Good illustration that a seemingly simple feature could require a ton of functionality under the hood. Would be nice to have this in Python.

If I follow, this isn't a compile time inline directive, it's a `go fix` time source transformation of client code calling the annotated function.

Per the post, it sounds like this is most effective in closed-ecosystem internal monorepo-like contexts where an organisation has control over every instance of client code & can `go fix` all of the call sites to completely eradicate all usage of a deprecated APIs:

> For many years now, our Google colleagues on the teams supporting Java, Kotlin, and C++ have been using source-level inliner tools like this. To date, these tools have eliminated millions of calls to deprecated functions in Google’s code base. Users simply add the directives, and wait. During the night, robots quietly prepare, test, and submit batches of code changes across a monorepo of billions of lines of code. If all goes well, by the morning the old code is no longer in use and can be safely deleted. Go’s inliner is a relative newcomer, but it has already been used to prepare more than 18,000 changelists to Google’s monorepo.

It could still have some incremental benefit for public APIs where client code is not under centralised control, but would not allow deprecated APIs to be removed without breakage.

yeah this is the part that got me excited honestly. we're not google-scale by any stretch but we have ~8 internal Go modules and deprecating old helper functions is always this awkward dance of "please update your imports" in slack for weeks. even if it doesn't let you delete the function immediately for external consumers, having the tooling nudge internal callers toward the replacement automatically is huge. way better than grep + manual PRs

it could be better than a nudge -- if you could get a mandatory `go fix` call into internal teams' CI pipelines that either fixes in place (perhaps risky) or fails the build if code isn't already identical to fixed code.

It looks the following code will be rewritten badly, but no ways to avoid it? If this is true, maybe the blog article should mention this.

    package main
    
    //go:fix inline
    func handle() {
        recover()
    }
    
    func foo() {
        handle()
    }
    
    func main() {
        defer foo()
        panic("bye")
    }

Another example (fixable):

    package main

    import "unsafe"

    //go:fix inline
    func foo[T any]() {
        var t T
        _ = 1 / unsafe.Sizeof(t)
    }

    func main() {
        foo[struct{}]()
    }

Go is a language full of details: https://go101.org/details-and-tips/101.html

Great example, illustrating go1.26.1 go fix source inline transformation breaking program semantics. Raise it as a bug against go fix?

As I have mentioned, no ways to fix it. Because it is hard to know whether or not the handle function is called in a deferred call.

Or: your buggy code is no longer buggy.

You claim listens right for this specified example. :D

It is just a demo.

Go designers distinguish between Go language as defined by Go spec and implementation details.

//go:fix is something understood by a particular implementation of Go. Another implementation could implement Go without implementing support for //go:fix and it would be a fully compliant implementation of Go, the language.

If they made it part of the syntax, that would require other implementations to implement it.

If the comments impact correctness (which inlining doesn't, but I believe there are other directives that do), saying it's "an implementation detail" waves away "it's an implementation detail that everyone needs" aka part of the spec.

The reason it feels like a kludge is that "comments" are normally understood to be non-impactful. Is a source transformation that removes all comments valid? If comments have no impact per the spec, yes. But that's not the case here.

In practice comments in go are defined to be able to carry semantic meaning extensibly. Whether they're safe to ignore depends on what meaning is given to the directives, e.g. conditional compilation directives.

> The reason it feels like a kludge is that "comments" are normally understood to be non-impactful. Is a source transformation that removes all comments valid? If comments have no impact per the spec, yes. But that's not the case here.

This is not inlining in the compiler. It's a directive to a source transformation (refactoring) tool. So yes, this has no impact on the code. It will do things if you run `go fix` on your codebase, otherwise it won't.

And yet it still breaks "comments aren't semantic". That transformation I described is still invalid.

That's such an elegant solution.

I keep being impressed at subtle but meaningful things that Go does right.

The //go:xyz comments are an established pattern in the Go tooling.

//go:xyz is dedicated syntax that is compatible with both the language spec and other toolchains that don't know about it.