cmd/go: escape quoted strings in GOFLAGS

[bcmills]

In https://golang.org/cl/126656, @rsc added the GOFLAGS environment variable.

The variable is space-separated, but it is sometimes useful to include spaces within flags passed to the go command (for example, as the final argument to list -f). It would be nice to recognize at least a subset of the usual quoting conventions when parsing GOFLAGS.

~/go/src/cmd/go$ go list -e -deps -f="{{if .Error}}{{.Error}}{{end}}"

~/go/src/cmd/go$ export GOFLAGS='-e -deps -f="{{if .Error}}{{.Error}}{{end}}"'

~/go/src/cmd/go$ go list
go: parsing $GOFLAGS: non-flag ".Error}}{{.Error}}{{end}}\""

[alexbrainman]

@bcmills if you want to support cmd.exe users on Windows, you should consider how quoting works in cmd.exe. For example, this http://daviddeley.com/autohotkey/parameters/parameters.htm#WINCMDRULES shows cmd.exe rules.

Alex

[rsc]

Sorry, but no. I looked at this when I added GOFLAGS, and we don't do any special quoting for the other environment variables (go help environment | grep FLAGS)

This means you cant use GOFLAGS for your example.
That's OK, GOFLAGS is for things like -ldflags=-w.

[tianon]

That's OK, GOFLAGS is for things like -ldflags=-w.

My usage of -ldflags almost always also includes spaces -- I frequently use -d -s -w in order to get smaller static binaries (where size is the primary concern); combined with -tags netgo and CGO_ENABLED=0, this works pretty well.

I think -tags is another great problematic example -- multiple instances of -tags replace each other, and the argument to -tags is space separated, so -tags can't easily be used via GOFLAGS today except for the absolute simplest cases.

Respectfully, I would request that this be reopened and reconsidered, especially since the primary use case where this feature got me excited (building the same binary for a load of different architectures in a row) aren't actually helped by this feature today. ❤️ 😅

(I commented on the CL and was redirected here. ❤️)

[ianlancetaylor]

@rsc I'm not sure I understand the argument for not permitting quoting in the environment variable given the special support we have for quoting in -gcflags and friends. It seems to me that there are clear uses for passing multiple options to all builds, such as the -l -N that delve uses.

[andybons]

Ping @rsc @bcmills.

[rsc]

Leaving for Go 1.13. GOFLAGS is relatively new and the workaround is to use the command line, like you had to do before Go 1.11.

[myitcv]

In case we do loosen this constraint on GOFLAGS, I think we will also need to add support for accepting multiple -tags settings.

At the moment the last -tags setting "wins":

$ GOFLAGS="-tags=banana" go list -tags apple -f "{{with context}}{{.BuildTags}}{{end}}" runtime
[apple]

Given my use-case, this is relatively easy to work around by parsing the space-separated GOFLAGS for -tags=-prefixed strings and adding the results to the last command line flag.

But if we allow escape quoted strings in GOFLAGS, this parsing becomes more difficult.

I suspect allowing multiple instances of -tags would be useful in any case? I can always spin off another proposal/CL if needs be.

[mvdan]

I suspect allowing multiple instances of -tags would be useful in any case?

Also note that the per-package flags like -ldflags also overwrite each other, but not always. For example, in -ldflags=-w -ldflags=-s the second wins, but in -ldflags=foo=-w -ldflags=bar=-s both apply (to different packages). In that flag, it makes sense as it allows to override a previous per-package flag instead of only appending to it.

Not saying that I disagree with allowing multiple -tags flags; I actually think what you're trying to do is reasonable. My point is that I think we should fix the GOFLAGS interaction with all these list-like flags in a consistent way.

[myitcv]

Re-reading what I wrote in #26849 (comment) I realise it wasn't that clear.

At the moment, because GOFLAGS is:

A space-separated list of -flag=value settings

it can't contain a multi-value -tags flag value because -tags is:

a space-separated list of build tags to consider satisfied during the build

Add to that, cmd/go does not understand multiple -tags values; the last one wins.

Hence at the moment, it is not possible to specify a multi-value -tags via GOFLAGS. This becomes problematic in situations like #27898 (comment) where the GOFLAGS variable could otherwise be used as a means of passing build tags in the environment go generate sets for each directive it runs.

For my specific case there are at least two possible non-mutually exclusive solutions:

• allowing quoted strings in GOFLAGS (this proposal)
• having cmd/go accept -tags multiple times, i.e. space-joining the multiple -tags values

It is for this second option that I can create a separate issue if required.

[ianthehat]

Another alternative that would only work for -tags would be to accept comma separated tags. This feels more natural anyway, and would match the syntax used in the +build lines anyway.
This would be very helpful for people needing to set multiple tags and have them obeyed by tools invoked by their editors.

[gopherbot]

Change https://golang.org/cl/173438 mentions this issue: cmd/go: change -tags to a comma-separated list

[mvdan]

Funnily enough, I thought that was how -tags worked years ago. That is why I filed #18800 and mailed a change for cmd/go to give a more obvious error. So I agree with @ianthehat; I'm not sure why that idea hadn't popped up again since 2017.