cmd/link: linker gives misleading advice on new -ldflags option when option contains spaces

[ae6rt]

I am migrating from Go 1.4 to Go 1.5. When I build my app, the compiler emits a warning that my -ldflags syntax is likely to be deprecated, and offers a misleading suggestion to correct the warning. My use case is a -X -ldflags value that contains spaces.

$ go build -ldflags "-X main.buildInfo 'Version: 2.9, commitID: 4d203fa, build date: Tue Aug 25 19:54:19 PDT 2015, SDK: go version go1.5 darwin/amd64'" -o stashkins-darwin-amd64
# github.com/xoom/stashkins
link: warning: option -X main.buildInfo Version: 2.9, commitID: 4d203fa, build date: Tue Aug 25 19:54:19 PDT 2015, SDK: go version go1.5 darwin/amd64 may not work in future releases; use -X main.buildInfo=Version: 2.9, commitID: 4d203fa, build date: Tue Aug 25 19:54:19 PDT 2015, SDK: go version go1.5 darwin/amd64

If I take a variant of the warning advice, I get

$ go build -ldflags -X main.buildInfo='Version: 2.9, commitID: 4d203fa, build date: Tue Aug 25 19:54:19 PDT 2015, SDK: go version go1.5 darwin/amd64' -o stashkins-darwin-amd64
can't load package: package main.buildInfo=Version: 2.9, commitID: 4d203fa, build date: Tue Aug 25 19:54:19 PDT 2015, SDK: go version go1.5 darwin/amd64: cannot find package "main.buildInfo=Version: 2.9, commitID: 4d203fa, build date: Tue Aug 25 19:54:19 PDT 2015, SDK: go version go1.5 darwin/amd64" in any of:
    /usr/local/go/src/main.buildInfo=Version: 2.9, commitID: 4d203fa, build date: Tue Aug 25 19:54:19 PDT 2015, SDK: go version go1.5 darwin/amd64 (from $GOROOT)
    /Users/mpetrovic/Projects/go/src/main.buildInfo=Version: 2.9, commitID: 4d203fa, build date: Tue Aug 25 19:54:19 PDT 2015, SDK: go version go1.5 darwin/amd64 (from $GOPATH)
can't load package: package -o: cannot find package "-o" in any of:
    /usr/local/go/src/-o (from $GOROOT)
    /Users/mpetrovic/Projects/go/src/-o (from $GOPATH)
can't load package: package stashkins-darwin-amd64: cannot find package "stashkins-darwin-amd64" in any of:
    /usr/local/go/src/stashkins-darwin-amd64 (from $GOROOT)
    /Users/mpetrovic/Projects/go/src/stashkins-darwin-amd64 (from $GOPATH)

Fiddling around with the quotes, I find this invocation works, which the warning did not help me arrive at:

$ go build -ldflags '-X "main.buildInfo=Version: 2.9, commitID: a03e9a7, build date: Tue Aug 25 20:51:38 PDT 2015, SDK: go version go1.5 darwin/amd64"' -o stashkins-darwin-amd64

[schleppy]

@ae6rt Thanks for figuring out the proper quoting. Having warnings of each flag for all 30 go binaries being built on our CI box was a bit verbose.

[ae6rt]

Thanks to Ian Taylor for responding to a user on go-nuts list. That's where I found the solution, and wanted to capture it here for a fix for posterity.

[rsc]

It's not possible to guess what quoting you need. The linker doesn't know. We could make the message less specific by saying

-X <name> <value> may not work in future releases; use -X <name>=<value>

but that's much less helpful. At least with the specifics you can try to grep for the name or value to find where it came from.

[rsc]

The quoting issue makes changing the error difficult.

I propose we do nothing about this for Go 1.6 and then remove the old format entirely in Go 1.7. Then the warning will be gone too.