add a fast path

Author: nikomatsakis

chalk-recursive/src/solve.rs

@@ -179,6 +179,12 @@ trait SolveIterationHelpers<I: Interner>: SolveDatabase<I> {
             } else {
                 debug!("Error");
             }
+
+            if let Some((cur_solution, _)) = cur_solution {
+                if cur_solution.is_trivial_and_always_true(self.interner()) {
+                    break;
+                }
+            }
         }
 
         if let Some((s, _)) = cur_solution {

chalk-solve/src/solve.rs

@@ -101,7 +101,7 @@ impl<I: Interner> Solution<I> {
         Solution::Ambig(guidance)
     }
 
-    fn is_trivial_and_always_true(&self, interner: I) -> bool {
+    pub fn is_trivial_and_always_true(&self, interner: I) -> bool {
         match self {
             Solution::Unique(constrained_subst) => {
                 constrained_subst.value.subst.is_identity_subst(interner)