Init GTK in NewFrontend, not init (#2841)

* Init GTK in `NewFrontend`, not `init`

So apps that have a headless / non-gui mode will be able to run, since
they needn't call `NewFrontend` (which is called by `CreateApp`).
Previously, `init` would call `C.gtk_init` regardless of whether
CreateApp was called.

Also change to call `C.gtk_init_check` with a panic, instead of
`C.gtk_init`, since `gtk_init` just exits the process if it fails,
without a sensible error message.

Fixes #2628.

* Update changelog

v2/internal/frontend/desktop/linux/frontend.go

@@ -76,6 +76,7 @@ import "C"
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log"
 	"net"
@@ -83,6 +84,7 @@ import (
 	"os"
 	"runtime"
 	"strings"
+	"sync"
 	"text/template"
 	"unsafe"
 
@@ -96,6 +98,8 @@ import (
 	"github.com/wailsapp/wails/v2/pkg/options"
 )
 
+var initOnce = sync.Once{}
+
 const startURL = "wails://wails/"
 
 type Frontend struct {
@@ -126,18 +130,19 @@ func (f *Frontend) WindowClose() {
 	f.mainWindow.Destroy()
 }
 
-func init() {
-	runtime.LockOSThread()
-
-	// Set GDK_BACKEND=x11 if currently unset and XDG_SESSION_TYPE is unset, unspecified or x11 to prevent warnings
-	if os.Getenv("GDK_BACKEND") == "" && (os.Getenv("XDG_SESSION_TYPE") == "" || os.Getenv("XDG_SESSION_TYPE") == "unspecified" || os.Getenv("XDG_SESSION_TYPE") == "x11") {
-		_ = os.Setenv("GDK_BACKEND", "x11")
-	}
-
-	C.gtk_init(nil, nil)
-}
-
 func NewFrontend(ctx context.Context, appoptions *options.App, myLogger *logger.Logger, appBindings *binding.Bindings, dispatcher frontend.Dispatcher) *Frontend {
+	initOnce.Do(func() {
+		runtime.LockOSThread()
+
+		// Set GDK_BACKEND=x11 if currently unset and XDG_SESSION_TYPE is unset, unspecified or x11 to prevent warnings
+		if os.Getenv("GDK_BACKEND") == "" && (os.Getenv("XDG_SESSION_TYPE") == "" || os.Getenv("XDG_SESSION_TYPE") == "unspecified" || os.Getenv("XDG_SESSION_TYPE") == "x11") {
+			_ = os.Setenv("GDK_BACKEND", "x11")
+		}
+
+		if ok := C.gtk_init_check(nil, nil); ok != 1 {
+			panic(errors.New("failed to init GTK"))
+		}
+	})
 
 	result := &Frontend{
 		frontendOptions: appoptions,

website/src/pages/changelog.mdx

@@ -21,9 +21,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Avoid app crashing when the Linux GTK key is empty. Fixed by @aminya in [PR](https://github.com/wailsapp/wails/pull/2672)
+- Fix issue where app would exit before main() on linux if $DISPLAY env var was not set. Fixed by @phildrip in [PR](https://github.com/wailsapp/wails/pull/2841)
 - Fixed a race condition when positioning the window on Linux. Added by @lyimmi in [PR](https://github.com/wailsapp/wails/pull/2850)
 - Fixed `SetBackgroundColour` so it sets the window's background color to reduce resize flickering on Linux. Added by @lyimmi in [PR](https://github.com/wailsapp/wails/pull/2853)
 
+
 ### Added
 
 - Added correct NodeJS and Docker package names for DNF package manager of Fedora 38. Added by @aranggitoar in [PR](https://github.com/wailsapp/wails/pull/2790)