How do I find the Go module source cache?

Question

I've upgraded a project to Go 1.11 and enabled module support for my project, but it seems that CircleCI is re-downloading the dependencies on every build. I know CircleCI allows caching between rebuilds, so I've looked at the documentation for Go modules, and while it mentions a cache, I can't seem to find where it actually exists.

Where is the source cache for Go modules?

Boylan

Are you using CircleCI 2.0? I'd assume so, since 1.0 is at end of life on August 31. – Traps

Yeah, CircleCI 2.0 – Boylan

Answer 1

As of the final 1.11 release, the go module cache (used for storing downloaded modules and source code), is in the $GOPATH/pkg/mod location (see the docs here). For clarification, the go build cache (used for storing recent compilation results) is in a different location.

This article, indicated that it's in the $GOPATH/src/mod, but in the timespan of the recent ~40 days, the golang team must have changed that target location. This message thread has some discussion on why the downloaded items ended up in $GOPATH/pkg.

You can also use the go mod download -json command to see the downloaded modules/source metadata and their location on your local disk. Example output below:

$ go mod download -json
go: finding github.com/aws/aws-sdk-go v1.14.5
go: finding github.com/aws/aws-lambda-go v1.2.0
{
    "Path": "github.com/aws/aws-lambda-go",
    "Version": "v1.2.0",
    "Info": "/go/pkg/mod/cache/download/github.com/aws/aws-lambda-go/@v/v1.2.0.info",
    "GoMod": "/go/pkg/mod/cache/download/github.com/aws/aws-lambda-go/@v/v1.2.0.mod",
    "Zip": "/go/pkg/mod/cache/download/github.com/aws/aws-lambda-go/@v/v1.2.0.zip",
    "Dir": "/go/pkg/mod/github.com/aws/[email protected]",
    "Sum": "h1:2f0pbAKMNNhvOkjI9BCrwoeIiduSTlYpD0iKEN1neuQ=",
    "GoModSum": "h1:zUsUQhAUjYzR8AuduJPCfhBuKWUaDbQiPOG+ouzmE1A="
}
{
    "Path": "github.com/aws/aws-sdk-go",
    "Version": "v1.14.5",
    "Info": "/go/pkg/mod/cache/download/github.com/aws/aws-sdk-go/@v/v1.14.5.info",
    "GoMod": "/go/pkg/mod/cache/download/github.com/aws/aws-sdk-go/@v/v1.14.5.mod",
    "Zip": "/go/pkg/mod/cache/download/github.com/aws/aws-sdk-go/@v/v1.14.5.zip",
    "Dir": "/go/pkg/mod/github.com/aws/[email protected]",
    "Sum": "h1:+l1m6QH6LypE2kL0p/G0Oh7ceCv+IVQ1h5UEBt2xjjU=",
    "GoModSum": "h1:ZRmQr0FajVIyZ4ZzBYKG5P3ZqPz9IHG41ZoMu1ADI3k="
}

That output is from a build on CircleCI 2.0, using their official circleci/golang:1.11 image. This is a contrived example to show how you would include the restore_cache and save_cache steps for the new golang module cache location:

steps:
    - checkout
    - restore_cache:
       keys:
         - gomod-cache-{{ checksum "go.sum" }}
    - run: go vet ./...
    - save_cache:
        key: gomod-cache-{{ checksum "go.sum" }}
        paths:
          - /go/pkg/mod

Traps

thank you! this command revealed that all the downloaded modules are kept in the location go/pkg/mod/cache under my $HOME – Viol