Rollup merge of #95920 - compiler-errors:cast-suggestion-span, 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 #95919

3 files changed, 42 insertions, 18 deletions

diff --git a/compiler/rustc_typeck/src/check/cast.rs b/compiler/rustc_typeck/src/check/cast.rs
index e73b9c979eb..47292b3e339 100644
--- a/compiler/rustc_typeck/src/check/cast.rs
+++ b/compiler/rustc_typeck/src/check/cast.rs
@@ -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,
@@ -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
@@ -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();
             }
@@ -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,
@@ -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");
@@ -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
@@ -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(),
                         ));
                     }
@@ -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
@@ -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`",
                     );
@@ -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()
@@ -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);
@@ -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(
@@ -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),
@@ -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,
diff --git a/src/test/ui/cast/cast-macro-lhs.rs b/src/test/ui/cast/cast-macro-lhs.rs
new file mode 100644
index 00000000000..b509b3239bc
--- /dev/null
+++ b/src/test/ui/cast/cast-macro-lhs.rs
@@ -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`
+}
diff --git a/src/test/ui/cast/cast-macro-lhs.stderr b/src/test/ui/cast/cast-macro-lhs.stderr
new file mode 100644
index 00000000000..db7ce57e150
--- /dev/null
+++ b/src/test/ui/cast/cast-macro-lhs.stderr
@@ -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`.