Refactor projection debug.

compiler/rustc_middle/src/mir/mod.rs

@@ -1575,7 +1575,7 @@ pub fn can_use_in_debuginfo(&self) -> bool {
 /// need neither the `V` parameter for `Index` nor the `T` for `Field`.
 pub type ProjectionKind = ProjectionElem<(), ()>;
 
-#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
 pub struct PlaceRef<'tcx> {
     pub local: Local,
     pub projection: &'tcx [PlaceElem<'tcx>],
@@ -1753,7 +1753,20 @@ pub fn project_deeper(
 
 impl Debug for Place<'_> {
     fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
-        for elem in self.projection.iter().rev() {
+        self.as_ref().fmt(fmt)
+    }
+}
+
+impl Debug for PlaceRef<'_> {
+    fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
+        pre_fmt_projection(self.projection, fmt)?;
+        write!(fmt, "{:?}", self.local)?;
+        post_fmt_projection(self.projection, fmt)
+    }
+}
+
+fn pre_fmt_projection(projection: &[PlaceElem<'_>], fmt: &mut Formatter<'_>) -> fmt::Result {
+    for &elem in projection.iter().rev() {
         match elem {
             ProjectionElem::OpaqueCast(_)
             | ProjectionElem::Downcast(_, _)
@@ -1769,9 +1782,11 @@ fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
         }
     }
 
-        write!(fmt, "{:?}", self.local)?;
+    Ok(())
+}
 
-        for elem in self.projection.iter() {
+fn post_fmt_projection(projection: &[PlaceElem<'_>], fmt: &mut Formatter<'_>) -> fmt::Result {
+    for &elem in projection.iter() {
         match elem {
             ProjectionElem::OpaqueCast(ty) => {
                 write!(fmt, " as {ty})")?;
@@ -1814,7 +1829,6 @@ fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
 
     Ok(())
 }
-}
 
 ///////////////////////////////////////////////////////////////////////////
 // Scopes