diff --git a/src/librustc_borrowck/borrowck/mod.rs b/src/librustc_borrowck/borrowck/mod.rs index 58112650c05d0..4529e4bab752c 100644 --- a/src/librustc_borrowck/borrowck/mod.rs +++ b/src/librustc_borrowck/borrowck/mod.rs @@ -772,11 +772,12 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> { &move_data::Assignment) { let mut err = self.cannot_reassign_immutable(span, &self.loan_path_to_string(lp), + false, Origin::Ast); err.span_label(span, "cannot assign twice to immutable variable"); if span != assign.span { err.span_label(assign.span, format!("first assignment to `{}`", - self.loan_path_to_string(lp))); + self.loan_path_to_string(lp))); } err.emit(); } diff --git a/src/librustc_mir/borrow_check/error_reporting.rs b/src/librustc_mir/borrow_check/error_reporting.rs index 19bebea7cb8f1..a3c1a4bd88c5c 100644 --- a/src/librustc_mir/borrow_check/error_reporting.rs +++ b/src/librustc_mir/borrow_check/error_reporting.rs @@ -10,7 +10,7 @@ use syntax_pos::Span; use rustc::middle::region::ScopeTree; -use rustc::mir::{BorrowKind, Field, Local, Location, Operand}; +use rustc::mir::{BorrowKind, Field, Local, LocalKind, Location, Operand}; use rustc::mir::{Place, ProjectionElem, Rvalue, Statement, StatementKind}; use rustc::ty::{self, RegionKind}; use rustc_data_structures::indexed_vec::Idx; @@ -568,19 +568,39 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> { (place, span): (&Place<'tcx>, Span), assigned_span: Span, ) { + let is_arg = if let Place::Local(local) = place { + if let LocalKind::Arg = self.mir.local_kind(*local) { + true + } else { + false + } + } else { + false + }; + let mut err = self.tcx.cannot_reassign_immutable( span, &self.describe_place(place).unwrap_or("_".to_owned()), + is_arg, Origin::Mir, ); - err.span_label(span, "cannot assign twice to immutable variable"); + let msg = if is_arg { + "cannot assign to immutable argument" + } else { + "cannot assign twice to immutable variable" + }; if span != assigned_span { - let value_msg = match self.describe_place(place) { - Some(name) => format!("`{}`", name), - None => "value".to_owned(), - }; - err.span_label(assigned_span, format!("first assignment to {}", value_msg)); + if is_arg { + err.span_label(assigned_span, "argument not declared as `mut`"); + } else { + let value_msg = match self.describe_place(place) { + Some(name) => format!("`{}`", name), + None => "value".to_owned(), + }; + err.span_label(assigned_span, format!("first assignment to {}", value_msg)); + } } + err.span_label(span, msg); err.emit(); } } diff --git a/src/librustc_mir/util/borrowck_errors.rs b/src/librustc_mir/util/borrowck_errors.rs index 38227bd713322..4a7ee397aec00 100644 --- a/src/librustc_mir/util/borrowck_errors.rs +++ b/src/librustc_mir/util/borrowck_errors.rs @@ -269,12 +269,17 @@ pub trait BorrowckErrors { self.cancel_if_wrong_origin(err, o) } - fn cannot_reassign_immutable(&self, span: Span, desc: &str, o: Origin) + fn cannot_reassign_immutable(&self, span: Span, desc: &str, is_arg: bool, o: Origin) -> DiagnosticBuilder { + let msg = if is_arg { + "to immutable argument" + } else { + "twice to immutable variable" + }; let err = struct_span_err!(self, span, E0384, - "cannot assign twice to immutable variable `{}`{OGN}", - desc, OGN=o); + "cannot assign {} `{}`{OGN}", + msg, desc, OGN=o); self.cancel_if_wrong_origin(err, o) } diff --git a/src/test/compile-fail/issue-45199.rs b/src/test/compile-fail/issue-45199.rs index af8f7dce60875..ecddb4c101fdf 100644 --- a/src/test/compile-fail/issue-45199.rs +++ b/src/test/compile-fail/issue-45199.rs @@ -31,11 +31,11 @@ fn test_call() { } fn test_args(b: Box) { //[ast]~ NOTE first assignment - //[mir]~^ NOTE first assignment + //[mir]~^ NOTE argument not declared as `mut` b = Box::new(2); //[ast]~ ERROR cannot assign twice to immutable variable - //[mir]~^ ERROR cannot assign twice to immutable variable `b` + //[mir]~^ ERROR cannot assign to immutable argument `b` //[ast]~| NOTE cannot assign twice to immutable - //[mir]~| NOTE cannot assign twice to immutable + //[mir]~| NOTE cannot assign to immutable argument } fn main() {} diff --git a/src/test/ui/borrowck/immutable-arg.rs b/src/test/ui/borrowck/immutable-arg.rs new file mode 100644 index 0000000000000..7c387ed080821 --- /dev/null +++ b/src/test/ui/borrowck/immutable-arg.rs @@ -0,0 +1,20 @@ +// Copyright 2018 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +//compile-flags: -Z emit-end-regions -Z borrowck=compare + +fn foo(_x: u32) { + _x = 4; + //~^ ERROR cannot assign to immutable argument `_x` (Mir) + //~^^ ERROR cannot assign twice to immutable variable `_x` (Ast) +} + +fn main() {} + diff --git a/src/test/ui/borrowck/immutable-arg.stderr b/src/test/ui/borrowck/immutable-arg.stderr new file mode 100644 index 0000000000000..40e1878f73214 --- /dev/null +++ b/src/test/ui/borrowck/immutable-arg.stderr @@ -0,0 +1,18 @@ +error[E0384]: cannot assign twice to immutable variable `_x` (Ast) + --> $DIR/immutable-arg.rs:14:5 + | +13 | fn foo(_x: u32) { + | -- first assignment to `_x` +14 | _x = 4; + | ^^^^^^ cannot assign twice to immutable variable + +error[E0384]: cannot assign to immutable argument `_x` (Mir) + --> $DIR/immutable-arg.rs:14:5 + | +13 | fn foo(_x: u32) { + | -- argument not declared as `mut` +14 | _x = 4; + | ^^^^^^ cannot assign to immutable argument + +error: aborting due to 2 previous errors +