rustc_typeck: ensure type alias bounds are implied by the type being well-formed.

Author: eddyb

src/librustc_typeck/check/mod.rs

@@ -1316,12 +1316,14 @@ pub fn check_item_type<'a,'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, it: &'tcx hir::Item
       hir::ItemKind::Union(..) => {
         check_union(tcx, it.id, it.span);
       }
-      hir::ItemKind::Existential(..) |
-      hir::ItemKind::Ty(..) => {
+      hir::ItemKind::Existential(..)
+      // HACK(eddyb) This is done in `wfcheck` for type aliases, instead.
+      // | hir::ItemKind::Ty(..)
+      => {
         let def_id = tcx.hir.local_def_id(it.id);
         let pty_ty = tcx.type_of(def_id);
         let generics = tcx.generics_of(def_id);
-        check_bounds_are_used(tcx, &generics, pty_ty);
+        let _ = check_params_are_used(tcx, &generics, pty_ty);
       }
       hir::ItemKind::ForeignMod(ref m) => {
         check_abi(tcx, it.span, m.abi);
@@ -5240,14 +5242,16 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
     }
 }
 
-pub fn check_bounds_are_used<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
-                                       generics: &ty::Generics,
-                                       ty: Ty<'tcx>) {
+fn check_params_are_used<'a, 'tcx>(
+    tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    generics: &ty::Generics,
+    ty: Ty<'tcx>,
+) -> Result<(), ErrorReported> {
     let own_counts = generics.own_counts();
-    debug!("check_bounds_are_used(n_tps={}, ty={:?})", own_counts.types, ty);
+    debug!("check_params_are_used(n_tps={}, ty={:?})", own_counts.types, ty);
 
     if own_counts.types == 0 {
-        return;
+        return Ok(());
     }
     // Make a vector of booleans initially false, set to true when used.
     let mut types_used = vec![false; own_counts.types];
@@ -5260,23 +5264,26 @@ pub fn check_bounds_are_used<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             // If there is already another error, do not emit
             // an error for not using a type Parameter.
             assert!(tcx.sess.err_count() > 0);
-            return;
+            return Err(ErrorReported);
         }
     }
 
     let types = generics.params.iter().filter(|param| match param.kind {
         ty::GenericParamDefKind::Type { .. } => true,
         _ => false,
     });
+    let mut result = Ok(());
     for (&used, param) in types_used.iter().zip(types) {
         if !used {
             let id = tcx.hir.as_local_node_id(param.def_id).unwrap();
             let span = tcx.hir.span(id);
             struct_span_err!(tcx.sess, span, E0091, "type parameter `{}` is unused", param.name)
                 .span_label(span, "unused type parameter")
                 .emit();
+            result = Err(ErrorReported);
         }
     }
+    result
 }
 
 fn fatally_break_rust(sess: &Session) {

src/librustc_typeck/check/wfcheck.rs

@@ -118,11 +118,53 @@ pub fn check_item_well_formed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: Def
         hir::ItemKind::Fn(..) => {
             check_item_fn(tcx, item);
         }
-        hir::ItemKind::Static(..) => {
-            check_item_type(tcx, item);
-        }
+        hir::ItemKind::Static(..) |
         hir::ItemKind::Const(..) => {
-            check_item_type(tcx, item);
+            for_item(tcx, item).with_fcx(|fcx, _this| {
+                let ty = fcx.tcx.type_of(fcx.tcx.hir.local_def_id(item.id));
+                let item_ty = fcx.normalize_associated_types_in(item.span, &ty);
+
+                fcx.register_wf_obligation(item_ty, item.span, ObligationCauseCode::MiscObligation);
+
+                vec![] // no implied bounds in a static/const
+            });
+        }
+        hir::ItemKind::Ty(..) => {
+            let def_id = tcx.hir.local_def_id(item.id);
+            let item_ty = tcx.type_of(def_id);
+            let generics = tcx.generics_of(def_id);
+            let used_params = super::check_params_are_used(tcx, &generics, item_ty);
+            for_item(tcx, item).with_fcx(|fcx, _this| {
+                let item_ty = fcx.normalize_associated_types_in(item.span, &item_ty);
+
+                // Check the user-declared bounds, assuming the type is WF.
+                // This ensures that by checking the WF of the aliased type, where
+                // the alias is used, we don't ignore bounds written on the alias.
+                // NB: this check only happens if *all* type parameters are used,
+                // otherwise every unused type parameter can cause errors here.
+                if let Ok(()) = used_params {
+                    let user_predicates = fcx.param_env.caller_bounds;
+                    let wf_predicates = ty::wf::obligations(
+                        &fcx.infcx,
+                        fcx.param_env,
+                        fcx.body_id,
+                        item_ty,
+                        item.span,
+                    ).into_iter().flatten().map(|o| o.predicate).collect();
+                    let wf_predicates = traits::elaborate_predicates(fcx.tcx, wf_predicates);
+                    let wf_param_env = ty::ParamEnv {
+                        caller_bounds: fcx.tcx.mk_predicates(wf_predicates),
+                        reveal: fcx.param_env.reveal,
+                    };
+                    fcx.register_predicates(user_predicates.iter().map(|&predicate| {
+                        let code = ObligationCauseCode::MiscObligation;
+                        let cause = traits::ObligationCause::new(item.span, fcx.body_id, code);
+                        traits::Obligation::new(cause, wf_param_env, predicate)
+                    }));
+                }
+
+                vec![item_ty]
+            });
         }
         hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
             check_type_defn(tcx, item, false, |fcx| {
@@ -322,21 +364,6 @@ fn check_item_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item: &hir::Item) {
     })
 }
 
-fn check_item_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
-                    item: &hir::Item)
-{
-    debug!("check_item_type: {:?}", item);
-
-    for_item(tcx, item).with_fcx(|fcx, _this| {
-        let ty = fcx.tcx.type_of(fcx.tcx.hir.local_def_id(item.id));
-        let item_ty = fcx.normalize_associated_types_in(item.span, &ty);
-
-        fcx.register_wf_obligation(item_ty, item.span, ObligationCauseCode::MiscObligation);
-
-        vec![] // no implied bounds in a const etc
-    });
-}
-
 fn check_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                 item: &hir::Item,
                 ast_self_ty: &hir::Ty,

src/test/incremental/hashes/type_defs.rs

@@ -132,12 +132,12 @@ type ChangeNestedTupleField = (i32, (i64, i8));
 
 // Add type param --------------------------------------------------------------
 #[cfg(cfail1)]
-type AddTypeParam<T1> = (T1, T1);
+type AddTypeParam<T1> = (T1, Option<T1>);
 
 #[cfg(not(cfail1))]
 #[rustc_clean(cfg="cfail2", except="Hir,HirBody")]
 #[rustc_clean(cfg="cfail3")]
-type AddTypeParam<T1, T2> = (T1, T2);
+type AddTypeParam<T1, T2> = (T1, Option<T2>);
 
 
 
@@ -148,18 +148,18 @@ type AddTypeParamBound<T1> = (T1, u32);
 #[cfg(not(cfail1))]
 #[rustc_clean(cfg="cfail2", except="Hir,HirBody")]
 #[rustc_clean(cfg="cfail3")]
-type AddTypeParamBound<T1: Clone> = (T1, u32);
+type AddTypeParamBound<T1: std::any::Any> = (T1, u32);
 
 
 
 // Add type param bound in where clause ----------------------------------------
 #[cfg(cfail1)]
-type AddTypeParamBoundWhereClause<T1> where T1: Clone = (T1, u32);
+type AddTypeParamBoundWhereClause<T1> where T1: Sized = (T1, u32);
 
 #[cfg(not(cfail1))]
 #[rustc_clean(cfg="cfail2", except="Hir,HirBody")]
 #[rustc_clean(cfg="cfail3")]
-type AddTypeParamBoundWhereClause<T1> where T1: Clone+Copy = (T1, u32);
+type AddTypeParamBoundWhereClause<T1> where T1: Sized+std::any::Any = (T1, u32);
 
 
 
@@ -203,7 +203,9 @@ where 'b: 'a,
 
 // Change Trait Bound Indirectly -----------------------------------------------
 trait ReferencedTrait1 {}
+impl<T> ReferencedTrait1 for T {}
 trait ReferencedTrait2 {}
+impl<T> ReferencedTrait2 for T {}
 
 mod change_trait_bound_indirectly {
     #[cfg(cfail1)]

src/test/run-pass/attr-on-generic-formals.rs

@@ -30,7 +30,7 @@ trait TrLt<#[rustc_lt_trait] 'c> { fn foo(&self, _: &'c [u32]) -> &'c u32; }
 trait TrTy<#[rustc_ty_trait] K> { fn foo(&self, _: K); }
 
 type TyLt<#[rustc_lt_type] 'd> = &'d u32;
-type TyTy<#[rustc_ty_type] L> = (L, );
+type TyTy<#[rustc_ty_type] L> = Option<L>;
 
 impl<#[rustc_lt_inherent] 'e> StLt<'e> { }
 impl<#[rustc_ty_inherent] M> StTy<M> { }

src/test/run-pass/type-param.rs

@@ -12,6 +12,6 @@
 
 // pretty-expanded FIXME #23616
 
-type lteq<T> = extern fn(T) -> bool;
+type lteq<T: ?Sized> = extern fn(T) -> bool;
 
 pub fn main() { }

src/test/ui/consts/const-eval/pub_const_err.stderr

@@ -1,22 +1,22 @@
-warning: this constant cannot be used
-  --> $DIR/pub_const_err.rs:16:1
+warning: attempt to subtract with overflow
+  --> $DIR/pub_const_err.rs:19:22
    |
-LL | pub const Z: u32 = 0 - 1;
-   | ^^^^^^^^^^^^^^^^^^^-----^
-   |                    |
-   |                    attempt to subtract with overflow
+LL | pub type Foo = [i32; 0 - 1];
+   |                      ^^^^^
    |
 note: lint level defined here
   --> $DIR/pub_const_err.rs:12:9
    |
 LL | #![warn(const_err)]
    |         ^^^^^^^^^
 
-warning: attempt to subtract with overflow
-  --> $DIR/pub_const_err.rs:19:22
+warning: this constant cannot be used
+  --> $DIR/pub_const_err.rs:16:1
    |
-LL | pub type Foo = [i32; 0 - 1];
-   |                      ^^^^^
+LL | pub const Z: u32 = 0 - 1;
+   | ^^^^^^^^^^^^^^^^^^^-----^
+   |                    |
+   |                    attempt to subtract with overflow
 
 warning: this array length cannot be used
   --> $DIR/pub_const_err.rs:19:22

src/test/ui/consts/const-eval/pub_const_err_bin.stderr

@@ -1,22 +1,22 @@
-warning: this constant cannot be used
-  --> $DIR/pub_const_err_bin.rs:14:1
+warning: attempt to subtract with overflow
+  --> $DIR/pub_const_err_bin.rs:17:22
    |
-LL | pub const Z: u32 = 0 - 1;
-   | ^^^^^^^^^^^^^^^^^^^-----^
-   |                    |
-   |                    attempt to subtract with overflow
+LL | pub type Foo = [i32; 0 - 1];
+   |                      ^^^^^
    |
 note: lint level defined here
   --> $DIR/pub_const_err_bin.rs:12:9
    |
 LL | #![warn(const_err)]
    |         ^^^^^^^^^
 
-warning: attempt to subtract with overflow
-  --> $DIR/pub_const_err_bin.rs:17:22
+warning: this constant cannot be used
+  --> $DIR/pub_const_err_bin.rs:14:1
    |
-LL | pub type Foo = [i32; 0 - 1];
-   |                      ^^^^^
+LL | pub const Z: u32 = 0 - 1;
+   | ^^^^^^^^^^^^^^^^^^^-----^
+   |                    |
+   |                    attempt to subtract with overflow
 
 warning: this array length cannot be used
   --> $DIR/pub_const_err_bin.rs:17:22

src/test/ui/dst/dst-bad-assign-3.rs

@@ -12,7 +12,7 @@
 
 #![feature(unsized_tuple_coercion)]
 
-type Fat<T> = (isize, &'static str, T);
+type Fat<T: ?Sized> = (isize, &'static str, T);
 
 #[derive(PartialEq,Eq)]
 struct Bar;

src/test/ui/feature-gates/feature-gate-trivial_bounds.rs

@@ -25,7 +25,7 @@ trait T where i32: Foo {} //~ ERROR
 
 union U where i32: Foo { f: i32 } //~ ERROR
 
-type Y where i32: Foo = (); // OK - bound is ignored
+type Y where i32: Foo = (); //~ ERROR
 
 impl Foo for () where i32: Foo { //~ ERROR
     fn test(&self) {

src/test/ui/feature-gates/feature-gate-trivial_bounds.stderr

@@ -34,6 +34,15 @@ LL | union U where i32: Foo { f: i32 } //~ ERROR
    = help: see issue #48214
    = help: add #![feature(trivial_bounds)] to the crate attributes to enable
 
+error[E0277]: the trait bound `i32: Foo` is not satisfied
+  --> $DIR/feature-gate-trivial_bounds.rs:28:1
+   |
+LL | type Y where i32: Foo = (); //~ ERROR
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `i32`
+   |
+   = help: see issue #48214
+   = help: add #![feature(trivial_bounds)] to the crate attributes to enable
+
 error[E0277]: the trait bound `i32: Foo` is not satisfied
   --> $DIR/feature-gate-trivial_bounds.rs:30:1
    |
@@ -125,6 +134,6 @@ LL | | }
    = help: see issue #48214
    = help: add #![feature(trivial_bounds)] to the crate attributes to enable
 
-error: aborting due to 11 previous errors
+error: aborting due to 12 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

src/test/ui/generic/generic-param-attrs.rs

@@ -28,7 +28,7 @@ enum EnTy<#[rustc_ty_enum] J> { A(J), B }
 trait TrLt<#[rustc_lt_trait] 'c> { fn foo(&self, _: &'c [u32]) -> &'c u32; }
 trait TrTy<#[rustc_ty_trait] K> { fn foo(&self, _: K); }
 type TyLt<#[rustc_lt_type] 'd> = &'d u32;
-type TyTy<#[rustc_ty_type] L> = (L, );
+type TyTy<#[rustc_ty_type] L> = Option<L>;
 
 impl<#[rustc_lt_inherent] 'e> StLt<'e> { }
 impl<#[rustc_ty_inherent] M> StTy<M> { }

src/test/ui/issues/issue-47715.rs

@@ -31,7 +31,7 @@ union Union<T: Iterable<Item = impl Foo> + Copy> {
     x: T,
 }
 
-type Type<T: Iterable<Item = impl Foo>> = T;
+type Type<T: Iterable<Item = impl Foo>> = Container<T>;
 //~^ ERROR `impl Trait` not allowed
 
 fn main() {

src/test/ui/issues/issue-47715.stderr

@@ -19,7 +19,7 @@ LL | union Union<T: Iterable<Item = impl Foo> + Copy> {
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
   --> $DIR/issue-47715.rs:34:30
    |
-LL | type Type<T: Iterable<Item = impl Foo>> = T;
+LL | type Type<T: Iterable<Item = impl Foo>> = Container<T>;
    |                              ^^^^^^^^
 
 error: aborting due to 4 previous errors

src/test/ui/issues/issue-6936.rs

@@ -31,7 +31,7 @@ mod t4 {
 }
 
 mod t5 {
-    type Bar<T> = T;
+    type Bar<T: ?Sized> = T;
     mod Bar {} //~ ERROR the name `Bar` is defined multiple times
 }
 

src/test/ui/issues/issue-6936.stderr

@@ -31,8 +31,8 @@ LL |     enum Foo {} //~ ERROR the name `Foo` is defined multiple times
 error[E0428]: the name `Bar` is defined multiple times
   --> $DIR/issue-6936.rs:35:5
    |
-LL |     type Bar<T> = T;
-   |     ---------------- previous definition of the type `Bar` here
+LL |     type Bar<T: ?Sized> = T;
+   |     ------------------------ previous definition of the type `Bar` here
 LL |     mod Bar {} //~ ERROR the name `Bar` is defined multiple times
    |     ^^^^^^^ `Bar` redefined here
    |