zcash_client_backend: Fix off-by-one in tree heights at NU activation.

zcash_client_backend/src/scanning.rs

@@ -335,14 +335,26 @@ pub(crate) fn scan_block_with_runner<
     let cur_hash = block.hash();
 
     let initial_sapling_tree_size = prior_block_metadata.and_then(|m| m.sapling_tree_size());
+    // If we're below Sapling activation, or Sapling activation is not set, the
+    // tree size is zero
+    let nu_sapling_tree_size =
+        params
+            .activation_height(NetworkUpgrade::Sapling)
+            .and_then(|sapling_activation| {
+                if cur_height < sapling_activation {
+                    Some(0)
+                } else {
+                    None
+                }
+            });
     let mut sapling_commitment_tree_size = initial_sapling_tree_size
         .or_else(|| {
             block
                 .chain_metadata
                 .as_ref()
                 .and_then(|m| {
                     if m.sapling_commitment_tree_size == 0 {
-                        None
+                        nu_sapling_tree_size
                     } else {
                         let block_output_count: u32 = block
                             .vtx
@@ -354,28 +366,34 @@ pub(crate) fn scan_block_with_runner<
                         Some(m.sapling_commitment_tree_size - block_output_count)
                     }
                 })
-                .or_else(|| {
-                    // If we're below Sapling activation, or Sapling activation is not set, the
-                    // tree size is zero
-                    params
-                        .activation_height(NetworkUpgrade::Sapling)
-                        .map_or(Some(0), |h| if h > cur_height { Some(0) } else { None })
-                })
+                .or(nu_sapling_tree_size)
         })
         .ok_or(ScanError::TreeSizeUnknown {
             protocol: ShieldedProtocol::Sapling,
             at_height: cur_height,
         })?;
 
     let initial_orchard_tree_size = prior_block_metadata.and_then(|m| m.orchard_tree_size());
+    // If we're below Nu5 activation, or Nu5 activation is not set, the tree size
+    // is zero
+    let nu_orchard_tree_size =
+        params
+            .activation_height(NetworkUpgrade::Nu5)
+            .and_then(|nu5_activation| {
+                if cur_height < nu5_activation {
+                    Some(0)
+                } else {
+                    None
+                }
+            });
     let mut orchard_commitment_tree_size = initial_orchard_tree_size
         .or_else(|| {
             block
                 .chain_metadata
                 .as_ref()
                 .and_then(|m| {
                     if m.orchard_commitment_tree_size == 0 {
-                        None
+                        nu_orchard_tree_size
                     } else {
                         let block_action_count: u32 = block
                             .vtx
@@ -387,13 +405,7 @@ pub(crate) fn scan_block_with_runner<
                         Some(m.orchard_commitment_tree_size - block_action_count)
                     }
                 })
-                .or_else(|| {
-                    // If we're below Nu5 activation, or Nu5 activation is not set, the tree size
-                    // is zero
-                    params
-                        .activation_height(NetworkUpgrade::Nu5)
-                        .map_or(Some(0), |h| if h > cur_height { Some(0) } else { None })
-                })
+                .or(nu_orchard_tree_size)
         })
         .ok_or(ScanError::TreeSizeUnknown {
             protocol: ShieldedProtocol::Orchard,