cmd/go: go vet does not support -overlay

[eandre]

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

$ go version
go version go1.16 darwin/arm64

Does this issue reproduce with the latest release?

Yes

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

go env Output

$ go env
GO111MODULE="on"
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/eandre/Library/Caches/go-build"
GOENV="/Users/eandre/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/eandre/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/eandre"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/homebrew/Cellar/go/1.16/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/homebrew/Cellar/go/1.16/libexec/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.16"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/hc/w9bwjfwd69dd6_6thw6xqmkw0000gn/T/go-build2213810525=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Consider the following txtar:

-- go.mod --
module test.pkg
-- foo/foo_test.go --
package foo

import "testing"

func TestFoo(t *testing.T) { }
-- tmp/bar.go --
package foo
-- foo/overlay.json --
{"Replace": {"bar.go": "../tmp/bar.go"}}

I ran cd foo && go test -overlay=overlay.json . and expected the tests to pass.

What did you expect to see?

$ go test -overlay=overlay.json .
ok  	test.pkg/foo 0.123s

What did you see instead?

$ go test -overlay=overlay.json .
# test.pkg/foo
vet: open bar.go: no such file or directory
FAIL	test.pkg/foo [build failed]
FAIL
exit status 2

The issue is because the overlay is added to GoTestFiles but go vet does not support (or receive information about) overlays, so it tries to read the overlaid file directly from the filesystem where it does not exist.

[jayconrod]

cc @matloob @bcmills