Auto merge of #45016 - pnkfelix:mir-borrowck-gather-and-signal-move-errors, r=nikomatsakis

MIR-borrowck: gather and signal any move errors

When building up the `MoveData` structure for a given MIR, also accumulate any erroneous actions, and then report all of those errors when the construction is complete.

This PR adds a host of move-related error constructor methods to `trait BorrowckErrors`. I think I got the notes right; but we should plan to audit all of the notes before turning MIR-borrowck on by default.

Fix #44830

Author: bors

src/librustc/mir/mod.rs

@@ -260,6 +260,19 @@ impl<'tcx> Mir<'tcx> {
         debug_assert!(location.statement_index < block.statements.len());
         block.statements[location.statement_index].make_nop()
     }
+
+    /// Returns the source info associated with `location`.
+    pub fn source_info(&self, location: Location) -> &SourceInfo {
+        let block = &self[location.block];
+        let stmts = &block.statements;
+        let idx = location.statement_index;
+        if location.statement_index < stmts.len() {
+            &stmts[idx].source_info
+        } else {
+            assert!(location.statement_index == stmts.len());
+            &block.terminator().source_info
+        }
+    }
 }
 
 #[derive(Clone, Debug)]

src/librustc_borrowck/borrowck/gather_loans/move_error.rs

@@ -14,6 +14,7 @@ use rustc::middle::mem_categorization::Categorization;
 use rustc::middle::mem_categorization::NoteClosureEnv;
 use rustc::middle::mem_categorization::InteriorOffsetKind as Kind;
 use rustc::ty;
+use rustc_mir::util::borrowck_errors::{BorrowckErrors, Origin};
 use syntax::ast;
 use syntax_pos;
 use errors::DiagnosticBuilder;
@@ -134,51 +135,29 @@ fn group_errors_with_same_origin<'tcx>(errors: &Vec<MoveError<'tcx>>)
 }
 
 // (keep in sync with gather_moves::check_and_get_illegal_move_origin )
-fn report_cannot_move_out_of<'a, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>,
+fn report_cannot_move_out_of<'a, 'tcx>(bccx: &'a BorrowckCtxt<'a, 'tcx>,
                                        move_from: mc::cmt<'tcx>)
                                        -> DiagnosticBuilder<'a> {
     match move_from.cat {
         Categorization::Deref(_, mc::BorrowedPtr(..)) |
         Categorization::Deref(_, mc::Implicit(..)) |
         Categorization::Deref(_, mc::UnsafePtr(..)) |
         Categorization::StaticItem => {
-            let mut err = struct_span_err!(bccx, move_from.span, E0507,
-                             "cannot move out of {}",
-                             move_from.descriptive_string(bccx.tcx));
-            err.span_label(
-                move_from.span,
-                format!("cannot move out of {}", move_from.descriptive_string(bccx.tcx))
-                );
-            err
+            bccx.cannot_move_out_of(
+                move_from.span, &move_from.descriptive_string(bccx.tcx), Origin::Ast)
         }
-
         Categorization::Interior(ref b, mc::InteriorElement(ik)) => {
-            let type_name = match (&b.ty.sty, ik) {
-                (&ty::TyArray(_, _), Kind::Index) => "array",
-                (&ty::TySlice(_), _) => "slice",
-                _ => {
-                    span_bug!(move_from.span, "this path should not cause illegal move");
-                },
-            };
-            let mut err = struct_span_err!(bccx, move_from.span, E0508,
-                                           "cannot move out of type `{}`, \
-                                            a non-copy {}",
-                                           b.ty, type_name);
-            err.span_label(move_from.span, "cannot move out of here");
-            err
+            bccx.cannot_move_out_of_interior_noncopy(
+                move_from.span, b.ty, ik == Kind::Index, Origin::Ast)
         }
 
         Categorization::Downcast(ref b, _) |
         Categorization::Interior(ref b, mc::InteriorField(_)) => {
             match b.ty.sty {
                 ty::TyAdt(def, _) if def.has_dtor(bccx.tcx) => {
-                    let mut err = struct_span_err!(bccx, move_from.span, E0509,
-                                                   "cannot move out of type `{}`, \
-                                                   which implements the `Drop` trait",
-                                                   b.ty);
-                    err.span_label(move_from.span, "cannot move out of here");
-                    err
-                },
+                    bccx.cannot_move_out_of_interior_of_drop(
+                        move_from.span, b.ty, Origin::Ast)
+                }
                 _ => {
                     span_bug!(move_from.span, "this path should not cause illegal move");
                 }

src/librustc_borrowck/diagnostics.rs

@@ -317,272 +317,6 @@ fn main() {
 ```
 "##,
 
-E0507: r##"
-You tried to move out of a value which was borrowed. Erroneous code example:
-
-```compile_fail,E0507
-use std::cell::RefCell;
-
-struct TheDarkKnight;
-
-impl TheDarkKnight {
-    fn nothing_is_true(self) {}
-}
-
-fn main() {
-    let x = RefCell::new(TheDarkKnight);
-
-    x.borrow().nothing_is_true(); // error: cannot move out of borrowed content
-}
-```
-
-Here, the `nothing_is_true` method takes the ownership of `self`. However,
-`self` cannot be moved because `.borrow()` only provides an `&TheDarkKnight`,
-which is a borrow of the content owned by the `RefCell`. To fix this error,
-you have three choices:
-
-* Try to avoid moving the variable.
-* Somehow reclaim the ownership.
-* Implement the `Copy` trait on the type.
-
-Examples:
-
-```
-use std::cell::RefCell;
-
-struct TheDarkKnight;
-
-impl TheDarkKnight {
-    fn nothing_is_true(&self) {} // First case, we don't take ownership
-}
-
-fn main() {
-    let x = RefCell::new(TheDarkKnight);
-
-    x.borrow().nothing_is_true(); // ok!
-}
-```
-
-Or:
-
-```
-use std::cell::RefCell;
-
-struct TheDarkKnight;
-
-impl TheDarkKnight {
-    fn nothing_is_true(self) {}
-}
-
-fn main() {
-    let x = RefCell::new(TheDarkKnight);
-    let x = x.into_inner(); // we get back ownership
-
-    x.nothing_is_true(); // ok!
-}
-```
-
-Or:
-
-```
-use std::cell::RefCell;
-
-#[derive(Clone, Copy)] // we implement the Copy trait
-struct TheDarkKnight;
-
-impl TheDarkKnight {
-    fn nothing_is_true(self) {}
-}
-
-fn main() {
-    let x = RefCell::new(TheDarkKnight);
-
-    x.borrow().nothing_is_true(); // ok!
-}
-```
-
-Moving a member out of a mutably borrowed struct will also cause E0507 error:
-
-```compile_fail,E0507
-struct TheDarkKnight;
-
-impl TheDarkKnight {
-    fn nothing_is_true(self) {}
-}
-
-struct Batcave {
-    knight: TheDarkKnight
-}
-
-fn main() {
-    let mut cave = Batcave {
-        knight: TheDarkKnight
-    };
-    let borrowed = &mut cave;
-
-    borrowed.knight.nothing_is_true(); // E0507
-}
-```
-
-It is fine only if you put something back. `mem::replace` can be used for that:
-
-```
-# struct TheDarkKnight;
-# impl TheDarkKnight { fn nothing_is_true(self) {} }
-# struct Batcave { knight: TheDarkKnight }
-use std::mem;
-
-let mut cave = Batcave {
-    knight: TheDarkKnight
-};
-let borrowed = &mut cave;
-
-mem::replace(&mut borrowed.knight, TheDarkKnight).nothing_is_true(); // ok!
-```
-
-You can find more information about borrowing in the rust-book:
-http://doc.rust-lang.org/book/first-edition/references-and-borrowing.html
-"##,
-
-E0508: r##"
-A value was moved out of a non-copy fixed-size array.
-
-Example of erroneous code:
-
-```compile_fail,E0508
-struct NonCopy;
-
-fn main() {
-    let array = [NonCopy; 1];
-    let _value = array[0]; // error: cannot move out of type `[NonCopy; 1]`,
-                           //        a non-copy fixed-size array
-}
-```
-
-The first element was moved out of the array, but this is not
-possible because `NonCopy` does not implement the `Copy` trait.
-
-Consider borrowing the element instead of moving it:
-
-```
-struct NonCopy;
-
-fn main() {
-    let array = [NonCopy; 1];
-    let _value = &array[0]; // Borrowing is allowed, unlike moving.
-}
-```
-
-Alternatively, if your type implements `Clone` and you need to own the value,
-consider borrowing and then cloning:
-
-```
-#[derive(Clone)]
-struct NonCopy;
-
-fn main() {
-    let array = [NonCopy; 1];
-    // Now you can clone the array element.
-    let _value = array[0].clone();
-}
-```
-"##,
-
-E0509: r##"
-This error occurs when an attempt is made to move out of a value whose type
-implements the `Drop` trait.
-
-Example of erroneous code:
-
-```compile_fail,E0509
-struct FancyNum {
-    num: usize
-}
-
-struct DropStruct {
-    fancy: FancyNum
-}
-
-impl Drop for DropStruct {
-    fn drop(&mut self) {
-        // Destruct DropStruct, possibly using FancyNum
-    }
-}
-
-fn main() {
-    let drop_struct = DropStruct{fancy: FancyNum{num: 5}};
-    let fancy_field = drop_struct.fancy; // Error E0509
-    println!("Fancy: {}", fancy_field.num);
-    // implicit call to `drop_struct.drop()` as drop_struct goes out of scope
-}
-```
-
-Here, we tried to move a field out of a struct of type `DropStruct` which
-implements the `Drop` trait. However, a struct cannot be dropped if one or
-more of its fields have been moved.
-
-Structs implementing the `Drop` trait have an implicit destructor that gets
-called when they go out of scope. This destructor may use the fields of the
-struct, so moving out of the struct could make it impossible to run the
-destructor. Therefore, we must think of all values whose type implements the
-`Drop` trait as single units whose fields cannot be moved.
-
-This error can be fixed by creating a reference to the fields of a struct,
-enum, or tuple using the `ref` keyword:
-
-```
-struct FancyNum {
-    num: usize
-}
-
-struct DropStruct {
-    fancy: FancyNum
-}
-
-impl Drop for DropStruct {
-    fn drop(&mut self) {
-        // Destruct DropStruct, possibly using FancyNum
-    }
-}
-
-fn main() {
-    let drop_struct = DropStruct{fancy: FancyNum{num: 5}};
-    let ref fancy_field = drop_struct.fancy; // No more errors!
-    println!("Fancy: {}", fancy_field.num);
-    // implicit call to `drop_struct.drop()` as drop_struct goes out of scope
-}
-```
-
-Note that this technique can also be used in the arms of a match expression:
-
-```
-struct FancyNum {
-    num: usize
-}
-
-enum DropEnum {
-    Fancy(FancyNum)
-}
-
-impl Drop for DropEnum {
-    fn drop(&mut self) {
-        // Destruct DropEnum, possibly using FancyNum
-    }
-}
-
-fn main() {
-    // Creates and enum of type `DropEnum`, which implements `Drop`
-    let drop_enum = DropEnum::Fancy(FancyNum{num: 10});
-    match drop_enum {
-        // Creates a reference to the inside of `DropEnum::Fancy`
-        DropEnum::Fancy(ref fancy_field) => // No error!
-            println!("It was fancy-- {}!", fancy_field.num),
-    }
-    // implicit call to `drop_enum.drop()` as drop_enum goes out of scope
-}
-```
-"##,
-
 E0595: r##"
 Closures cannot mutate immutable captured variables.