mod/vendor: broken support for git-submodules in vendoring mode

[gucio321]

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

$ go version
go version go1.19.2 linux/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="/home/mszeptuch/.cache/go-build"
GOENV="/home/mszeptuch/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/mszeptuch/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/mszeptuch/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.19.2"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
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 -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build4114909537=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Hi there!
I'm using giu with docking branch.
This branch uses cimgui-go that is a bit complex construct.
in short, it wraps C version of DearImGui
The cimgui is added to cimgui-go as a git submodule.
Everything works fine, until using a global modules system..
But after running go mod vendor, CGO complains about missing C includes - submodule doesn't get into vendor directory somehow.

What did you expect to see?

dependencies should be fully cloned into vendor directory

What did you see instead?

git modules that are a part of go module are missing in vendoring mode

[gucio321]

to reproduce

• git clone https://github.com/AllenDang/giu
• cd giu/examples/helloworld
• git checkout docking
• go run .
• everyghing works fine
• go mod vendor
• go run .
• compiler's crash

[seankhliao]

Working as intended, vendoring only includes directories with .go files that are included in the build.
Notably, it does not directly use git clone anywhere.

[gucio321]

@seankhliao so would it be possible to transfer this bug report into a proposal?
E.g like mod/vendor: check for cgo dependencies

Or it is better me to open a new issue?

[seankhliao]

No, we've decided this is not something we will support, see #26366 (comment)

[gucio321]

@seankhliao are you sure this comment is still up to data?
as far as I can see, sometimes some subdirectories that does not contain go files are included in vendor dir:

[assets (0) ]$ pwd;tree
/home/me/git/my-project/vendor/github.com/TheGreaterHeptavirate/ConstiTutor/internal/assets
.
├── assets.go
├── css
│   └── stylesheet.css
├── fonts
│   └── times_new_roman
│       ├── times_new_roman_bold.ttf
│       └── times_new_roman.ttf
├── icons
│   ├── 1.png
│   └── icon.png
└── sounds
    └── click.mp3

5 directories, 7 files

[seankhliao]

Those are presumably referenced via //go:embed

[gucio321]

So maybe cgo includes could be processed the same way??

[seankhliao]

The issues with finding C dependencies described in #26366 remain the same, nothing has changed on that front.
//go:embed well defined (since Go is in control of it) so it is easy to support.