Thanks Ian for the fast and authoritative answer. I'll do what you suggest.
Cheers,
Tom
On Tuesday, March 31, 2020 at 2:31:19 AM UTC+1, Ian Lance Taylor wrote:
>
> On Mon, Mar 30, 2020 at 6:22 PM Tom Payne <twp...@gmail.com <javascript:>>
> wrote:
> >
> > Go's backwards compatibility guarantee is fantastic, but only applies to
> the language, not the standard library. How to I cause a build-time failure
> if someone tries to build my project with a too-old Go version?
>
> Pedantically, I would say that Go's backward compatibility does apply
> to the standard library, but that what you are talking about is
> forward compatibility.
>
>
> > I have a Go project that uses (or would like to use) a few features
> introduced in the standard library more recently, e.g. the %w verb in
> fmt.Errorf for wrapping errors (introduced in Go 1.13), and a fix to the
> text/template library (merged for Go 1.14). The nature of these features
> and fixes mean that my code will compile and build fine, but will fail at
> runtime when a codepath that relies on the feature or fix is executed,
> which will result in a late, weird error. I would like an early, loud
> failure at build time instead.
> >
> > What's the best way to achieve this? As far as I can tell, there are a
> few options:
> >
> >
> > The Go version can be determined by either the runtime.Version()
> function or by the presence of build flags (e.g. go1.13, go1.14, etc.).
> >
> >
> > Calling runtime.Version() cannot result in a build time error (it can
> only be called once the code is running, which can only happen after a
> successful build) but could be used in either a test (so the old Go version
> gets caught when "go test" is run) or in an init() function to (say) panic
> on startup when tests or the program are run. This would look something
> like:
> >
> > import "runtime"
> >
> > func init() {
> > if runtime.Version() < "1.13" { // string comparisons are not a
> good way to compare version strings, but you get the idea
> > panic("go version too old")
> > }
> > }
> >
> >
> > I can create a Go file with build flags that is only built on older
> versions of Go, something like:
> >
> > // +build !go1.13
> >
> > build with go 1.13 or later // this is deliberately not valid go
> syntax
> >
> > This causes an error if built with an earlier version of Go than 1.13,
> but the error message isn't very intuitive (something like
> "filename.go:3:1: expected 'package', found build") and the invalid Go
> syntax might confuse other Go tooling which tends to assume that every .go
> file contains more-or-less valid Go code.
> >
> >
> > Please note that I want to use these Go standard library features and
> fixes and provide an early, loud warning if they are not available. I know
> that I can use build flags to provide different code to different Go
> versions, but if I do that then I still have to maintain code for older Go
> versions. The core of this question is: how do I get a build error if my Go
> version is too old?
> >
> >
> > What's the recommended way to ensure a minimum Go version at build time?
> One of the above suggestions or another way?
>
>
> I think that most people use build tags, but instead of introducing a
> compilation error, they either provide reduced functionality when
> built with older Go versions, or they write something like
>
> const s = "this package requires Go 1.14" + 0
>
> Ian
>
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