add docstrings and add issue to FIXMEs

Author: ChrisPardy

Diff for: compiler/rustc_middle/src/mir/mod.rs

@@ -2378,7 +2378,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                             };
                             let mut struct_fmt = fmt.debug_struct(&name);
 
-                            // FIXME: This should be a list of capture names/places
+                            // FIXME(project-rfc-2229#48): This should be a list of capture names/places
                             if let Some(upvars) = tcx.upvars_mentioned(def_id) {
                                 for (&var_id, place) in iter::zip(upvars.keys(), places) {
                                     let var_name = tcx.hir().name(var_id);
@@ -2398,7 +2398,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                             let name = format!("[generator@{:?}]", tcx.hir().span(hir_id));
                             let mut struct_fmt = fmt.debug_struct(&name);
 
-                            // FIXME: This should be a list of capture names/places
+                            // FIXME(project-rfc-2229#48): This should be a list of capture names/places
                             if let Some(upvars) = tcx.upvars_mentioned(def_id) {
                                 for (&var_id, place) in iter::zip(upvars.keys(), places) {
                                     let var_name = tcx.hir().name(var_id);

Diff for: compiler/rustc_mir/src/borrow_check/diagnostics/mod.rs

@@ -608,6 +608,7 @@ impl UseSpans<'_> {
         }
     }
 
+    /// Returns the span of `self`, in the case of a `ClosureUse` returns the `path_span`
     pub(super) fn var_or_use_path_span(self) -> Span {
         match self {
             UseSpans::ClosureUse { path_span: span, .. }
@@ -620,6 +621,7 @@ impl UseSpans<'_> {
         }
     }
 
+    /// Returns the span of `self`, in the case of a `ClosureUse` returns the `capture_kind_span`
     pub(super) fn var_or_use(self) -> Span {
         match self {
             UseSpans::ClosureUse { capture_kind_span: span, .. }

Diff for: compiler/rustc_mir/src/borrow_check/diagnostics/region_errors.rs

@@ -385,7 +385,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
 
         diag.span_label(*span, message);
 
-        // FIXME: This should store a captured_place not a hir id
+        // FIXME(project-rfc-2229#48): This should store a captured_place not a hir id
         if let ReturnConstraint::ClosureUpvar(upvar) = kind {
             let def_id = match self.regioncx.universal_regions().defining_ty {
                 DefiningTy::Closure(def_id, _) => def_id,