cmd/go: list -compiled -find ignores cgo caching

[heschi]

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

$ go version
go version devel +90dca98d33 Thu Dec 20 22:11:45 2018 +0000 linux/amd64

Does this issue reproduce with the latest release?

Think so.

What did you do?

time ~/go/bin/go list -e -json -compiled -x net >/dev/null      
~/go/bin/go list -e -json -compiled -x net > /dev/null  0.14s user 0.07s system 216% cpu 0.094 total

time ~/go/bin/go list -e -json -compiled -find net >/dev/null   
~/go/bin/go list -e -json -compiled -find net > /dev/null  0.45s user 0.27s system 106% cpu 0.674 total

What did you expect to see?

I expected -find to make it faster or at least not slower.

What did you see instead?

It made it slower, because it's rerunning cgo compilation with -find for some reason.

[jayconrod]

When "go list" is invoked with -find, it clears the list of imports for each package matched on the command line. This affects action IDs, since they incorporate dependencies' action IDs. Consequently, the build triggered by -compiled won't find sources cached by "go build".

I don't think there's any reason we shouldn't use sources produced by previous runs of "go list -find -compiled" though. cgo-generated sources are not affected by imported packages, as far as I know.

[gopherbot]

Change https://golang.org/cl/155481 mentions this issue: cmd/go: use cached source files in "go list -find -compiled"