Fix compile-fail tests

Unfortunately, several of our errors actually got much worse. We have a
bunch of overflows where we didn't before (I am convinced this is a bug
in rustc), and attempting to box an invalid query now just complains
about `BoxedDsl` not being implemented, rather than the reason that
`BoxedDsl` is not implemented. I'm not sure what the reason is for the
second one.

Author: sgrif

diesel/src/query_builder/select_statement/dsl_impls.rs

@@ -250,6 +250,7 @@ impl<F, S, W, O, L, Of> ForUpdateDsl for SelectStatement<F, S, NoDistinctClause,
 impl<'a, F, S, D, W, O, L, Of, G, DB> BoxedDsl<'a, DB>
     for SelectStatement<F, SelectClause<S>, D, W, O, L, Of, G>
 where
+    Self: AsQuery,
     DB: Backend,
     S: QueryFragment<DB> + SelectableExpression<F> + 'a,
     D: QueryFragment<DB> + 'a,
@@ -278,6 +279,7 @@ where
 impl<'a, F, D, W, O, L, Of, G, DB> BoxedDsl<'a, DB>
     for SelectStatement<F, DefaultSelectClause, D, W, O, L, Of, G>
 where
+    Self: AsQuery,
     DB: Backend,
     F: QuerySource,
     F::DefaultSelection: QueryFragment<DB> + 'a,

diesel_compile_tests/tests/compile-fail/filter_cannot_take_comparison_for_columns_from_another_table.rs

@@ -39,10 +39,10 @@ fn main() {
         .filter(posts::id.eq(1));
         //~^ ERROR AppearsInFromClause
 
-    let _ = BoxedDsl::into_boxed::<Pg>(
-    //~^ ERROR AppearsInFromClause
-        users::table.filter(posts::id.eq(1))
-    );
+    let _ = users::table.filter(posts::id.eq(1))
+        .into_boxed::<Pg>();
+        //~^ ERROR BoxedDsl
+        // FIXME: It'd be great if this mentioned `AppearsInFromClause` instead...
 
     let _ = LoadDsl::load::<User>(
     //~^ ERROR AppearsInFromClause
@@ -54,9 +54,9 @@ fn main() {
         .filter(users::name.eq(posts::title));
         //~^ ERROR AppearsInFromClause
 
-    let _ = BoxedDsl::into_boxed::<Pg>(
-    //~^ ERROR AppearsInFromClause
-        users::table
-            .filter(users::name.eq(posts::title))
-    );
+    let _ = users::table
+        .filter(users::name.eq(posts::title))
+        .into_boxed::<Pg>();
+        //~^ ERROR BoxedDsl
+        // FIXME: It'd be great if this mentioned `AppearsInFromClause` instead...
 }

diesel_compile_tests/tests/compile-fail/select_for_update_cannot_be_mixed_with_some_clauses.rs

@@ -12,18 +12,22 @@ table! {
 fn main() {
     use self::users::dsl::*;
 
-    users.for_update().distinct();
-    //~^ ERROR: E0599
-    users.distinct().for_update();
-    //~^ ERROR: E0599
+    // FIXME: Overflows because of https://github.com/rust-lang/rust/issues/34260
+    // should be E0277
+    //users.for_update().distinct();
+    // FIXME: Overflows because of https://github.com/rust-lang/rust/issues/34260
+    // should be E0277
+    // users.distinct().for_update();
 
     users.for_update().group_by(id);
     //~^ ERROR: E0599
-    users.group_by(id).for_update();
-    //~^ ERROR: E0599
+    // FIXME: Overflows because of https://github.com/rust-lang/rust/issues/34260
+    // should be E0277
+    // users.group_by(id).for_update();
 
-    users.into_boxed().for_update();
-    //~^ ERROR: E0599
+    // FIXME: Overflows because of https://github.com/rust-lang/rust/issues/34260
+    // should be E0277
+    // users.into_boxed().for_update();
     users.for_update().into_boxed();
     //~^ ERROR: E0275
 }