[v3 linux] Panic when attempting to getTheme from empty dbus Signal

[StephenBrown2]

Loving the progress, posting an issue here because the discord invite link here is invalid: https://discord.gg/3mgVyGua

I just pulled the v3-alpha branch and wanted to try out the systray implementation. It started fine, but it panicked here when I clicked the "Hello World" Menu option:

https://github.com/wailsapp/wails/blob/412c3a5ed1c764100fe00ba14b2a7afda6a44e4f/v3/pkg/application/application_linux.go#L155-L166

Because the Body of the DBus signal is empty. I'd recommend adding a check for the body length in the getTheme function.

        getTheme := func(body []interface{}) (string, bool) {
            if len(body) < 1 {
                return "", false
            }

With that added, the question dialog successfully pops up, albeit "unthemed", and I can also have it open the window.

Hope this doesn't clutter things too much, feel free to close and reorganize elsewhere.

---

Logs:

❯ go1.21.4 run .
# github.com/wailsapp/wails/v3/pkg/application
cgo-gcc-prolog: In function ‘_cgo_4865b4e94e09_Cfunc_webkit_javascript_result_get_global_context’:
cgo-gcc-prolog:2296:2: warning: ‘webkit_javascript_result_get_global_context’ is deprecated [-Wdeprecated-declarations]
In file included from /usr/include/webkitgtk-4.0/webkit2/webkit2.h:58,
                 from ../../pkg/application/linux_cgo.go:21:
/usr/include/webkitgtk-4.0/webkit/WebKitJavascriptResult.h:51:1: note: declared here
   51 | webkit_javascript_result_get_global_context (WebKitJavascriptResult *js_result);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cgo-gcc-prolog: In function ‘_cgo_4865b4e94e09_Cfunc_webkit_javascript_result_get_value’:
cgo-gcc-prolog:2332:2: warning: ‘webkit_javascript_result_get_value’ is deprecated: Use 'webkit_javascript_result_get_js_value' instead [-Wdeprecated-declarations]
/usr/include/webkitgtk-4.0/webkit/WebKitJavascriptResult.h:54:1: note: declared here
   54 | webkit_javascript_result_get_value          (WebKitJavascriptResult *js_result);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4:10PM INF Build Info: Wails=v3.0.0-alpha.0 Compiler=go1.21.4 CGO_CXXFLAGS="" CGO_LDFLAGS="" GOAMD64=v1 -buildmode=exe -compiler=gc CGO_CPPFLAGS="" GOOS=linux CGO_ENABLED=1 CGO_CFLAGS="" GOARCH=amd64
4:10PM INF AssetServer Info: assetsFS=true middleware=false handler=false externalURL=""
4:10PM INF Platform Info: ID=fedora Name="Fedora Linux" Version=38 Branding="38 (KDE Plasma)"
2023/11/08 16:10:16 linuxApp.setIcon not implemented
2023/11/08 16:10:16 linuxApp.on() 1032
on() 1181
on() 1187
Overriding existing handler for signal 10. Set JSC_SIGNAL_FOR_GC if you want WebKit to use a different signal
attempting to set in the center
on() 1143
4:10PM INF Asset Request: windowName="" windowID=1 code=200 method=GET path=/ duration=1.259374ms
4:10PM INF Asset Request: windowName="" windowID=1 code=200 method=GET path=/wails/ipc.js duration=36.43µs
4:10PM INF Asset Request: windowName="" windowID=1 code=200 method=GET path=/wails/runtime.js duration=125.416µs
4:10PM INF Asset Request: windowName="" windowID=1 code=200 method=GET path=/wails/flags duration=112.222µs
4:10PM INF Asset Request: windowName="" windowID=1 code=200 method=GET path=/wails/capabilities duration=69.857µs
Hello World!
panic: runtime error: index out of range [0] with length 0

goroutine 20 [running]:
github.com/wailsapp/wails/v3/pkg/application.(*linuxApp).monitorThemeChanges.func1.1(...)
        /home/sb/wails/v3/pkg/application/application_linux.go:156
github.com/wailsapp/wails/v3/pkg/application.(*linuxApp).monitorThemeChanges.func1()
        /home/sb/wails/v3/pkg/application/application_linux.go:166 +0x55b
created by github.com/wailsapp/wails/v3/pkg/application.(*linuxApp).monitorThemeChanges in goroutine 1
        /home/sb/wails/v3/pkg/application/application_linux.go:138 +0x4f
exit status 2

wails3 doctor output:

# Build Environment
Wails CLI    | v3.0.0-alpha.0                          
Go Version   | go1.21.4                                
Revision     | 412c3a5ed1c764100fe00ba14b2a7afda6a44e4f
Modified     | true                                    
-buildmode   | exe                                     
-compiler    | gc                                      
CGO_CFLAGS   |                                         
CGO_CPPFLAGS |                                         
CGO_CXXFLAGS |                                         
CGO_ENABLED  | 1                                       
CGO_LDFLAGS  |                                         
GOAMD64      | v1                                      
GOARCH       | amd64                                   
GOOS         | linux                                   
vcs          | git                                     
vcs.modified | true                                    
vcs.revision | 412c3a5ed1c764100fe00ba14b2a7afda6a44e4f
vcs.time     | 2023-11-08T11:36:47Z                    

# System
Name         | Fedora Linux                                                           
Version      | 38                                                                     
ID           | fedora                                                                 
Branding     | 38 (KDE Plasma)                                                        
Platform     | linux                                                                  
Architecture | amd64                                                                  
gcc          | 13.2.1                                                                 
libgtk-3     | 3.24.38                                                                
libwebkit    | 2.42.1                                                                 
npm          | 9.8.1                                                                  
pkg-config   | 1.8.0                                                                  
CPU          | 12th Gen Intel(R) Core(TM) i7-12800H                                   
GPU 1        | Alder Lake-P GT2 [Iris Xe Graphics] (Intel Corporation) - Driver: i915 
Memory       | 66GB                                                                   

# Diagnosis
 SUCCESS  Your system is ready for Wails development!

[tmclane]

Let me know if that fixes it for you. The theme in this case is merely to know if we are using light or dark but unless you added a handler to your application nothing else happens at this time.

[sbrownjc]

Yup, works for me now! Thanks, and godspeed!