Mnemonic Parsing doesn't appear to work properly

[John Hendrikx]

The fix is in progress here: https://github.com/openjdk/jfx/pull/647

On 29/10/2021 22:12, John Hendrikx wrote:
> Looking a bit further, and I noticed this code has recently been
> rewritten. The old code used StringBuffer and wasn't that easy to read,
> but the new code although easier to read seems to contain several
> changes in how things used to work.
>
> The most noticable is that it doesn't stop after it finds the first
> mnemonic (probably because it is now building a new string and stopping
> half way would result in an incomplete string -- the old code instead
> would delete parts from a copy so it could stop early, although that has
> some bugs too I noticed).
>
> The new code therefore finds the last mnemonic instead of the first, but
> unfortunately, there is an off by one error that becomes gradually worse
> as more underscores are encountered.
>
> Compare the outputs (Input: How_to_test_mnemonics):
>
> Old version
> (https://github.com/openjdk/jfx/blob/jfx16/modules/javafx.controls/src/main/java/com/sun/javafx/scene/control/behavior/TextBinding.java):
>
> =========================
>
> Resulting Label = Howto_test_mnemonics; mnemonicIndex = 3; mnemonic = t
>
> Current version (master):
> =========================
>
> Resulting Label = Howtotestmnemonics; mnemonicIndex = 11; mnemonic = m
>
> It looks like a significant change in how things used to work which the
> tests didn't catch at all.
>
> --John
>
> On 29/10/2021 21:45, John Hendrikx wrote:
>> Hm, I can confirm it appears under the "e", also under Windows, but I
>> suspect the platform will make no difference.
>>
>> I tested a bit further, and I found the following:
>>
>> 1) The mnemonic key seems to be "m", and it appears under the "e"
>> because it deleted two more underscores (index is off by 2). What makes
>> this hard to discover however is my second finding:
>>
>> 2) Checkbox doesn't toggle at all when you use the correct mnemonic, a
>> Button however works.
>>
>> 3) If you add an "onAction" to the Checkbox that prints something on the
>> console, you can see the mnemonic working, but the Checkbox is still not
>> toggled.
>>
>> I checked the mnemonic parsing code, and if you run it in isolation, it
>> finds the first underscore and has the correct index
>> (TextBinding#parseAndSplit). I stopped there, but perhaps the code
>> actually runs for each underscore found (it updates the text, perhaps
>> this triggers another parsing run).
>>
>> --John
>>
>> On 29/10/2021 19:53, Scott Palmer wrote:
>>> I looked in the bug database and while there are lots of bugs reported
>>> against the mnemonic parsing, they claim to be fixed.
>>>
>>> After noticing something peculiar on a control in my app (it was
>>> showing a
>>> file path and I hadn't disabled the mnemonic parsing) I did some tests.
>>>
>>> The documentation is unclear on what should happen if multiple
>>> underscores
>>> are in the text.  It just says if the mnemonic parsing character '_'
>>> appears that the key combination will be based on the succeeding
>>> character.  I presume that it should pick only ONE of the underscores
>>> and
>>> subsequent character, either the first or the last would make sense.
>>> However, the behavior is that an unrelated character is shown as the
>>> mnemonic and even it doesn't actually do anything.  Tested with JDK
>>> 17.0.1
>>> and JavaFX 17.0.1.
>>>
>>> Does this behave as expected for you?
>>>
>>>
>>> package mnemonic_parsing_bug;
>>>
>>> import javafx.application.Application;
>>> import javafx.geometry.Insets;
>>> import javafx.scene.Scene;
>>> import javafx.scene.control.CheckBox;
>>> import javafx.scene.control.Label;
>>> import javafx.scene.layout.VBox;
>>> import javafx.stage.Stage;
>>>
>>> public class Main extends Application {
>>>
>>>     public static void main(String[] args) {
>>>         launch(args);
>>>     }
>>>
>>>     @Override
>>>     public void start(Stage primaryStage) throws Exception {
>>>         Label titleLabel = new Label("""
>>>             The CheckBox below has text set to 'How_to_Test_Mnemonics'.
>>>             On Windows press the Alt key to see where the underlined
>>> character appears.
>>>             It shows under the 'e' in Mnemonics for me, and I can't
>>> figure
>>> out
>>>             what key combination (if any) actually does something.
>>>             [JavaFX Version %s]""".formatted(System.getProperty(
>>> "javafx.version")) );
>>>         titleLabel.setMnemonicParsing(false);
>>>         CheckBox mnemonicCB = new CheckBox("How_to_Test_Mnemonics");
>>>         mnemonicCB.setMnemonicParsing(true);
>>>         VBox box = new VBox(8,titleLabel, mnemonicCB);
>>>         box.setPadding(new Insets(16));
>>>         Scene scene = new Scene(box);
>>>         primaryStage.setTitle("Mnemonic Parsing Bug");
>>>         primaryStage.setScene(scene);
>>>         primaryStage.show();
>>>     }
>>>
>>> }
>>>
>>
>