One error message that we are not reporting in Go 1.18 is at least one kind of "channel too large" error. In particular, see test/fixedbugs/issue42058a.go and test/fixedbugs/issue42058b.go. In Go 1.17 or -G=0 mode, we give errors like:
fixedbugs/issue42058a.go:9:7: channel element type too large (>64kB)
fixedbugs/issue42058a.go:13:7: channel element type too large (>64kB)
but no errors in Go1.18 default mode (which is why those tests are currently disabled in run.go). This is for statically declared channels whose element are too large.
Looks like there is a separate just-reported issue #49767 for Go 1.17.2 and Go 1.18 that causes a compiler crash when a channel with a too-large element size is created via make and a channel type literal.