cmd/go: suppress errors for 'go get' of package paths whose source files are all excluded by build constraints #33526
Description
What version of Go are you using (go version)?
$ go version go version go1.13beta1 darwin/amd64
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="" GOARCH="amd64" GOBIN="" GOCACHE="/Users/deklerk/Library/Caches/go-build" GOENV="/Users/deklerk/Library/Application Support/go/env" GOEXE="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="darwin" GONOPROXY="" GONOSUMDB="" GOOS="darwin" GOPATH="/Users/deklerk/workspace/go" GOPRIVATE="" GOPROXY="https://proxy.golang.org,direct" GOROOT="/usr/local/go" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64" GCCGO="gccgo" AR="ar" CC="clang" CXX="clang++" CGO_ENABLED="1" GOMOD="/tmp/foo/go.mod" 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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/c2/cvxltzcd66v5lx14hm1j76q000h16k/T/go-build777475143=/tmp/go-build -gno-record-gcc-switches -fno-common"
What did you do?
deklerk at deklerk-macbookpro2 in /tmp/foo
$ go get google.golang.org/genproto@v0.0.0-20190801165951-fa694d86fc64
go: downloading golang.org/x/lint v0.0.0-20190227174305-5b3e6a55c961
go: downloading golang.org/x/tools v0.0.0-20190226205152-f727befe758c
go: downloading honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099
go: extracting honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099
go: extracting golang.org/x/lint v0.0.0-20190227174305-5b3e6a55c961
go: extracting golang.org/x/tools v0.0.0-20190226205152-f727befe758c
can't load package: package google.golang.org/genproto: build constraints exclude all Go files in /Users/deklerk/workspace/go/pkg/mod/google.golang.org/genproto@v0.0.0-20190801165951-fa694d86fc64
deklerk at deklerk-macbookpro2 in /tmp/foo
What did you expect to see?
deklerk at deklerk-macbookpro2 in /tmp/foo
$ go get google.golang.org/genproto/...
go: downloading golang.org/x/sys v0.0.0-20180830151530-49385e6e1522
go: extracting golang.org/x/sys v0.0.0-20180830151530-49385e6e1522
go: finding google.golang.org/genproto latest
deklerk at deklerk-macbookpro2 in /tmp/foo
What did you see instead?
(see above)
TLDR genproto has a build constraint at the root (+tools, nothing else at root), but many packages below the root do not have this build constraint. When I use go get in module mode - esp when I provide a version - I expect to only interact with the module system. Instead, it's a weird mix of module and package, and in this case though I wanted to get a module it gave me an error about a package of the same name.