cmd/fmt: tries to download dependencies

[jsha]

go version go1.12 linux/amd64

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/jsha/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/jsha/gopkg"
GOPROXY=""
GORACE=""
GOROOT="/home/jsha/go1.12"
GOTMPDIR=""
GOTOOLDIR="/home/jsha/go1.12/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build307902328=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Create a tiny package using modules:

foo.go

package main

import _ "golang.org/x/crypto/sha3"

func main() {
}

go.mod

module foo

go 1.12

require golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529 // indirect

Clear the module cache:

$ sudo rm -r $GOPATH/pkg/mod/

# Alternately, a less invasive option:
$ sudo rm -r $GOPATH/pkg/mod/cache/download/golang.org/x/crypto/ $GOPATH/pkg/mod/golang.org/x/crypto@v0.0.0-20190510104115-cbcb75029529/

Disconnect from the Internet.

Run go fmt:

$ go fmt foo.go
go: golang.org/x/crypto@v0.0.0-20190510104115-cbcb75029529: unrecognized import path "golang.org/x/crypto" (https fetch: Get https://golang.org/x/crypto?go-get=1: dial tcp: lookup golang.org on [::1]:53: read udp [::1]:46842->[::1]:53: read: connection refused)
go: error loading module requirements

What did you expect to see?

A successful run of go fmt.

What did you see instead?

An error message.

It appears that go fmt attempts to download all module dependencies if they aren't present. However, as far as I can tell, there is no reason for go fmt to do this, since it doesn't process dependencies at all; it just changes the formatting of a single file (or a group of files).

At a minimum, go fmt should obey GOFLAGS=-mod=readonly, but I think even when that's not present, it shouldn't attempt to download dependencies.

This came up in practice on the Boulder project, where we vendor our dependencies and run tests inside a container that does not have Internet access. One of those tests is a check for correct formatting with go fmt.

[mvdan]

Duplicate of #30577?

[andybons]

Duplicate of #27841