Auto merge of #116300 - cjgillot:split-move, r=petrochenkov

Separate move path tracking between borrowck and drop elaboration.

The primary goal of this PR is to skip creating a `MovePathIndex` for path that do not need dropping in drop elaboration.

The 2 first commits are cleanups.

The next 2 commits displace `move` errors from move-path builder to borrowck. Move-path builder keeps the same logic, but does not carry error information any more.

The remaining commits allow to filter `MovePathIndex` creation according to types. This is used in drop elaboration, to avoid computing dataflow for paths that do not need dropping.

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2633,9 +2633,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         /* Check if the mpi is initialized as an argument */
         let mut is_argument = false;
         for arg in self.body.args_iter() {
-            let path = self.move_data.rev_lookup.find_local(arg);
-            if mpis.contains(&path) {
-                is_argument = true;
+            if let Some(path) = self.move_data.rev_lookup.find_local(arg) {
+                if mpis.contains(&path) {
+                    is_argument = true;
+                }
             }
         }
 

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -46,6 +46,7 @@ mod mutability_errors;
 mod region_errors;
 
 pub(crate) use bound_region_errors::{ToUniverseInfo, UniverseInfo};
+pub(crate) use move_errors::{IllegalMoveOriginKind, MoveError};
 pub(crate) use mutability_errors::AccessKind;
 pub(crate) use outlives_suggestion::OutlivesSuggestionBuilder;
 pub(crate) use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionErrors};

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -1,16 +1,50 @@
 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
 use rustc_middle::mir::*;
-use rustc_middle::ty;
-use rustc_mir_dataflow::move_paths::{
-    IllegalMoveOrigin, IllegalMoveOriginKind, LookupResult, MoveError, MovePathIndex,
-};
+use rustc_middle::ty::{self, Ty};
+use rustc_mir_dataflow::move_paths::{LookupResult, MovePathIndex};
 use rustc_span::{BytePos, Span};
 
 use crate::diagnostics::CapturedMessageOpt;
 use crate::diagnostics::{DescribePlaceOpt, UseSpans};
 use crate::prefixes::PrefixSet;
 use crate::MirBorrowckCtxt;
 
+#[derive(Debug)]
+pub enum IllegalMoveOriginKind<'tcx> {
+    /// Illegal move due to attempt to move from behind a reference.
+    BorrowedContent {
+        /// The place the reference refers to: if erroneous code was trying to
+        /// move from `(*x).f` this will be `*x`.
+        target_place: Place<'tcx>,
+    },
+
+    /// Illegal move due to attempt to move from field of an ADT that
+    /// implements `Drop`. Rust maintains invariant that all `Drop`
+    /// ADT's remain fully-initialized so that user-defined destructor
+    /// can safely read from all of the ADT's fields.
+    InteriorOfTypeWithDestructor { container_ty: Ty<'tcx> },
+
+    /// Illegal move due to attempt to move out of a slice or array.
+    InteriorOfSliceOrArray { ty: Ty<'tcx>, is_index: bool },
+}
+
+#[derive(Debug)]
+pub(crate) struct MoveError<'tcx> {
+    place: Place<'tcx>,
+    location: Location,
+    kind: IllegalMoveOriginKind<'tcx>,
+}
+
+impl<'tcx> MoveError<'tcx> {
+    pub(crate) fn new(
+        place: Place<'tcx>,
+        location: Location,
+        kind: IllegalMoveOriginKind<'tcx>,
+    ) -> Self {
+        MoveError { place, location, kind }
+    }
+}
+
 // Often when desugaring a pattern match we may have many individual moves in
 // MIR that are all part of one operation from the user's point-of-view. For
 // example:
@@ -53,87 +87,77 @@ enum GroupedMoveError<'tcx> {
 }
 
 impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
-    pub(crate) fn report_move_errors(&mut self, move_errors: Vec<(Place<'tcx>, MoveError<'tcx>)>) {
-        let grouped_errors = self.group_move_errors(move_errors);
+    pub(crate) fn report_move_errors(&mut self) {
+        let grouped_errors = self.group_move_errors();
         for error in grouped_errors {
             self.report(error);
         }
     }
 
-    fn group_move_errors(
-        &self,
-        errors: Vec<(Place<'tcx>, MoveError<'tcx>)>,
-    ) -> Vec<GroupedMoveError<'tcx>> {
+    fn group_move_errors(&mut self) -> Vec<GroupedMoveError<'tcx>> {
         let mut grouped_errors = Vec::new();
-        for (original_path, error) in errors {
-            self.append_to_grouped_errors(&mut grouped_errors, original_path, error);
+        let errors = std::mem::take(&mut self.move_errors);
+        for error in errors {
+            self.append_to_grouped_errors(&mut grouped_errors, error);
         }
         grouped_errors
     }
 
     fn append_to_grouped_errors(
         &self,
         grouped_errors: &mut Vec<GroupedMoveError<'tcx>>,
-        original_path: Place<'tcx>,
         error: MoveError<'tcx>,
     ) {
-        match error {
-            MoveError::UnionMove { .. } => {
-                unimplemented!("don't know how to report union move errors yet.")
-            }
-            MoveError::IllegalMove { cannot_move_out_of: IllegalMoveOrigin { location, kind } } => {
-                // Note: that the only time we assign a place isn't a temporary
-                // to a user variable is when initializing it.
-                // If that ever stops being the case, then the ever initialized
-                // flow could be used.
-                if let Some(StatementKind::Assign(box (
-                    place,
-                    Rvalue::Use(Operand::Move(move_from)),
-                ))) = self.body.basic_blocks[location.block]
-                    .statements
-                    .get(location.statement_index)
-                    .map(|stmt| &stmt.kind)
+        let MoveError { place: original_path, location, kind } = error;
+
+        // Note: that the only time we assign a place isn't a temporary
+        // to a user variable is when initializing it.
+        // If that ever stops being the case, then the ever initialized
+        // flow could be used.
+        if let Some(StatementKind::Assign(box (place, Rvalue::Use(Operand::Move(move_from))))) =
+            self.body.basic_blocks[location.block]
+                .statements
+                .get(location.statement_index)
+                .map(|stmt| &stmt.kind)
+        {
+            if let Some(local) = place.as_local() {
+                let local_decl = &self.body.local_decls[local];
+                // opt_match_place is the
+                // match_span is the span of the expression being matched on
+                // match *x.y { ... }        match_place is Some(*x.y)
+                //       ^^^^                match_span is the span of *x.y
+                //
+                // opt_match_place is None for let [mut] x = ... statements,
+                // whether or not the right-hand side is a place expression
+                if let LocalInfo::User(BindingForm::Var(VarBindingForm {
+                    opt_match_place: Some((opt_match_place, match_span)),
+                    binding_mode: _,
+                    opt_ty_info: _,
+                    pat_span: _,
+                })) = *local_decl.local_info()
                 {
-                    if let Some(local) = place.as_local() {
-                        let local_decl = &self.body.local_decls[local];
-                        // opt_match_place is the
-                        // match_span is the span of the expression being matched on
-                        // match *x.y { ... }        match_place is Some(*x.y)
-                        //       ^^^^                match_span is the span of *x.y
-                        //
-                        // opt_match_place is None for let [mut] x = ... statements,
-                        // whether or not the right-hand side is a place expression
-                        if let LocalInfo::User(BindingForm::Var(VarBindingForm {
-                            opt_match_place: Some((opt_match_place, match_span)),
-                            binding_mode: _,
-                            opt_ty_info: _,
-                            pat_span: _,
-                        })) = *local_decl.local_info()
-                        {
-                            let stmt_source_info = self.body.source_info(location);
-                            self.append_binding_error(
-                                grouped_errors,
-                                kind,
-                                original_path,
-                                *move_from,
-                                local,
-                                opt_match_place,
-                                match_span,
-                                stmt_source_info.span,
-                            );
-                            return;
-                        }
-                    }
+                    let stmt_source_info = self.body.source_info(location);
+                    self.append_binding_error(
+                        grouped_errors,
+                        kind,
+                        original_path,
+                        *move_from,
+                        local,
+                        opt_match_place,
+                        match_span,
+                        stmt_source_info.span,
+                    );
+                    return;
                 }
-
-                let move_spans = self.move_spans(original_path.as_ref(), location);
-                grouped_errors.push(GroupedMoveError::OtherIllegalMove {
-                    use_spans: move_spans,
-                    original_path,
-                    kind,
-                });
             }
         }
+
+        let move_spans = self.move_spans(original_path.as_ref(), location);
+        grouped_errors.push(GroupedMoveError::OtherIllegalMove {
+            use_spans: move_spans,
+            original_path,
+            kind,
+        });
     }
 
     fn append_binding_error(