cmd/compile: internal compiler error using type parameters with local type alias

[dsnet]

I apologize for all the bug reports, but I'm hitting another internal compiler error.

$ go.tip version
go version devel go1.18-d9244f8b64 Fri Sep 3 21:31:30 2021 +0000 linux/amd64

$ go.tip build
# github.com/go-json-experiment/json
panic: interface conversion: ir.Node is *ir.typeNode, not *ir.Name

goroutine 1 [running]:
cmd/compile/internal/ir.(*Decl).editChildren(0xc001068930, 0xe65358)
	/usr/local/go.tip/src/cmd/compile/internal/ir/node_gen.go:462 +0x87
cmd/compile/internal/ir.EditChildren(...)
	/usr/local/go.tip/src/cmd/compile/internal/ir/visit.go:185
cmd/compile/internal/noder.(*subster).node.func1({0xe65358, 0xc000d2e6c0})
	/usr/local/go.tip/src/cmd/compile/internal/noder/stencil.go:942 +0x486
cmd/compile/internal/noder.(*subster).node(0xc000feba80, {0xe65358, 0xc000d2e6c0})
	/usr/local/go.tip/src/cmd/compile/internal/noder/stencil.go:1248 +0xa5
cmd/compile/internal/noder.(*subster).list(0xc00000ee98, {0xc0000b0f00, 0x9, 0xc000072640})
	/usr/local/go.tip/src/cmd/compile/internal/noder/stencil.go:1362 +0x8e
cmd/compile/internal/noder.(*irgen).genericSubst(0xc0004a8700, 0xc001063ae0, 0xc0005d4270, {0xc00106a0a0, 0x2, 0x2}, 0x1, 0xc00012d600)
	/usr/local/go.tip/src/cmd/compile/internal/noder/stencil.go:726 +0xce6
cmd/compile/internal/noder.(*irgen).getInstantiation(0xc0004a8700, 0xc0005d4270, {0xc00056c330, 0x2, 0x2}, 0x30)
	/usr/local/go.tip/src/cmd/compile/internal/noder/stencil.go:608 +0x33d
cmd/compile/internal/noder.(*irgen).instantiateMethods(0xc0004a8700)
	/usr/local/go.tip/src/cmd/compile/internal/noder/stencil.go:511 +0x248
cmd/compile/internal/noder.(*irgen).stencil(0xc0004a8700)
	/usr/local/go.tip/src/cmd/compile/internal/noder/stencil.go:50 +0x9b
cmd/compile/internal/noder.(*irgen).generate(0xc0004a8700, {0xc000069aa0, 0xc, 0x0})
	/usr/local/go.tip/src/cmd/compile/internal/noder/irgen.go:304 +0x359
cmd/compile/internal/noder.check2({0xc000069aa0, 0xc, 0xc})
	/usr/local/go.tip/src/cmd/compile/internal/noder/irgen.go:92 +0x175
cmd/compile/internal/noder.LoadPackage({0xc000001ae0, 0xc, 0x0})
	/usr/local/go.tip/src/cmd/compile/internal/noder/noder.go:90 +0x335
cmd/compile/internal/gc.Main(0xd1dcb0)
	/usr/local/go.tip/src/cmd/compile/internal/gc/main.go:190 +0xaf3
main.main()
	/usr/local/go.tip/src/cmd/compile/main.go:55 +0xdd

Reproduction:

$ git clone https://github.com/go-json-experiment/json.git
$ cd json
$ git checkout origin/generics-bug3
$ go build

Based on @mdempsky's comment in #48016 (comment), I tried building this with GOEXPERIMENT=unified and it seems to work.

The relevant change that seems to cause an ICE is the presence of a local type alias:

func (a *arshalers[Options, Coder]) lookup(fnc func(Options, *Coder, addressableValue) error, t reflect.Type) func(Options, *Coder, addressableValue) error {
	type F = func(Options, *Coder, addressableValue) error
	...
}

\cc @danscales @mdempsky @griesemer @ianlancetaylor

[cherrymui]

Yeah, local type with type parameter is not fully implemented yet.

[randall77]

Dup of #47631
(Although it may have a slightly different cause, they will probably be fixed together.)