Go 1.22 introduces significant for Loop Scoping change to resolve persistent coding issue

Go (Programming Language) 1.22 is set to introduce a significant change in for loop scoping to address an ongoing problem in Go programming. The problem involves maintaining references to loop variables beyond their intended scope, causing unexpected code behavior. This issue has caused production problems in several companies, including Let's Encrypt. Existing tools have been unable to identify all problematic cases due to false negatives and positives.

To address this, Go 1.22 will change for loops to have per-iteration scope as opposed to per-loop scope. This change will only apply to packages that declare Go 1.22 or later in their go.mod files, ensuring backwards compatibility. Developers can control the transition to the new semantics at a module or file level using //go:build lines. Old code will continue to function as before, allowing for a gradual transition to the new semantics.

Go 1.21 includes a preview of the scoping change, allowing developers to test their code with the new semantics using the GOEXPERIMENT=loopvar environment variable. Google has already adopted the new mode for all builds without any issues in production code. However, the scoping change could cause problematic tests, requiring developers to update their test cases to accommodate the new loop semantics. To assist with this, the loopclosure analyzer in Go 1.21 has improved precision to identify and report issues related to the new semantics. Furthermore, a tool provided by the Go team can help identify specific loops causing test failures when using the new semantics. You can check the full documentation here!