x/tools/go/packages: relative "files=" query path are not relative to Config.Dir

[fho]

Go version

go version go1.22.0 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN='/home/fho/go/bin/'
GOCACHE='/home/fho/.cache/go-build'
GOENV='/home/fho/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/fho/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/fho/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/lib/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/lib/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.0'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/tmp/repro/go.mod'
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 -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3159040424=/tmp/go-build -gno-record-gcc-switches'

What did you do?

packages.Load accepts file paths via the file= pattern.
The *packages.Config parameter has a Dir field that is documented as:

Dir is the directory in which to run the build system's query tool
that provides information about the packages.
If Dir is empty, the tool is run in the current directory.

Therefore I expect that relative file query paths are relative to cfg.Dir.

I wrote a small tool to reproduce the issue.
The first command-line argument is used as cfg.Dir parameter, the second command line argument is passed as file= query pattern.

Tool + package to test the query can be found in: https://github.com/fho/golist_rel_file_query

What did you see happen?

When a relative path is specified as file= pattern, the path is made absolute to the current working directory instead of to cfg.Dir.

The go list query results in 0 packages:

$ pwd
/tmp/repro

$ tree
.
├── golist.go
├── go.mod
├── go.sum
├── oneprinter
│   └── main.go
└── util
    └── util.go
$ go run golist.go /tmp/repro/oneprinter/ main.go
packages.Load returned 0 packages

What did you expect to see?

When a relative path is specified as file= pattern, the path is made absolute to the cfg.Dir field.

Same results for running in the directory /tmp/repro:

go run golist.go /tmp/repro/oneprinter/ main.go

and running in the directory /tmp/repro/oneprinter

$ go run ../golist.go /tmp/repro/oneprinter/ main.go
packages.Load returned 1 packages
{"ID":"repro/oneprinter","Name":"main","PkgPath":"repro/oneprinter","GoFiles":["/tmp/repro/oneprinter/main.go"],"Imports":{"fmt":"fmt","repro/util":"repro/util"}}

---

This might be the cause for: #58726
Thanks to @barash-simplesurance for discovering the issue.

[adonovan]

Most filenames in the go/packages API are specified as absolute, and relative paths are (implicitly) relative to the application's working directory, as usual. The documentation for Config.Dir says only that it is the working directory of the query tool, not the base for all relative paths in the API.

So I think this is really a problem of documentation, and that we should clarify that file= patterns follow the usual convention.

[fho]

I think what makes it confusing and non-intuitive is that the base of the
relative paths changes depending on the query pattern type and if an external or
the goListDriver is used:

• When the golistDriver is used, relative file query paths are relative to the
  application's working directory (cwd).
• When an externalDriver is used, relative file query paths are relative to
  cfg.Dir.
  (The externalDriver is executed in cfg.Dir and the file query path is passed
  as specified in the call to packages.Load.)
• When a package path is passed as query, e.g. ./..., ./ specifies the
  current directory. The relative path is interpreted as relative to cfg.Dir
  not the applications's cwd.

I would expect a consistent behavior in all these cases. The current directory
should always either be cfg.Dir or the application's cwd.
What makes it inconsistent is that the golistDriver uses the application's cwd
and not cfg.Dir to make file= query paths absolute.
In all other cases, that I'm aware of, relative paths are relative to cfg.Dir.

Documenting this different behavior would help a lot. I think making it
consistent would be even better.