1 files changed, 32 insertions, 0 deletions
diff --git a/src/cmd/go/internal/modload/stat_unix.go b/src/cmd/go/internal/modload/stat_unix.go
new file mode 100644
index 0000000..a0d5f4d
--- /dev/null
+++ b/src/cmd/go/internal/modload/stat_unix.go
@@ -0,0 +1,32 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix
+
+package modload
+
+import (
+	"io/fs"
+	"os"
+	"syscall"
+)
+
+// hasWritePerm reports whether the current user has permission to write to the
+// file with the given info.
+//
+// Although the root user on most Unix systems can write to files even without
+// permission, hasWritePerm reports false if no appropriate permission bit is
+// set even if the current user is root.
+func hasWritePerm(path string, fi fs.FileInfo) bool {
+	if os.Getuid() == 0 {
+		// The root user can access any file, but we still want to default to
+		// read-only mode if the go.mod file is marked as globally non-writable.
+		// (If the user really intends not to be in readonly mode, they can
+		// pass -mod=mod explicitly.)
+		return fi.Mode()&0222 != 0
+	}
+
+	const W_OK = 0x2
+	return syscall.Access(path, W_OK) == nil
+}