Rollup merge of #132243 - compiler-errors:no-span, r=jieyouxu

Remove `ObligationCause::span()` method

I think it's an incredibly confusing footgun to expose both `obligation_cause.span` and `obligation_cause.span()`. Especially because `ObligationCause::span()` (the method) seems to just be hacking around a single quirk in the way we set up obligation causes for match arms.

First commit removes the need for that hack, with only one diagnostic span changing (but IMO not really getting worse -- I'd argue that it was already confusing).

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -611,7 +611,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
         Err(terr) => {
             let mut diag = struct_span_code_err!(
                 tcx.dcx(),
-                cause.span(),
+                cause.span,
                 E0053,
                 "method `{}` has an incompatible return type for trait",
                 trait_m.name
@@ -1169,7 +1169,7 @@ fn extract_spans_for_error_reporting<'tcx>(
         TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(ExpectedFound { .. }, i) => {
             (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
         }
-        _ => (cause.span(), tcx.hir().span_if_local(trait_m.def_id)),
+        _ => (cause.span, tcx.hir().span_if_local(trait_m.def_id)),
     }
 }
 

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -612,7 +612,7 @@ fn extract_span_for_error_reporting<'tcx>(
         match err {
             TypeError::ArgumentMutability(i)
             | TypeError::ArgumentSorts(ExpectedFound { .. }, i) => args.nth(i).unwrap(),
-            _ => cause.span(),
+            _ => cause.span,
         }
     }
 

compiler/rustc_hir_typeck/src/_match.rs

@@ -94,14 +94,11 @@ pub(crate) fn check_match(
                 (None, arm.body.span)
             };
 
-            let (span, code) = match prior_arm {
+            let code = match prior_arm {
                 // The reason for the first arm to fail is not that the match arms diverge,
                 // but rather that there's a prior obligation that doesn't hold.
-                None => {
-                    (arm_span, ObligationCauseCode::BlockTailExpression(arm.body.hir_id, match_src))
-                }
-                Some((prior_arm_block_id, prior_arm_ty, prior_arm_span)) => (
-                    expr.span,
+                None => ObligationCauseCode::BlockTailExpression(arm.body.hir_id, match_src),
+                Some((prior_arm_block_id, prior_arm_ty, prior_arm_span)) => {
                     ObligationCauseCode::MatchExpressionArm(Box::new(MatchExpressionArmCause {
                         arm_block_id,
                         arm_span,
@@ -110,13 +107,14 @@ pub(crate) fn check_match(
                         prior_arm_ty,
                         prior_arm_span,
                         scrut_span: scrut.span,
+                        expr_span: expr.span,
                         source: match_src,
                         prior_non_diverging_arms: prior_non_diverging_arms.clone(),
                         tail_defines_return_position_impl_trait,
-                    })),
-                ),
+                    }))
+                }
             };
-            let cause = self.cause(span, code);
+            let cause = self.cause(arm_span, code);
 
             // This is the moral equivalent of `coercion.coerce(self, cause, arm.body, arm_ty)`.
             // We use it this way to be able to expand on the potential error and detect when a

compiler/rustc_hir_typeck/src/expr.rs

@@ -2027,7 +2027,7 @@ fn check_expr_struct_fields(
                                     }
                                     Err(_) => {
                                         span_bug!(
-                                            cause.span(),
+                                            cause.span,
                                             "subtyping remaining fields of type changing FRU failed: {target_ty} != {fru_ty}: {}::{}",
                                             variant.name,
                                             ident.name,

compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -550,7 +550,7 @@ fn unify_receivers(
                     // This has/will have errored in wfcheck, which we cannot depend on from here, as typeck on functions
                     // may run before wfcheck if the function is used in const eval.
                     self.dcx().span_delayed_bug(
-                        cause.span(),
+                        cause.span,
                         format!("{self_ty} was a subtype of {method_self_ty} but now is not?"),
                     );
                 }

compiler/rustc_middle/src/traits/mod.rs

@@ -92,16 +92,6 @@ pub fn dummy_with_span(span: Span) -> ObligationCause<'tcx> {
         ObligationCause { span, body_id: CRATE_DEF_ID, code: Default::default() }
     }
 
-    pub fn span(&self) -> Span {
-        match *self.code() {
-            ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
-                arm_span,
-                ..
-            }) => arm_span,
-            _ => self.span,
-        }
-    }
-
     #[inline]
     pub fn code(&self) -> &ObligationCauseCode<'tcx> {
         &self.code
@@ -517,10 +507,17 @@ pub struct MatchExpressionArmCause<'tcx> {
     pub prior_arm_block_id: Option<HirId>,
     pub prior_arm_ty: Ty<'tcx>,
     pub prior_arm_span: Span,
+    /// Span of the scrutinee of the match (the matched value).
     pub scrut_span: Span,
+    /// Source of the match, i.e. `match` or a desugaring.
     pub source: hir::MatchSource,
+    /// Span of the *whole* match expr.
+    pub expr_span: Span,
+    /// Spans of the previous arms except for those that diverge (i.e. evaluate to `!`).
+    ///
+    /// These are used for pointing out errors that may affect several arms.
     pub prior_non_diverging_arms: Vec<Span>,
-    // Is the expectation of this match expression an RPIT?
+    /// Is the expectation of this match expression an RPIT?
     pub tail_defines_return_position_impl_trait: Option<LocalDefId>,
 }
 

compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs

@@ -392,7 +392,7 @@ fn note_error_origin(
                         Some(ty) if expected == ty => {
                             let source_map = self.tcx.sess.source_map();
                             err.span_suggestion(
-                                source_map.end_point(cause.span()),
+                                source_map.end_point(cause.span),
                                 "try removing this `?`",
                                 "",
                                 Applicability::MachineApplicable,
@@ -412,6 +412,7 @@ fn note_error_origin(
                 source,
                 ref prior_non_diverging_arms,
                 scrut_span,
+                expr_span,
                 ..
             }) => match source {
                 hir::MatchSource::TryDesugar(scrut_hir_id) => {
@@ -430,7 +431,7 @@ fn note_error_origin(
                             Some(ty) if expected == ty => {
                                 let source_map = self.tcx.sess.source_map();
                                 err.span_suggestion(
-                                    source_map.end_point(cause.span()),
+                                    source_map.end_point(cause.span),
                                     "try removing this `?`",
                                     "",
                                     Applicability::MachineApplicable,
@@ -460,12 +461,12 @@ fn note_error_origin(
                             format!("this and all prior arms are found to be of type `{t}`"),
                         );
                     }
-                    let outer = if any_multiline_arm || !source_map.is_multiline(cause.span) {
+                    let outer = if any_multiline_arm || !source_map.is_multiline(expr_span) {
                         // Cover just `match` and the scrutinee expression, not
                         // the entire match body, to reduce diagram noise.
-                        cause.span.shrink_to_lo().to(scrut_span)
+                        expr_span.shrink_to_lo().to(scrut_span)
                     } else {
-                        cause.span
+                        expr_span
                     };
                     let msg = "`match` arms have incompatible types";
                     err.span_label(outer, msg);
@@ -1148,7 +1149,7 @@ pub fn note_type_err(
         terr: TypeError<'tcx>,
         prefer_label: bool,
     ) {
-        let span = cause.span();
+        let span = cause.span;
 
         // For some types of errors, expected-found does not make
         // sense, so just ignore the values we were given.
@@ -1642,7 +1643,7 @@ pub fn type_error_additional_suggestions(
         terr: TypeError<'tcx>,
     ) -> Vec<TypeErrorAdditionalDiags> {
         let mut suggestions = Vec::new();
-        let span = trace.cause.span();
+        let span = trace.cause.span;
         let values = self.resolve_vars_if_possible(trace.values);
         if let Some((expected, found)) = values.ty() {
             match (expected.kind(), found.kind()) {
@@ -1792,7 +1793,7 @@ pub fn report_and_explain_type_error(
     ) -> Diag<'a> {
         debug!("report_and_explain_type_error(trace={:?}, terr={:?})", trace, terr);
 
-        let span = trace.cause.span();
+        let span = trace.cause.span;
         let failure_code = trace.cause.as_failure_code_diag(
             terr,
             span,

compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/placeholder_error.rs

@@ -237,7 +237,7 @@ fn report_trait_placeholder_mismatch(
         expected_args: GenericArgsRef<'tcx>,
         actual_args: GenericArgsRef<'tcx>,
     ) -> Diag<'tcx> {
-        let span = cause.span();
+        let span = cause.span;
 
         let (leading_ellipsis, satisfy_span, where_span, dup_span, def_id) =
             if let ObligationCauseCode::WhereClause(def_id, span)

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1180,7 +1180,7 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
                                             selcx.tcx(),
                                             selcx.tcx().require_lang_item(
                                                 LangItem::Sized,
-                                                Some(obligation.cause.span()),
+                                                Some(obligation.cause.span),
                                             ),
                                             [self_ty],
                                         ),
@@ -1600,7 +1600,7 @@ fn confirm_builtin_candidate<'cx, 'tcx>(
                 // exist. Instead, `Pointee<Metadata = ()>` should be a supertrait of `Sized`.
                 let sized_predicate = ty::TraitRef::new(
                     tcx,
-                    tcx.require_lang_item(LangItem::Sized, Some(obligation.cause.span())),
+                    tcx.require_lang_item(LangItem::Sized, Some(obligation.cause.span)),
                     [self_ty],
                 );
                 obligations.push(obligation.with(tcx, sized_predicate));

compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs

@@ -90,7 +90,7 @@ fn evaluate_obligation(
             assert!(!self.intercrate);
             let c_pred =
                 self.canonicalize_query(param_env.and(obligation.predicate), &mut _orig_values);
-            self.tcx.at(obligation.cause.span()).evaluate_obligation(c_pred)
+            self.tcx.at(obligation.cause.span).evaluate_obligation(c_pred)
         }
     }
 

tests/ui/wf/wf-dyn-incompat-trait-obj-match.rs

@@ -22,8 +22,8 @@ fn main() {
         Some(()) => &S,
         None => &R,  //~ ERROR E0308
     }
-    let t: &dyn Trait = match opt() { //~ ERROR E0038
+    let t: &dyn Trait = match opt() {
         Some(()) => &S, //~ ERROR E0038
-        None => &R,
+        None => &R, //~ ERROR E0038
     };
 }

tests/ui/wf/wf-dyn-incompat-trait-obj-match.stderr

@@ -31,14 +31,10 @@ LL | trait Trait: Sized {}
    = note: required for the cast from `&S` to `&dyn Trait`
 
 error[E0038]: the trait `Trait` cannot be made into an object
-  --> $DIR/wf-dyn-incompat-trait-obj-match.rs:25:25
+  --> $DIR/wf-dyn-incompat-trait-obj-match.rs:27:17
    |
-LL |       let t: &dyn Trait = match opt() {
-   |  _________________________^
-LL | |         Some(()) => &S,
-LL | |         None => &R,
-LL | |     };
-   | |_____^ `Trait` cannot be made into an object
+LL |         None => &R,
+   |                 ^^ `Trait` cannot be made into an object
    |
 note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/wf-dyn-incompat-trait-obj-match.rs:6:14