Auto merge of #46054 - nikomatsakis:nll-master-to-rust-master-1, r=arielb1

typeck aggregate rvalues in MIR type checker

This branch is an attempt to land content by @spastorino and @Nashenas88 that was initially landed on nll-master while we waited for https://github.com/rust-lang/rust/pull/45825 to land.

The biggest change it contains is that it extends the MIR type-checker to also type-check MIR aggregate rvalues (at least partially). Specifically, it checks that the operands provided for each field have the right type.

It does not yet check that their well-formedness predicates are met. That is https://github.com/rust-lang/rust/issues/45827. It also does not check other kinds of rvalues (that is https://github.com/rust-lang/rust/issues/45959). @spastorino is working on those issues now.

r? @arielb1

9 files changed, 169 insertions, 37 deletions

diff --git a/src/librustc/infer/lexical_region_resolve/mod.rs b/src/librustc/infer/lexical_region_resolve/mod.rs
index 0692d284d7c..5a4f2157298 100644
--- a/src/librustc/infer/lexical_region_resolve/mod.rs
+++ b/src/librustc/infer/lexical_region_resolve/mod.rs
@@ -171,7 +171,7 @@ impl<'cx, 'gcx, 'tcx> LexicalResolver<'cx, 'gcx, 'tcx> {
         for (r, vid) in seeds {
             // While all things transitively reachable in the graph
             // from the variable (`'0` in the example above).
-            let seed_index = NodeIndex(vid.index as usize);
+            let seed_index = NodeIndex(vid.index() as usize);
             for succ_index in graph.depth_traverse(seed_index, OUTGOING) {
                 let succ_index = succ_index.0;
 
@@ -512,16 +512,16 @@ impl<'cx, 'gcx, 'tcx> LexicalResolver<'cx, 'gcx, 'tcx> {
             match *constraint {
                 Constraint::VarSubVar(a_id, b_id) => {
                     graph.add_edge(
-                        NodeIndex(a_id.index as usize),
-                        NodeIndex(b_id.index as usize),
+                        NodeIndex(a_id.index() as usize),
+                        NodeIndex(b_id.index() as usize),
                         *constraint,
                     );
                 }
                 Constraint::RegSubVar(_, b_id) => {
-                    graph.add_edge(dummy_source, NodeIndex(b_id.index as usize), *constraint);
+                    graph.add_edge(dummy_source, NodeIndex(b_id.index() as usize), *constraint);
                 }
                 Constraint::VarSubReg(a_id, _) => {
-                    graph.add_edge(NodeIndex(a_id.index as usize), dummy_sink, *constraint);
+                    graph.add_edge(NodeIndex(a_id.index() as usize), dummy_sink, *constraint);
                 }
                 Constraint::RegSubReg(..) => {
                     // this would be an edge from `dummy_source` to
@@ -630,9 +630,9 @@ impl<'cx, 'gcx, 'tcx> LexicalResolver<'cx, 'gcx, 'tcx> {
             let node_idx = state.stack.pop().unwrap();
 
             // check whether we've visited this node on some previous walk
-            if dup_vec[node_idx.index as usize] == u32::MAX {
-                dup_vec[node_idx.index as usize] = orig_node_idx.index;
-            } else if dup_vec[node_idx.index as usize] != orig_node_idx.index {
+            if dup_vec[node_idx.index() as usize] == u32::MAX {
+                dup_vec[node_idx.index() as usize] = orig_node_idx.index() as u32;
+            } else if dup_vec[node_idx.index() as usize] != orig_node_idx.index() as u32 {
                 state.dup_found = true;
             }
 
@@ -659,7 +659,7 @@ impl<'cx, 'gcx, 'tcx> LexicalResolver<'cx, 'gcx, 'tcx> {
         ) {
             debug!("process_edges(source_vid={:?}, dir={:?})", source_vid, dir);
 
-            let source_node_index = NodeIndex(source_vid.index as usize);
+            let source_node_index = NodeIndex(source_vid.index() as usize);
             for (_, edge) in graph.adjacent_edges(source_node_index, dir) {
                 match edge.data {
                     Constraint::VarSubVar(from_vid, to_vid) => {
diff --git a/src/librustc/infer/region_constraints/mod.rs b/src/librustc/infer/region_constraints/mod.rs
index 096037ebe88..72740dd40be 100644
--- a/src/librustc/infer/region_constraints/mod.rs
+++ b/src/librustc/infer/region_constraints/mod.rs
@@ -16,7 +16,7 @@ use self::CombineMapType::*;
 use super::{MiscVariable, RegionVariableOrigin, SubregionOrigin};
 use super::unify_key;
 
-use rustc_data_structures::indexed_vec::IndexVec;
+use rustc_data_structures::indexed_vec::{IndexVec, Idx};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::unify::{self, UnificationTable};
 use ty::{self, Ty, TyCtxt};
@@ -404,7 +404,7 @@ impl<'tcx> RegionConstraintCollector<'tcx> {
             }
             AddVar(vid) => {
                 self.var_origins.pop().unwrap();
-                assert_eq!(self.var_origins.len(), vid.index as usize);
+                assert_eq!(self.var_origins.len(), vid.index() as usize);
             }
             AddConstraint(ref constraint) => {
                 self.data.constraints.remove(constraint);
diff --git a/src/librustc/infer/unify_key.rs b/src/librustc/infer/unify_key.rs
index d7e3a53ff25..99b11794cc5 100644
--- a/src/librustc/infer/unify_key.rs
+++ b/src/librustc/infer/unify_key.rs
@@ -33,7 +33,7 @@ pub struct RegionVidKey {
 
 impl Combine for RegionVidKey {
     fn combine(&self, other: &RegionVidKey) -> RegionVidKey {
-        let min_vid = if self.min_vid.index < other.min_vid.index {
+        let min_vid = if self.min_vid.index() < other.min_vid.index() {
             self.min_vid
         } else {
             other.min_vid
@@ -45,8 +45,8 @@ impl Combine for RegionVidKey {
 
 impl UnifyKey for ty::RegionVid {
     type Value = RegionVidKey;
-    fn index(&self) -> u32 { self.index }
-    fn from_index(i: u32) -> ty::RegionVid { ty::RegionVid { index: i } }
+    fn index(&self) -> u32 { self.0 }
+    fn from_index(i: u32) -> ty::RegionVid { ty::RegionVid(i) }
     fn tag(_: Option<ty::RegionVid>) -> &'static str { "RegionVid" }
 }
 
diff --git a/src/librustc/mir/mod.rs b/src/librustc/mir/mod.rs
index 355fb570c00..94e8033ed16 100644
--- a/src/librustc/mir/mod.rs
+++ b/src/librustc/mir/mod.rs
@@ -1375,10 +1375,14 @@ pub enum AggregateKind<'tcx> {
     /// The type is of the element
     Array(Ty<'tcx>),
     Tuple,
-    /// The second field is variant number (discriminant), it's equal to 0
-    /// for struct and union expressions. The fourth field is active field
-    /// number and is present only for union expressions.
+
+    /// The second field is variant number (discriminant), it's equal
+    /// to 0 for struct and union expressions. The fourth field is
+    /// active field number and is present only for union expressions
+    /// -- e.g. for a union expression `SomeUnion { c: .. }`, the
+    /// active field index would identity the field `c`
     Adt(&'tcx AdtDef, usize, &'tcx Substs<'tcx>, Option<usize>),
+
     Closure(DefId, ClosureSubsts<'tcx>),
     Generator(DefId, ClosureSubsts<'tcx>, GeneratorInterior<'tcx>),
 }
diff --git a/src/librustc/ty/sty.rs b/src/librustc/ty/sty.rs
index 85755c01d31..caf78309cc2 100644
--- a/src/librustc/ty/sty.rs
+++ b/src/librustc/ty/sty.rs
@@ -998,22 +998,11 @@ pub struct FloatVid {
     pub index: u32,
 }
 
-#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Copy, PartialOrd, Ord)]
-pub struct RegionVid {
-    pub index: u32,
-}
-
-// FIXME: We could convert this to use `newtype_index!`
-impl Idx for RegionVid {
-    fn new(value: usize) -> Self {
-        assert!(value < ::std::u32::MAX as usize);
-        RegionVid { index: value as u32 }
-    }
-
-    fn index(self) -> usize {
-        self.index as usize
-    }
-}
+newtype_index!(RegionVid
+    {
+        pub idx
+        DEBUG_FORMAT = custom,
+    });
 
 #[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, PartialOrd, Ord)]
 pub struct SkolemizedRegionVid {
diff --git a/src/librustc/util/ppaux.rs b/src/librustc/util/ppaux.rs
index 2c3a32b2d15..9ff3d73f5c4 100644
--- a/src/librustc/util/ppaux.rs
+++ b/src/librustc/util/ppaux.rs
@@ -726,7 +726,7 @@ define_print! {
                     }
                 }
                 ty::ReVar(region_vid) if cx.identify_regions => {
-                    write!(f, "'{}rv", region_vid.index)
+                    write!(f, "'{}rv", region_vid.index())
                 }
                 ty::ReScope(_) |
                 ty::ReVar(_) |
@@ -850,7 +850,7 @@ impl fmt::Debug for ty::FloatVid {
 
 impl fmt::Debug for ty::RegionVid {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "'_#{}r", self.index)
+        write!(f, "'_#{}r", self.index())
     }
 }
 
diff --git a/src/librustc_mir/shim.rs b/src/librustc_mir/shim.rs
index d31f3812e9a..15c68954230 100644
--- a/src/librustc_mir/shim.rs
+++ b/src/librustc_mir/shim.rs
@@ -825,10 +825,16 @@ pub fn build_adt_ctor<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
                                       -> Mir<'tcx>
 {
     let tcx = infcx.tcx;
+    let gcx = tcx.global_tcx();
     let def_id = tcx.hir.local_def_id(ctor_id);
-    let sig = tcx.no_late_bound_regions(&tcx.fn_sig(def_id))
+    let sig = gcx.no_late_bound_regions(&gcx.fn_sig(def_id))
         .expect("LBR in ADT constructor signature");
-    let sig = tcx.erase_regions(&sig);
+    let sig = gcx.erase_regions(&sig);
+    let param_env = gcx.param_env(def_id);
+
+    // Normalize the sig now that we have liberated the late-bound
+    // regions.
+    let sig = gcx.normalize_associated_type_in_env(&sig, param_env);
 
     let (adt_def, substs) = match sig.output().sty {
         ty::TyAdt(adt_def, substs) => (adt_def, substs),
diff --git a/src/librustc_mir/transform/type_check.rs b/src/librustc_mir/transform/type_check.rs
index cc6b7020903..ade5cf8b70c 100644
--- a/src/librustc_mir/transform/type_check.rs
+++ b/src/librustc_mir/transform/type_check.rs
@@ -549,6 +549,7 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
                         terr
                     );
                 }
+                self.check_rvalue(mir, rv, location);
             }
             StatementKind::SetDiscriminant {
                 ref lvalue,
@@ -1011,6 +1012,111 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
         }
     }
 
+    fn aggregate_field_ty(
+        &mut self,
+        ak: &Box<AggregateKind<'tcx>>,
+        field_index: usize,
+        location: Location,
+    ) -> Result<Ty<'tcx>, FieldAccessError> {
+        let tcx = self.tcx();
+
+        match **ak {
+            AggregateKind::Adt(def, variant_index, substs, active_field_index) => {
+                let variant = &def.variants[variant_index];
+                let adj_field_index = active_field_index.unwrap_or(field_index);
+                if let Some(field) = variant.fields.get(adj_field_index) {
+                    Ok(self.normalize(&field.ty(tcx, substs), location))
+                } else {
+                    Err(FieldAccessError::OutOfRange {
+                        field_count: variant.fields.len(),
+                    })
+                }
+            }
+            AggregateKind::Closure(def_id, substs) => {
+                match substs.upvar_tys(def_id, tcx).nth(field_index) {
+                    Some(ty) => Ok(ty),
+                    None => Err(FieldAccessError::OutOfRange {
+                        field_count: substs.upvar_tys(def_id, tcx).count(),
+                    }),
+                }
+            }
+            AggregateKind::Generator(def_id, substs, _) => {
+                if let Some(ty) = substs.upvar_tys(def_id, tcx).nth(field_index) {
+                    Ok(ty)
+                } else {
+                    match substs.field_tys(def_id, tcx).nth(field_index) {
+                        Some(ty) => Ok(ty),
+                        None => Err(FieldAccessError::OutOfRange {
+                            field_count: substs.field_tys(def_id, tcx).count() + 1,
+                        }),
+                    }
+                }
+            }
+            AggregateKind::Array(ty) => {
+                Ok(ty)
+            }
+            AggregateKind::Tuple => {
+                unreachable!("This should have been covered in check_rvalues");
+            }
+        }
+    }
+
+    fn check_rvalue(&mut self, mir: &Mir<'tcx>, rv: &Rvalue<'tcx>, location: Location) {
+        let tcx = self.tcx();
+        match rv {
+            Rvalue::Aggregate(ak, ops) => {
+                match **ak {
+                    // tuple rvalue field type is always the type of the op. Nothing to check here.
+                    AggregateKind::Tuple => {}
+                    _ => {
+                        for (i, op) in ops.iter().enumerate() {
+                            let field_ty = match self.aggregate_field_ty(ak, i, location) {
+                                Ok(field_ty) => field_ty,
+                                Err(FieldAccessError::OutOfRange { field_count }) => {
+                                    span_mirbug!(
+                                        self,
+                                        rv,
+                                        "accessed field #{} but variant only has {}",
+                                        i,
+                                        field_count
+                                    );
+                                    continue;
+                                }
+                            };
+                            let op_ty = op.ty(mir, tcx);
+                            if let Err(terr) = self.sub_types(
+                                op_ty,
+                                field_ty,
+                                location.at_successor_within_block(),
+                            )
+                                {
+                                    span_mirbug!(
+                                    self,
+                                    rv,
+                                    "{:?} is not a subtype of {:?}: {:?}",
+                                    op_ty,
+                                    field_ty,
+                                    terr
+                                );
+                                }
+                        }
+                    }
+                }
+            }
+            // FIXME: These other cases have to be implemented in future PRs
+            Rvalue::Use(..) |
+            Rvalue::Repeat(..) |
+            Rvalue::Ref(..) |
+            Rvalue::Len(..) |
+            Rvalue::Cast(..) |
+            Rvalue::BinaryOp(..) |
+            Rvalue::CheckedBinaryOp(..) |
+            Rvalue::UnaryOp(..) |
+            Rvalue::Discriminant(..) |
+            Rvalue::NullaryOp(..) => {}
+        }
+    }
+
     fn typeck_mir(&mut self, mir: &Mir<'tcx>) {
         self.last_span = mir.span;
         debug!("run_on_mir: {:?}", mir.span);
diff --git a/src/test/compile-fail/nll/reference-carried-through-struct-field.rs b/src/test/compile-fail/nll/reference-carried-through-struct-field.rs
new file mode 100644
index 00000000000..afde2540829
--- /dev/null
+++ b/src/test/compile-fail/nll/reference-carried-through-struct-field.rs
@@ -0,0 +1,27 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+//revisions: ast mir
+//[mir] compile-flags: -Z emit-end-regions -Z borrowck-mir -Z nll
+
+#![allow(unused_assignments)]
+
+struct Wrap<'a> { w: &'a mut u32 }
+
+fn foo() {
+    let mut x = 22;
+    let wrapper = Wrap { w: &mut x };
+    x += 1; //[ast]~ ERROR cannot assign to `x` because it is borrowed [E0506]
+    //[mir]~^ ERROR cannot assign to `x` because it is borrowed (Ast) [E0506]
+    //[mir]~^^ ERROR cannot assign to `x` because it is borrowed (Mir) [E0506]
+    //[mir]~^^^ ERROR cannot use `x` because it was mutably borrowed (Mir) [E0503]
+    *wrapper.w += 1;
+}
+
+fn main() { }
\ No newline at end of file