Prefer to return error rather than ? them,

avoid return when it cant be early (in a simple if-else)

crypto-primitives/src/merkle_tree/mod.rs

@@ -200,7 +200,7 @@ impl MerkleHashTree
 
         // Check that the given index corresponds to the correct leaf.
         if leaf_hash != self.tree[tree_index] {
-            Err(MerkleTreeError::IncorrectLeafIndex(tree_index))?
+            return Err(MerkleTreeError::IncorrectLeafIndex(tree_index).into())
         }
 
         // Iterate from the leaf up to the root, storing all intermediate hash values.
@@ -230,7 +230,7 @@ impl MerkleHashTree
         }
         end_timer!(prove_time);
         if path.len() != (Self::HEIGHT - 1) as usize {
-            Err(MerkleTreeError::IncorrectPathLength(path.len()))?
+            return Err(MerkleTreeError::IncorrectPathLength(path.len()).into())
         } else {
             Ok(MerkleTreePath { path })
         }

r1cs-std/src/bits/boolean.rs

@@ -681,7 +681,7 @@ impl ConditionalEqGadget for Boolean {
             // 1 - 1 = 0 - 0 = 0
             (Constant(true), Constant(true)) | (Constant(false), Constant(false)) => return Ok(()),
             // false != true
-            (Constant(_), Constant(_)) => Err(SynthesisError::AssignmentMissing)?,
+            (Constant(_), Constant(_)) => return Err(SynthesisError::AssignmentMissing),
             // 1 - a
             (Constant(true), Is(a)) | (Is(a), Constant(true)) => {
                 LinearCombination::zero() + one - a.get_variable()