Rollup merge of #85935 - tmiasko:validate-indexing, r=jonas-schievink

Validate type of locals used as indices

compiler/rustc_mir/src/transform/validate.rs

@@ -11,8 +11,9 @@
 use rustc_middle::mir::traversal;
 use rustc_middle::mir::visit::{PlaceContext, Visitor};
 use rustc_middle::mir::{
-    AggregateKind, BasicBlock, Body, BorrowKind, Local, Location, MirPhase, Operand, PlaceRef,
-    Rvalue, SourceScope, Statement, StatementKind, Terminator, TerminatorKind,
+    AggregateKind, BasicBlock, Body, BorrowKind, Local, Location, MirPhase, Operand, PlaceElem,
+    PlaceRef, ProjectionElem, Rvalue, SourceScope, Statement, StatementKind, Terminator,
+    TerminatorKind,
 };
 use rustc_middle::ty::fold::BottomUpFolder;
 use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt, TypeFoldable};
@@ -217,6 +218,23 @@ fn visit_operand(&mut self, operand: &Operand<'tcx>, location: Location) {
         self.super_operand(operand, location);
     }
 
+    fn visit_projection_elem(
+        &mut self,
+        local: Local,
+        proj_base: &[PlaceElem<'tcx>],
+        elem: PlaceElem<'tcx>,
+        context: PlaceContext,
+        location: Location,
+    ) {
+        if let ProjectionElem::Index(index) = elem {
+            let index_ty = self.body.local_decls[index].ty;
+            if index_ty != self.tcx.types.usize {
+                self.fail(location, format!("bad index ({:?} != usize)", index_ty))
+            }
+        }
+        self.super_projection_elem(local, proj_base, elem, context, location);
+    }
+
     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
         match &statement.kind {
             StatementKind::Assign(box (dest, rvalue)) => {