Implement setRangeText API

Spec: https://html.spec.whatwg.org/multipage/#dom-textarea/input-setrangetext

In order to do this, we need to define the SelectionMode enum in WebIDL:
https://html.spec.whatwg.org/multipage/#selectionmode

Since the enum is used by HTMLTextAreaElement and HTMLInputElement, it
doesn't seem to make sense to define it in the WebIDL file for one or
other of those.

However, we also can't create a stand-alone SelectionMode.webidl file,
because the current binding-generation code won't generate a "pub mod
SelectionMode;" line in mod.rs unless SelectionMode.webidl contains
either an interface or a namespace. (This logic happens in
components/script/dom/bindings/codegen/Configuration.py:35, in the
Configuration.__init__ method.)

I thought about changing the binding-generation code, but that seems
difficult. So I settled for placing the enum inside
HTMLFormElement.webidl, as that seems like a "neutral" location. We
could equally settle for putting it under HTMLTextAreaElement or
HTMLInputElement, it probably doesn't really matter.

The setRangeText algorithm set the "dirty value flag" on the
input/textarea. I made some clean-ups related to this:

1. HTMLTextAreaElement called its dirty value flag "value_changed"; I
   changed this to "value_dirty" to be consistent with the spec.

2. HTMLInputElement had a "value_changed" field and also a "value_dirty"
   field, which were each used in slightly different places (and
   sometimes in both places). I consolidated these into a single
   "value_dirty" field, which was necessary in order to make some of the
   tests pass.

TextControl::set_dom_range_text replaces part of the existing textinput
content with the replacement string (steps 9-10 of the algorithm). My
implementation changes the textinput's selection and then replaces the
selection. A downside of this approach is that we lose the original
selection state from before the call to setRangeText. Therefore, we have
to save the state into the original_selection_state variable so that we
can later pass it into TextControl::set_selection_range. This allows
TextControl::set_selection_range to correctly decide whether or not to
fire the select event.

An alternative approach would be to implement a method on TextInput
which allows a subtring of the content to be mutated, without touching
the current selection state. However, any such method would potentially
put the TextInput into an inconsistent state where the edit_point and/or
selection_origin is a TextPoint which doesn't exist in the content. It
would be up to the caller to subsequently make sure that the TextInput
gets put back into a valid state (which would actually happen, when
TextControl::set_selection_range is called).

I think TextInput's public API should not make it possible to put it
into an invalid state, as that would be a potential source of bugs.
That's why I didn't take this approach. (TextInput's public API does
currently make it possible to create an invalid state, but I'd like to
submit a follow-up patch to lock this down.)

1 files changed, 14 insertions, 4 deletions

diff --git a/components/script/textinput.rs b/components/script/textinput.rs
index 7883b471117..bf165148f0f 100644
--- a/components/script/textinput.rs
+++ b/components/script/textinput.rs
@@ -56,6 +56,13 @@ pub struct TextPoint {
     pub index: usize,
 }
 
+#[derive(Clone, Copy, PartialEq)]
+pub struct SelectionState {
+    start: TextPoint,
+    end: TextPoint,
+    direction: SelectionDirection,
+}
+
 /// Encapsulated state for handling keyboard input in a single or multiline text input control.
 #[derive(JSTraceable, MallocSizeOf)]
 pub struct TextInput<T: ClipboardProvider> {
@@ -242,10 +249,13 @@ impl<T: ClipboardProvider> TextInput<T> {
         self.selection_start_offset() .. self.selection_end_offset()
     }
 
-    /// A tuple containing the (start, end, direction) of the current selection. Can be used to
-    /// compare whether selection state has changed.
-    pub fn selection_state(&self) -> (TextPoint, TextPoint, SelectionDirection) {
-        (self.selection_start(), self.selection_end(), self.selection_direction)
+    /// The state of the current selection. Can be used to compare whether selection state has changed.
+    pub fn selection_state(&self) -> SelectionState {
+        SelectionState {
+            start: self.selection_start(),
+            end: self.selection_end(),
+            direction: self.selection_direction,
+        }
     }
 
     // Check that the selection is valid.