Golang compiler detects module based on current working directory

Go version

go version go1.22.4 darwin/amd64

Output of `go env` in your module/workspace:

GO111MODULE='auto'
GOARCH='amd64'
GOBIN=''
GOCACHE='/tmp/.gocache'
GOENV='/Users/rittneje/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/rittneje/go/pkg/mod'
GONOPROXY='<redacted>'
GONOSUMDB='<redacted>'
GOOS='darwin'
GOPATH='/Users/rittneje/go'
GOPRIVATE='git.intra.lutron.com'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/rittneje/go1.22.4'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/Users/rittneje/go1.22.4/pkg/tool/darwin_amd64'
GOVCS='<redacted>'
GOVERSION='go1.22.4'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD=''
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/kf/kr7_s3xx0l12zbj3jrn082hmzy5gvy/T/go-build3773258374=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

We originally noticed this issue because debug.ReadBuildInfo() was not reporting the expected value for DefaultGODEBUG.

It seems that go build will only detect that we are building a module if the current working directory is with the module root.

module godebugbug

go 1.22.4

package main

import (
    "fmt"
    "runtime/debug"
)

func main() {
    fmt.Println(debug.ReadBuildInfo())
}

What did you see happen?

It ignores go.mod completely, and uses the 1.21 DefaultGODEBUG settings.

Inside the module folder: go build && ./godebugbug

go go1.22.4 path godebugbug mod godebugbug (devel) build -buildmode=exe build -compiler=gc build CGO_ENABLED=1 build CGO_CFLAGS= build CGO_CPPFLAGS= build CGO_CXXFLAGS= build CGO_LDFLAGS= build GOARCH=amd64 build GOOS=darwin build GOAMD64=v1 true

Outside the module folder: go build -o main ./godebugbug && ./main

go go1.22.4 path _/Users/jrittner/gomodtest/src/godebugbug build -buildmode=exe build -compiler=gc build DefaultGODEBUG=httplaxcontentlength=1,httpmuxgo121=1,panicnil=1,tls10server=1,tlsrsakex=1,tlsunsafeekm=1 build CGO_ENABLED=1 build CGO_CFLAGS= build CGO_CPPFLAGS= build CGO_CXXFLAGS= build CGO_LDFLAGS= build GOARCH=amd64 build GOOS=darwin build GOAMD64=v1 true

What did you expect to see?

It should instead detect it based upon the target package being within a module.

That is, if I run go build ./foo/bar/baz, where the go.mod file is located at ./foo/go.mod, then it should detect the module and build properly, using the DefaultGODEBUG that goes with the version of Go listed in the go.mod file.

Comment From: gabyhelp

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Comment From: rittneje

Adding to the confusion, the 1.22 compiler will compile with 1.22 loop semantics when it cannot find the go.mod file, even though it will also use the 1.21 DefaultGODEBUG.

Comment From: seankhliao

I believe this is working as intended for your setting of GO111MODULE=auto where it falls back to GOPATH mode if a module is not found. The default setting is GO111MODULE=on, which should report an error like:

go: go.mod file not found in current directory or any parent directory; see 'go help modules'

Using the module based on the go command is the intended behaviour, see also the -C flag.