Initial work for doing minimum capture analysis for RFC-2229

Co-authored-by: Chris Pardy <chrispardy36@gmail.com>
Co-authored-by: Logan Mosier <logmosier@gmail.com>

Author: 3 people

compiler/rustc_middle/src/ty/context.rs

@@ -415,9 +415,10 @@ pub struct TypeckResults<'tcx> {
     /// entire variable.
     pub closure_captures: ty::UpvarListMap,
 
-    /// Given the closure ID this map provides the list of
-    /// `Place`s and how/why are they captured by the closure.
-    pub closure_capture_information: ty::CaptureInformationMap<'tcx>,
+    /// Given the closure DefId this map provides a map of
+    /// root variables to minimum set of `Place`s (and how) that need to be tracked
+    /// to support all captures of that closure.
+    pub closure_min_captures: ty::MinCaptureInformationMap<'tcx>,
 
     /// Stores the type, expression, span and optional scope span of all types
     /// that are live across the yield of this generator (if a generator).
@@ -446,7 +447,7 @@ impl<'tcx> TypeckResults<'tcx> {
             tainted_by_errors: None,
             concrete_opaque_types: Default::default(),
             closure_captures: Default::default(),
-            closure_capture_information: Default::default(),
+            closure_min_captures: Default::default(),
             generator_interior_types: Default::default(),
         }
     }
@@ -681,7 +682,7 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for TypeckResults<'tcx> {
             tainted_by_errors,
             ref concrete_opaque_types,
             ref closure_captures,
-            ref closure_capture_information,
+            ref closure_min_captures,
             ref generator_interior_types,
         } = *self;
 
@@ -715,7 +716,7 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for TypeckResults<'tcx> {
             tainted_by_errors.hash_stable(hcx, hasher);
             concrete_opaque_types.hash_stable(hcx, hasher);
             closure_captures.hash_stable(hcx, hasher);
-            closure_capture_information.hash_stable(hcx, hasher);
+            closure_min_captures.hash_stable(hcx, hasher);
             generator_interior_types.hash_stable(hcx, hasher);
         })
     }

compiler/rustc_middle/src/ty/mod.rs

@@ -788,30 +788,18 @@ pub struct CaptureInfo<'tcx> {
     pub capture_kind: UpvarCapture<'tcx>,
 }
 
+#[derive(PartialEq, Clone, Debug, TyEncodable, TyDecodable, HashStable)]
+pub struct CapturedPlace<'tcx> {
+    pub place: HirPlace<'tcx>,
+    pub info: CaptureInfo<'tcx>,
+}
+
 pub type UpvarListMap = FxHashMap<DefId, FxIndexMap<hir::HirId, UpvarId>>;
 pub type UpvarCaptureMap<'tcx> = FxHashMap<UpvarId, UpvarCapture<'tcx>>;
 
-/// Consider closure where s.str1 is captured via an ImmutableBorrow and s.str2 via a MutableBorrow
-///
-/// ```rust
-/// // Assume that thte HirId for the variable definition is `V1`
-/// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") }
-///
-/// let fix_s = |new_s2| {
-///     // Assume that the HirId for the expression `s.str1` is `E1`
-///     println!("Updating SomeStruct with str1=", s.str1);
-///     // Assume that the HirId for the expression `*s.str2` is `E2`
-///     s.str2 = new_s2;
-/// }
-/// ```
-///
-/// For closure `fix_s`, (at a high level) the IndexMap will contain:
-///
-/// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
-/// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
-///
-pub type CaptureInformationMap<'tcx> =
-    FxHashMap<DefId, FxIndexMap<HirPlace<'tcx>, CaptureInfo<'tcx>>>;
+pub type MinCaptureList<'tcx> = Vec<CapturedPlace<'tcx>>;
+pub type RootVariableMinCaptureList<'tcx> = FxIndexMap<hir::HirId, MinCaptureList<'tcx>>;
+pub type MinCaptureInformationMap<'tcx> = FxHashMap<DefId, RootVariableMinCaptureList<'tcx>>;
 
 #[derive(Clone, Copy, PartialEq, Eq)]
 pub enum IntVarValue {

compiler/rustc_mir/src/borrow_check/diagnostics/mod.rs

@@ -383,16 +383,14 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     self.describe_field_from_ty(&ty, field, variant_index)
                 }
                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
-                    // `tcx.upvars_mentioned(def_id)` returns an `Option`, which is `None` in case
-                    // the closure comes from another crate. But in that case we wouldn't
-                    // be borrowck'ing it, so we can just unwrap:
-                    let (&var_id, _) = self
-                        .infcx
-                        .tcx
-                        .upvars_mentioned(def_id)
-                        .unwrap()
-                        .get_index(field.index())
-                        .unwrap();
+                    // We won't be borrowck'ing here if the closure came from another crate,
+                    // so it's safe to call `expect_local`.
+                    //
+                    // We know the field exists so it's safe to call operator[] and `unwrap` here.
+                    let (&var_id, _) =
+                        self.infcx.tcx.typeck(def_id.expect_local()).closure_captures[&def_id]
+                            .get_index(field.index())
+                            .unwrap();
 
                     self.infcx.tcx.hir().name(var_id).to_string()
                 }
@@ -967,9 +965,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
         if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
-            for ((upvar_hir_id, upvar), place) in
-                self.infcx.tcx.upvars_mentioned(def_id)?.iter().zip(places)
+            for (upvar_hir_id, place) in
+                self.infcx.tcx.typeck(def_id.expect_local()).closure_captures[&def_id]
+                    .keys()
+                    .zip(places)
             {
+                let span = self.infcx.tcx.upvars_mentioned(local_did)?[upvar_hir_id].span;
                 match place {
                     Operand::Copy(place) | Operand::Move(place)
                         if target_place == place.as_ref() =>
@@ -991,7 +992,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         let usage_span =
                             match self.infcx.tcx.typeck(local_did).upvar_capture(upvar_id) {
                                 ty::UpvarCapture::ByValue(Some(span)) => span,
-                                _ => upvar.span,
+                                _ => span,
                             };
                         return Some((*args_span, generator_kind, usage_span));
                     }