Improve cannot move out of error message

Author: obeis

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -39,7 +39,7 @@ use crate::{
 
 use super::{
     explain_borrow::{BorrowExplanation, LaterUseKind},
-    IncludingDowncast, RegionName, RegionNameSource, UseSpans,
+    DescribePlaceOpt, RegionName, RegionNameSource, UseSpans,
 };
 
 #[derive(Debug)]
@@ -137,7 +137,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 span,
                 desired_action.as_noun(),
                 partially_str,
-                self.describe_place_with_options(moved_place, IncludingDowncast(true)),
+                self.describe_place_with_options(
+                    moved_place,
+                    DescribePlaceOpt { including_downcast: true, including_tuple_field: true },
+                ),
             );
 
             let reinit_spans = maybe_reinitialized_locations
@@ -274,8 +277,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 }
             }
 
-            let opt_name =
-                self.describe_place_with_options(place.as_ref(), IncludingDowncast(true));
+            let opt_name = self.describe_place_with_options(
+                place.as_ref(),
+                DescribePlaceOpt { including_downcast: true, including_tuple_field: true },
+            );
             let note_msg = match opt_name {
                 Some(ref name) => format!("`{}`", name),
                 None => "value".to_owned(),
@@ -341,12 +346,17 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             }
         }
 
-        let (name, desc) =
-            match self.describe_place_with_options(moved_place, IncludingDowncast(true)) {
-                Some(name) => (format!("`{name}`"), format!("`{name}` ")),
-                None => ("the variable".to_string(), String::new()),
-            };
-        let path = match self.describe_place_with_options(used_place, IncludingDowncast(true)) {
+        let (name, desc) = match self.describe_place_with_options(
+            moved_place,
+            DescribePlaceOpt { including_downcast: true, including_tuple_field: true },
+        ) {
+            Some(name) => (format!("`{name}`"), format!("`{name}` ")),
+            None => ("the variable".to_string(), String::new()),
+        };
+        let path = match self.describe_place_with_options(
+            used_place,
+            DescribePlaceOpt { including_downcast: true, including_tuple_field: true },
+        ) {
             Some(name) => format!("`{name}`"),
             None => "value".to_string(),
         };

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -4,7 +4,7 @@ use itertools::Itertools;
 use rustc_const_eval::util::{call_kind, CallDesugaringKind};
 use rustc_errors::{Applicability, Diagnostic};
 use rustc_hir as hir;
-use rustc_hir::def::Namespace;
+use rustc_hir::def::{CtorKind, Namespace};
 use rustc_hir::GeneratorKind;
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::mir::tcx::PlaceTy;
@@ -16,7 +16,7 @@ use rustc_middle::ty::print::Print;
 use rustc_middle::ty::{self, DefIdTree, Instance, Ty, TyCtxt};
 use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult};
 use rustc_span::def_id::LocalDefId;
-use rustc_span::{symbol::sym, Span, DUMMY_SP};
+use rustc_span::{symbol::sym, Span, Symbol, DUMMY_SP};
 use rustc_target::abi::VariantIdx;
 use rustc_trait_selection::traits::type_known_to_meet_bound_modulo_regions;
 
@@ -43,7 +43,15 @@ pub(crate) use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionError
 pub(crate) use region_name::{RegionName, RegionNameSource};
 pub(crate) use rustc_const_eval::util::CallKind;
 
-pub(super) struct IncludingDowncast(pub(super) bool);
+pub(super) struct DescribePlaceOpt {
+    pub including_downcast: bool,
+
+    /// Enable/Disable tuple fields.
+    /// For example `x` tuple. if it's `true` `x.0`. Otherwise `x`
+    pub including_tuple_field: bool,
+}
+
+pub(super) struct IncludingTupleField(pub(super) bool);
 
 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
     /// Adds a suggestion when a closure is invoked twice with a moved variable or when a closure
@@ -164,7 +172,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
     /// End-user visible description of `place` if one can be found.
     /// If the place is a temporary for instance, `None` will be returned.
     pub(super) fn describe_place(&self, place_ref: PlaceRef<'tcx>) -> Option<String> {
-        self.describe_place_with_options(place_ref, IncludingDowncast(false))
+        self.describe_place_with_options(
+            place_ref,
+            DescribePlaceOpt { including_downcast: false, including_tuple_field: true },
+        )
     }
 
     /// End-user visible description of `place` if one can be found. If the place is a temporary
@@ -174,7 +185,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
     pub(super) fn describe_place_with_options(
         &self,
         place: PlaceRef<'tcx>,
-        including_downcast: IncludingDowncast,
+        opt: DescribePlaceOpt,
     ) -> Option<String> {
         let local = place.local;
         let mut autoderef_index = None;
@@ -224,7 +235,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         }
                     }
                 }
-                ProjectionElem::Downcast(..) if including_downcast.0 => return None,
+                ProjectionElem::Downcast(..) if opt.including_downcast => return None,
                 ProjectionElem::Downcast(..) => (),
                 ProjectionElem::Field(field, _ty) => {
                     // FIXME(project-rfc_2229#36): print capture precisely here.
@@ -238,9 +249,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         let field_name = self.describe_field(
                             PlaceRef { local, projection: place.projection.split_at(index).0 },
                             *field,
+                            IncludingTupleField(opt.including_tuple_field),
                         );
-                        buf.push('.');
-                        buf.push_str(&field_name);
+                        if let Some(field_name_str) = field_name {
+                            buf.push('.');
+                            buf.push_str(&field_name_str);
+                        }
                     }
                 }
                 ProjectionElem::Index(index) => {
@@ -261,6 +275,18 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         ok.ok().map(|_| buf)
     }
 
+    fn describe_name(&self, place: PlaceRef<'tcx>) -> Option<Symbol> {
+        for elem in place.projection.into_iter() {
+            match elem {
+                ProjectionElem::Downcast(Some(name), _) => {
+                    return Some(*name);
+                }
+                _ => {}
+            }
+        }
+        None
+    }
+
     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
     /// a name, or its name was generated by the compiler, then `Err` is returned
     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
@@ -275,7 +301,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
     }
 
     /// End-user visible description of the `field`nth field of `base`
-    fn describe_field(&self, place: PlaceRef<'tcx>, field: Field) -> String {
+    fn describe_field(
+        &self,
+        place: PlaceRef<'tcx>,
+        field: Field,
+        including_tuple_field: IncludingTupleField,
+    ) -> Option<String> {
         let place_ty = match place {
             PlaceRef { local, projection: [] } => PlaceTy::from_ty(self.body.local_decls[local].ty),
             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
@@ -289,7 +320,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 ProjectionElem::Field(_, field_type) => PlaceTy::from_ty(*field_type),
             },
         };
-        self.describe_field_from_ty(place_ty.ty, field, place_ty.variant_index)
+        self.describe_field_from_ty(
+            place_ty.ty,
+            field,
+            place_ty.variant_index,
+            including_tuple_field,
+        )
     }
 
     /// End-user visible description of the `field_index`nth field of `ty`
@@ -298,10 +334,11 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         ty: Ty<'_>,
         field: Field,
         variant_index: Option<VariantIdx>,
-    ) -> String {
+        including_tuple_field: IncludingTupleField,
+    ) -> Option<String> {
         if ty.is_box() {
             // If the type is a box, the field is described from the boxed type
-            self.describe_field_from_ty(ty.boxed_ty(), field, variant_index)
+            self.describe_field_from_ty(ty.boxed_ty(), field, variant_index, including_tuple_field)
         } else {
             match *ty.kind() {
                 ty::Adt(def, _) => {
@@ -311,14 +348,17 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     } else {
                         def.non_enum_variant()
                     };
-                    variant.fields[field.index()].name.to_string()
+                    if !including_tuple_field.0 && variant.ctor_kind == CtorKind::Fn {
+                        return None;
+                    }
+                    Some(variant.fields[field.index()].name.to_string())
                 }
-                ty::Tuple(_) => field.index().to_string(),
+                ty::Tuple(_) => Some(field.index().to_string()),
                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
-                    self.describe_field_from_ty(ty, field, variant_index)
+                    self.describe_field_from_ty(ty, field, variant_index, including_tuple_field)
                 }
                 ty::Array(ty, _) | ty::Slice(ty) => {
-                    self.describe_field_from_ty(ty, field, variant_index)
+                    self.describe_field_from_ty(ty, field, variant_index, including_tuple_field)
                 }
                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
                     // We won't be borrowck'ing here if the closure came from another crate,
@@ -335,7 +375,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         .unwrap()
                         .get_root_variable();
 
-                    self.infcx.tcx.hir().name(var_id).to_string()
+                    Some(self.infcx.tcx.hir().name(var_id).to_string())
                 }
                 _ => {
                     // Might need a revision when the fields in trait RFC is implemented

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -6,7 +6,7 @@ use rustc_mir_dataflow::move_paths::{
 };
 use rustc_span::Span;
 
-use crate::diagnostics::UseSpans;
+use crate::diagnostics::{DescribePlaceOpt, UseSpans};
 use crate::prefixes::PrefixSet;
 use crate::MirBorrowckCtxt;
 
@@ -368,13 +368,31 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             }
             _ => {
                 let source = self.borrowed_content_source(deref_base);
-                match (self.describe_place(move_place.as_ref()), source.describe_for_named_place())
-                {
-                    (Some(place_desc), Some(source_desc)) => self.cannot_move_out_of(
+                let move_place_ref = move_place.as_ref();
+                match (
+                    self.describe_place_with_options(
+                        move_place_ref,
+                        DescribePlaceOpt {
+                            including_downcast: false,
+                            including_tuple_field: false,
+                        },
+                    ),
+                    self.describe_name(move_place_ref),
+                    source.describe_for_named_place(),
+                ) {
+                    (Some(place_desc), Some(name), Some(source_desc)) => self.cannot_move_out_of(
+                        span,
+                        &format!("`{place_desc}` as enum variant `{name}` which is behind a {source_desc}"),
+                    ),
+                    (Some(place_desc), Some(name), None) => self.cannot_move_out_of(
+                        span,
+                        &format!("`{place_desc}` as enum variant `{name}`"),
+                    ),
+                    (Some(place_desc), _, Some(source_desc)) => self.cannot_move_out_of(
                         span,
                         &format!("`{place_desc}` which is behind a {source_desc}"),
                     ),
-                    (_, _) => self.cannot_move_out_of(
+                    (_, _, _) => self.cannot_move_out_of(
                         span,
                         &source.describe_for_unnamed_place(self.infcx.tcx),
                     ),

src/test/ui/borrowck/access-mode-in-closures.stderr

@@ -1,4 +1,4 @@
-error[E0507]: cannot move out of `s.0` which is behind a shared reference
+error[E0507]: cannot move out of `s` which is behind a shared reference
   --> $DIR/access-mode-in-closures.rs:8:15
    |
 LL |         match *s { S(v) => v }

src/test/ui/borrowck/borrowck-move-error-with-note.stderr

@@ -1,4 +1,4 @@
-error[E0507]: cannot move out of `f.0` which is behind a shared reference
+error[E0507]: cannot move out of `f` as enum variant `Foo1` which is behind a shared reference
   --> $DIR/borrowck-move-error-with-note.rs:11:11
    |
 LL |     match *f {

src/test/ui/moves/issue-99470-move-out-of-some.rs

@@ -0,0 +1,9 @@
+fn main() {
+    let x: &Option<Box<i32>> = &Some(Box::new(0));
+
+    match x {
+    //~^ ERROR cannot move out of `x` as enum variant `Some` which is behind a shared reference
+        &Some(_y) => (),
+        &None => (),
+    }
+}

src/test/ui/moves/issue-99470-move-out-of-some.stderr

@@ -0,0 +1,16 @@
+error[E0507]: cannot move out of `x` as enum variant `Some` which is behind a shared reference
+  --> $DIR/issue-99470-move-out-of-some.rs:4:11
+   |
+LL |     match x {
+   |           ^
+LL |
+LL |         &Some(_y) => (),
+   |         ---------
+   |         |     |
+   |         |     data moved here
+   |         |     move occurs because `_y` has type `Box<i32>`, which does not implement the `Copy` trait
+   |         help: consider removing the `&`: `Some(_y)`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0507`.

src/test/ui/moves/moves-based-on-type-block-bad.stderr

@@ -1,4 +1,4 @@
-error[E0507]: cannot move out of `hellothere.x.0` which is behind a shared reference
+error[E0507]: cannot move out of `hellothere.x` as enum variant `Bar` which is behind a shared reference
   --> $DIR/moves-based-on-type-block-bad.rs:22:19
    |
 LL |             match hellothere.x {

src/test/ui/nll/move-errors.stderr

@@ -45,7 +45,7 @@ LL |     let a = [A("".to_string())][0];
    |             move occurs because value has type `A`, which does not implement the `Copy` trait
    |             help: consider borrowing here: `&[A("".to_string())][0]`
 
-error[E0507]: cannot move out of `a.0` which is behind a shared reference
+error[E0507]: cannot move out of `a` which is behind a shared reference
   --> $DIR/move-errors.rs:38:16
    |
 LL |     let A(s) = *a;
@@ -134,7 +134,7 @@ LL |         F(s, mut t) => (),
    |
    = note: move occurs because these variables have types that don't implement the `Copy` trait
 
-error[E0507]: cannot move out of `x.0` which is behind a shared reference
+error[E0507]: cannot move out of `x` as enum variant `Err` which is behind a shared reference
   --> $DIR/move-errors.rs:110:11
    |
 LL |     match *x {