cmd/go: rebuilds standard library inappropriately in modules mode

[svmax]

Please answer these questions before submitting your issue. Thanks!

What did you do?

package main

import (
	"log"
	"net/http"
)

func main() {
	log.Fatal(http.ListenAndServe(":8080", nil))
}

What did you expect to see?

Listening of http server

What did you see instead?

 net
/usr/local/go/src/net/cgo_bsd.go:11:10: fatal error: 'netdb.h' file not found
#include <netdb.h>
         ^~~~~~~~~
1 error generated.

System details

go version go1.11.1 darwin/amd64
GOARCH="amd64"
GOBIN="/Users/max/Projects/go/bin"
GOCACHE="/Users/max/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/max/Projects/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/max/Projects/edu/go/polygraph/go.mod"
GOROOT/bin/go version: go version go1.11.1 darwin/amd64
GOROOT/bin/go tool compile -V: compile version go1.11.1
uname -v: Darwin Kernel Version 18.0.0: Wed Aug 22 20:13:40 PDT 2018; root:xnu-4903.201.2~1/RELEASE_X86_64
ProductName:	Mac OS X
ProductVersion:	10.14
BuildVersion:	18A391
lldb --version: lldb-1000.11.37.1
  Swift-4.2

[svmax]

After Google search, I've decided to create this ticket, because INET don't know about this issue ....
From beginning, I've used 1.11 version, but after facing with this bug - made upgrade to the 1.11.1, but still have the same trouble.

[ianlancetaylor]

What command did you run to get that error?

[svmax]

@ianlancetaylor just go build ./path/to/the/file.go. Listing of the file on top of the conversation

[svmax]

Go was installed using official bundle and tried with brew.... Nothing helps

[svmax]

I recently used MacOS 10.13 and everything worked fine .... Maybe after update to 10.14 some required by Go system dependencies was lost (I mean, Apple developers deprecated or changed some things and we got this issues)

[svmax]

Little bit about C

$(go env CC) --version:

clang version 5.0.1 (tags/RELEASE_501/final)
Target: x86_64-apple-darwin18.0.0
Thread model: posix
InstalledDir: /usr/local/opt/llvm/bin

===

which $(go env CC):

/usr/local/opt/llvm/bin/clang

[agnivade]

Can you do a GOCACHE=off go build -x -v path/to/file.go ?

[svmax]

@agnivade I've got

WORK=/var/folders/q4/gxzbpbqx7bgcllkbph02xcmm0000gn/T/go-build066535883
go: cannot use modules with build cache disabled

[agnivade]

Since you are just compiling a single file, you don't need modules. Can you try without module mode ?

[svmax]

@agnivade I have a multi bundled project, few entry points .... My code described above - just an example

[svmax]

@agnivade Ok, I will in another project to run without modules

[svmax]

@agnivade Yeah, without module mode - it is working. Compiled successfully

[svmax]

@agnivade So, I've moved my project to the $GOPATH and it was compiled successfully. Looks like this is issue in module mode.

[agnivade]

I am still unable to reproduce this.

In an empty dir, I copied your file. Then

go mod init .
GO111MODULE=on go build -x -v file.go

This prints a long log, but builds successfully. I am on linux though.

Can you try doing a go clean -i -r -modcache and then compiling again ?

[svmax]

@agnivade Unfortunately the same error. I think it is can be reproduced with latest MacOS. By the way, it's worked before upgrade of OS.... Maybe something was changed into the OS core things... Because, i've defiged go.mod through go mod init, it was created file with module github.com/sviechnikov/project_name and all was fine

[svmax]

@agnivade How do you think, it is can be an issue?
I've reinstalled xcode tools again (how told stackoverflow and my colleagues), but it's won't help

[svmax]

One more thing, I've searched for this file netdb.h and found it in /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/, but looks like go dependencies not looking there

[svmax]

how I understand, Clang expecting /usr/include to be this libraries folder .... Maybe I'm something missing, because Clang is not my strong point

[svmax]

@agnivade In module mode works with CGO_ENABLED=0 go build cmd/server/main.go

[svmax]

But I hope, this is temporary ...

[ianlancetaylor]

Likely the same as #26988: in some cases the go tool is incorrectly deciding that it needs to rebuild the standard library.

[bcmills]

Closing as duplicate of #26988.