Auto merge of #63497 - eddyb:miri-subst, r=oli-obk

rustc_mir: fix miri substitution/"universe" discipline.

Alternative to #61041, based on @RalfJung's own attempt at it.
I haven't done a full audit, but I believe everything is fixed now.

Fixes #61432.
Closes #61336, as a drive-by fix (for a subset of #43408, that is already special-cased).

r? @oli-obk / @RalfJung cc @varkor @yodaldevoid

src/librustc_mir/interpret/cast.rs

@@ -1,4 +1,4 @@
-use rustc::ty::{self, Ty, TypeAndMut};
+use rustc::ty::{self, Ty, TypeAndMut, TypeFoldable};
 use rustc::ty::layout::{self, TyLayout, Size};
 use rustc::ty::adjustment::{PointerCast};
 use syntax::ast::FloatTy;
@@ -36,15 +36,15 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 // The src operand does not matter, just its type
                 match src.layout.ty.sty {
                     ty::FnDef(def_id, substs) => {
+                        // All reifications must be monomorphic, bail out otherwise.
+                        if src.layout.ty.needs_subst() {
+                            throw_inval!(TooGeneric);
+                        }
+
                         if self.tcx.has_attr(def_id, sym::rustc_args_required_const) {
                             bug!("reifying a fn ptr that requires const arguments");
                         }
-                        let instance = ty::Instance::resolve(
+                        let instance = self.resolve(def_id, substs)?;
-                            *self.tcx,
-                            self.param_env,
-                            def_id,
-                            substs,
-                        ).ok_or_else(|| err_inval!(TooGeneric))?;
                         let fn_ptr = self.memory.create_fn_alloc(FnVal::Instance(instance));
                         self.write_scalar(Scalar::Ptr(fn_ptr.into()), dest)?;
                     }
@@ -67,7 +67,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 // The src operand does not matter, just its type
                 match src.layout.ty.sty {
                     ty::Closure(def_id, substs) => {
-                        let substs = self.subst_and_normalize_erasing_regions(substs)?;
+                        // All reifications must be monomorphic, bail out otherwise.
+                        if src.layout.ty.needs_subst() {
+                            throw_inval!(TooGeneric);
+                        }
+
                         let instance = ty::Instance::resolve_closure(
                             *self.tcx,
                             def_id,

src/librustc_mir/interpret/eval_context.rs

@@ -9,7 +9,7 @@ use rustc::mir;
 use rustc::ty::layout::{
     self, Size, Align, HasDataLayout, LayoutOf, TyLayout
 };
-use rustc::ty::subst::{Subst, SubstsRef};
+use rustc::ty::subst::SubstsRef;
 use rustc::ty::{self, Ty, TyCtxt, TypeFoldable};
 use rustc::ty::query::TyCtxtAt;
 use rustc_data_structures::indexed_vec::IndexVec;
@@ -291,41 +291,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         ty.is_freeze(*self.tcx, self.param_env, DUMMY_SP)
     }
 
-    pub(super) fn subst_and_normalize_erasing_regions<T: TypeFoldable<'tcx>>(
-        &self,
-        substs: T,
-    ) -> InterpResult<'tcx, T> {
-        match self.stack.last() {
-            Some(frame) => Ok(self.tcx.subst_and_normalize_erasing_regions(
-                frame.instance.substs,
-                self.param_env,
-                &substs,
-            )),
-            None => if substs.needs_subst() {
-                throw_inval!(TooGeneric)
-            } else {
-                Ok(substs)
-            },
-        }
-    }
-
-    pub(super) fn resolve(
-        &self,
-        def_id: DefId,
-        substs: SubstsRef<'tcx>
-    ) -> InterpResult<'tcx, ty::Instance<'tcx>> {
-        trace!("resolve: {:?}, {:#?}", def_id, substs);
-        trace!("param_env: {:#?}", self.param_env);
-        let substs = self.subst_and_normalize_erasing_regions(substs)?;
-        trace!("substs: {:#?}", substs);
-        ty::Instance::resolve(
-            *self.tcx,
-            self.param_env,
-            def_id,
-            substs,
-        ).ok_or_else(|| err_inval!(TooGeneric).into())
-    }
-
     pub fn load_mir(
         &self,
         instance: ty::InstanceDef<'tcx>,
@@ -349,34 +314,34 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         }
     }
 
-    pub(super) fn monomorphize<T: TypeFoldable<'tcx> + Subst<'tcx>>(
+    /// Call this on things you got out of the MIR (so it is as generic as the current
+    /// stack frame), to bring it into the proper environment for this interpreter.
+    pub(super) fn subst_from_frame_and_normalize_erasing_regions<T: TypeFoldable<'tcx>>(
         &self,
-        t: T,
+        value: T,
-    ) -> InterpResult<'tcx, T> {
+    ) -> T {
-        match self.stack.last() {
+        self.tcx.subst_and_normalize_erasing_regions(
-            Some(frame) => Ok(self.monomorphize_with_substs(t, frame.instance.substs)?),
+            self.frame().instance.substs,
-            None => if t.needs_subst() {
+            self.param_env,
-                throw_inval!(TooGeneric)
+            &value,
-            } else {
+        )
-                Ok(t)
-            },
-        }
     }
 
-    fn monomorphize_with_substs<T: TypeFoldable<'tcx> + Subst<'tcx>>(
+    /// The `substs` are assumed to already be in our interpreter "universe" (param_env).
+    pub(super) fn resolve(
         &self,
-        t: T,
+        def_id: DefId,
         substs: SubstsRef<'tcx>
-    ) -> InterpResult<'tcx, T> {
+    ) -> InterpResult<'tcx, ty::Instance<'tcx>> {
-        // miri doesn't care about lifetimes, and will choke on some crazy ones
+        trace!("resolve: {:?}, {:#?}", def_id, substs);
-        // let's simply get rid of them
+        trace!("param_env: {:#?}", self.param_env);
-        let substituted = t.subst(*self.tcx, substs);
+        trace!("substs: {:#?}", substs);
-
+        ty::Instance::resolve(
-        if substituted.needs_subst() {
+            *self.tcx,
-            throw_inval!(TooGeneric)
+            self.param_env,
-        }
+            def_id,
-
+            substs,
-        Ok(self.tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), substituted))
+        ).ok_or_else(|| err_inval!(TooGeneric).into())
     }
 
     pub fn layout_of_local(
@@ -391,7 +356,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             None => {
                 let layout = crate::interpret::operand::from_known_layout(layout, || {
                     let local_ty = frame.body.local_decls[local].ty;
-                    let local_ty = self.monomorphize_with_substs(local_ty, frame.instance.substs)?;
+                    let local_ty = self.tcx.subst_and_normalize_erasing_regions(
+                        frame.instance.substs,
+                        self.param_env,
+                        &local_ty,
+                    );
                     self.layout_of(local_ty)
                 })?;
                 if let Some(state) = frame.locals.get(local) {

src/librustc_mir/interpret/operand.rs

@@ -522,7 +522,10 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             Move(ref place) =>
                 self.eval_place_to_op(place, layout)?,
 
-            Constant(ref constant) => self.eval_const_to_op(constant.literal, layout)?,
+            Constant(ref constant) => {
+                let val = self.subst_from_frame_and_normalize_erasing_regions(constant.literal);
+                self.eval_const_to_op(val, layout)?
+            }
         };
         trace!("{:?}: {:?}", mir_op, *op);
         Ok(op)
@@ -540,6 +543,8 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
     // Used when the miri-engine runs into a constant and for extracting information from constants
     // in patterns via the `const_eval` module
+    /// The `val` and `layout` are assumed to already be in our interpreter
+    /// "universe" (param_env).
     crate fn eval_const_to_op(
         &self,
         val: &'tcx ty::Const<'tcx>,
@@ -552,7 +557,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // Early-return cases.
         match val.val {
             ConstValue::Param(_) =>
-                // FIXME(oli-obk): try to monomorphize
                 throw_inval!(TooGeneric),
             ConstValue::Unevaluated(def_id, substs) => {
                 let instance = self.resolve(def_id, substs)?;
@@ -565,7 +569,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         }
         // Other cases need layout.
         let layout = from_known_layout(layout, || {
-            self.layout_of(self.monomorphize(val.ty)?)
+            self.layout_of(val.ty)
         })?;
         let op = match val.val {
             ConstValue::ByRef { alloc, offset } => {

src/librustc_mir/interpret/place.rs

@@ -640,8 +640,11 @@ where
                         // their layout on return.
                         PlaceTy {
                             place: *return_place,
-                            layout: self
+                            layout: self.layout_of(
-                                .layout_of(self.monomorphize(self.frame().body.return_ty())?)?,
+                                self.subst_from_frame_and_normalize_erasing_regions(
+                                    self.frame().body.return_ty()
+                                )
+                            )?,
                         }
                     }
                     None => throw_unsup!(InvalidNullPointerUsage),

src/librustc_mir/interpret/step.rs

@@ -254,7 +254,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
 
             NullaryOp(mir::NullOp::SizeOf, ty) => {
-                let ty = self.monomorphize(ty)?;
+                let ty = self.subst_from_frame_and_normalize_erasing_regions(ty);
                 let layout = self.layout_of(ty)?;
                 assert!(!layout.is_unsized(),
                         "SizeOf nullary MIR operator called for unsized type");

src/librustc_mir/interpret/traits.rs

@@ -1,4 +1,4 @@
-use rustc::ty::{self, Ty, Instance};
+use rustc::ty::{self, Ty, Instance, TypeFoldable};
 use rustc::ty::layout::{Size, Align, LayoutOf};
 use rustc::mir::interpret::{Scalar, Pointer, InterpResult, PointerArithmetic,};
 
@@ -20,6 +20,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
         let (ty, poly_trait_ref) = self.tcx.erase_regions(&(ty, poly_trait_ref));
 
+        // All vtables must be monomorphic, bail out otherwise.
+        if ty.needs_subst() || poly_trait_ref.needs_subst() {
+            throw_inval!(TooGeneric);
+        }
+
         if let Some(&vtable) = self.vtables.get(&(ty, poly_trait_ref)) {
             // This means we guarantee that there are no duplicate vtables, we will
             // always use the same vtable for the same (Type, Trait) combination.
@@ -77,7 +82,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         for (i, method) in methods.iter().enumerate() {
             if let Some((def_id, substs)) = *method {
                 // resolve for vtable: insert shims where needed
-                let substs = self.subst_and_normalize_erasing_regions(substs)?;
                 let instance = ty::Instance::resolve_for_vtable(
                     *self.tcx,
                     self.param_env,

src/librustc_typeck/collect.rs

@@ -900,6 +900,20 @@ fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::Generics {
             let parent_id = tcx.hir().get_parent_item(hir_id);
             Some(tcx.hir().local_def_id(parent_id))
         }
+        // FIXME(#43408) enable this in all cases when we get lazy normalization.
+        Node::AnonConst(&anon_const) => {
+            // HACK(eddyb) this provides the correct generics when the workaround
+            // for a const parameter `AnonConst` is being used elsewhere, as then
+            // there won't be the kind of cyclic dependency blocking #43408.
+            let expr = &tcx.hir().body(anon_const.body).value;
+            let icx = ItemCtxt::new(tcx, def_id);
+            if AstConv::const_param_def_id(&icx, expr).is_some() {
+                let parent_id = tcx.hir().get_parent_item(hir_id);
+                Some(tcx.hir().local_def_id(parent_id))
+            } else {
+                None
+            }
+        }
         Node::Expr(&hir::Expr {
             node: hir::ExprKind::Closure(..),
             ..

src/test/ui/const-generics/issue-61432.rs

@@ -0,0 +1,17 @@
+// run-pass
+
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+fn promote<const N: i32>() {
+    // works:
+    //
+    // let n = N;
+    // &n;
+
+    &N;
+}
+
+fn main() {
+    promote::<0>();
+}

src/test/ui/const-generics/issue-61432.stderr

@@ -0,0 +1,8 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-61432.rs:3:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+

src/test/ui/consts/too_generic_eval_ice.rs

@@ -0,0 +1,13 @@
+pub struct Foo<A, B>(A, B);
+
+impl<A, B> Foo<A, B> {
+    const HOST_SIZE: usize = std::mem::size_of::<B>();
+
+    pub fn crash() -> bool {
+        [5; Self::HOST_SIZE] == [6; 0] //~ ERROR no associated item named `HOST_SIZE`
+        //~^ the size for values of type `A` cannot be known
+        //~| the size for values of type `B` cannot be known
+    }
+}
+
+fn main() {}

src/test/ui/consts/too_generic_eval_ice.stderr

@@ -0,0 +1,47 @@
+error[E0599]: no associated item named `HOST_SIZE` found for type `Foo<A, B>` in the current scope
+  --> $DIR/too_generic_eval_ice.rs:7:19
+   |
+LL | pub struct Foo<A, B>(A, B);
+   | --------------------------- associated item `HOST_SIZE` not found for this
+...
+LL |         [5; Self::HOST_SIZE] == [6; 0]
+   |                   ^^^^^^^^^ associated item not found in `Foo<A, B>`
+   |
+   = note: the method `HOST_SIZE` exists but the following trait bounds were not satisfied:
+           `A : std::marker::Sized`
+           `B : std::marker::Sized`
+
+error[E0277]: the size for values of type `A` cannot be known at compilation time
+  --> $DIR/too_generic_eval_ice.rs:7:13
+   |
+LL |         [5; Self::HOST_SIZE] == [6; 0]
+   |             ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `std::marker::Sized` is not implemented for `A`
+   = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+   = help: consider adding a `where A: std::marker::Sized` bound
+note: required by `Foo`
+  --> $DIR/too_generic_eval_ice.rs:1:1
+   |
+LL | pub struct Foo<A, B>(A, B);
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the size for values of type `B` cannot be known at compilation time
+  --> $DIR/too_generic_eval_ice.rs:7:13
+   |
+LL |         [5; Self::HOST_SIZE] == [6; 0]
+   |             ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `std::marker::Sized` is not implemented for `B`
+   = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+   = help: consider adding a `where B: std::marker::Sized` bound
+note: required by `Foo`
+  --> $DIR/too_generic_eval_ice.rs:1:1
+   |
+LL | pub struct Foo<A, B>(A, B);
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0277, E0599.
+For more information about an error, try `rustc --explain E0277`.