Add Go 1.21 loopvar=2 GC flag in CI tests to surface loops which compile differently

[atc0005]

From https://www.sethvargo.com/things-im-excited-for-in-go-1-21/:

...

The Go team made it very easy to identify places where your code might be affected by this change. Building your Go program with Go 1.21 and a special GC flag will print out the loops that are compiling differently:

go build -gcflags=all=-d=loopvar=2 ./...

I can add this as a new linting task specific to the stable go-ci image.

EDIT:

I can add this as a new linting task specific to a particular "mirror" go-ci image.

See later notes on this GH issue.

References:

• https://www.sethvargo.com/things-im-excited-for-in-go-1-21/
• https://go.dev/wiki/LoopvarExperiment
  • https://go.dev/wiki/LoopvarExperiment#my-test-fails-with-the-change-how-can-i-debug-it
• gosec G601: Implicit memory aliasing in for loop linting errors check-vmware#916

[atc0005]

From earlier testing as part of the work on atc0005/check-vmware#916:

podman container run --platform linux/amd64 --rm -it -v $PWD:/code -w /code golang:1.21.0
go build -gcflags=all=-d=loopvar=2 ./...

Output:

root@c70a67fbeea0:/code# go build -gcflags=all=-d=loopvar=2 ./...
# runtime
/usr/local/go/src/runtime/proc.go:1907:7: loop variable freem now per-iteration, stack-allocated
/usr/local/go/src/runtime/proc.go:3269:7: loop variable enum now per-iteration, stack-allocated
/usr/local/go/src/runtime/mgcmark.go:810:6: loop variable d now per-iteration, stack-allocated
/usr/local/go/src/runtime/traceback.go:623:7: loop variable iu now per-iteration, stack-allocated
/usr/local/go/src/runtime/traceback.go:980:7: loop variable iu now per-iteration, stack-allocated
# vendor/golang.org/x/net/dns/dnsmessage
/usr/local/go/src/vendor/golang.org/x/net/dns/dnsmessage/message.go:1161:10: loop variable q now per-iteration, stack-allocated
/usr/local/go/src/vendor/golang.org/x/net/dns/dnsmessage/message.go:1168:10: loop variable a now per-iteration, stack-allocated
/usr/local/go/src/vendor/golang.org/x/net/dns/dnsmessage/message.go:1175:10: loop variable a now per-iteration, stack-allocated
/usr/local/go/src/vendor/golang.org/x/net/dns/dnsmessage/message.go:1182:10: loop variable a now per-iteration, stack-allocated
/usr/local/go/src/vendor/golang.org/x/net/dns/dnsmessage/message.go:2633:9: loop variable o now per-iteration, stack-allocated
# net
/usr/local/go/src/net/cgo_unix.go:74:9: loop variable addr now per-iteration, stack-allocated
/usr/local/go/src/net/dnsclient_unix.go:567:9: loop variable ip now per-iteration, stack-allocated
/usr/local/go/src/net/interface_linux.go:27:9: loop variable m now per-iteration, stack-allocated
/usr/local/go/src/net/interface_linux.go:150:9: loop variable m now per-iteration, stack-allocated
/usr/local/go/src/net/sockopt_posix.go:28:9: loop variable ifi now per-iteration, heap-allocated
/usr/local/go/src/net/interface.go:147:9: loop variable ifi now per-iteration, heap-allocated (loop inlined into /usr/local/go/src/net/interface.go:139)
/usr/local/go/src/net/interface.go:147:9: loop variable ifi now per-iteration, heap-allocated (loop inlined into /usr/local/go/src/net/interface_linux.go:159)
# crypto/x509
/usr/local/go/src/crypto/x509/x509.go:1208:11: loop variable name now per-iteration, stack-allocated
/usr/local/go/src/crypto/x509/x509.go:1220:11: loop variable ipNet now per-iteration, stack-allocated
/usr/local/go/src/crypto/x509/x509.go:1228:11: loop variable email now per-iteration, stack-allocated
/usr/local/go/src/crypto/x509/x509.go:1240:11: loop variable uriDomain now per-iteration, stack-allocated
/usr/local/go/src/crypto/x509/verify.go:856:9: loop variable ext now per-iteration, heap-allocated
/usr/local/go/src/crypto/x509/verify.go:871:10: loop variable ext now per-iteration, heap-allocated
# crypto/tls
/usr/local/go/src/crypto/tls/common.go:1146:9: loop variable cert now per-iteration, heap-allocated
/usr/local/go/src/crypto/tls/ticket.go:121:10: loop variable extra now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/ticket.go:143:10: loop variable chain now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/ticket.go:150:12: loop variable cert now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/ticket.go:374:9: loop variable key now per-iteration, heap-allocated
/usr/local/go/src/crypto/tls/handshake_messages.go:195:12: loop variable proto now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/handshake_messages.go:233:12: loop variable ks now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/handshake_messages.go:268:12: loop variable psk now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/handshake_messages.go:276:12: loop variable binder now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/handshake_messages.go:355:11: loop variable binder now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/handshake_messages.go:693:12: loop variable sct now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/handshake_messages.go:1186:14: loop variable ca now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/handshake_messages.go:1389:7: loop variable i now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/handshake_messages.go:1389:10: loop variable cert now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/handshake_messages.go:1411:15: loop variable sct now per-iteration, stack-allocated
/usr/local/go/src/crypto/tls/handshake_client.go:1080:9: loop variable chain now per-iteration, heap-allocated
/usr/local/go/src/crypto/tls/handshake_server_tls13.go:186:10: loop variable ks now per-iteration, heap-allocated
# github.com/vmware/govmomi/vim25/xml
vendor/github.com/vmware/govmomi/vim25/xml/typeinfo.go:82:13: loop variable finfo now per-iteration, stack-allocated
# net/http/cookiejar
/usr/local/go/src/net/http/cookiejar/jar.go:188:10: loop variable e now per-iteration, stack-allocated
# github.com/vmware/govmomi/object
vendor/github.com/vmware/govmomi/object/authorization_manager.go:43:9: loop variable role now per-iteration, heap-allocated (loop inlined into <autogenerated>:1)
vendor/github.com/vmware/govmomi/object/authorization_manager.go:53:9: loop variable role now per-iteration, heap-allocated (loop inlined into <autogenerated>:1)
vendor/github.com/vmware/govmomi/object/custom_fields_manager.go:140:9: loop variable def now per-iteration, heap-allocated (loop inlined into <autogenerated>:1)
# github.com/atc0005/check-vmware/internal/vsphere
internal/vsphere/snapshots.go:877:10: loop variable snapTree now per-iteration, heap-allocated
internal/vsphere/snapshots.go:984:10: loop variable snapTree now per-iteration, heap-allocated
# github.com/atc0005/check-vmware/cmd/check_vmware_hs2ds2vms
cmd/check_vmware_hs2ds2vms/main.go:297:14: loop variable pairing now per-iteration, stack-allocated

root@c70a67fbeea0:/code# echo $?
0

root@c70a67fbeea0:/code# go build -gcflags=all=-d=loopvar=2 ./... 2>&1 | grep -Ev '/usr|vendor'
# runtime
# net
# crypto/x509
# crypto/tls
# github.com/vmware/govmomi/vim25/xml
# net/http/cookiejar
# github.com/vmware/govmomi/object
# github.com/atc0005/check-vmware/internal/vsphere
internal/vsphere/snapshots.go:877:10: loop variable snapTree now per-iteration, heap-allocated
internal/vsphere/snapshots.go:984:10: loop variable snapTree now per-iteration, heap-allocated

root@c70a67fbeea0:/code# go build -gcflags=all=-d=loopvar=2 ./... 2>&1 | grep -Ev '/usr|vendor|^#'
internal/vsphere/snapshots.go:877:10: loop variable snapTree now per-iteration, heap-allocated
internal/vsphere/snapshots.go:984:10: loop variable snapTree now per-iteration, heap-allocated

The latter approach will collect just the relevant bits I'm interested in.

The CI check could look for any captured content from that build attempt (e.g., as a Bash array) and emit the entries for review.

[atc0005]

Based on the Go 1.22 release notes (https://go.dev/doc/go1.22), the 1.22 series should work just as well as the 1.21 series provided that the go.mod file does not specify a version of Go newer than 1.21.

To be on the safe side, I should probably explicitly specify a 1.21 series image (and disable any automatic "upgrade" of the toolchain).