Merge #2455

2455: Add BuiltinShadowMode r=flodiebold a=edwin0cheng

This PR try to fix #1905 by introduce an `BuiltinShadowMode` in name resolving functions. 

cc @flodiebold 

Co-authored-by: Edwin Cheng <edwin0cheng@gmail.com>

crates/ra_hir_ty/src/tests.rs

@@ -3693,6 +3693,42 @@ fn main() {
     assert_eq!(t, "Foo");
 }
 
+#[test]
+fn not_shadowing_primitive_by_module() {
+    let t = type_at(
+        r#"
+//- /str.rs
+fn foo() {}
+
+//- /main.rs
+mod str;
+fn foo() -> &'static str { "" }
+
+fn main() {
+    foo()<|>;
+}"#,
+    );
+    assert_eq!(t, "&str");
+}
+
+#[test]
+fn not_shadowing_module_by_primitive() {
+    let t = type_at(
+        r#"
+//- /str.rs
+fn foo() -> u32 {0}
+
+//- /main.rs
+mod str;
+fn foo() -> &'static str { "" }
+
+fn main() {
+    str::foo()<|>;
+}"#,
+    );
+    assert_eq!(t, "u32");
+}
+
 #[test]
 fn deref_trait() {
     let t = type_at(