fix(coverage): stream coverage data json to disk

.changeset/loud-pumas-jump.md

@@ -0,0 +1,5 @@
+---
+"hardhat": patch
+---
+
+Fixed `--coverage` runs failing with `RangeError: Invalid string length` when coverage data exceeds Node's `JSON.stringify` string-length ceiling.

packages/hardhat/src/internal/builtin-plugins/coverage/coverage-manager.ts

@@ -14,10 +14,10 @@ import { formatTable } from "@nomicfoundation/hardhat-utils/format";
 import {
   ensureDir,
   getAllFilesMatching,
-  readJsonFile,
+  readJsonFileAsStream,
   readUtf8File,
   remove,
-  writeJsonFile,
+  writeJsonFileAsStream,
   writeUtf8File,
 } from "@nomicfoundation/hardhat-utils/fs";
 
@@ -130,7 +130,9 @@ export class CoverageManagerImplementation implements CoverageManager {
     const dataPath = await this.#getDataPath(id);
     const filePath = path.join(dataPath, `${crypto.randomUUID()}.json`);
     const data = Object.fromEntries(this.data);
-    await writeJsonFile(filePath, data);
+    // NOTE: We use writeJsonFileAsStream here because the coverage data for large runs
+    // can exceed the maximum string length when calling JSON.stringify.
+    await writeJsonFileAsStream(filePath, data);
     log("Saved data", id, filePath);
   }
 
@@ -177,7 +179,10 @@ export class CoverageManagerImplementation implements CoverageManager {
       const filePaths = await getAllFilesMatching(dataPath);
 
       for (const filePath of filePaths) {
-        const entries = await readJsonFile<Record<string, number>>(filePath);
+        // NOTE: We use readJsonFileAsStream here because the coverage data for large runs
+        // can exceed the maximum string length when calling JSON.parse.
+        const entries =
+          await readJsonFileAsStream<Record<string, number>>(filePath);
 
         for (const [tag, count] of Object.entries(entries)) {
           this.data.set(tag, (this.data.get(tag) ?? 0) + count);