refactor(pxe): avoid expensive toTx() call when computing tx hash (#23136)

Author: nchamo

yarn-project/pxe/src/pxe.ts

@@ -849,8 +849,7 @@ export class PXE {
         // storing the tags here prevents linkage of txs sent from the same PXE.
         const taggingIndexRangesUsedInTheTx = privateExecutionResult.entrypoint.taggingIndexRanges;
         if (taggingIndexRangesUsedInTheTx.length > 0) {
-          // TODO(benesjan): The following is an expensive operation. Figure out a way to avoid it.
-          const txHash = (await txProvingResult.toTx()).txHash;
+          const txHash = await txProvingResult.getTxHash();
 
           await this.senderTaggingStore.storePendingIndexes(taggingIndexRangesUsedInTheTx, txHash, jobId);
           this.log.debug(`Stored used tagging index ranges as sender for the tx`, {

yarn-project/stdlib/src/tx/proven_tx.ts

@@ -13,6 +13,7 @@ import {
 } from './private_execution_result.js';
 import { type ProvingStats, ProvingTimingsSchema } from './profiling.js';
 import { Tx } from './tx.js';
+import type { TxHash } from './tx_hash.js';
 
 export class TxProvingResult {
   constructor(
@@ -22,6 +23,11 @@ export class TxProvingResult {
     public stats?: ProvingStats,
   ) {}
 
+  getTxHash(): Promise<TxHash> {
+    // Equivalent to `(await this.toTx()).txHash` but skips walking the execution result tree to collect logs.
+    return Tx.computeTxHash({ data: this.publicInputs });
+  }
+
   async toTx(): Promise<Tx> {
     const contractClassLogs = collectSortedContractClassLogs(this.privateExecutionResult);