cmd/compile: compiler crash with circular (but valid) generic alias

[ianlancetaylor]

Compiling this program with tip crashes the compiler.

package p

type AC interface {
	C
}

type ST []int

type R[S any, P any] struct {}

type SR = R[SS, ST]

type SS interface {
	NSR(any) *SR
}

type C interface {
	NSR(any) *SR
}

<autogenerated>:1: internal compiler error: panic: runtime error: invalid memory address or nil pointer dereference

goroutine 1 [running]:
runtime/debug.Stack()
	/home/iant/go/src/runtime/debug/stack.go:24 +0x65
cmd/compile/internal/base.FatalfAt({0x4?, 0x0?}, {0xd1f6c4, 0x9}, {0xc0000d6b08, 0x1, 0x1})
	/home/iant/go/src/cmd/compile/internal/base/print.go:227 +0x1ca
cmd/compile/internal/base.Fatalf(...)
	/home/iant/go/src/cmd/compile/internal/base/print.go:196
cmd/compile/internal/gc.handlePanic()
	/home/iant/go/src/cmd/compile/internal/gc/main.go:49 +0x85
panic({0xca9460, 0x130cdf0})
	/home/iant/go/src/runtime/panic.go:838 +0x207
cmd/compile/internal/types.PtrDataSize(0xe972b8?)
	/home/iant/go/src/cmd/compile/internal/types/size.go:646 +0x18
cmd/compile/internal/types.(*Type).HasPointers(...)
	/home/iant/go/src/cmd/compile/internal/types/type.go:1682
cmd/compile/internal/escape.(*escape).exprSkipInit(0xc0003dc4c0, {0xc000636bd0?, 0x6f3008?, 0x0?, 0x0?}, {0xe972b8, 0xc0003241b0?})
	/home/iant/go/src/cmd/compile/internal/escape/expr.go:33 +0x176
cmd/compile/internal/escape.(*escape).expr(0xc000636bd0?, {0xc000636bd0?, 0x0?, 0x0?, 0x10?}, {0xe972b8, 0xc0003241b0})
	/home/iant/go/src/cmd/compile/internal/escape/expr.go:20 +0xad
cmd/compile/internal/escape.(*escape).assignList(0xc0003dc4c0, {0xc0000a6500, 0x1, 0x0?}, {0xc0000a64b0, 0x1, 0x203000?}, {0xd1b025, 0x6}, {0xe98e10, ...})
	/home/iant/go/src/cmd/compile/internal/escape/assign.go:93 +0x3d6
cmd/compile/internal/escape.(*escape).stmt(0xc0003dc4c0, {0xe98e10, 0xc00007ca00?})
	/home/iant/go/src/cmd/compile/internal/escape/stmt.go:175 +0x1577
cmd/compile/internal/escape.(*escape).stmts(...)
	/home/iant/go/src/cmd/compile/internal/escape/stmt.go:190
cmd/compile/internal/escape.(*escape).block(0xc0003dc4c0?, {0xc0000a64c0?, 0x1?, 0xc000326480?})
	/home/iant/go/src/cmd/compile/internal/escape/stmt.go:197 +0x72
cmd/compile/internal/escape.(*batch).walkFunc(0xc000326480, 0xc0003d6c60)
	/home/iant/go/src/cmd/compile/internal/escape/escape.go:227 +0xe5
cmd/compile/internal/escape.Batch({0xc0000d76b0?, 0x1, 0x1}, 0xc8?)
	/home/iant/go/src/cmd/compile/internal/escape/escape.go:143 +0x228
cmd/compile/internal/reflectdata.methodWrapper(0xc0003b2d20, 0xc0003ec1e0, 0x88?)
	/home/iant/go/src/cmd/compile/internal/reflectdata/reflect.go:1974 +0x1871
cmd/compile/internal/reflectdata.imethods(0xc0003b2d20)
	/home/iant/go/src/cmd/compile/internal/reflectdata/reflect.go:395 +0x2d9
cmd/compile/internal/reflectdata.writeType(0xc0003b2d90?)
	/home/iant/go/src/cmd/compile/internal/reflectdata/reflect.go:1054 +0x5cd
cmd/compile/internal/reflectdata.WriteRuntimeTypes()
	/home/iant/go/src/cmd/compile/internal/reflectdata/reflect.go:1266 +0x3d8
cmd/compile/internal/gc.dumpdata()
	/home/iant/go/src/cmd/compile/internal/gc/obj.go:118 +0x6e
cmd/compile/internal/gc.Main(0xd4f728)
	/home/iant/go/src/cmd/compile/internal/gc/main.go:328 +0x11ab
main.main()
	/home/iant/go/src/cmd/compile/main.go:55 +0xdd

CC @randall77 @danscales

[griesemer]

This will report an error with forthcoming CL 379916. Leaving open for now so I can add a test. Not a release blocker.

[gopherbot]

Change https://golang.org/cl/379916 mentions this issue: go/types, types2: report an error when using a broken alias