Rust: Avoid unnecessary constraint satisfaction

Author: paldepind

rust/ql/lib/codeql/rust/internal/typeinference/Type.qll

@@ -589,7 +589,23 @@ final class ImplTypeAbstraction extends TypeAbstraction, Impl {
   }
 }
 
+private predicate idDynTraitTypeRepr(@dyn_trait_type_repr x, @dyn_trait_type_repr y) { x = y }
+
+private predicate idOfDynTraitTypeRepr(@dyn_trait_type_repr x, int y) =
+  equivalenceRelation(idDynTraitTypeRepr/2)(x, y)
+
+private int idOfDynTraitTypeRepr(DynTraitTypeRepr node) {
+  idOfDynTraitTypeRepr(Synth::convertAstNodeToRaw(node), result)
+}
+
+/** Holds if `dt` is the canonical dyn trait type abstraction for `trait`. */
+private predicate canonicalDynTraitTypeAbstraction(DynTraitTypeRepr dt, Trait trait) {
+  dt = min(DynTraitTypeRepr d | d.getTrait() = trait | d order by idOfDynTraitTypeRepr(d))
+}
+
 final class DynTypeAbstraction extends TypeAbstraction, DynTraitTypeRepr {
+  DynTypeAbstraction() { canonicalDynTraitTypeAbstraction(this, this.getTrait()) }
+
   override TypeParameter getATypeParameter() {
     result = any(DynTraitTypeParameter tp | tp.getTrait() = this.getTrait()).getTraitTypeParameter()
   }