Rollup merge of #103226 - compiler-errors:delay-if-need-infer, r=lcnr

Check `needs_infer` before `needs_drop` during HIR generator analysis

This is kinda a revival of #103036, but with the understanding that after fallback, a generator-interior type will only have `needs_infer` true if there's an error that prevented int or float variable fallback to occur (modulo region variables, which are erased).

Therefore the best choice here is to delay a bug and skip the `needs_drop` call altogether.

r? `@lcnr` feel free to reassign though

2 files changed, 23 insertions, 18 deletions

diff --git a/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/record_consumed_borrow.rs b/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/record_consumed_borrow.rs
index 7954ddc4166..bfe95852aa7 100644
--- a/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/record_consumed_borrow.rs
+++ b/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/record_consumed_borrow.rs
@@ -6,8 +6,11 @@ use crate::{
 use hir::{def_id::DefId, Body, HirId, HirIdMap};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
-use rustc_middle::hir::place::{PlaceBase, Projection, ProjectionKind};
 use rustc_middle::ty::{ParamEnv, TyCtxt};
+use rustc_middle::{
+    hir::place::{PlaceBase, Projection, ProjectionKind},
+    ty::TypeVisitable,
+};
 
 pub(super) fn find_consumed_and_borrowed<'a, 'tcx>(
     fcx: &'a FnCtxt<'a, 'tcx>,
@@ -198,11 +201,13 @@ impl<'tcx> expr_use_visitor::Delegate<'tcx> for ExprUseDelegate<'tcx> {
 
         // If the type being assigned needs dropped, then the mutation counts as a borrow
         // since it is essentially doing `Drop::drop(&mut x); x = new_value;`.
-        //
-        // FIXME(drop-tracking): We need to be more responsible about inference
-        // variables here, since `needs_drop` is a "raw" type query, i.e. it
-        // basically requires types to have been fully resolved.
-        if assignee_place.place.base_ty.needs_drop(self.tcx, self.param_env) {
+        let ty = self.tcx.erase_regions(assignee_place.place.base_ty);
+        if ty.needs_infer() {
+            self.tcx.sess.delay_span_bug(
+                self.tcx.hir().span(assignee_place.hir_id),
+                &format!("inference variables in {ty}"),
+            );
+        } else if ty.needs_drop(self.tcx, self.param_env) {
             self.places
                 .borrowed
                 .insert(TrackedValue::from_place_with_projections_allowed(assignee_place));
diff --git a/compiler/rustc_hir_typeck/src/generator_interior/mod.rs b/compiler/rustc_hir_typeck/src/generator_interior/mod.rs
index 898419b5b23..b7dd599cd43 100644
--- a/compiler/rustc_hir_typeck/src/generator_interior/mod.rs
+++ b/compiler/rustc_hir_typeck/src/generator_interior/mod.rs
@@ -377,15 +377,6 @@ impl<'a, 'tcx> Visitor<'tcx> for InteriorVisitor<'a, 'tcx> {
         debug!("is_borrowed_temporary: {:?}", self.drop_ranges.is_borrowed_temporary(expr));
 
         let ty = self.fcx.typeck_results.borrow().expr_ty_adjusted_opt(expr);
-        let may_need_drop = |ty: Ty<'tcx>| {
-            // Avoid ICEs in needs_drop.
-            let ty = self.fcx.resolve_vars_if_possible(ty);
-            let ty = self.fcx.tcx.erase_regions(ty);
-            if ty.needs_infer() {
-                return true;
-            }
-            ty.needs_drop(self.fcx.tcx, self.fcx.param_env)
-        };
 
         // Typically, the value produced by an expression is consumed by its parent in some way,
         // so we only have to check if the parent contains a yield (note that the parent may, for
@@ -403,9 +394,18 @@ impl<'a, 'tcx> Visitor<'tcx> for InteriorVisitor<'a, 'tcx> {
         // src/test/ui/generator/drop-tracking-parent-expression.rs.
         let scope = if self.drop_ranges.is_borrowed_temporary(expr)
             || ty.map_or(true, |ty| {
-                let needs_drop = may_need_drop(ty);
-                debug!(?needs_drop, ?ty);
-                needs_drop
+                // Avoid ICEs in needs_drop.
+                let ty = self.fcx.resolve_vars_if_possible(ty);
+                let ty = self.fcx.tcx.erase_regions(ty);
+                if ty.needs_infer() {
+                    self.fcx
+                        .tcx
+                        .sess
+                        .delay_span_bug(expr.span, &format!("inference variables in {ty}"));
+                    true
+                } else {
+                    ty.needs_drop(self.fcx.tcx, self.fcx.param_env)
+                }
             }) {
             self.rvalue_scopes.temporary_scope(self.region_scope_tree, expr.hir_id.local_id)
         } else {