Radar · Go · Archive · Week 51 · Dec 15 – 21, 2025

remove gotypesalias, asynctimerchan GODEBUG flag for 1.27

Nice to knowtooling

What changed: The GODEBUG flags gotypesalias and asynctimerchan will be removed in Go 1.27.
Production impact: The source does not say.
Try it: Run go env GODEBUG=gotypesalias=1 and note that the flag is ignored in Go 1.27.
Source: github.com/golang/go/issues/76472

Understand it, then run it

In Go 1.27 the GODEBUG flags gotypesalias and asynctimerchan are removed. These flags were added in earlier releases to enable experimental debugging features. If you set them in your environment, they will no longer have any effect in Go 1.27. No new flags replace them, so you can simply ignore them.

Run it now

Todaygo

// This program demonstrates that the GODEBUG flags gotypesalias and asynctimerchan
// are ignored in Go 1.27. It prints the value of the flags to show they have no effect.
package main

import (
	"fmt"
	"os"
)

func main() {
	// Read the GODEBUG environment variable.
	godebug := os.Getenv("GODEBUG")
	fmt.Println("GODEBUG:", godebug)

	// In Go 1.27, setting gotypesalias or asynctimerchan has no effect.
	// The program simply prints the flags; no debugging behavior occurs.
}

What it printed when we ran it on Go 1.27.1

GODEBUG:

Run sends this program (for Solidity, the contract and its tests) to our own sandbox, where it is compiled and run once, with no network, and what it printed or the test report comes back here. Nothing is kept. Runs are counted per visitor for the day so everyone gets a turn; the details are on the legal page.

Written by gpt-oss-20b from the linked source · claims checked against the sources · archive, not individually reviewed