cmd/go: second parameter of replace is a network package, it behavior needs to be like require

[yesuu]

What version of Go are you using (go version)?

go version go1.11beta2 linux/amd64
go version devel +6b9c782f9f Wed Aug 1 00:57:00 2018 +0000 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What did you do?

this is go.mod:

module project/deploy

require (
    github.com/gin-gonic/gin v1.1.4
    golang.org/x/net/context v0.0.0 // indirect
)

replace (
    golang.org/x/net/context => github.com/golang/net/context v0.0.0-20180724234803-3673e40ba22
)

execute the command go build:

go: finding github.com/golang/net/context v0.0.0-20180724234803-3673e40ba225
go: github.com/golang/net/[email protected]: missing github.com/golang/net/context/go.mod at revision 3673e40ba225
go: error loading module requirements

if the version of the second parameter is write as v0.0.0:

module project/deploy

require (
    github.com/gin-gonic/gin v1.1.4
    golang.org/x/net/context v0.0.0 // indirect
)

replace (
    golang.org/x/net/context => github.com/golang/net/context v0.0.0
)

it's actually trying to find v0.0.0:

go: finding github.com/golang/net/context v0.0.0
go: github.com/golang/net/[email protected]: unknown revision context/v0.0.0
go: error loading module requirements

As the title says, it's a bug.

[yesuu]

When retesting this problem, I found out if:

module project/deploy
require (
    github.com/gin-gonic/gin/binding v0.0.0-20180720165255-220e8d34538f
)

the go build output:

go: finding github.com/gin-gonic/gin/binding v0.0.0-20180720165255-220e8d34538f
go: github.com/gin-gonic/gin/[email protected]: missing github.com/gin-gonic/gin/binding/go.mod at revision 220e8d34538f
go: error loading module requirements

Obviously the second parameter of replace is same with the behavior of require.

The real problem is go.mod only supports module and don't support package. Because if I write module path, it works fine:

module project/deploy
require (
    github.com/gin-gonic/gin v0.0.0-20180720165255-220e8d34538f
)

even if I import github.com/gin-gonic/gin/binding, it still can use the module path github.com/gin-gonic/gin.

When I try use this conclusion on replace, I was frustrated again:

module project/deploy
require (
    golang.org/x/net v0.0.0
)
replace (
    golang.org/x/net => github.com/golang/net v0.0.0-20180724234803-3673e40ba22
)

try go build -v:

Fetching https://golang.org/x/net?go-get=1

The replace do not take effect.

Can anyone tell me the true usage?

[ianlancetaylor]

CC @bcmills

[bcmills]

github.com/golang/net/context is a package path, not a module path. (The corresponding module path is just github.com/golang/net.)

If you use go get to construct the go.mod file rather than writing it by hand, you should find that go get github.com/golang/net/[email protected] actually resolves that to a go.mod line like:

require github.com/golang/net v0.0.0-20180724234803-3673e40ba22

(#26602 notwithstanding)

The same is true for your replace directive: it must use module paths, not package paths.

replace (
	golang.org/x/net => github.com/golang/net v0.0.0-20180724234803-3673e40ba22
)

[bcmills]

The fact that we attempt a network fetch despite the replacement is #26241.

With the issue of module path vs. package path cleared up, I believe that this issue is a duplicate of that one. Please let me know if there are any remaining issues reported here that I've missed.