cmd/compile: internal compiler error: unexpected type: <nil> (<nil>) in for-range

[griesemer]

Reproducer (1.22 and at tip, playground):

package main

func main() {
	var i float64
	for i = range 10 {
		_ = i
	}
}

Running the code leads to:

<unknown line number>: internal compiler error: unexpected type: <nil> (<nil>)

goroutine 1 [running]:
runtime/debug.Stack()
	/usr/local/go/src/runtime/debug/stack.go:26 +0x5e
cmd/compile/internal/base.FatalfAt({0x212300?, 0xc0?}, {0xe130b2, 0x18}, {0xc00008ece0, 0x2, 0x2})
	/usr/local/go/src/cmd/compile/internal/base/print.go:225 +0x1d7
cmd/compile/internal/base.Fatalf(...)
	/usr/local/go/src/cmd/compile/internal/base/print.go:194
cmd/compile/internal/noder.(*pkgWriter).typIdx(0xc000212300, {0x0, 0x0}, 0xc0001aa6e0)
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:505 +0x8d9
cmd/compile/internal/noder.(*writer).itab(0xc0004d06e0, {0x0?, 0x0?}, {0xf66fe8, 0x14a7be0})
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:2401 +0xa5
cmd/compile/internal/noder.(*writer).convRTTI(0xc0004d06e0, {0x0, 0x0}, {0xf66fe8, 0x14a7be0})
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:2415 +0x58
cmd/compile/internal/noder.(*writer).forStmt.func1(0xf66fe8?, {0x0, 0x0})
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:1475 +0x127
cmd/compile/internal/noder.(*writer).forStmt(0xc0004d06e0, 0xc0004c68c0)
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:1479 +0x313
cmd/compile/internal/noder.(*writer).stmt1(0xc0004d06e0, {0xf690d0?, 0xc0004c68c0})
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:1308 +0x25a
cmd/compile/internal/noder.(*writer).stmts(...)
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:1239
cmd/compile/internal/noder.(*pkgWriter).bodyIdx(0xd79800?, 0xc0004c8580, 0xc0004c8480, 0xc0001aa6e0)
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:1136 +0x1b3
cmd/compile/internal/noder.(*writer).funcExt(0xc0004d0370, 0xc0004c4700)
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:1071 +0x328
cmd/compile/internal/noder.(*writer).doObj(0xc0004d02c0, 0xc0004d0370, {0xf6ef80, 0xc0004c4700})
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:828 +0x213
cmd/compile/internal/noder.(*pkgWriter).objIdx(0xc000212300, {0xf6ef80, 0xc0004c4700})
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:787 +0x612
cmd/compile/internal/noder.(*pkgWriter).objInstIdx(0xc000212300, {0xf6ef80, 0xc0004c4700}, 0x0, 0x0)
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:728 +0xf0
cmd/compile/internal/noder.(*writer).obj(0xc0004d0000, {0xf6ef80?, 0xc0004c4700?}, 0xc0004c4700?)
	/usr/local/go/src/cmd/compile/internal/noder/writer.go:704 +0x2f
cmd/compile/internal/noder.writePkgStub({0x0?, {0x0?, 0x0?}}, {0xc0001a0598, 0x1, 0x1})
	/usr/local/go/src/cmd/compile/internal/noder/unified.go:325 +0x53e
cmd/compile/internal/noder.unified({0x0?, {0x0?, 0x0?}}, {0xc0001a0598?, 0xd44cc0?, 0x0?})
	/usr/local/go/src/cmd/compile/internal/noder/unified.go:180 +0x9a
cmd/compile/internal/noder.LoadPackage({0xc0001b6100, 0x1, 0x2})
	/usr/local/go/src/cmd/compile/internal/noder/noder.go:77 +0x43a
cmd/compile/internal/gc.Main(0xe3aec0)
	/usr/local/go/src/cmd/compile/internal/gc/main.go:197 +0xbbd
main.main()
	/usr/local/go/src/cmd/compile/main.go:57 +0xf9

[griesemer]

This code should not make it through the type checker.

[gopherbot]

Change https://go.dev/cl/580937 mentions this issue: go/types, types2: allow range over untyped constants representable as integers

[mknyszek]

In triage, ping @findleyr for review.

[gopherbot]

Change https://go.dev/cl/590056 mentions this issue: [release-branch.go1.22] go/types, types2: report error for floating-point iteration variable

[griesemer]

@gopherbot please consider this for backport to 1.22.

[gopherbot]

Backport issue(s) opened: #67798 (for 1.22).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.