ethereum: Improve comments

Author: leoyvens

chain/ethereum/src/block_stream.rs

@@ -63,7 +63,9 @@ enum BlockStreamState {
 /// A single next step to take in reconciling the state of the subgraph store with the state of the
 /// chain store.
 enum ReconciliationStep {
-    /// Revert the current block pointed at by the subgraph pointer.
+    /// Revert the current block pointed at by the subgraph pointer. The pointer is to the current
+    /// subgraph head, and a single block will be reverted so the new head will be the parent of the
+    /// current one.
     Revert(EthereumBlockPointer),
 
     /// Move forwards, processing one or more blocks. Second element is the block range size.
@@ -126,9 +128,12 @@ pub struct BlockStream<S, C> {
     ctx: BlockStreamContext<S, C>,
 }
 
+// This is the same as `ReconciliationStep` but without retries.
 enum NextBlocks {
     /// Blocks and range size
     Blocks(VecDeque<EthereumBlockWithTriggers>, u64),
+
+    /// Revert the current block pointed at by the subgraph pointer.
     Revert(EthereumBlockPointer),
     Done,
 }

core/src/subgraph/instance_manager.rs

@@ -535,8 +535,10 @@ where
                     // - Remove hosts for reverted dynamic data sources.
                     // - Clear the entity cache.
                     //
-                    // Note that we do not currently revert the filters,
-                    // which is not ideal, but also not incorrect.
+                    // Note that we do not currently revert the filters, which means the filters
+                    // will be broader than necessary. This is not ideal for performance, but is not
+                    // incorrect since we will discard triggers that match the filters but do not
+                    // match any data sources.
                     ctx.state.instance.revert_data_sources(subgraph_ptr.number);
                     ctx.state.entity_lfu_cache = LfuCache::new();
                     continue;

runtime/wasm/src/host.rs

@@ -736,7 +736,7 @@ impl PartialEq for RuntimeHost {
             data_source_block_handlers,
             host_exports,
 
-            // Data sources created at different blocks can be considered duplicated.
+            // The creation block is ignored for detection duplicate data sources.
             data_source_creation_block: _,
             mapping_request_sender: _,
             metrics: _,