Using 'go build' fetches dependencies even though they are in vendor/

Question

I am trying to fetch a Go project and copy the dependencies under the vendor/ directory so I have the complete source code of the project and its dependencies in my project. However, even after doing that, deleting the packages under $GOPATH/pkg/mod and rebuilding cause the Go compiler to re-fetch all dependencies, which takes a considerable of time.

This is what I did:

# Fetch the project, e.g. influx/telegraf
go get -d github.com/influxdata/telegraf

# CD into the project
cd $GOPATH/src/influxdata/telegraf

# Fetch the modules under vendor/ directory
go mod vendor

After calling the last command, Go will fetch all the dependencies under pkg/mod . Not sure why it is doing that, but I assume it is because it needs to build the project normally, and then move the fetched dependencies under the vendor/ folder. After that, I can build successfully. However, to make sure I no longer require those dependencies, I deleted the pkg/mod directory completely and rebuilt the project. Go compiler, for some reason, fetched the packages again.

Is there anything I am doing wrong?

Thanks!

Answer 1

The vendor folder is not used automatically in all cases.

To make sure dependencies are loaded from the main module's vendor folder, pass -mod=vendor to the go tool.

The vendor folder if present is only used automatically (if not specified otherwise with -mod=mod ) if the go version specified by go.mod file is 1.14 or higher.

These are detailed in Command go: Maintaining module requirements :

If invoked with -mod=vendor, the go command loads packages from the main module's vendor directory instead of downloading modules to and loading packages from the module cache. The go command assumes the vendor directory holds correct copies of dependencies, and it does not compute the set of required module versions from go.mod files. However, the go command does check that vendor/modules.txt (generated by 'go mod vendor') contains metadata consistent with go.mod.

If invoked with -mod=mod, the go command loads modules from the module cache even if there is a vendor directory present.

If the go command is not invoked with a -mod flag and the vendor directory is present and the "go" version in go.mod is 1.14 or higher, the go command will act as if it were invoked with -mod=vendor.