Updating defaultValue in a non-dirty TEXTAREA should not move the caret to the end

According to the HTML standard, updating defaultValue should keep
selectionStart/End, and clamp them if the new value is shorter than them.
defaultValue setter doesn't have any explicit selection behavior [1], and
we should apply default selection adjustment algorithm in such case [2].

The new behavior matches to Edge, Firefox, and Safari.

Some test cases in selection-start-end-extra.html were not correct. This CL
fixes them.  Remove some test cases in textarea-selection-preservation.html
because they are covered by WPT.

[1] https://html.spec.whatwg.org/multipage/form-elements.html#the-textarea-element:dom-textarea-defaultvalue-2
[2] https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#textFieldSelection:concept-textarea/input-relevant-value

Bug: 822639
Change-Id: I77db0934bb10774561e947f64b4cb3f88c293679
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1575317
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653487}

third_party/blink/renderer/core/html/forms/html_text_area_element.cc

@@ -108,7 +108,7 @@ void HTMLTextAreaElement::ChildrenChanged(const ChildrenChange& change) {
   if (is_dirty_)
     SetInnerEditorValue(value());
   else
-    SetNonDirtyValue(defaultValue());
+    SetNonDirtyValue(defaultValue(), TextControlSetValueSelection::kClamp);
 }
 
 bool HTMLTextAreaElement::IsPresentationAttribute(
@@ -231,7 +231,8 @@ void HTMLTextAreaElement::AppendToFormData(FormData& form_data) {
 }
 
 void HTMLTextAreaElement::ResetImpl() {
-  SetNonDirtyValue(defaultValue());
+  SetNonDirtyValue(defaultValue(),
+                   TextControlSetValueSelection::kSetSelectionToEnd);
 }
 
 bool HTMLTextAreaElement::HasCustomFocusLogic() const {
@@ -386,9 +387,10 @@ void HTMLTextAreaElement::setValue(const String& value,
   is_dirty_ = true;
 }
 
-void HTMLTextAreaElement::SetNonDirtyValue(const String& value) {
-  SetValueCommon(value, TextFieldEventBehavior::kDispatchNoEvent,
-                 TextControlSetValueSelection::kSetSelectionToEnd);
+void HTMLTextAreaElement::SetNonDirtyValue(
+    const String& value,
+    TextControlSetValueSelection selection) {
+  SetValueCommon(value, TextFieldEventBehavior::kDispatchNoEvent, selection);
   is_dirty_ = false;
 }
 
@@ -411,6 +413,13 @@ void HTMLTextAreaElement::SetValueCommon(
   if (normalized_value == value())
     return;
 
+  // selectionStart and selectionEnd values can be changed by
+  // SetInnerEditorValue(). We need to get them before SetInnerEditorValue() to
+  // clamp them later in a case of kClamp.
+  const bool is_clamp = selection == TextControlSetValueSelection::kClamp;
+  const unsigned selection_start = is_clamp ? selectionStart() : 0;
+  const unsigned selection_end = is_clamp ? selectionEnd() : 0;
+
   if (event_behavior != TextFieldEventBehavior::kDispatchNoEvent)
     SetValueBeforeFirstUserEditIfNotSet();
   value_ = normalized_value;
@@ -429,6 +438,10 @@ void HTMLTextAreaElement::SetValueCommon(
     // Set the caret to the end of the text value except for initialize.
     unsigned end_of_string = value_.length();
     SetSelectionRange(end_of_string, end_of_string);
+  } else if (is_clamp) {
+    const unsigned end_of_string = value_.length();
+    SetSelectionRange(std::min(end_of_string, selection_start),
+                      std::min(end_of_string, selection_end));
   }
 
   NotifyFormStateChanged();

third_party/blink/renderer/core/html/forms/html_text_area_element.h

@@ -80,7 +80,7 @@ class CORE_EXPORT HTMLTextAreaElement final : public TextControlElement {
   void HandleBeforeTextInsertedEvent(BeforeTextInsertedEvent*) const;
   static String SanitizeUserInputValue(const String&, unsigned max_length);
   void UpdateValue();
-  void SetNonDirtyValue(const String&);
+  void SetNonDirtyValue(const String&, TextControlSetValueSelection);
   void SetValueCommon(const String&,
                       TextFieldEventBehavior,
                       TextControlSetValueSelection);

third_party/blink/renderer/core/html/forms/text_control_element.h

@@ -50,6 +50,7 @@ enum class TextFieldEventBehavior {
 
 enum class TextControlSetValueSelection {
   kSetSelectionToEnd,
+  kClamp,
   kDoNotSet,
 };
 

third_party/blink/web_tests/external/wpt/html/semantics/forms/textfieldselection/selection-start-end-extra-expected.txt

-This is a testharness.js-based test.
-PASS Setting defaultValue in a textarea should move the cursor to the end
-PASS Setting defaultValue in a textarea with a value should NOT make any difference
-PASS Setting textContent in a textarea should move selection{Start,End} to the end
-PASS Adding children to a textarea should move selection{Start,End} to the end
-PASS Removing children from a textarea should update selection{Start,End}
-PASS Setting the same value (with different newlines) in a textarea should NOT update selection{Start,End}
-FAIL Removing child nodes in non-dirty textarea should make selection{Start,End} 0 assert_equals: selectionStart after appendChild expected 0 but got 6
-PASS Setting value to a shorter string than defaultValue should correct the cursor position
-PASS Shortening value by turning the input type into 'url' should correct selection{Start,End}
-PASS Shortening value by turning the input type into 'color' and back to 'text' should correct selection{Start,End}
-PASS Resetting a value to a shorter string than defaultValue should correct the cursor position
-Harness: the test ran to completion.
-

third_party/blink/web_tests/external/wpt/html/semantics/forms/textfieldselection/selection-start-end-extra.html

@@ -16,9 +16,9 @@
     assert_equals(el.selectionEnd, 0);
     el.defaultValue = "123";
     assert_equals(el.value.length, 3);
-    assert_equals(el.selectionStart, 3);
-    assert_equals(el.selectionEnd, 3);
-  }, "Setting defaultValue in a textarea should move the cursor to the end");
+    assert_equals(el.selectionStart, 0);
+    assert_equals(el.selectionEnd, 0);
+  }, "Setting defaultValue in a textarea should NOT move the cursor to the end");
 
   test(function() {
     var el = document.createElement("textarea");
@@ -34,34 +34,34 @@
   test(function() {
     var el = document.createElement("textarea");
     el.appendChild(document.createTextNode("abcdef"));
-    assert_equals(el.selectionStart, 6);
-    assert_equals(el.selectionEnd, 6);
+    assert_equals(el.selectionStart, 0);
+    assert_equals(el.selectionEnd, 0);
     el.textContent = "abcdef123456";
-    assert_equals(el.selectionStart, 12);
-    assert_equals(el.selectionEnd, 12);
-  }, "Setting textContent in a textarea should move selection{Start,End} to the end");
+    assert_equals(el.selectionStart, 0);
+    assert_equals(el.selectionEnd, 0);
+  }, "Setting textContent in a textarea should NOT move selection{Start,End} to the end");
 
   test(function() {
     var el = document.createElement("textarea");
     el.appendChild(document.createTextNode("abcdef"));
-    assert_equals(el.selectionStart, 6);
-    assert_equals(el.selectionEnd, 6);
+    assert_equals(el.selectionStart, 0);
+    assert_equals(el.selectionEnd, 0);
     el.appendChild(document.createTextNode("123456"));
-    assert_equals(el.selectionStart, 12);
-    assert_equals(el.selectionEnd, 12);
-  }, "Adding children to a textarea should move selection{Start,End} to the end");
+    assert_equals(el.selectionStart, 0);
+    assert_equals(el.selectionEnd, 0);
+  }, "Adding children to a textarea should NOT move selection{Start,End} to the end");
 
   test(function() {
     var el = document.createElement("textarea");
     el.appendChild(document.createTextNode("abcdef"));
     el.appendChild(document.createTextNode("123"));
-    assert_equals(el.selectionStart, 9);
-    assert_equals(el.selectionEnd, 9);
+    assert_equals(el.selectionStart, 0);
+    assert_equals(el.selectionEnd, 0);
 
     el.removeChild(el.firstChild);
-    assert_equals(el.selectionStart, 3);
-    assert_equals(el.selectionEnd, 3);
-  }, "Removing children from a textarea should update selection{Start,End}");
+    assert_equals(el.selectionStart, 0);
+    assert_equals(el.selectionEnd, 0);
+  }, "Removing children from a textarea should NOT update selection{Start,End}");
 
   test(function() {
     var el = document.createElement("textarea");
@@ -104,8 +104,8 @@
     var el = document.createElement("textarea");
     el.defaultValue = "123";
     assert_equals(el.value.length, 3);
-    assert_equals(el.selectionStart, 3);
-    assert_equals(el.selectionEnd, 3);
+    el.selectionStart = 3;
+    el.selectionEnd = 3;
     el.value = "12";
     assert_equals(el.value.length, 2);
     assert_equals(el.selectionStart, 2);

third_party/blink/web_tests/fast/forms/textarea/textarea-selection-preservation-expected.txt

@@ -27,15 +27,6 @@ PASS ta.selectionEnd is 4
 - reset form
 PASS ta.selectionStart is 7
 PASS ta.selectionEnd is 7
-- set new defaultValue
-PASS ta.selectionStart is 9
-PASS ta.selectionEnd is 9
-- set same defaultValue
-PASS ta.selectionStart is 2
-PASS ta.selectionEnd is 3
-- append a text node
-PASS ta.selectionStart is 12
-PASS ta.selectionEnd is 12
 - append a empty text node
 PASS ta.selectionStart is 2
 PASS ta.selectionEnd is 3

third_party/blink/web_tests/fast/forms/textarea/textarea-selection-preservation.html

@@ -49,22 +49,6 @@
     shouldBe('ta.selectionStart', '7');
     shouldBe('ta.selectionEnd', '7');
 
-    debug("- set new defaultValue");
-    ta.defaultValue = 'abc123456';
-    shouldBe('ta.selectionStart', '9');
-    shouldBe('ta.selectionEnd', '9');
-
-    debug("- set same defaultValue");
-    ta.setSelectionRange(2, 3);
-    ta.defaultValue = 'abc123456';
-    shouldBe('ta.selectionStart', '2');
-    shouldBe('ta.selectionEnd', '3');
-
-    debug("- append a text node");
-    ta.appendChild(document.createTextNode('foo'));
-    shouldBe('ta.selectionStart', '12');
-    shouldBe('ta.selectionEnd', '12');
-
     debug("- append a empty text node");
     ta.setSelectionRange(2, 3);
     ta.appendChild(document.createTextNode(''));