V3 Backport [#10909]: Reduce Wrangler disk IO

.changeset/tame-rocks-nail.md

@@ -0,0 +1,5 @@
+---
+"wrangler": patch
+---
+
+Only write Wrangler logs to a debug file if `WRANGLER_LOG=debug` is set, or a custom path is provided via `WRANGLER_LOG_PATH`

packages/wrangler/src/__tests__/friendly-validator-errors.test.ts

@@ -46,7 +46,8 @@ describe("helpIfErrorIsSizeOrScriptStartup", () => {
 
 		expect(std).toMatchInlineSnapshot(`
 			Object {
-			  "debug": "An error occurred while trying to locally profile the Worker: Error: workerd profiling failed",
+			  "debug": "🪵  Writing logs to \\"/Users/penalosa/.wrangler/logs/wrangler-2025-10-07_23-25-03_725.log\\"
+			An error occurred while trying to locally profile the Worker: Error: workerd profiling failed",
 			  "err": "",
 			  "info": "",
 			  "out": "",

packages/wrangler/src/__tests__/metrics.test.ts

@@ -95,7 +95,10 @@ describe("metrics", () => {
 				await Promise.all(dispatcher.requests);
 				expect(requests.count).toBe(1);
 				expect(std.debug).toMatchInlineSnapshot(
-					`"Metrics dispatcher: Posting data {\\"deviceId\\":\\"f82b1f46-eb7b-4154-aa9f-ce95f23b2288\\",\\"event\\":\\"some-event\\",\\"timestamp\\":1733961600000,\\"properties\\":{\\"category\\":\\"Workers\\",\\"wranglerVersion\\":\\"1.2.3\\",\\"os\\":\\"foo:bar\\",\\"a\\":1,\\"b\\":2}}"`
+					`
+					"🪵  Writing logs to \\"/Users/penalosa/.wrangler/logs/wrangler-2025-10-07_23-25-03_753.log\\"
+					Metrics dispatcher: Posting data {\\"deviceId\\":\\"f82b1f46-eb7b-4154-aa9f-ce95f23b2288\\",\\"event\\":\\"some-event\\",\\"timestamp\\":1733961600000,\\"properties\\":{\\"category\\":\\"Workers\\",\\"wranglerVersion\\":\\"1.2.3\\",\\"os\\":\\"foo:bar\\",\\"a\\":1,\\"b\\":2}}"
+				`
 				);
 				expect(std.out).toMatchInlineSnapshot(`""`);
 				expect(std.warn).toMatchInlineSnapshot(`""`);

packages/wrangler/src/__tests__/utils/log-file.test.ts

@@ -1,9 +1,12 @@
 import { existsSync, readdirSync, readFileSync } from "node:fs";
 import { join } from "node:path";
 import { beforeEach, describe, expect, it, vi } from "vitest";
+import { logger } from "../../logger";
 import { appendToDebugLogFile, debugLogFilepath } from "../../utils/log-file";
 import { runInTempDir } from "../helpers/run-in-tmp";
 
+vi.mock("../../utils/log-file", { spy: true });
+
 describe("appendToDebugLogFile", () => {
 	runInTempDir();
 
@@ -63,6 +66,28 @@ describe("appendToDebugLogFile", () => {
 		expect(logContent).toContain(plainMessage);
 	});
 
+	it("should not write to log file with default log path & non debug level", async () => {
+		vi.stubEnv("WRANGLER_LOG_PATH", "");
+		const plainMessage = "This is a random plain log message";
+
+		logger.info(plainMessage);
+
+		expect(vi.mocked(appendToDebugLogFile).mock.calls.length).toBe(0);
+	});
+
+	it("should write to log file with default path & debug level", async () => {
+		vi.stubEnv("WRANGLER_LOG_PATH", "");
+
+		vi.stubEnv("WRANGLER_LOG", "debug");
+		const plainMessage = "This is a debug log message";
+
+		logger.info(plainMessage);
+
+		expect(vi.mocked(appendToDebugLogFile).mock.calls.length).toBeGreaterThan(
+			0
+		);
+	});
+
 	it("should handle multiline messages with ANSI codes", async () => {
 		const multilineMessageWithAnsi =
 			"\u001b[31mLine 1 with color\u001b[0m\nLine 2 plain\n\u001b[32mLine 3 with different color\u001b[0m";

packages/wrangler/src/logger.ts

@@ -152,9 +152,16 @@ export class Logger {
 			? this.formatMessage(messageLevel, format(...args))
 			: args;
 
-		// unless in unit-tests, send ALL logs to the debug log file (even non-debug logs for context & order)
-		const inUnitTests = typeof vitest !== "undefined";
-		if (!inUnitTests) {
+		if (
+			// only send logs to the debug log file if either
+			//  - `WRANGLER_LOG_PATH` has been set by the user (and is not the default)
+			//  - the configured log level is debug
+			// Even though we send non debug logs to the log file, we shouldn't overwhelm the user's
+			// system with loads of needless log files. There's very little value in non debug log files
+			process.env.WRANGLER_LOG_PATH ||
+			this.loggerLevel === "debug"
+		) {
+			// send ALL logs to the debug log file (even non-debug logs for context & order)
 			void appendToDebugLogFile(messageLevel, message);
 		}