[v2 - Linux] Fix backend drag and drop on Linux

[makew0rld]

Description

This PR fixes #3686 by copying a dead PR, #3704.

Type of change

Please select the option that is relevant.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration using wails doctor.

• [x] Windows: works
• [x] macOS: works
• [x] Linux: works

If you checked Linux, please specify the distro and version: Arch Linux latest

Test Configuration

# Wails
Version         | v2.9.2
Package Manager | pacman

# System
┌───────────────────────────────────────────────────────────────────────────────────────┐
| OS           | Arch Linux                                                             |
| Version      | Unknown                                                                |
| ID           | arch                                                                   |
| Go Version   | go1.23.3                                                               |
| Platform     | linux                                                                  |
| Architecture | amd64                                                                  |
| CPU          | 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz                         |
| GPU          | TigerLake-LP GT2 [Iris Xe Graphics] (Intel Corporation) - Driver: i915 |
| Memory       | 15GB                                                                   |
└───────────────────────────────────────────────────────────────────────────────────────┘

# Dependencies
┌─────────────────────────────────────────────────────────────────────┐
| Dependency | Package Name | Status    | Version                     |
| *docker    | docker       | Installed | 1:27.3.1-1                  |
| gcc        | gcc          | Installed | 14.2.1+r134+gab884fffe3fc-1 |
| libgtk-3   | gtk3         | Installed | 1:3.24.43-4                 |
| libwebkit  | webkit2gtk   | Installed | 2.46.4-1                    |
| npm        | npm          | Installed | 10.9.0-1                    |
| pkg-config | pkgconf      | Installed | 2.1.1-1                     |
└────────────────────── * - Optional Dependency ──────────────────────┘

# Diagnosis
 SUCCESS  Your system is ready for Wails development!

Checklist:

• [ ] I have updated website/src/pages/changelog.mdx with details of this PR
• [ ] My code follows the general coding style of this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes

---

I don't fully understand this PR (hopefully you do instead) but the basic reason why it works is because it registers event listeners that call e.PreventDefault() so the default file drop behaviour is stopped.

This requires doc updates because callers need to know that backend file drop handlers should be registered in OnDomReady, not OnStartup.

Summary by CodeRabbit

• New Features

  • Enhanced drag-and-drop functionality with improved event listener management.
  • Added support for file drop events, ensuring listeners are registered only once during initialization.

• Bug Fixes

  • Improved handling of drag-and-drop operations to ensure callbacks are invoked only on valid drop targets.

[coderabbitai[bot]]

Walkthrough

The changes in this pull request focus on enhancing the drag-and-drop functionality within the application. Key modifications include the introduction of an EventsOnce listener that initializes drag-and-drop event handlers when the "wails:init-file-drop" event is triggered. This ensures that event listeners are registered only once, improving efficiency. Additionally, the OnFileDrop function has been updated to emit an event at the start of the file drop process while maintaining its original logic.

Changes

File Path	Change Summary
v2/internal/frontend/runtime/desktop/draganddrop.js	Added EventsOnce import and listener for "wails:init-file-drop" to manage drag-and-drop events.
v2/internal/frontend/runtime/runtime_debug_desktop.js	Introduced EventsOnce listener for drag-and-drop initialization based on the enableWailsDragAndDrop flag.
v2/pkg/runtime/draganddrop.go	Modified OnFileDrop to emit "wails:init-file-drop" event at the start of the drop process.

Assessment against linked issues

Objective	Addressed	Explanation
Ensure file view does not appear when dropping files (3686)	✅

Possibly related PRs

• #3742: Addresses a bug related to drag-and-drop functionality, relevant to the enhancements made in this PR.
• #3856: Introduces a test for the HTML Drag and Drop API, aligning with the focus on improving drag-and-drop functionality.
• #3886: Includes fixes for drag-and-drop functionality, making it relevant to the changes in this PR.
• #3907: Discusses improvements to systray click handling, which may relate to drag-and-drop interactions.
• #3925: Addresses a bug in the Linux dialog for multiple selections, potentially involving drag-and-drop operations.

Suggested reviewers

• atterpac

🐰 In the land of code where rabbits play,
Drag-and-drop now works in a better way!
Events registered just once, oh so neat,
Our UI stays intact, a real treat!
With each file dropped, a new event sings,
Hopping along, we embrace these changes! 🐇✨

[!TIP] CodeRabbit's docstrings feature is now available as part of our Early Access Program! Simply use the command @coderabbitai generate docstrings to have CodeRabbit automatically generate docstrings for your pull request. This feature will be included in our Pro Plan when released.

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[leaanthony]

@atterpac - any thoughts on this?

[makew0rld]

Any chance this could be merged soon? Thanks.

[makew0rld]

Ok I am seeing one issue with this PR so far, which is that it doesn't seem to work properly with a built binary (wails build) even though wails dev works fine.

• Linux binary: reverts back to original behaviour described in #3686
• ~~macOS binary: the file drop is not detected, no green plus shows up on hover/drag~~

I don't get why this would happen. Maybe related to #3563?

It would be good if someone else could confirm this.

[leaanthony]

I can try to look at this this week at some point. Perhaps @atterpac could look at it if he has time.

[atterpac]

I can try to look at this this week at some point. Perhaps @atterpac could look at it if he has time.

I can look into it

[atterpac]

This looks gtg to me @leaanthony

[leaanthony]

Thanks @makew0rld 🙏 Please could you add an entry to the changelog located at website/src/pages/changelog.mdx? Could you also please revert the changes to the debug runtime file? We'll need to generate both debug and prod versions, which I'm happy to do 👍

[makew0rld]

I actually I am not very confident in this PR, I think it may be an incomplete solution. See my comment above, and also this comment which explains what I currently do in my actual application.

I would need to do more testing before I consider it ready to merge. I don't have a lot of time for it at the moment but I'll see what I can do.

[leaanthony]

Fair enough. Converted to draft 👍

[leaanthony]

@makew0rld - I'm assuming this is abandoned now? Please reopen if not 🙏