set: Print an error when setting a special var in the wrong scope

When attempting to set a readonly or electric variable in the local or
universal scopes, print an appropriate error. Similarly, print an error
when setting an electric variable as exported. In most cases this is
simply a nicer error instead of the 'read-only' one, but for the 'umask'
variable it prevents `set -l umask 0023` from silently changing the
global value.

1 files changed, 7 insertions, 0 deletions

diff --git a/builtin_set.cpp b/builtin_set.cpp
index 9068372f..aae87550 100644
--- a/builtin_set.cpp
+++ b/builtin_set.cpp
@@ -157,6 +157,13 @@ static int my_env_set(const wchar_t *key, const wcstring_list_t &val, int scope)
             break;
         }
 
+        case ENV_SCOPE:
+        {
+            append_format(stderr_buffer, _(L"%ls: Tried to set the special variable '%ls' with the wrong scope\n"), L"set", key);
+            retcode=1;
+            break;
+        }
+
         case ENV_INVALID:
         {
             append_format(stderr_buffer, _(L"%ls: Unknown error"), L"set");