Locate the limactl executable via os.Args[0] instead of os.Executable()

We need the symlink directory to find the the ../share/lima directory
relative to it. os.Executable() uses /proc/self/exe on Linux and returns
the symlink target, which will break things with a Homebrew installation.

This commit also removes the dead code that pretends to resolve any
symlinks. It never worked because it called os.Stat() instead of os.Lstat().
If it had worked, then code would have been broken on macOS too.

Signed-off-by: Jan Dubois <jan.dubois@suse.com>

Author: jandubois

pkg/usrlocalsharelima/usrlocalsharelima.go

@@ -8,29 +8,40 @@ import (
 	"fmt"
 	"io/fs"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"runtime"
+	"sync"
 
 	"github.com/lima-vm/lima/pkg/debugutil"
 	"github.com/lima-vm/lima/pkg/limayaml"
 	"github.com/sirupsen/logrus"
 )
 
-func Dir() (string, error) {
-	self, err := os.Executable()
+// executableViaArgs0 returns the absolute path to the executable used to start this process.
+// It will also append the file extension on Windows, if necessary.
+// This function is different from os.Executable(), which will use /proc/self/exe on Linux
+// and therefore will resolve any symlink used to locate the executable. This function will
+// return the symlink instead because we want to locate ../share/lima relative to the location
+// of the symlink, and not the actual executable. This is important when using Homebrew.
+var executableViaArgs0 = sync.OnceValues(func() (string, error) {
+	executable, err := exec.LookPath(os.Args[0])
 	if err != nil {
 		return "", err
 	}
-	selfSt, err := os.Stat(self)
+	// LookPath() will add the `.exe` file extension on Windows, but will not return an
+	// absolute path if the argument contained any of `:/\` (or just `/` on Unix).
+	return filepath.Abs(executable)
+})
+
+// Dir returns the location of the <PREFIX>/lima/share directory, relative to the location
+// of the current executable. It checks for multiple possible filesystem layouts and returns
+// the first candidate that contains the native guest agent binary.
+func Dir() (string, error) {
+	self, err := executableViaArgs0()
 	if err != nil {
 		return "", err
 	}
-	if selfSt.Mode()&fs.ModeSymlink != 0 {
-		self, err = os.Readlink(self)
-		if err != nil {
-			return "", err
-		}
-	}
 
 	ostype := limayaml.NewOS("linux")
 	arch := limayaml.NewArch(runtime.GOARCH)
@@ -80,7 +91,7 @@ func Dir() (string, error) {
 		ostype, arch, self, gaCandidates)
 }
 
-// GuestAgentBinary returns the guest agent binary, possibly with ".gz" suffix.
+// GuestAgentBinary returns the absolute path of the guest agent binary, possibly with ".gz" suffix.
 func GuestAgentBinary(ostype limayaml.OS, arch limayaml.Arch) (string, error) {
 	if ostype == "" {
 		return "", errors.New("os must be set")