diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs index 1181ba6bbf9..d6d76595f3b 100644 --- a/compiler/rustc_middle/src/mir/mod.rs +++ b/compiler/rustc_middle/src/mir/mod.rs @@ -899,6 +899,8 @@ pub enum LocalInfo<'tcx> { User(ClearCrossCrate>), /// A temporary created that references the static with the given `DefId`. StaticRef { def_id: DefId, is_thread_local: bool }, + /// A temporary created that references the const with the given `DefId` + ConstRef { def_id: DefId }, } impl<'tcx> LocalDecl<'tcx> { diff --git a/compiler/rustc_mir/src/borrow_check/diagnostics/mod.rs b/compiler/rustc_mir/src/borrow_check/diagnostics/mod.rs index 88ff0271228..f51bf7730ea 100644 --- a/compiler/rustc_mir/src/borrow_check/diagnostics/mod.rs +++ b/compiler/rustc_mir/src/borrow_check/diagnostics/mod.rs @@ -804,68 +804,51 @@ pub(super) fn move_spans( debug!("move_spans: target_temp = {:?}", target_temp); if let Some(Terminator { - kind: TerminatorKind::Call { func, args, fn_span, from_hir_call, .. }, - .. + kind: TerminatorKind::Call { fn_span, from_hir_call, .. }, .. }) = &self.body[location.block].terminator { - let mut method_did = None; - if let Operand::Constant(box Constant { literal: ty::Const { ty, .. }, .. }) = func { - if let ty::FnDef(def_id, _) = *ty.kind() { - debug!("move_spans: fn = {:?}", def_id); - if let Some(ty::AssocItem { fn_has_self_parameter, .. }) = - self.infcx.tcx.opt_associated_item(def_id) - { - if *fn_has_self_parameter { - method_did = Some(def_id); - } - } - } - } + let method_did = if let Some(method_did) = + crate::util::find_self_call(self.infcx.tcx, &self.body, target_temp, location.block) + { + method_did + } else { + return normal_ret; + }; let tcx = self.infcx.tcx; - let method_did = if let Some(did) = method_did { did } else { return normal_ret }; - if let [Operand::Move(self_place), ..] = **args { - if self_place.as_local() == Some(target_temp) { - let parent = tcx.parent(method_did); - let is_fn_once = parent == tcx.lang_items().fn_once_trait(); - let is_operator = !from_hir_call - && parent.map_or(false, |p| { - tcx.lang_items().group(LangItemGroup::Op).contains(&p) - }); - let fn_call_span = *fn_span; + let parent = tcx.parent(method_did); + let is_fn_once = parent == tcx.lang_items().fn_once_trait(); + let is_operator = !from_hir_call + && parent.map_or(false, |p| tcx.lang_items().group(LangItemGroup::Op).contains(&p)); + let fn_call_span = *fn_span; - let self_arg = tcx.fn_arg_names(method_did)[0]; + let self_arg = tcx.fn_arg_names(method_did)[0]; - let kind = if is_fn_once { - FnSelfUseKind::FnOnceCall - } else if is_operator { - FnSelfUseKind::Operator { self_arg } - } else { - debug!( - "move_spans: method_did={:?}, fn_call_span={:?}", - method_did, fn_call_span - ); - let implicit_into_iter = matches!( - fn_call_span.desugaring_kind(), - Some(DesugaringKind::ForLoop(ForLoopLoc::IntoIter)) - ); - FnSelfUseKind::Normal { self_arg, implicit_into_iter } - }; + let kind = if is_fn_once { + FnSelfUseKind::FnOnceCall + } else if is_operator { + FnSelfUseKind::Operator { self_arg } + } else { + debug!("move_spans: method_did={:?}, fn_call_span={:?}", method_did, fn_call_span); + let implicit_into_iter = matches!( + fn_call_span.desugaring_kind(), + Some(DesugaringKind::ForLoop(ForLoopLoc::IntoIter)) + ); + FnSelfUseKind::Normal { self_arg, implicit_into_iter } + }; - return FnSelfUse { - var_span: stmt.source_info.span, - fn_call_span, - fn_span: self - .infcx - .tcx - .sess - .source_map() - .guess_head_span(self.infcx.tcx.def_span(method_did)), - kind, - }; - } - } + return FnSelfUse { + var_span: stmt.source_info.span, + fn_call_span, + fn_span: self + .infcx + .tcx + .sess + .source_map() + .guess_head_span(self.infcx.tcx.def_span(method_did)), + kind, + }; } normal_ret } diff --git a/compiler/rustc_mir/src/transform/check_const_item_mutation.rs b/compiler/rustc_mir/src/transform/check_const_item_mutation.rs new file mode 100644 index 00000000000..589268e39bd --- /dev/null +++ b/compiler/rustc_mir/src/transform/check_const_item_mutation.rs @@ -0,0 +1,114 @@ +use rustc_errors::DiagnosticBuilder; +use rustc_middle::lint::LintDiagnosticBuilder; +use rustc_middle::mir::visit::Visitor; +use rustc_middle::mir::*; +use rustc_middle::ty::TyCtxt; +use rustc_session::lint::builtin::CONST_ITEM_MUTATION; +use rustc_span::def_id::DefId; + +use crate::transform::{MirPass, MirSource}; + +pub struct CheckConstItemMutation; + +impl<'tcx> MirPass<'tcx> for CheckConstItemMutation { + fn run_pass(&self, tcx: TyCtxt<'tcx>, _src: MirSource<'tcx>, body: &mut Body<'tcx>) { + let mut checker = ConstMutationChecker { body, tcx, target_local: None }; + checker.visit_body(&body); + } +} + +struct ConstMutationChecker<'a, 'tcx> { + body: &'a Body<'tcx>, + tcx: TyCtxt<'tcx>, + target_local: Option, +} + +impl<'a, 'tcx> ConstMutationChecker<'a, 'tcx> { + fn is_const_item(&self, local: Local) -> Option { + if let Some(box LocalInfo::ConstRef { def_id }) = self.body.local_decls[local].local_info { + Some(def_id) + } else { + None + } + } + fn lint_const_item_usage( + &self, + const_item: DefId, + location: Location, + decorate: impl for<'b> FnOnce(LintDiagnosticBuilder<'b>) -> DiagnosticBuilder<'b>, + ) { + let source_info = self.body.source_info(location); + let lint_root = self.body.source_scopes[source_info.scope] + .local_data + .as_ref() + .assert_crate_local() + .lint_root; + + self.tcx.struct_span_lint_hir(CONST_ITEM_MUTATION, lint_root, source_info.span, |lint| { + decorate(lint) + .span_note(self.tcx.def_span(const_item), "`const` item defined here") + .emit() + }); + } +} + +impl<'a, 'tcx> Visitor<'tcx> for ConstMutationChecker<'a, 'tcx> { + fn visit_statement(&mut self, stmt: &Statement<'tcx>, loc: Location) { + if let StatementKind::Assign(box (lhs, _)) = &stmt.kind { + // Check for assignment to fields of a constant + // Assigning directly to a constant (e.g. `FOO = true;`) is a hard error, + // so emitting a lint would be redundant. + if !lhs.projection.is_empty() { + if let Some(def_id) = self.is_const_item(lhs.local) { + self.lint_const_item_usage(def_id, loc, |lint| { + let mut lint = lint.build("attempting to modify a `const` item"); + lint.note("each usage of a `const` item creates a new temporary - the original `const` item will not be modified"); + lint + }) + } + } + // We are looking for MIR of the form: + // + // ``` + // _1 = const FOO; + // _2 = &mut _1; + // method_call(_2, ..) + // ``` + // + // Record our current LHS, so that we can detect this + // pattern in `visit_rvalue` + self.target_local = lhs.as_local(); + } + self.super_statement(stmt, loc); + self.target_local = None; + } + fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, loc: Location) { + if let Rvalue::Ref(_, BorrowKind::Mut { .. }, place) = rvalue { + let local = place.local; + if let Some(def_id) = self.is_const_item(local) { + // If this Rvalue is being used as the right-hand side of a + // `StatementKind::Assign`, see if it ends up getting used as + // the `self` parameter of a method call (as the terminator of our current + // BasicBlock). If so, we emit a more specific lint. + let method_did = self.target_local.and_then(|target_local| { + crate::util::find_self_call(self.tcx, &self.body, target_local, loc.block) + }); + let lint_loc = + if method_did.is_some() { self.body.terminator_loc(loc.block) } else { loc }; + self.lint_const_item_usage(def_id, lint_loc, |lint| { + let mut lint = lint.build("taking a mutable reference to a `const` item"); + lint + .note("each usage of a `const` item creates a new temporary") + .note("the mutable reference will refer to this temporary, not the original `const` item"); + + if let Some(method_did) = method_did { + lint.span_note(self.tcx.def_span(method_did), "mutable reference created due to call to this method"); + } + + lint + }); + } + } + self.super_rvalue(rvalue, loc); + } +} diff --git a/compiler/rustc_mir/src/transform/mod.rs b/compiler/rustc_mir/src/transform/mod.rs index c3a34756122..98f93ae6da0 100644 --- a/compiler/rustc_mir/src/transform/mod.rs +++ b/compiler/rustc_mir/src/transform/mod.rs @@ -16,6 +16,7 @@ pub mod add_call_guards; pub mod add_moves_for_packed_drops; pub mod add_retag; +pub mod check_const_item_mutation; pub mod check_consts; pub mod check_packed_ref; pub mod check_unsafety; @@ -307,6 +308,7 @@ fn mir_const<'tcx>( &[&[ // MIR-level lints. &check_packed_ref::CheckPackedRef, + &check_const_item_mutation::CheckConstItemMutation, // What we need to do constant evaluation. &simplify::SimplifyCfg::new("initial"), &rustc_peek::SanityCheck, diff --git a/compiler/rustc_mir/src/util/find_self_call.rs b/compiler/rustc_mir/src/util/find_self_call.rs new file mode 100644 index 00000000000..049b5f01214 --- /dev/null +++ b/compiler/rustc_mir/src/util/find_self_call.rs @@ -0,0 +1,35 @@ +use rustc_middle::mir::*; +use rustc_middle::ty::{self, TyCtxt}; +use rustc_span::def_id::DefId; + +/// Checks if the specified `local` is used as the `self` prameter of a method call +/// in the provided `BasicBlock`. If it is, then the `DefId` of the called method is +/// returned. +pub fn find_self_call( + tcx: TyCtxt<'_>, + body: &Body<'_>, + local: Local, + block: BasicBlock, +) -> Option { + debug!("find_self_call(local={:?}): terminator={:?}", local, &body[block].terminator); + if let Some(Terminator { kind: TerminatorKind::Call { func, args, .. }, .. }) = + &body[block].terminator + { + debug!("find_self_call: func={:?}", func); + if let Operand::Constant(box Constant { literal: ty::Const { ty, .. }, .. }) = func { + if let ty::FnDef(def_id, _) = *ty.kind() { + if let Some(ty::AssocItem { fn_has_self_parameter: true, .. }) = + tcx.opt_associated_item(def_id) + { + debug!("find_self_call: args={:?}", args); + if let [Operand::Move(self_place) | Operand::Copy(self_place), ..] = **args { + if self_place.as_local() == Some(local) { + return Some(def_id); + } + } + } + } + } + } + None +} diff --git a/compiler/rustc_mir/src/util/mod.rs b/compiler/rustc_mir/src/util/mod.rs index ed0fafb1aac..699f3bcf014 100644 --- a/compiler/rustc_mir/src/util/mod.rs +++ b/compiler/rustc_mir/src/util/mod.rs @@ -7,12 +7,14 @@ mod alignment; pub mod collect_writes; +mod find_self_call; mod graphviz; pub(crate) mod pretty; pub(crate) mod spanview; pub use self::aggregate::expand_aggregate; pub use self::alignment::is_disaligned; +pub use self::find_self_call::find_self_call; pub use self::graphviz::write_node_label as write_graphviz_node_label; pub use self::graphviz::{graphviz_safe_def_name, write_mir_graphviz}; pub use self::pretty::{dump_enabled, dump_mir, write_mir_pretty, PassWhere}; diff --git a/compiler/rustc_mir_build/src/build/expr/as_constant.rs b/compiler/rustc_mir_build/src/build/expr/as_constant.rs index 982aefcf604..244a70f83b0 100644 --- a/compiler/rustc_mir_build/src/build/expr/as_constant.rs +++ b/compiler/rustc_mir_build/src/build/expr/as_constant.rs @@ -21,7 +21,7 @@ fn expr_as_constant(&mut self, expr: Expr<'tcx>) -> Constant<'tcx> { let Expr { ty, temp_lifetime: _, span, kind } = expr; match kind { ExprKind::Scope { region_scope: _, lint_level: _, value } => this.as_constant(value), - ExprKind::Literal { literal, user_ty } => { + ExprKind::Literal { literal, user_ty, const_id: _ } => { let user_ty = user_ty.map(|user_ty| { this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation { span, diff --git a/compiler/rustc_mir_build/src/build/expr/as_temp.rs b/compiler/rustc_mir_build/src/build/expr/as_temp.rs index a9cc0cc2f24..9984b527ffd 100644 --- a/compiler/rustc_mir_build/src/build/expr/as_temp.rs +++ b/compiler/rustc_mir_build/src/build/expr/as_temp.rs @@ -76,6 +76,9 @@ fn expr_as_temp( local_decl.local_info = Some(box LocalInfo::StaticRef { def_id, is_thread_local: true }); } + ExprKind::Literal { const_id: Some(def_id), .. } => { + local_decl.local_info = Some(box LocalInfo::ConstRef { def_id }); + } _ => {} } this.local_decls.push(local_decl) diff --git a/compiler/rustc_mir_build/src/thir/cx/expr.rs b/compiler/rustc_mir_build/src/thir/cx/expr.rs index e9e49d054b8..70c7abc2654 100644 --- a/compiler/rustc_mir_build/src/thir/cx/expr.rs +++ b/compiler/rustc_mir_build/src/thir/cx/expr.rs @@ -247,6 +247,7 @@ fn make_mirror_unadjusted<'a, 'tcx>( hir::ExprKind::Lit(ref lit) => ExprKind::Literal { literal: cx.const_eval_literal(&lit.node, expr_ty, lit.span, false), user_ty: None, + const_id: None, }, hir::ExprKind::Binary(op, ref lhs, ref rhs) => { @@ -306,6 +307,7 @@ fn make_mirror_unadjusted<'a, 'tcx>( ExprKind::Literal { literal: cx.const_eval_literal(&lit.node, expr_ty, lit.span, true), user_ty: None, + const_id: None, } } else { ExprKind::Unary { op: UnOp::Neg, arg: arg.to_ref() } @@ -447,6 +449,7 @@ fn make_mirror_unadjusted<'a, 'tcx>( kind: ExprKind::Literal { literal: ty::Const::zero_sized(cx.tcx, ty), user_ty, + const_id: None, }, } .to_ref(), @@ -473,6 +476,7 @@ fn make_mirror_unadjusted<'a, 'tcx>( kind: ExprKind::Literal { literal: ty::Const::zero_sized(cx.tcx, ty), user_ty: None, + const_id: None, }, } .to_ref(), @@ -585,7 +589,7 @@ fn make_mirror_unadjusted<'a, 'tcx>( temp_lifetime, ty: var_ty, span: expr.span, - kind: ExprKind::Literal { literal, user_ty: None }, + kind: ExprKind::Literal { literal, user_ty: None, const_id: None }, } .to_ref() }; @@ -714,7 +718,11 @@ fn method_callee<'a, 'tcx>( temp_lifetime, ty, span, - kind: ExprKind::Literal { literal: ty::Const::zero_sized(cx.tcx(), ty), user_ty }, + kind: ExprKind::Literal { + literal: ty::Const::zero_sized(cx.tcx(), ty), + user_ty, + const_id: None, + }, } } @@ -777,6 +785,7 @@ fn convert_path_expr<'a, 'tcx>( ExprKind::Literal { literal: ty::Const::zero_sized(cx.tcx, cx.typeck_results().node_type(expr.hir_id)), user_ty, + const_id: None, } } @@ -794,6 +803,7 @@ fn convert_path_expr<'a, 'tcx>( .tcx .mk_const(ty::Const { val, ty: cx.typeck_results().node_type(expr.hir_id) }), user_ty: None, + const_id: Some(def_id), } } @@ -810,6 +820,7 @@ fn convert_path_expr<'a, 'tcx>( ty: cx.typeck_results().node_type(expr.hir_id), }), user_ty, + const_id: Some(def_id), } } diff --git a/compiler/rustc_mir_build/src/thir/mod.rs b/compiler/rustc_mir_build/src/thir/mod.rs index 2837bfa040f..4d57fd5c64f 100644 --- a/compiler/rustc_mir_build/src/thir/mod.rs +++ b/compiler/rustc_mir_build/src/thir/mod.rs @@ -273,6 +273,10 @@ Literal { literal: &'tcx Const<'tcx>, user_ty: Option>>, + /// The `DefId` of the `const` item this literal + /// was produced from, if this is not a user-written + /// literal value. + const_id: Option, }, /// A literal containing the address of a `static`. /// diff --git a/compiler/rustc_session/src/lint/builtin.rs b/compiler/rustc_session/src/lint/builtin.rs index 2db4d2a7f51..74b68bfe2a5 100644 --- a/compiler/rustc_session/src/lint/builtin.rs +++ b/compiler/rustc_session/src/lint/builtin.rs @@ -232,6 +232,12 @@ "detects unaligned references to fields of packed structs", } +declare_lint! { + pub CONST_ITEM_MUTATION, + Warn, + "detects attempts to mutate a `const` item", +} + declare_lint! { pub SAFE_PACKED_BORROWS, Warn, @@ -572,6 +578,7 @@ CONST_ERR, RENAMED_AND_REMOVED_LINTS, UNALIGNED_REFERENCES, + CONST_ITEM_MUTATION, SAFE_PACKED_BORROWS, PATTERNS_IN_FNS_WITHOUT_BODY, LATE_BOUND_LIFETIME_ARGUMENTS, diff --git a/src/test/ui/error-codes/E0017.rs b/src/test/ui/error-codes/E0017.rs index 818dec1207b..54d3cc54a84 100644 --- a/src/test/ui/error-codes/E0017.rs +++ b/src/test/ui/error-codes/E0017.rs @@ -3,9 +3,11 @@ static mut M: i32 = 3; const CR: &'static mut i32 = &mut C; //~ ERROR E0764 + //~| WARN taking a mutable static STATIC_REF: &'static mut i32 = &mut X; //~ ERROR E0764 //~| ERROR E0019 //~| ERROR cannot borrow static CONST_REF: &'static mut i32 = &mut C; //~ ERROR E0764 + //~| WARN taking a mutable static STATIC_MUT_REF: &'static mut i32 = unsafe { &mut M }; //~ ERROR E0764 fn main() {} diff --git a/src/test/ui/error-codes/E0017.stderr b/src/test/ui/error-codes/E0017.stderr index c1d96de1dca..40ef6bd97b3 100644 --- a/src/test/ui/error-codes/E0017.stderr +++ b/src/test/ui/error-codes/E0017.stderr @@ -1,3 +1,18 @@ +warning: taking a mutable reference to a `const` item + --> $DIR/E0017.rs:5:30 + | +LL | const CR: &'static mut i32 = &mut C; + | ^^^^^^ + | + = note: `#[warn(const_item_mutation)]` on by default + = note: each usage of a `const` item creates a new temporary + = note: the mutable reference will refer to this temporary, not the original `const` item +note: `const` item defined here + --> $DIR/E0017.rs:2:1 + | +LL | const C: i32 = 2; + | ^^^^^^^^^^^^^^^^^ + error[E0764]: mutable references are not allowed in constants --> $DIR/E0017.rs:5:30 | @@ -5,7 +20,7 @@ LL | const CR: &'static mut i32 = &mut C; | ^^^^^^ `&mut` is only allowed in `const fn` error[E0019]: static contains unimplemented expression type - --> $DIR/E0017.rs:6:39 + --> $DIR/E0017.rs:7:39 | LL | static STATIC_REF: &'static mut i32 = &mut X; | ^^^^^^ @@ -13,30 +28,44 @@ LL | static STATIC_REF: &'static mut i32 = &mut X; = help: add `#![feature(const_mut_refs)]` to the crate attributes to enable error[E0764]: mutable references are not allowed in statics - --> $DIR/E0017.rs:6:39 + --> $DIR/E0017.rs:7:39 | LL | static STATIC_REF: &'static mut i32 = &mut X; | ^^^^^^ `&mut` is only allowed in `const fn` error[E0596]: cannot borrow immutable static item `X` as mutable - --> $DIR/E0017.rs:6:39 + --> $DIR/E0017.rs:7:39 | LL | static STATIC_REF: &'static mut i32 = &mut X; | ^^^^^^ cannot borrow as mutable +warning: taking a mutable reference to a `const` item + --> $DIR/E0017.rs:10:38 + | +LL | static CONST_REF: &'static mut i32 = &mut C; + | ^^^^^^ + | + = note: each usage of a `const` item creates a new temporary + = note: the mutable reference will refer to this temporary, not the original `const` item +note: `const` item defined here + --> $DIR/E0017.rs:2:1 + | +LL | const C: i32 = 2; + | ^^^^^^^^^^^^^^^^^ + error[E0764]: mutable references are not allowed in statics - --> $DIR/E0017.rs:9:38 + --> $DIR/E0017.rs:10:38 | LL | static CONST_REF: &'static mut i32 = &mut C; | ^^^^^^ `&mut` is only allowed in `const fn` error[E0764]: mutable references are not allowed in statics - --> $DIR/E0017.rs:10:52 + --> $DIR/E0017.rs:12:52 | LL | static STATIC_MUT_REF: &'static mut i32 = unsafe { &mut M }; | ^^^^^^ `&mut` is only allowed in `const fn` -error: aborting due to 6 previous errors +error: aborting due to 6 previous errors; 2 warnings emitted Some errors have detailed explanations: E0019, E0596, E0764. For more information about an error, try `rustc --explain E0019`. diff --git a/src/test/ui/error-codes/E0388.rs b/src/test/ui/error-codes/E0388.rs index 13131017c2e..8ad586bb30f 100644 --- a/src/test/ui/error-codes/E0388.rs +++ b/src/test/ui/error-codes/E0388.rs @@ -2,9 +2,11 @@ const C: i32 = 2; const CR: &'static mut i32 = &mut C; //~ ERROR E0764 + //~| WARN taking a mutable static STATIC_REF: &'static mut i32 = &mut X; //~ ERROR E0019 //~| ERROR cannot borrow //~| ERROR E0764 static CONST_REF: &'static mut i32 = &mut C; //~ ERROR E0764 + //~| WARN taking a mutable fn main() {} diff --git a/src/test/ui/error-codes/E0388.stderr b/src/test/ui/error-codes/E0388.stderr index f09100bac43..39bc717ceec 100644 --- a/src/test/ui/error-codes/E0388.stderr +++ b/src/test/ui/error-codes/E0388.stderr @@ -1,3 +1,18 @@ +warning: taking a mutable reference to a `const` item + --> $DIR/E0388.rs:4:30 + | +LL | const CR: &'static mut i32 = &mut C; + | ^^^^^^ + | + = note: `#[warn(const_item_mutation)]` on by default + = note: each usage of a `const` item creates a new temporary + = note: the mutable reference will refer to this temporary, not the original `const` item +note: `const` item defined here + --> $DIR/E0388.rs:2:1 + | +LL | const C: i32 = 2; + | ^^^^^^^^^^^^^^^^^ + error[E0764]: mutable references are not allowed in constants --> $DIR/E0388.rs:4:30 | @@ -5,7 +20,7 @@ LL | const CR: &'static mut i32 = &mut C; | ^^^^^^ `&mut` is only allowed in `const fn` error[E0019]: static contains unimplemented expression type - --> $DIR/E0388.rs:5:39 + --> $DIR/E0388.rs:6:39 | LL | static STATIC_REF: &'static mut i32 = &mut X; | ^^^^^^ @@ -13,24 +28,38 @@ LL | static STATIC_REF: &'static mut i32 = &mut X; = help: add `#![feature(const_mut_refs)]` to the crate attributes to enable error[E0764]: mutable references are not allowed in statics - --> $DIR/E0388.rs:5:39 + --> $DIR/E0388.rs:6:39 | LL | static STATIC_REF: &'static mut i32 = &mut X; | ^^^^^^ `&mut` is only allowed in `const fn` error[E0596]: cannot borrow immutable static item `X` as mutable - --> $DIR/E0388.rs:5:39 + --> $DIR/E0388.rs:6:39 | LL | static STATIC_REF: &'static mut i32 = &mut X; | ^^^^^^ cannot borrow as mutable +warning: taking a mutable reference to a `const` item + --> $DIR/E0388.rs:9:38 + | +LL | static CONST_REF: &'static mut i32 = &mut C; + | ^^^^^^ + | + = note: each usage of a `const` item creates a new temporary + = note: the mutable reference will refer to this temporary, not the original `const` item +note: `const` item defined here + --> $DIR/E0388.rs:2:1 + | +LL | const C: i32 = 2; + | ^^^^^^^^^^^^^^^^^ + error[E0764]: mutable references are not allowed in statics - --> $DIR/E0388.rs:8:38 + --> $DIR/E0388.rs:9:38 | LL | static CONST_REF: &'static mut i32 = &mut C; | ^^^^^^ `&mut` is only allowed in `const fn` -error: aborting due to 5 previous errors +error: aborting due to 5 previous errors; 2 warnings emitted Some errors have detailed explanations: E0019, E0596, E0764. For more information about an error, try `rustc --explain E0019`. diff --git a/src/test/ui/lint/lint-const-item-mutation.rs b/src/test/ui/lint/lint-const-item-mutation.rs new file mode 100644 index 00000000000..92d29a7dae4 --- /dev/null +++ b/src/test/ui/lint/lint-const-item-mutation.rs @@ -0,0 +1,21 @@ +// check-pass + +struct MyStruct { + field: bool, + inner_array: [char; 1], +} +impl MyStruct { + fn use_mut(&mut self) {} +} + +const ARRAY: [u8; 1] = [25]; +const MY_STRUCT: MyStruct = MyStruct { field: true, inner_array: ['a'] }; + +fn main() { + ARRAY[0] = 5; //~ WARN attempting to modify + MY_STRUCT.field = false; //~ WARN attempting to modify + MY_STRUCT.inner_array[0] = 'b'; //~ WARN attempting to modify + MY_STRUCT.use_mut(); //~ WARN taking + &mut MY_STRUCT; //~ WARN taking + (&mut MY_STRUCT).use_mut(); //~ WARN taking +} diff --git a/src/test/ui/lint/lint-const-item-mutation.stderr b/src/test/ui/lint/lint-const-item-mutation.stderr new file mode 100644 index 00000000000..2d8f2c49744 --- /dev/null +++ b/src/test/ui/lint/lint-const-item-mutation.stderr @@ -0,0 +1,89 @@ +warning: attempting to modify a `const` item + --> $DIR/lint-const-item-mutation.rs:15:5 + | +LL | ARRAY[0] = 5; + | ^^^^^^^^^^^^ + | + = note: `#[warn(const_item_mutation)]` on by default + = note: each usage of a `const` item creates a new temporary - the original `const` item will not be modified +note: `const` item defined here + --> $DIR/lint-const-item-mutation.rs:11:1 + | +LL | const ARRAY: [u8; 1] = [25]; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +warning: attempting to modify a `const` item + --> $DIR/lint-const-item-mutation.rs:16:5 + | +LL | MY_STRUCT.field = false; + | ^^^^^^^^^^^^^^^^^^^^^^^ + | + = note: each usage of a `const` item creates a new temporary - the original `const` item will not be modified +note: `const` item defined here + --> $DIR/lint-const-item-mutation.rs:12:1 + | +LL | const MY_STRUCT: MyStruct = MyStruct { field: true, inner_array: ['a'] }; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +warning: attempting to modify a `const` item + --> $DIR/lint-const-item-mutation.rs:17:5 + | +LL | MY_STRUCT.inner_array[0] = 'b'; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = note: each usage of a `const` item creates a new temporary - the original `const` item will not be modified +note: `const` item defined here + --> $DIR/lint-const-item-mutation.rs:12:1 + | +LL | const MY_STRUCT: MyStruct = MyStruct { field: true, inner_array: ['a'] }; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +warning: taking a mutable reference to a `const` item + --> $DIR/lint-const-item-mutation.rs:18:5 + | +LL | MY_STRUCT.use_mut(); + | ^^^^^^^^^^^^^^^^^^^ + | + = note: each usage of a `const` item creates a new temporary + = note: the mutable reference will refer to this temporary, not the original `const` item +note: mutable reference created due to call to this method + --> $DIR/lint-const-item-mutation.rs:8:5 + | +LL | fn use_mut(&mut self) {} + | ^^^^^^^^^^^^^^^^^^^^^ +note: `const` item defined here + --> $DIR/lint-const-item-mutation.rs:12:1 + | +LL | const MY_STRUCT: MyStruct = MyStruct { field: true, inner_array: ['a'] }; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +warning: taking a mutable reference to a `const` item + --> $DIR/lint-const-item-mutation.rs:19:5 + | +LL | &mut MY_STRUCT; + | ^^^^^^^^^^^^^^ + | + = note: each usage of a `const` item creates a new temporary + = note: the mutable reference will refer to this temporary, not the original `const` item +note: `const` item defined here + --> $DIR/lint-const-item-mutation.rs:12:1 + | +LL | const MY_STRUCT: MyStruct = MyStruct { field: true, inner_array: ['a'] }; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +warning: taking a mutable reference to a `const` item + --> $DIR/lint-const-item-mutation.rs:20:5 + | +LL | (&mut MY_STRUCT).use_mut(); + | ^^^^^^^^^^^^^^^^ + | + = note: each usage of a `const` item creates a new temporary + = note: the mutable reference will refer to this temporary, not the original `const` item +note: `const` item defined here + --> $DIR/lint-const-item-mutation.rs:12:1 + | +LL | const MY_STRUCT: MyStruct = MyStruct { field: true, inner_array: ['a'] }; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +warning: 6 warnings emitted +