RFR: 8155030: The Menu Mnemonics are always displayed for GTK LAF [v17]

[Abhishek Kumar]

On Mon, 8 Jul 2024 09:39:11 GMT, Abhishek Kumar <abhiscxk at openjdk.org> wrote:

>> In GTK LAF, the menu mnemonics are always displayed which is different from the native behavior. In native application **(tested with gedit for normal buttons and tested with libreoffice for menu**), the menu mnemonics toggle on press of `ALT` key. Menu mnemonics are hidden initially and then toggles between show/hide on `ALT` press. 
>> Proposed fix is to handle the `ALT` key press for GTK LAF and mimic the native behavior. Fix is similar to the `ALT` key processing in  Windows LAF. Automated test case is added to verify the fix and tested in Ubuntu and Oracle linux.
>> 
>> CI testing is green and link attached in JBS.
>
> Abhishek Kumar has updated the pull request incrementally with one additional commit since the last revision:
> 
>   wild import expand. SynthGraphicsUtils revert back

Adding a brief details for the changes in PR as it got multiple commits and will be hard to track those changes.

Initial proposed fix was to handle the **mnemonic show/hide on Alt press for GTK in Synth based classes** where

- `SynthLookAndFeel` class installed the AltProcessor handler after the conditional check of current L&F is GTK. public APIs `setMnemonicHidden and isMnemonicHidden` were added as part of fix.
- `SynthRootPaneUI` class is having the AltProcessor class to handle the press and release of ALT key press.
- `SynthGraphicsUtils` class is responsible for rendering the mnemonics based on the `show/hide status of isMnemonicHidden flag` for GTK L&F.

@prrace suggested that checking for GTK L&F is not an ideal way of implementation and we should look for other alternative mentioned [here](https://github.com/openjdk/jdk/pull/18992#discussion_r1595782003).

Based on the suggestion, `AltPressProperty` was added in `GTKLookAndFeel` to ensure the ALT key press event is handled only for GTK and thus moving the installation / uninstallation of ALTProcessor handler code in SynthRootPaneUI class.
**This fix required a CSR because of few public APIs which were added as a part of fix.**

Later on @aivanov-jdk suggested to move the **public APIs in a separate class MnemonicHandler (under sun.swing package) as the code was duplicated among Windows/Mac/Linux OSes** and a separate `AltProcessor class to handle the Alt key press/release for GTK and Aqua L&F` (same logic was implemented for them), Windows is having it's own version of AltProcessor.

Current implementation details are:

- Duplicate code removed, helper methods are moved to one common file (MnemonicHandler.java)
- Common AltProcessor handler class for GTK and Aqua (AltProcessor.java)
- Refactoring code for Windows and Aqua to access the helper methods from MnemonicHandler class and remove unused code.
- Mnemonic hidden condition check moved to `GTKGraphicsUtils` so that only GTK L&F will call `isMnemonicHidden` to avoid the performance issue. 
- No need of CSR as [sun.swing package is not public](https://github.com/openjdk/jdk/pull/18992#discussion_r1654417685)

**The fix is extended for Labels and Buttons as well along with Menus for GTK L&F.**
Further the wild imports were expanded wherever applicable.

Automated test enhanced to test menu mnemonic behavior for Aqua L&F also. Few existing regression tests also modified to access the helper methods from MnemonicHandler class.

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PR Comment: https://git.openjdk.org/jdk/pull/18992#issuecomment-2214042122