Fix some things with builtin derives

1. Err on unions on derive where it's required.
 2. Err on `#[derive(Default)]` on enums without `#[default]` variant.
 3. Don't add where bounds `T: Default` when expanding `Default` on enums (structs need that, enums not).

Also, because I was annoyed by that, in minicore, add a way to filter on multiple flags in the line-filter (`// :`). This is required for the `Debug` and `Hash` derives, because the derive should be in the prelude but the trait not.

crates/hir-def/src/macro_expansion_tests/builtin_derive_macro.rs

@@ -746,3 +746,83 @@ struct Struct9<#[pointee] T, U>(T) where T: ?Sized;
             623..690: `derive(CoercePointee)` requires `T` to be marked `?Sized`"#]],
     );
 }
+
+#[test]
+fn union_derive() {
+    check_errors(
+        r#"
+//- minicore: clone, copy, default, fmt, hash, ord, eq, derive
+
+#[derive(Copy)]
+union Foo1 { _v: () }
+#[derive(Clone)]
+union Foo2 { _v: () }
+#[derive(Default)]
+union Foo3 { _v: () }
+#[derive(Debug)]
+union Foo4 { _v: () }
+#[derive(Hash)]
+union Foo5 { _v: () }
+#[derive(Ord)]
+union Foo6 { _v: () }
+#[derive(PartialOrd)]
+union Foo7 { _v: () }
+#[derive(Eq)]
+union Foo8 { _v: () }
+#[derive(PartialEq)]
+union Foo9 { _v: () }
+    "#,
+        expect![[r#"
+            78..118: this trait cannot be derived for unions
+            119..157: this trait cannot be derived for unions
+            158..195: this trait cannot be derived for unions
+            196..232: this trait cannot be derived for unions
+            233..276: this trait cannot be derived for unions
+            313..355: this trait cannot be derived for unions"#]],
+    );
+}
+
+#[test]
+fn default_enum_without_default_attr() {
+    check_errors(
+        r#"
+//- minicore: default, derive
+
+#[derive(Default)]
+enum Foo {
+    Bar,
+}
+    "#,
+        expect!["1..41: `#[derive(Default)]` on enum with no `#[default]`"],
+    );
+}
+
+#[test]
+fn generic_enum_default() {
+    check(
+        r#"
+//- minicore: default, derive
+
+#[derive(Default)]
+enum Foo<T> {
+    Bar(T),
+    #[default]
+    Baz,
+}
+"#,
+        expect![[r#"
+
+#[derive(Default)]
+enum Foo<T> {
+    Bar(T),
+    #[default]
+    Baz,
+}
+
+impl <T, > $crate::default::Default for Foo<T, > where {
+    fn default() -> Self {
+        Foo::Baz
+    }
+}"#]],
+    );
+}