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

$ go version
GOVERSION=go1.21.2

Does this issue reproduce with the latest release?

Yes

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

GOHOSTOS=windows
GOHOSTARCH=amd64

What did you do?

I ran the go mod vendor command and then edited a file within the vendor folder to troubleshoot a personal problem. However, when building, the compiler did not take into account the vendor folder with the file I modified.

Then I needed to build with the flag "go build -mod=vendor maing.go" and yes, it took into account the file I modified.

I looked in the Go doc (https://go.dev/ref/mod#build-commands) (By default, if the go version in go.mod is 1.14 or higher and a vendor directory is present, the go command acts as if -mod=vendor were used. Otherwise, the go command acts as if -mod=readonly were used.)

I then realized that it could be a possible bug because the vendor folder exists and therefore the compiler should take it into consideration without the need to explicitly pass the -mod=vendor flag.

What did you expect to see?

When modifying a file within the vendor folder I expected to know if a block of code was executed but it did not execute.

Example a simple log.Println("Ok Ok")

however it didn't happen.

What did you see instead?

That the compiler does not take into account the vendor folder