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, 9 insertions, 0 deletions

diff --git a/env.cpp b/env.cpp
index 821bd8f1..77ee75aa 100644
--- a/env.cpp
+++ b/env.cpp
@@ -634,6 +634,15 @@ int env_set(const wcstring &key, const wchar_t *val, int var_mode)
         }
     }
 
+    if ((var_mode & (ENV_LOCAL | ENV_UNIVERSAL)) && (is_read_only(key) || is_electric(key)))
+    {
+        return ENV_SCOPE;
+    }
+    if ((var_mode & ENV_EXPORT) && is_electric(key))
+    {
+        return ENV_SCOPE;
+    }
+
     if ((var_mode & ENV_USER) && is_read_only(key))
     {
         return ENV_PERM;