fix usage on NixOS

main_test.go

@@ -43,8 +43,6 @@ func TestExecutable(t *testing.T) {
 		t.Fatal("Failed to compile binary:", err)
 	}
 
-	t.Setenv("PATH", fmt.Sprintf("%s:%s", path, os.Getenv("PATH")))
-
 	e := script.NewEngine()
 	e.Cmds["glob-exists"] = globExists
 	e.Cmds["gdb"] = gdbStub
@@ -61,7 +59,7 @@ func TestExecutable(t *testing.T) {
 		s.Setenv("TMPDIR", t.TempDir())
 		return nil, nil
 	})
-	e.Cmds["vimto"] = script.Program("vimto", nil, time.Second)
+	e.Cmds["vimto"] = script.Program(filepath.Join(path, "vimto"), nil, time.Second)
 	e.Cmds["config"] = script.Command(script.CmdUsage{
 		Summary: "Write to the configuration file",
 		Args:    "items...",

qemu.go

@@ -252,6 +252,25 @@ func (cmd *command) Start(ctx context.Context) (err error) {
 		return strings.HasPrefix(env, "TMPDIR=")
 	})
 
+	// Resolve symlinks in PATH entries and warn about opaque directories
+	for i, e := range env {
+		if key, value, ok := strings.Cut(e, "="); ok && key == "PATH" {
+			parts := filepath.SplitList(value)
+			for j, p := range parts {
+				resolved := resolvePath(p)
+				parts[j] = resolved
+				// Warn if resolved path still under opaque directory
+				for _, opaque := range opaqueDirectories {
+					if resolved == opaque || strings.HasPrefix(resolved, opaque+"/") {
+						fmt.Fprintf(os.Stderr, "warning: PATH entry %q resolves to %q which is shadowed in the VM\n", p, resolved)
+						break
+					}
+				}
+			}
+			env[i] = "PATH=" + strings.Join(parts, string(filepath.ListSeparator))
+		}
+	}
+
 	execCmd := execCommand{
 		cmd.Path,
 		cmd.Args,
@@ -720,6 +739,50 @@ func (*p9SharedDirectory) KArgs() []string {
 	return nil
 }
 
+// resolvePath resolves symlinks in a path segment by segment.
+// Returns original path if resolution fails at any point.
+func resolvePath(path string) string {
+	if path == "" {
+		return path
+	}
+
+	var resolved string
+	if filepath.IsAbs(path) {
+		resolved = "/"
+	}
+
+	segments := strings.Split(path, string(filepath.Separator))
+	for _, seg := range segments {
+		if seg == "" {
+			continue
+		}
+
+		current := filepath.Join(resolved, seg)
+		info, err := os.Lstat(current)
+		if err != nil {
+			// Path doesn't exist or can't be accessed, return original
+			return path
+		}
+
+		if info.Mode()&os.ModeSymlink != 0 {
+			target, err := os.Readlink(current)
+			if err != nil {
+				return path
+			}
+
+			if filepath.IsAbs(target) {
+				resolved = target
+			} else {
+				resolved = filepath.Join(resolved, target)
+			}
+		} else {
+			resolved = current
+		}
+	}
+
+	return filepath.Clean(resolved)
+}
+
 // virtioRandom and arbitraryArgs were copied from u-root, available under BSD-3-Clause.
 // Copyright (c) 2012-2019, u-root Authors
 

testdata/nixos-path.txt

@@ -0,0 +1,24 @@
+# Test PATH symlink resolution
+#
+# On NixOS, PATH contains entries like /run/current-system/sw/bin which are
+# symlinks into /nix/store. Since /run is made opaque in the VM, we resolve
+# symlinks in PATH entries before passing them to the guest.
+#
+# This test verifies symlink resolution works. Since $WORK is under /tmp
+# (an opaque directory), we expect a warning but the resolution should
+# still transform link-dir -> real-dir in the PATH.
+
+config kernel="${KERNEL}"
+
+# Create target directory and symlink to it
+mkdir real-dir
+symlink link-dir -> real-dir
+
+# Set PATH through the symlink
+env PATH=$PATH:$WORK/link-dir
+
+# Verify PATH inside VM contains resolved path, not symlink
+vimto exec -- sh -c 'echo $PATH'
+stderr 'warning: PATH entry'
+stdout real-dir
+! stdout link-dir