Avoid unnecessary RefCell::borrow_mut

2 files changed, 37 insertions, 20 deletions

diff --git a/dhall/src/normalize.rs b/dhall/src/normalize.rs
index cff7fdc..5749989 100644
--- a/dhall/src/normalize.rs
+++ b/dhall/src/normalize.rs
@@ -1002,9 +1002,11 @@ mod thunk {
         }
 
         fn normalize_nf(&mut self) {
-            self.normalize_whnf();
             match self {
-                ThunkInternal::Unnormalized(_, _) => unreachable!(),
+                ThunkInternal::Unnormalized(_, _) => {
+                    self.normalize_whnf();
+                    self.normalize_nf();
+                }
                 ThunkInternal::Value(m @ WHNF, v) => {
                     v.normalize_mut();
                     *m = NF;
@@ -1091,17 +1093,42 @@ mod thunk {
             }
         }
 
+        fn do_normalize_whnf(&self) {
+            let borrow = self.0.borrow();
+            match &*borrow {
+                ThunkInternal::Unnormalized(_, _) => {
+                    drop(borrow);
+                    self.0.borrow_mut().normalize_whnf();
+                }
+                // Already at least in WHNF
+                ThunkInternal::Value(_, _) => {}
+            }
+        }
+
+        fn do_normalize_nf(&self) {
+            let borrow = self.0.borrow();
+            match &*borrow {
+                ThunkInternal::Unnormalized(_, _)
+                | ThunkInternal::Value(WHNF, _) => {
+                    drop(borrow);
+                    self.0.borrow_mut().normalize_nf();
+                }
+                // Already in NF
+                ThunkInternal::Value(NF, _) => {}
+            }
+        }
+
         // WARNING: avoid normalizing any thunk while holding on to this ref
-        // or you will run into BorrowMut panics
+        // or you could run into BorrowMut panics
         pub(crate) fn normalize_whnf(&self) -> Ref<Value> {
-            self.0.borrow_mut().normalize_whnf();
+            self.do_normalize_whnf();
             Ref::map(self.0.borrow(), ThunkInternal::as_whnf)
         }
 
         // WARNING: avoid normalizing any thunk while holding on to this ref
-        // or you will run into BorrowMut panics
+        // or you could run into BorrowMut panics
         pub(crate) fn normalize_nf(&self) -> Ref<Value> {
-            self.0.borrow_mut().normalize_nf();
+            self.do_normalize_nf();
             Ref::map(self.0.borrow(), ThunkInternal::as_nf)
         }
 
diff --git a/dhall/src/typecheck.rs b/dhall/src/typecheck.rs
index c6f3645..d68d304 100644
--- a/dhall/src/typecheck.rs
+++ b/dhall/src/typecheck.rs
@@ -901,13 +901,9 @@ fn type_last_layer(
             ))
         }
         Field(r, x) => {
-            let tr = r.get_type()?;
-            let tr_internal = tr.internal_whnf();
-            match &tr_internal {
+            match &r.get_type()?.internal_whnf() {
                 Some(Value::RecordType(kts)) => match kts.get(&x) {
                     Some(tth) => {
-                        let tth = tth.clone();
-                        drop(tr_internal);
                         Ok(RetType(tth.to_type(ctx)?))
                     },
                     None => Err(mkerr(MissingRecordField(x, r.clone()))),
@@ -915,31 +911,26 @@ fn type_last_layer(
                 // TODO: branch here only when r.get_type() is a Const
                 _ => {
                     let r = r.to_type();
-                    let r_internal = r.internal_whnf();
-                    match &r_internal {
+                    match &r.internal_whnf() {
                         Some(Value::UnionType(kts)) => match kts.get(&x) {
                             // Constructor has type T -> < x: T, ... >
                             // TODO: use "_" instead of x (i.e. compare types using equivalence in tests)
                             Some(Some(t)) => {
-                                let t = t.clone();
-                                drop(r_internal);
                                 Ok(RetType(
                                     TypeIntermediate::Pi(
                                         ctx.clone(),
                                         x.clone(),
                                         t.to_type(ctx)?,
-                                        r,
+                                        r.clone(),
                                     )
                                     .typecheck()?
                                     .to_type(),
                                 ))
                             },
                             Some(None) => {
-                                drop(r_internal);
-                                Ok(RetType(r))
+                                Ok(RetType(r.clone()))
                             },
                             None => {
-                                drop(r_internal);
                                 Err(mkerr(MissingUnionField(
                                     x,
                                     r.to_normalized(),
@@ -947,7 +938,6 @@ fn type_last_layer(
                             },
                         },
                         _ => {
-                            drop(r_internal);
                             Err(mkerr(NotARecord(
                                 x,
                                 r.to_normalized()