cmd/go: replace directive for go modules does not work recursively

[ghost]

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

1.14

Does this issue reproduce with the latest release?

YES

What operating system and processor architecture are you using (go env)?

Linux, AMD64

What did you do?

I have the directory structure as follows:

top-dir/
|-- module1
|   |-- go.mod
|   `-- test.go
|-- module2
|   |-- go.mod
|   `-- test.go
`-- module3
    |-- go.mod
    `-- test.go

3 directories, 6 files

File module1/go.mod:

module company.com/module1

go 1.14

replace company.com/module2 => ../module2

require company.com/module2 v0.0.0

File module1/test.go:

package main

import "company.com/module2"

func main() {
	module2.Test()
}

File module2/go.mod:

module company.com/module2

go 1.14

replace company.com/module3 => ../module3

require company.com/module3 v0.0.0

File module2/test.go:

package module2

import "company.com/module3"

func Test() {
	println("this is company.com/module2")
	module3.Test()
}

File module3/go.mod:

module company.com/module3

go 1.14

File module3/test.go:

package module3

func Test() {
	println("this is company.com/module3")
}

Summary:
module1 depends on a local module module2, and module2 depends on another local module module3. I use replace directive in the two go.mod files in module1 and module2.

What did you expect to see?

When I try go build in module1, it is expected that the compiler find module2 and module3 in the local filesystem, rather than fetching them from a remote server.

What did you see instead?

The go compiler succeeded in figuring out the right source of module2 (in local directory top-dir/module2), but failed for module3. It attempted to fetch module3 from the server company.com:

go: company.com/module2@v0.0.0 requires
	company.com/module3@v0.0.0: unrecognized import path "company.com/module3": https fetch: Get "https://company.com/module3?go-get=1": x509: certificate signed by unknown authority

[magical]

This is by design. Only replace directives in the top-level go.mod are considered during the build.

[andybons]

Adding @bcmills @jayconrod @matloob to confirm if it’s by design or not.

[bcmills]

This is by design. Per go help go.mod:

Exclude and replace apply only in the main module's go.mod and are ignored in dependencies. See https://research.swtch.com/vgo-mvs for details.