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Auto merge of #86815 - FabianWolff:issue-84210, r=varkor

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Improve error reporting for modifications behind `&` references

I had a look at #84210 and noticed that #85823 has effectively already fixed #84210.

However, the string matching in #85823 is _very_ crude and already breaks down when a variable name starts with `mut`. I have made this a bit more robust; further improvements could definitely be made but are complicated by the lack of information provided by an earlier pass:
ce331ee6ee/compiler/rustc_mir_build/src/build/matches/mod.rs (L2103-L2107)

I have also fixed a missing comma in the error message.
This commit is contained in:
bors 2021-07-12 01:00:43 +00:00
commit e97c29bda2
34 changed files with 90 additions and 57 deletions
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24
compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs
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@ -147,7 +147,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
if let Some(desc) = access_place_desc {
item_msg = format!("`{}`", desc);
reason = match error_access {
AccessKind::Mutate => format!(" which is behind {}", pointer_type),
AccessKind::Mutate => format!(", which is behind {}", pointer_type),
AccessKind::MutableBorrow => {
format!(", as it is behind {}", pointer_type)
}
@ -897,16 +897,32 @@ fn suggest_ampmut<'tcx>(
) -> (Span, String) {
if let Some(assignment_rhs_span) = opt_assignment_rhs_span {
if let Ok(src) = tcx.sess.source_map().span_to_snippet(assignment_rhs_span) {
let is_mutbl = |ty: &str| -> bool {
if ty.starts_with("mut") {
let rest = &ty[3..];
match rest.chars().next() {
// e.g. `&mut x`
Some(c) if c.is_whitespace() => true,
// e.g. `&mut(x)`
Some('(') => true,
// e.g. `&mutablevar`
_ => false,
}
} else {
false
}
};
if let (true, Some(ws_pos)) =
(src.starts_with("&'"), src.find(|c: char| -> bool { c.is_whitespace() }))
{
let lt_name = &src[1..ws_pos];
let ty = &src[ws_pos..];
if !ty.trim_start().starts_with("mut") {
let ty = src[ws_pos..].trim_start();
if !is_mutbl(ty) {
return (assignment_rhs_span, format!("&{} mut {}", lt_name, ty));
}
} else if let Some(stripped) = src.strip_prefix('&') {
if !stripped.trim_start().starts_with("mut") {
let stripped = stripped.trim_start();
if !is_mutbl(stripped) {
return (assignment_rhs_span, format!("&mut {}", stripped));
}
}