cmd/go: "go work sync" simply panics

[mvdan]

I come with more workspaces bugs :) Using https://github.com/mvdan/sh as a sample module:

$ git rev-parse HEAD
946fb5b53d67e4a36af33c0ef2d870ed5543ee7d
$ go version
go version devel go1.18-c2397905e0 Sat Nov 13 03:33:55 2021 +0000 linux/amd64
$ go work init
$ go work sync
panic: in workspace mode, but pruning is not workspace in newRequirements

goroutine 1 [running]:
cmd/go/internal/modload.newRequirements(0x0, {0x0?, 0x0, 0x5?}, 0x0)
	/home/mvdan/tip/src/cmd/go/internal/modload/buildlist.go:118 +0x718
cmd/go/internal/modload.LoadModFile({0xad5000, 0xc000024160})
	/home/mvdan/tip/src/cmd/go/internal/modload/init.go:695 +0x599
cmd/go/internal/modload.LoadModGraph({0xad5000, 0xc000024160}, {0x0, 0x0})
	/home/mvdan/tip/src/cmd/go/internal/modload/buildlist.go:473 +0x3d
cmd/go/internal/workcmd.runSync({0xad5000, 0xc000024160}, 0xc0002a23f0?, {0x14?, 0x4?, 0x2?})
	/home/mvdan/tip/src/cmd/go/internal/workcmd/sync.go:39 +0x5e
main.invoke(0xdab5e0, {0xc0000201a0, 0x1, 0x1})
	/home/mvdan/tip/src/cmd/go/main.go:218 +0x2ee
main.main()
	/home/mvdan/tip/src/cmd/go/main.go:175 +0x78e

Even if I'm holding go work sync wrong, surely it's not expected that it would panic. cc @matloob @bcmills

[n4j]

I am able to reproduce this

➜  sh git:(master) ✗ uname -a
Linux turing 5.11.0-40-generic #44~20.04.2-Ubuntu SMP Tue Oct 26 18:07:44 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

➜  sh git:(master) git rev-parse HEAD
423f205ca37b9933907c589bd90f0f095ccf84ec
➜  sh git:(master) go version
go version devel go1.18-9e13a8876f Mon Nov 15 23:55:09 2021 +0000 linux/amd64
➜  sh git:(master) go work init 
➜  sh git:(master) ✗ go work sync 
panic: in workspace mode, but pruning is not workspace in newRequirements

goroutine 1 [running]:
cmd/go/internal/modload.newRequirements(0x0, {0x0?, 0x0, 0x5?}, 0x0)
	/mnt/giga-chad/github/go/src/cmd/go/internal/modload/buildlist.go:118 +0x718
cmd/go/internal/modload.LoadModFile({0xad6060, 0xc00002c0b8})
	/mnt/giga-chad/github/go/src/cmd/go/internal/modload/init.go:695 +0x599
cmd/go/internal/modload.LoadModGraph({0xad6060, 0xc00002c0b8}, {0x0, 0x0})
	/mnt/giga-chad/github/go/src/cmd/go/internal/modload/buildlist.go:473 +0x3d
cmd/go/internal/workcmd.runSync({0xad6060, 0xc00002c0b8}, 0xc00002a498?, {0x14?, 0x4?, 0x2?})
	/mnt/giga-chad/github/go/src/cmd/go/internal/workcmd/sync.go:39 +0x5e
main.invoke(0xdae5e0, {0xc000020110, 0x1, 0x1})
	/mnt/giga-chad/github/go/src/cmd/go/main.go:218 +0x2ee
main.main()
	/mnt/giga-chad/github/go/src/cmd/go/main.go:175 +0x78e

[gopherbot]

Change https://golang.org/cl/365234 mentions this issue: cmd/go: fix go work sync when there are zero workspace modules