[gcc/devel/rust/master] Merge #820

[gcc/devel/rust/master] Merge #820

[Thomas Schwinge]

https://gcc.gnu.org/g:98fb902fb3029da33c5a8d2fd4bd7d7bcb7271ee

commit 98fb902fb3029da33c5a8d2fd4bd7d7bcb7271ee
Merge: 295f0ae1661 a2f59f14cea
Author: bors[bot] <26634292+bors[bot]@users.noreply.github.com>
Date:   Thu Nov 25 15:28:54 2021 +0000

    Merge #820
    
    820: Bug fix mutability checks in can_eq for autoderef r=philberty a=philberty
    
    Rust is permissive about mutablity in type checking for example, if we have
    a function:
    
      fn foo(a:&bar) { ... }
    
      fn caller() {
        let a:&mut bar = ...;
        foo(a);
      }
    
    This is valid since the mutable reference to bar is valid to be turned into
    an immutable reference without any conversion. Like in C a non-const
    pointer is valid to be passed to a const pointer inferface.
    
    
    Co-authored-by: Philip Herron <philip.herron@embecosm.com>

Diff:

 gcc/rust/typecheck/rust-hir-dot-operator.h |  6 ++---
 gcc/rust/typecheck/rust-tyty-cmp.h         | 42 +++++++++++++++++++++++++-----
 gcc/rust/typecheck/rust-tyty-rules.h       | 10 +++++--
 gcc/rust/typecheck/rust-tyty.cc            |  2 +-
 4 files changed, 48 insertions(+), 12 deletions(-)