cmd/go: GONOPROXY is undocumented

[bcmills]

GOSUMDB, GONOSUMDB, and GONOPROXY variables were added in CL 173951.

Documentation for GOSUMDB and GONOSUMDB was added to https://tip.golang.org/cmd/go/#hdr-Module_authentication_failures, but I don't see any mention of GONOPROXY in the cmd/go docs at all.

CC @jayconrod @rsc

[bcmills]

Some specific questions:

• Should GOPROXY=off with GONOPROXY=*/x disable all fetches, or allow (only) */x to be fetched directly?
• What should happen if GOPROXY includes off explicitly in the fallback chain, such as GOPROXY=https://my.proxy,https://other.proxy,off? (In that case, should fetches of the GONOPROXY paths be disabled?)

[ianlancetaylor]

Also note that all environment variables should be documented at https://golang.org/cmd/go/#hdr-Environment_variables. These new variables are not mentioned there.

[bcmills]

One more question to document:

• If GOPROXY does not include direct as a fallback, should GONOPROXY fall back to direct implicitly, or behave as if GOPROXY were set to off for that module?

[rogpeppe]

I find it a bit odd that GONOPROXY is using sh-style globs anyway, given that GONOPROXY holds a set of package paths (AIUI) not URLs, and package paths are almost always matched with patterns as documented in go help packages.

That is, I'd expect:

GONOPROXY=myorg.com/...

to avoid the proxy for all modules under myorg.com.

[rsc]

If GOPROXY=off and GONOPROXY=* (say), then I think GONOPROXY wins. No matter what GOPROXY is set to, GONOPROXY matching the module means don't pay attention to that.

[rsc]

@rogpeppe, I see your point but I was trying to line up a bit with the standard NO_PROXY (for example https://www.gnu.org/software/emacs/manual/html_node/url/Proxies.html). Also I think it would be just too hard to write something like GONOPROXY=*.corp.yourcompany.com using ... (its not actually possible at all).

[rogpeppe]

I guess I don't understand the GONOPROXY semantics (the whole point of this thread, and probably why I can't get it to work for me); how is GONOPROXY=*.corp.yourcompany.com different from GONOPROXY=....corp.yourcompany.com ?

[bcmills]

how is GONOPROXY=*.corp.yourcompany.com different from GONOPROXY=....corp.yourcompany.com ?

The have different behavior for packages such as contrived.example.com/not.your.corp.yourcompany.com.

[gopherbot]

Change https://golang.org/cl/178179 mentions this issue: cmd/go: default to GOPROXY=https://proxy.golang.org and GOSUMDB=sum.golang.org

[gopherbot]

Change https://golang.org/cl/179219 mentions this issue: cmd/go: document GO{NO}SUMDB in 'go help environment' and 'go help modules'