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Rollup merge of rust-lang#95920 - compiler-errors:cast-suggestion-spa…
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…n, r=oli-obk

use `Span::find_ancestor_inside` to get right span in CastCheck

This is a quick fix. This bad suggestion likely lives in other places... but thought it would be useful to fix all of the CastCheck ones first.

Let me know if reviewer would prefer I add more tests for each of the diagnostics in CastCheck, or would like to do a more thorough review of other suggestions that use spans in typeck. I would also be open to further suggestions on how to better expose an API that gives us the "best" span for a diagnostic suggestion.

Fixed rust-lang#95919
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@Dylan-DPC
Dylan-DPC authored Apr 12, 2022
2 parents 443de03 + d2b1bb8 commit 06cc32f
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Showing 3 changed files with 42 additions and 18 deletions.
37 changes: 19 additions & 18 deletions compiler/rustc_typeck/src/check/cast.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,7 @@ use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
pub struct CastCheck<'tcx> {
expr: &'tcx hir::Expr<'tcx>,
expr_ty: Ty<'tcx>,
expr_span: Span,
cast_ty: Ty<'tcx>,
cast_span: Span,
span: Span,
Expand Down Expand Up @@ -207,7 +208,8 @@ impl<'a, 'tcx> CastCheck<'tcx> {
cast_span: Span,
span: Span,
) -> Result<CastCheck<'tcx>, ErrorGuaranteed> {
let check = CastCheck { expr, expr_ty, cast_ty, cast_span, span };
let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span);
let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span };

// For better error messages, check for some obviously unsized
// cases now. We do a more thorough check at the end, once
Expand Down Expand Up @@ -240,15 +242,15 @@ impl<'a, 'tcx> CastCheck<'tcx> {
error_span,
format!("cannot cast `{}` as `{}`", fcx.ty_to_string(self.expr_ty), cast_ty),
);
if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr.span) {
if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr_span) {
err.span_suggestion(
self.expr.span,
self.expr_span,
"dereference the expression",
format!("*{}", snippet),
Applicability::MaybeIncorrect,
);
} else {
err.span_help(self.expr.span, "dereference the expression with `*`");
err.span_help(self.expr_span, "dereference the expression with `*`");
}
err.emit();
}
Expand Down Expand Up @@ -315,7 +317,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {
struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`");

if self.expr_ty.is_numeric() {
match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
match fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
Ok(snippet) => {
err.span_suggestion(
self.span,
Expand Down Expand Up @@ -440,7 +442,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {
}
if sugg_mutref {
err.span_label(self.span, "invalid cast");
err.span_note(self.expr.span, "this reference is immutable");
err.span_note(self.expr_span, "this reference is immutable");
err.span_note(self.cast_span, "trying to cast to a mutable reference type");
} else if let Some((sugg, remove_cast)) = sugg {
err.span_label(self.span, "invalid cast");
Expand All @@ -449,7 +451,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {
.tcx
.sess
.source_map()
.span_to_snippet(self.expr.span)
.span_to_snippet(self.expr_span)
.map_or(false, |snip| snip.starts_with('('));

// Very crude check to see whether the expression must be wrapped
Expand All @@ -458,14 +460,14 @@ impl<'a, 'tcx> CastCheck<'tcx> {
let needs_parens =
!has_parens && matches!(self.expr.kind, hir::ExprKind::Cast(..));

let mut suggestion = vec![(self.expr.span.shrink_to_lo(), sugg)];
let mut suggestion = vec![(self.expr_span.shrink_to_lo(), sugg)];
if needs_parens {
suggestion[0].1 += "(";
suggestion.push((self.expr.span.shrink_to_hi(), ")".to_string()));
suggestion.push((self.expr_span.shrink_to_hi(), ")".to_string()));
}
if remove_cast {
suggestion.push((
self.expr.span.shrink_to_hi().to(self.cast_span),
self.expr_span.shrink_to_hi().to(self.cast_span),
String::new(),
));
}
Expand All @@ -481,7 +483,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {
) {
let mut label = true;
// Check `impl From<self.expr_ty> for self.cast_ty {}` for accurate suggestion:
if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
if let Some(from_trait) = fcx.tcx.get_diagnostic_item(sym::From) {
let ty = fcx.resolve_vars_if_possible(self.cast_ty);
// Erase regions to avoid panic in `prove_value` when calling
Expand Down Expand Up @@ -550,7 +552,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {

if fcx.tcx.sess.is_nightly_build() {
err.span_label(
self.expr.span,
self.expr_span,
"consider casting this expression to `*const ()`, \
then using `core::ptr::from_raw_parts`",
);
Expand Down Expand Up @@ -651,7 +653,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {
}
}
_ => {
err.span_help(self.expr.span, "consider using a box or reference as appropriate");
err.span_help(self.expr_span, "consider using a box or reference as appropriate");
}
}
err.emit()
Expand Down Expand Up @@ -685,7 +687,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {

#[instrument(skip(fcx), level = "debug")]
pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
self.expr_ty = fcx.structurally_resolved_type(self.expr.span, self.expr_ty);
self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty);
self.cast_ty = fcx.structurally_resolved_type(self.cast_span, self.cast_ty);

debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
Expand Down Expand Up @@ -741,7 +743,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {
ty::FnDef(..) => {
// Attempt a coercion to a fn pointer type.
let f = fcx.normalize_associated_types_in(
self.expr.span,
self.expr_span,
self.expr_ty.fn_sig(fcx.tcx),
);
let res = fcx.try_coerce(
Expand Down Expand Up @@ -997,7 +999,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {
));

let msg = "use `.addr()` to obtain the address of a pointer";
if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
let scalar_cast = match t_c {
ty::cast::IntTy::U(ty::UintTy::Usize) => String::new(),
_ => format!(" as {}", self.cast_ty),
Expand Down Expand Up @@ -1027,13 +1029,12 @@ impl<'a, 'tcx> CastCheck<'tcx> {
self.expr.hir_id,
self.span,
|err| {

let mut err = err.build(&format!(
"strict provenance disallows casting integer `{}` to pointer `{}`",
self.expr_ty, self.cast_ty
));
let msg = "use `.with_addr()` to adjust a valid pointer in the same allocation, to this address";
if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
err.span_suggestion(
self.span,
msg,
Expand Down
12 changes: 12 additions & 0 deletions src/test/ui/cast/cast-macro-lhs.rs
View file
Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
// Test to make sure we suggest "consider casting" on the right span

macro_rules! foo {
() => { 0 }
}

fn main() {
let x = foo!() as *const [u8];
//~^ ERROR cannot cast `usize` to a pointer that is wide
//~| NOTE creating a `*const [u8]` requires both an address and a length
//~| NOTE consider casting this expression to `*const ()`, then using `core::ptr::from_raw_parts`
}
11 changes: 11 additions & 0 deletions src/test/ui/cast/cast-macro-lhs.stderr
View file
Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
error[E0606]: cannot cast `usize` to a pointer that is wide
--> $DIR/cast-macro-lhs.rs:8:23
|
LL | let x = foo!() as *const [u8];
| ------ ^^^^^^^^^^^ creating a `*const [u8]` requires both an address and a length
| |
| consider casting this expression to `*const ()`, then using `core::ptr::from_raw_parts`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0606`.

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