8 @@ WebIDL::ExceptionOr<void> FormAssociatedElement::set_selection_start(WebIDL::Uns
 // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#dom-textarea/input-selectionend
 WebIDL::UnsignedLong FormAssociatedElement::selection_end() const
 {
-    // FIXME: 1. If this element is an input element, and selectionEnd does not apply to this element, return null.
+    // 1. If this element is an input element, and selectionEnd does not apply to this element, return null.
+    // NOTE: This is done by HTMLInputElement before calling this function
 
     // 2. If there is no selection, return the code unit offset within the relevant value to the character that
     //    immediately follows the text entry cursor.
@@ -199,10 +202,11 @@ WebIDL::UnsignedLong FormAssociatedElement::selection_end() const
 }
 
 // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#textFieldSelection:dom-textarea/input-selectionend-3
-WebIDL::ExceptionOr<void> FormAssociatedElement::set_selection_end(WebIDL::UnsignedLong)
+WebIDL::ExceptionOr<void> FormAssociatedElement::set_selection_end(Optional<WebIDL::UnsignedLong> const&)
 {
-    // FIXME: 1. If this element is an input element, and selectionEnd does not apply to this element, throw an
+    // 1. If this element is an input element, and selectionEnd does not apply to this element, throw an
     //    "InvalidStateError" DOMException.
+    // NOTE: This is done by HTMLInputElement before calling this function
 
     // FIXME: 2. Set the selection range with the value of this element's selectionStart attribute, the given value, and the
     //           value of this element's selectionDirection attribute.

Userland/Libraries/LibWeb/HTML/FormAssociatedElement.h

@@ -90,10 +90,10 @@ public:
     virtual void reset_algorithm() {};
 
     WebIDL::UnsignedLong selection_start() const;
-    WebIDL::ExceptionOr<void> set_selection_start(WebIDL::UnsignedLong);
+    WebIDL::ExceptionOr<void> set_selection_start(Optional<WebIDL::UnsignedLong> const&);
 
     WebIDL::UnsignedLong selection_end() const;
-    WebIDL::ExceptionOr<void> set_selection_end(WebIDL::UnsignedLong);
+    WebIDL::ExceptionOr<void> set_selection_end(Optional<WebIDL::UnsignedLong> const&);
 
 protected:
     FormAssociatedElement() = default;

Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -2,7 +2,7 @@
  * Copyright (c) 2018-2023, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2022, Adam Hodgen <ant1441@gmail.com>
  * Copyright (c) 2022, Andrew Kaster <akaster@serenityos.org>
- * Copyright (c) 2023, Shannon Booth <shannon@serenityos.org>
+ * Copyright (c) 2023-2024, Shannon Booth <shannon@serenityos.org>
  * Copyright (c) 2023, Bastiaan van der Plaat <bastiaan.v.d.plaat@gmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
@@ -2070,6 +2070,52 @@ WebIDL::ExceptionOr<void> HTMLInputElement::set_selection_range(u32 start, u32 e
     return {};
 }
 
+// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#textFieldSelection:dom-textarea/input-selectionstart-2
+WebIDL::ExceptionOr<void> HTMLInputElement::set_selection_start_for_bindings(Optional<WebIDL::UnsignedLong> const& value)
+{
+    // 1. If this element is an input element, and selectionStart does not apply to this element, throw an
+    //    "InvalidStateError" DOMException.
+    if (!selection_or_range_applies())
+        return WebIDL::InvalidStateError::create(realm(), "setSelectionStart does not apply to this input type"_fly_string);
+
+    // NOTE: Steps continued below:
+    return set_selection_start(value);
+}
+
+// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#dom-textarea/input-selectionstart
+Optional<WebIDL::UnsignedLong> HTMLInputElement::selection_start_for_bindings() const
+{
+    // 1. If this element is an input element, and selectionStart does not apply to this element, return null.
+    if (!selection_or_range_applies())
+        return {};
+
+    // NOTE: Steps continued below:
+    return selection_start();
+}
+
+// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#textFieldSelection:dom-textarea/input-selectionend-3
+WebIDL::ExceptionOr<void> HTMLInputElement::set_selection_end_for_bindings(Optional<WebIDL::UnsignedLong> const& value)
+{
+    // 1. If this element is an input element, and selectionEnd does not apply to this element, throw an
+    //    "InvalidStateError" DOMException.
+    if (!selection_or_range_applies())
+        return WebIDL::InvalidStateError::create(realm(), "setSelectionEnd does not apply to this input type"_fly_string);
+
+    // NOTE: Steps continued below:
+    return set_selection_end(value);
+}
+
+// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#dom-textarea/input-selectionend
+Optional<WebIDL::UnsignedLong> HTMLInputElement::selection_end_for_bindings() const
+{
+    // 1. If this element is an input element, and selectionEnd does not apply to this element, return null.
+    if (!selection_or_range_applies())
+        return {};
+
+    // NOTE: Steps continued below:
+    return selection_end();
+}
+
 Optional<ARIA::Role> HTMLInputElement::default_role() const
 {
     // https://www.w3.org/TR/html-aria/#el-input-button
@@ -2198,6 +2244,21 @@ bool HTMLInputElement::has_input_activation_behavior() const
     }
 }
 
+// https://html.spec.whatwg.org/multipage/input.html#do-not-apply
+bool HTMLInputElement::selection_or_range_applies() const
+{
+    switch (type_state()) {
+    case TypeAttributeState::Text:
+    case TypeAttributeState::Search:
+    case TypeAttributeState::Telephone:
+    case TypeAttributeState::URL:
+    case TypeAttributeState::Password:
+        return true;
+    default:
+        return false;
+    }
+}
+
 // https://html.spec.whatwg.org/multipage/input.html#the-input-element:event-change-2
 bool HTMLInputElement::change_event_applies() const
 {

Userland/Libraries/LibWeb/HTML/HTMLInputElement.h

@@ -196,6 +196,13 @@ public:
     bool value_as_number_applies() const;
     bool step_applies() const;
     bool step_up_or_down_applies() const;
+    bool selection_or_range_applies() const;
+
+    WebIDL::ExceptionOr<void> set_selection_start_for_bindings(Optional<WebIDL::UnsignedLong> const&);
+    Optional<WebIDL::UnsignedLong> selection_start_for_bindings() const;
+
+    WebIDL::ExceptionOr<void> set_selection_end_for_bindings(Optional<WebIDL::UnsignedLong> const&);
+    Optional<WebIDL::UnsignedLong> selection_end_for_bindings() const;
 
 private:
     HTMLInputElement(DOM::Document&, DOM::QualifiedName);

Userland/Libraries/LibWeb/HTML/HTMLInputElement.idl

@@ -58,8 +58,8 @@ interface HTMLInputElement : HTMLElement {
     readonly attribute NodeList? labels;
 
     undefined select();
-    [FIXME] attribute unsigned long? selectionStart;
-    [FIXME] attribute unsigned long? selectionEnd;
+    [ImplementedAs=selection_start_for_bindings] attribute unsigned long? selectionStart;
+    [ImplementedAs=selection_end_for_bindings] attribute unsigned long? selectionEnd;
     [FIXME] attribute DOMString? selectionDirection;
     [FIXME] undefined setRangeText(DOMString replacement);
     [FIXME] undefined setRangeText(DOMString replacement, unsigned long start, unsigned long end, optional SelectionMode selectionMode = "preserve");