go/types: panic when enabling reverseTypeInference with -lang=go1.17

[findleyr]

The following test crashes go/types:

// -reverseTypeInference -lang=go1.17

// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package p

func f[P any](P) {}

var v func(int) = f

Output:

    --- FAIL: TestFixedbugs/issueNNNNN.go (0.00s)
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x573f55]

goroutine 471 [running]:
testing.tRunner.func1.2({0x697cc0, 0x8c5fa0})
	/usr/local/google/home/rfindley/src/go/src/testing/testing.go:1545 +0x238
testing.tRunner.func1()
	/usr/local/google/home/rfindley/src/go/src/testing/testing.go:1548 +0x39f
panic({0x697cc0?, 0x8c5fa0?})
	/usr/local/google/home/rfindley/src/go/src/runtime/panic.go:913 +0x21f
go/types.(*Checker).handleBailout(0xc0001c4b40, 0xc0003b78e8)
	/usr/local/google/home/rfindley/src/go/src/go/types/check.go:332 +0x88
panic({0x697cc0?, 0x8c5fa0?})
	/usr/local/google/home/rfindley/src/go/src/runtime/panic.go:913 +0x21f
go/types.(*Checker).funcInst(0xc0001c4b40, 0xc000262240, 0xc0002622c0?, 0xc000262300, 0x0)
	/usr/local/google/home/rfindley/src/go/src/go/types/call.go:29 +0x95
go/types.(*Checker).nonGeneric(0xc0001c4b40, {0x74dc88?, 0xc000262240?}, 0xc000262300)
	/usr/local/google/home/rfindley/src/go/src/go/types/expr.go:1282 +0x145
go/types.(*Checker).rawExpr(0xc0001c4b40, {0x74dc88, 0xc000262240}, 0xc000262300, {0x74e4c0?, 0xc0001f1200?}, {0x0?, 0x0?}, 0x0)
	/usr/local/google/home/rfindley/src/go/src/go/types/expr.go:1257 +0x1e5
go/types.(*Checker).expr(0x40380b?, {0x74dc88?, 0xc000262240?}, 0x0?, {0x74e4c0?, 0xc0001f1200?})
	/usr/local/google/home/rfindley/src/go/src/go/types/expr.go:1787 +0x45
go/types.(*Checker).varDecl(0x695940?, 0xc0000b19e0, {0xc000057ee8?, 0x1, 0x1}, {0x74e430, 0xc0001f11e0}, {0x74e4c0, 0xc0001f1200})
	/usr/local/google/home/rfindley/src/go/src/go/types/decl.go:513 +0x16c
go/types.(*Checker).objDecl(0xc0001c4b40, {0x7503f8, 0xc0000b19e0}, 0x0?)
	/usr/local/google/home/rfindley/src/go/src/go/types/decl.go:194 +0x95e
go/types.(*Checker).packageObjects(0xc0001c4b40)
	/usr/local/google/home/rfindley/src/go/src/go/types/resolver.go:662 +0x465
go/types.(*Checker).checkFiles(0xc0001c4b40, {0xc000057ec8, 0x1, 0x1})
	/usr/local/google/home/rfindley/src/go/src/go/types/check.go:362 +0x149
go/types.(*Checker).Files(...)
	/usr/local/google/home/rfindley/src/go/src/go/types/check.go:337
go/types.(*Config).Check(0xc000262080?, {0x8bdc80?, 0x6?}, 0x0?, {0xc000057ec8, 0x1, 0x1}, 0x0?)
	/usr/local/google/home/rfindley/src/go/src/go/types/api.go:422 +0x7c
go/types_test.testFiles(0xc0000836c0, {0x0?, 0x0}, {0xc0003b7f50?, 0x1, 0x1}, {0xc0003a6768?, 0x1, 0x1}, 0x0, ...)
	/usr/local/google/home/rfindley/src/go/src/go/types/check_test.go:188 +0x5e5
go/types_test.testPkg(0xc0000836c0, {0xc0000c1f50, 0x1, 0x1}, 0x0?)
	/usr/local/google/home/rfindley/src/go/src/go/types/check_test.go:431 +0x20b
go/types_test.testDirFiles.func1(0x0?)
	/usr/local/google/home/rfindley/src/go/src/go/types/check_test.go:396 +0x3c
testing.tRunner(0xc0000836c0, 0xc0001f1080)
	/usr/local/google/home/rfindley/src/go/src/testing/testing.go:1595 +0xff
created by testing.(*T).Run in goroutine 277
	/usr/local/google/home/rfindley/src/go/src/testing/testing.go:1648 +0x3ad

Fix incoming.

[gopherbot]

Change https://go.dev/cl/484757 mentions this issue: go/types,types2: fix panic in reverse type inference when -lang<go1.18