Fix crash when using uninstantiated generic (#22379)

* Add test case

* Add in a bounds check when accessing generic types

Removes idnex out of bounds exception when comparing a generic that isn't fully instantiated

1 files changed, 16 insertions, 0 deletions

diff --git a/tests/generics/tuninstantiated_failure.nim b/tests/generics/tuninstantiated_failure.nim
new file mode 100644
index 000000000..f09b115d6
--- /dev/null
+++ b/tests/generics/tuninstantiated_failure.nim
@@ -0,0 +1,16 @@
+discard """
+cmd: "nim check $file"
+"""
+
+type
+  Test[T, K] = object
+    name: string
+  Something = Test[int]
+
+func `[]`[T, K](x: var Test[T, K], idx: int): var Test[T, K] =
+  x
+
+var b: Something
+# Should give a type-mismatch since Something isn't a valid Test
+b[0].name = "Test" #[tt.Error
+            ^  type mismatch]#