Q:

What causes "Pattern matched no module dependencies" when using go mod download?

When running go mod download the warning (warning: pattern "all" matched no module dependencies) is shown and none of the modules in my go.mod file are download to the local cache.
I've spent the last hour on google trying to find similar errors but have been  stuck with the only results being broken CI build logs. 
My go.mod file is as follows:
module github.com/j4ng5y/scraper-api

go 1.12

require (
    github.com/PuerkitoBio/goquery v1.5.0 // indirect
    github.com/antchfx/htmlquery v1.0.0 // indirect
    github.com/antchfx/xmlquery v1.0.0 // indirect
    github.com/antchfx/xpath v0.0.0-20190319080838-ce1d48779e67 // indirect
    github.com/go-yaml/yaml v2.1.0+incompatible
    github.com/gobwas/glob v0.2.3 // indirect
    github.com/gocolly/colly v1.2.0 // indirect
    github.com/gorilla/mux v1.7.1
    github.com/kennygrant/sanitize v1.2.4 // indirect
    github.com/saintfish/chardet v0.0.0-20120816061221-3af4cd4741ca // indirect
    github.com/temoto/robotstxt v0.0.0-20180810133444-97ee4a9ee6ea // indirect
    golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3 // indirect
    google.golang.org/appengine v1.5.0 // indirect
)

I would expect go mod download to pull all of the modules to the local cache but instead I get the warning and nothing is downloaded.

A:

Try enabling go modules. This works for me with go 1.12
GO111MODULE=on go mod download

Note: If you're working inside $GOPATH/src, go modules are disabled by default and can be enabled by setting GO111MODULE=on.
From https://blog.golang.org/using-go-modules,

(Inside $GOPATH/src, for compatibility, the go command still runs in the old GOPATH mode, even if a go.mod is found. See the go command documentation for details.)

A:

I have had the same issue and I resolved it by changing the version of go to v1.11.9.
go mod download
go: modules disabled inside GOPATH/src by GO111MODULE=auto; see 'go help modules'

export GO111MODULE=on

