From 87b5e407db1e7f2780a93d8cdf6bd867415ab054 Mon Sep 17 00:00:00 2001 From: Gurinder Singh Date: Fri, 3 Nov 2023 07:18:10 +0530 Subject: [PATCH] Emit explanatory note for move errors in packed struct derives Derive expansions for packed structs cause move errors because they prefer copying over borrowing since borrowing the fields of a packed struct can result in unaligned access and therefore undefined behaviour. This underlying cause of the errors, however, is not apparent to the user. We add a diagnostic note here to remedy that. --- .../src/diagnostics/move_errors.rs | 23 ++- .../deriving-with-repr-packed-move-errors.rs | 96 ++++++++++ ...riving-with-repr-packed-move-errors.stderr | 174 ++++++++++++++++++ .../derives/deriving-with-repr-packed.stderr | 1 + 4 files changed, 293 insertions(+), 1 deletion(-) create mode 100644 tests/ui/derives/deriving-with-repr-packed-move-errors.rs create mode 100644 tests/ui/derives/deriving-with-repr-packed-move-errors.stderr diff --git a/compiler/rustc_borrowck/src/diagnostics/move_errors.rs b/compiler/rustc_borrowck/src/diagnostics/move_errors.rs index 695ac6980cd71..3d94a046e6284 100644 --- a/compiler/rustc_borrowck/src/diagnostics/move_errors.rs +++ b/compiler/rustc_borrowck/src/diagnostics/move_errors.rs @@ -2,7 +2,7 @@ use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed use rustc_middle::mir::*; use rustc_middle::ty::{self, Ty}; use rustc_mir_dataflow::move_paths::{LookupResult, MovePathIndex}; -use rustc_span::{BytePos, Span}; +use rustc_span::{BytePos, ExpnKind, MacroKind, Span}; use crate::diagnostics::CapturedMessageOpt; use crate::diagnostics::{DescribePlaceOpt, UseSpans}; @@ -488,6 +488,8 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> { args_span, } }); + + self.add_note_for_packed_struct_derive(err, original_path.local); } } } @@ -594,4 +596,23 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> { ); } } + + /// Adds an explanatory note if the move error occurs in a derive macro + /// expansion of a packed struct. + /// Such errors happen because derive macro expansions shy away from taking + /// references to the struct's fields since doing so would be undefined behaviour + fn add_note_for_packed_struct_derive(&self, err: &mut Diagnostic, local: Local) { + let local_place: PlaceRef<'tcx> = local.into(); + let local_ty = local_place.ty(self.body.local_decls(), self.infcx.tcx).ty.peel_refs(); + + if let Some(adt) = local_ty.ty_adt_def() { + if adt.repr().packed() { + if let ExpnKind::Macro(MacroKind::Derive, name) = + self.body.span.ctxt().outer_expn_data().kind + { + err.note(format!("`#[derive({name})]` triggers a move because taking references to the fields of a packed struct is undefined behaviour")); + } + } + } + } } diff --git a/tests/ui/derives/deriving-with-repr-packed-move-errors.rs b/tests/ui/derives/deriving-with-repr-packed-move-errors.rs new file mode 100644 index 0000000000000..ffeb02d78b848 --- /dev/null +++ b/tests/ui/derives/deriving-with-repr-packed-move-errors.rs @@ -0,0 +1,96 @@ +// Check that deriving builtin traits for a packed struct with +// non-Copy fields emits move errors along with an additional +// diagnostic note explaining the reason +// See issue #117406 + +use std::fmt::{Debug, Formatter, Result}; +use std::cmp::Ordering; + +// Packed + derives: additional diagnostic should be emitted +// for each of Debug, PartialEq and PartialOrd +#[repr(packed)] +#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Default)] +struct StructA(String); +//~^ ERROR: cannot move out of `self` which is behind a shared reference +//~| ERROR: cannot move out of `self` which is behind a shared reference +//~| ERROR: cannot move out of `other` which is behind a shared reference +//~| ERROR: cannot move out of `self` which is behind a shared reference +//~| ERROR: cannot move out of `other` which is behind a shared reference +//~| ERROR: cannot move out of `self` which is behind a shared reference +//~| ERROR: cannot move out of `other` which is behind a shared reference +//~| ERROR: cannot move out of `self` which is behind a shared reference +//~| ERROR: cannot move out of `self` which is behind a shared reference + + +// Unrelated impl: additinal diagnostic should NOT be emitted +impl StructA { + fn fmt(&self) -> String { + self.0 //~ ERROR: cannot move out of `self` which is behind a shared reference + } +} + +// Packed + manual impls: additional diagnostic should NOT be emitted +#[repr(packed)] +struct StructB(String); + +impl Debug for StructB { + fn fmt(&self, f: &mut Formatter) -> Result { + let x = &{ self.0 }; //~ ERROR: cannot move out of `self` which is behind a shared reference + write!(f, "{}", x) + } +} + +impl PartialEq for StructB { + fn eq(&self, other: &StructB) -> bool { + ({ self.0 }) == ({ other.0 }) + //~^ ERROR: cannot move out of `self` which is behind a shared reference + //~| ERROR: cannot move out of `other` which is behind a shared reference + } +} + +impl PartialOrd for StructB { + fn partial_cmp(&self, other: &StructB) -> Option { + PartialOrd::partial_cmp(&{ self.0 }, &{ other.0 }) + //~^ ERROR: cannot move out of `self` which is behind a shared reference + //~| ERROR: cannot move out of `other` which is behind a shared reference + } +} + +// NOT packed + derives: additinal diagnostic should NOT be emitted +#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Default)] +struct StructC(String); + +// NOT packed + manual impls: additinal dignostic should NOT be emitted +struct StructD(String); + +impl Debug for StructD { + fn fmt(&self, f: &mut Formatter) -> Result { + let x = &{ self.0 }; //~ ERROR: cannot move out of `self` which is behind a shared reference + write!(f, "{}", x) + } +} + +impl PartialEq for StructD { + fn eq(&self, other: &StructD) -> bool { + ({ self.0 }) == ({ other.0 }) + //~^ ERROR: cannot move out of `self` which is behind a shared reference + //~| ERROR: cannot move out of `other` which is behind a shared reference + } +} + +impl PartialOrd for StructD { + fn partial_cmp(&self, other: &StructD) -> Option { + PartialOrd::partial_cmp(&{ self.0 }, &{ other.0 }) + //~^ ERROR: cannot move out of `self` which is behind a shared reference + //~| ERROR: cannot move out of `other` which is behind a shared reference + } +} + +// Packed + derives but the move is outside of a derive +// expansion: additinal diagnostic should NOT be emitted +fn func(arg: &StructA) -> String { + arg.0 //~ ERROR: cannot move out of `arg` which is behind a shared reference +} + +fn main(){ +} diff --git a/tests/ui/derives/deriving-with-repr-packed-move-errors.stderr b/tests/ui/derives/deriving-with-repr-packed-move-errors.stderr new file mode 100644 index 0000000000000..c538061b365e2 --- /dev/null +++ b/tests/ui/derives/deriving-with-repr-packed-move-errors.stderr @@ -0,0 +1,174 @@ +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:13:16 + | +LL | #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Default)] + | ----- in this derive macro expansion +LL | struct StructA(String); + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + | + = note: `#[derive(Debug)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour + = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info) + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:13:16 + | +LL | #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Default)] + | --------- in this derive macro expansion +LL | struct StructA(String); + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + | + = note: `#[derive(PartialEq)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour + = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info) + +error[E0507]: cannot move out of `other` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:13:16 + | +LL | #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Default)] + | --------- in this derive macro expansion +LL | struct StructA(String); + | ^^^^^^ move occurs because `other.0` has type `String`, which does not implement the `Copy` trait + | + = note: `#[derive(PartialEq)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour + = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info) + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:13:16 + | +LL | #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Default)] + | ---------- in this derive macro expansion +LL | struct StructA(String); + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + | + = note: `#[derive(PartialOrd)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour + = note: this error originates in the derive macro `PartialOrd` (in Nightly builds, run with -Z macro-backtrace for more info) + +error[E0507]: cannot move out of `other` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:13:16 + | +LL | #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Default)] + | ---------- in this derive macro expansion +LL | struct StructA(String); + | ^^^^^^ move occurs because `other.0` has type `String`, which does not implement the `Copy` trait + | + = note: `#[derive(PartialOrd)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour + = note: this error originates in the derive macro `PartialOrd` (in Nightly builds, run with -Z macro-backtrace for more info) + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:13:16 + | +LL | #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Default)] + | --- in this derive macro expansion +LL | struct StructA(String); + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + | + = note: `#[derive(Ord)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour + = note: this error originates in the derive macro `Ord` (in Nightly builds, run with -Z macro-backtrace for more info) + +error[E0507]: cannot move out of `other` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:13:16 + | +LL | #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Default)] + | --- in this derive macro expansion +LL | struct StructA(String); + | ^^^^^^ move occurs because `other.0` has type `String`, which does not implement the `Copy` trait + | + = note: `#[derive(Ord)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour + = note: this error originates in the derive macro `Ord` (in Nightly builds, run with -Z macro-backtrace for more info) + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:13:16 + | +LL | #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Default)] + | ---- in this derive macro expansion +LL | struct StructA(String); + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + | + = note: `#[derive(Hash)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour + = note: this error originates in the derive macro `Hash` (in Nightly builds, run with -Z macro-backtrace for more info) + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:13:16 + | +LL | #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Default)] + | ----- in this derive macro expansion +LL | struct StructA(String); + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + | + = note: `#[derive(Clone)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour + = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info) + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:28:9 + | +LL | self.0 + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:38:20 + | +LL | let x = &{ self.0 }; + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:45:12 + | +LL | ({ self.0 }) == ({ other.0 }) + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + +error[E0507]: cannot move out of `other` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:45:28 + | +LL | ({ self.0 }) == ({ other.0 }) + | ^^^^^^^ move occurs because `other.0` has type `String`, which does not implement the `Copy` trait + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:53:36 + | +LL | PartialOrd::partial_cmp(&{ self.0 }, &{ other.0 }) + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + +error[E0507]: cannot move out of `other` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:53:49 + | +LL | PartialOrd::partial_cmp(&{ self.0 }, &{ other.0 }) + | ^^^^^^^ move occurs because `other.0` has type `String`, which does not implement the `Copy` trait + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:68:20 + | +LL | let x = &{ self.0 }; + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:75:12 + | +LL | ({ self.0 }) == ({ other.0 }) + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + +error[E0507]: cannot move out of `other` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:75:28 + | +LL | ({ self.0 }) == ({ other.0 }) + | ^^^^^^^ move occurs because `other.0` has type `String`, which does not implement the `Copy` trait + +error[E0507]: cannot move out of `self` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:83:36 + | +LL | PartialOrd::partial_cmp(&{ self.0 }, &{ other.0 }) + | ^^^^^^ move occurs because `self.0` has type `String`, which does not implement the `Copy` trait + +error[E0507]: cannot move out of `other` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:83:49 + | +LL | PartialOrd::partial_cmp(&{ self.0 }, &{ other.0 }) + | ^^^^^^^ move occurs because `other.0` has type `String`, which does not implement the `Copy` trait + +error[E0507]: cannot move out of `arg` which is behind a shared reference + --> $DIR/deriving-with-repr-packed-move-errors.rs:92:5 + | +LL | arg.0 + | ^^^^^ move occurs because `arg.0` has type `String`, which does not implement the `Copy` trait + +error: aborting due to 21 previous errors + +For more information about this error, try `rustc --explain E0507`. diff --git a/tests/ui/derives/deriving-with-repr-packed.stderr b/tests/ui/derives/deriving-with-repr-packed.stderr index 0cfe03869af1b..bb1fab343a3e1 100644 --- a/tests/ui/derives/deriving-with-repr-packed.stderr +++ b/tests/ui/derives/deriving-with-repr-packed.stderr @@ -36,6 +36,7 @@ LL | #[repr(packed)] LL | struct X(Y); | ^ move occurs because `self.0` has type `Y`, which does not implement the `Copy` trait | + = note: `#[derive(Debug)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info) error: aborting due to previous error; 2 warnings emitted