Fix span lookup for function signature during erasure

Author: utaal

verify/rust_verify/src/erase.rs

@@ -274,13 +274,13 @@ fn erase_block(ctxt: &Ctxt, is_exec: bool, block: &Block) -> Block {
     Block { stmts, id, rules, span, tokens: block.tokens.clone() }
 }
 
-fn erase_fn(ctxt: &Ctxt, f_span: &Span, f: &FnKind) -> Option<FnKind> {
-    let f_vir = &ctxt.functions_by_span[f_span];
+fn erase_fn(ctxt: &Ctxt, f: &FnKind) -> Option<FnKind> {
+    let FnKind(defaultness, sig, generics, body_opt) = f;
+    let f_vir = &ctxt.functions_by_span[&sig.span];
     match f_vir.x.mode {
         Mode::Spec | Mode::Proof => return None,
         Mode::Exec => {}
     }
-    let FnKind(defaultness, sig, generics, body_opt) = f;
     let FnSig { header: _, decl, span: _ } = sig;
     let FnDecl { inputs, output } = &**decl;
     let mut new_inputs: Vec<Param> = Vec::new();
@@ -318,7 +318,7 @@ fn erase_item(ctxt: &Ctxt, item: &Item) -> Vec<P<Item>> {
             if vattrs.external {
                 return vec![P(item.clone())];
             }
-            match erase_fn(ctxt, &item.span, kind) {
+            match erase_fn(ctxt, kind) {
                 None => return vec![],
                 Some(kind) => ItemKind::Fn(Box::new(kind)),
             }

verify/rust_verify/src/rust_to_vir.rs

@@ -14,7 +14,7 @@ use crate::util::unsupported_err_span;
 use crate::{err_unless, unsupported_err, unsupported_err_unless, unsupported_unless};
 use rustc_ast::Attribute;
 use rustc_hir::{
-    AssocItemKind, Crate, ForeignItem, ForeignItemId, ForeignItemKind, HirId, ImplItemKind, Item,
+    Crate, ForeignItem, ForeignItemId, ForeignItemKind, HirId, Item,
     ItemId, ItemKind, ModuleItems, QPath, TraitRef, TyKind,
 };
 use rustc_middle::ty::TyCtxt;