incr.comp.: Fix potential unstable Fingerprint error for BorrowCheckResult.

Author: michaelwoerister

compiler/rustc_borrowck/src/lib.rs

@@ -236,7 +236,7 @@ fn do_mir_borrowck<'a, 'tcx>(
     // Compute non-lexical lifetimes.
     let nll::NllOutput {
         regioncx,
-        opaque_type_values,
+        mut opaque_type_values,
         polonius_input,
         polonius_output,
         opt_closure_req,
@@ -437,6 +437,12 @@ fn do_mir_borrowck<'a, 'tcx>(
 
     let tainted_by_errors = mbcx.emit_errors();
 
+    // Since `BorrowCheckResult` is a query result, let's make sure that its `concrete_opaque_types`
+    // field is in deterministic order.
+    // Note, that this is not the best solution. It would be better to use a collection type
+    // that does not expose its internal order at all once that's available (see #63713).
+    opaque_type_values.sort_deterministically(&infcx.tcx.create_stable_hashing_context());
+
     let result = BorrowCheckResult {
         concrete_opaque_types: opaque_type_values,
         closure_requirements: opt_closure_req,

compiler/rustc_data_structures/src/vec_map.rs

@@ -4,7 +4,7 @@ use std::iter::FromIterator;
 use std::slice::Iter;
 use std::vec::IntoIter;
 
-use crate::stable_hasher::{HashStable, StableHasher};
+use crate::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
 
 /// A map type implemented as a vector of pairs `K` (key) and `V` (value).
 /// It currently provides a subset of all the map operations, the rest could be added as needed.
@@ -190,5 +190,14 @@ where
     }
 }
 
+impl<K, V> VecMap<K, V> {
+    pub fn sort_deterministically<HCX>(&mut self, hcx: &HCX)
+    where
+        K: ToStableHashKey<HCX>,
+    {
+        self.0.sort_by_cached_key(|(k, _)| k.to_stable_hash_key(hcx));
+    }
+}
+
 #[cfg(test)]
 mod tests;