Add warning for incorrect usage of Nushell activation script (#2906)

Co-authored-by: Emre Şafak <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Bernát Gábor <[email protected]>

Author: 3 people

docs/changelog/nushell_activation.feature.rst

@@ -0,0 +1 @@
+Warn on incorrect invocation of Nushell activation script - by :user:`esafak`.

src/virtualenv/activation/nushell/activate.nu

@@ -6,6 +6,18 @@
 # but then simply `deactivate` won't work because it is just an alias to hide
 # the "activate" overlay. You'd need to call `overlay hide foo` manually.
 
+# Warn users who accidentally 'source' it
+module warning {
+	export-env {
+		const file = path self
+		error make -u {
+			msg: $"`($file | path basename)` is meant to be used with `overlay use`, not `source`"
+		}
+	}
+}
+
+use warning
+
 export-env {
     def is-string [x] {
         ($x | describe) == 'string'