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.)
The implementation of adjust_horizontal_to_limit() is written with UI in
mind. As such, when there's a selection and we "adjust horizontal", the
selection will be cleared and the cursor will and up at the start/end of
the previous selection. This is what happens when you have a selection
and you press an arrow key on your keyboard, but it isn't the behaviour
we want when programmatically changing the value.
Instead, we need to first clear the selection, and then move the cursor
to the end. (We also need to reset the selection direction when clearing
the selection.)
Per the spec, selectionStart and selectionEnd should return the same
values regardless of the selectionDirection. (That is, selectionStart is
always less than or equal to selectionEnd; the direction then implies
which of selectionStart or selectionEnd is the cursor position.)
There was no explicit WPT test for this, so I added one.
This bug was initially quite hard to wrap my head around, and I think
part of the problem is the code in TextInput. Therefore, in the process
of fixing it I have refactored the implementation of TextInput:
* Rename selection_begin to selection_origin. This value doesn't
necessarily correspond directly to the selectionStart DOM value - in
the case of a backward selection, it corresponds to selectionEnd.
I feel that "origin" doesn't imply a specific ordering as strongly as
"begin" (or "start" for that matter) does.
* In various other cases where "begin" is used as a synonym for "start",
just use "start" for consistency.
* Implement selection_start() and selection_end() methods (and their
_offset() variants) which directly correspond to their DOM
equivalents.
* Rename other related methods to make them less wordy and more
consistent / intention-revealing.
* Add assertions to assert_ok_selection() to ensure that our assumptions
about the ordering of selection_origin and edit_point are met. This
then revealed a bug in adjust_selection_for_horizontal_change() where
the value of selection_direction was not maintained correctly (causing
a unit test failure when the new assertion failed).
The selection API only applies to certain <input> types:
https://html.spec.whatwg.org/multipage/#do-not-apply
This commit ensures that we handle that correctly.
Some notes:
1. TextControl::set_dom_selection_direction now calls
set_selection_range(), which means that setting selectionDirection will
now fire a selection event, as it should per the spec.
2. There is a test for the firing of the select event in
tests/wpt/web-platform-tests/html/semantics/forms/textfieldselection/select-event.html,
however the test did not run due to this syntax error:
(pid:26017) "ERROR:script::dom::bindings::error: Error at http://web-platform.test:8000/html/semantics/forms/textfieldselection/select-event.html:50:11 missing = in const declaration"
This happens due to the us of the "for (const foo of ...)" construct.
Per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of
this should actually work, so it's somewhat unsatisfying to have to
change the test.
4. If an <input>'s type is unset, it defaults to a text, and the
selection API applies. Also, if an <input>'s type is set to an
invalid value, it defaults to a text too. I've expanded the tests
to account for this second case.
The API for text control selection is the same for both <input> and
<textarea>:
https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#textFieldSelection
Before this change, they had similar but not identical implementations
with duplicate code. Now there is a common TextControl trait which
contains the implementation used by both. As a result, some previously
failing tests now pass.
Move assertions about the initial value of selection{Start,End} to their
own tests. This ensures that when one of these assertions fails, it
doesn't prevent other tests from being defined. Thus we have a clearer
view of which tests are passing or failing, since all tests get defined
regardless of which assertions fail.
