go/types, types2: index out of range panic in Checker.arguments

[kralicky]

gopls version: (devel) (go1.21.0) (built from 47c5305)
gopls flags:
update flags: proxy
extension version: 0.39.1
go version: 1.21.0
environment: Visual Studio Code linux
initialization error: undefined
issue timestamp: Thu, 10 Aug 2023 15:53:47 GMT
restart history:
Thu, 10 Aug 2023 15:33:15 GMT: activation (enabled: true)
Thu, 10 Aug 2023 15:52:58 GMT: manual (enabled: true)
Thu, 10 Aug 2023 15:53:29 GMT: manual (enabled: true)

panic: runtime error: index out of range [2] with length 2 [recovered]
	panic: runtime error: index out of range [2] with length 2

goroutine 227 [running]:
go/types.(*Checker).handleBailout(0xc0002c05a0, 0xc0004a7578)
	/home/joe/sdk/go1.21.0/src/go/types/check.go:336 +0x88
panic({0xe748e0?, 0xc00003c7e0?})
	/home/joe/sdk/go1.21.0/src/runtime/panic.go:914 +0x21f
go/types.(*Checker).arguments(0xc0002c05a0, 0xc0000fc300, 0xc000381a80, {0x0, 0x0, 0x0}, {0x0, 0x0, 0x0}, {0xc0008204f8, ...}, ...)
	/home/joe/sdk/go1.21.0/src/go/types/call.go:648 +0x17a5
go/types.(*Checker).callExpr(0xc0002c05a0, 0xc000381800, 0xc0000fc300)
	/home/joe/sdk/go1.21.0/src/go/types/call.go:302 +0x86d
go/types.(*Checker).exprInternal(0xc0002c05a0, {0x0, 0x0}, 0xc000381800, {0x116bf60, 0xc0000fc300?}, {0x0?, 0x0?})
	/home/joe/sdk/go1.21.0/src/go/types/expr.go:1359 +0x1809
go/types.(*Checker).rawExpr(0xc0002c05a0, {0x0, 0x0}, 0xc000381800, {0x116bf60?, 0xc0000fc300?}, {0x0?, 0x0?}, 0x0)
	/home/joe/sdk/go1.21.0/src/go/types/expr.go:965 +0x1a5
go/types.(*Checker).stmt(0xc0002c05a0, 0x0, {0x116c3b0?, 0xc000692070?})
	/home/joe/sdk/go1.21.0/src/go/types/stmt.go:397 +0x19a
go/types.(*Checker).stmtList(0xc0002c05a0?, 0x0, {0xc000692080?, 0x0?, 0x6d4cfb?})
	/home/joe/sdk/go1.21.0/src/go/types/stmt.go:124 +0x85
go/types.(*Checker).funcBody(0xc0002c05a0, 0xc00052c720, {0xc00061e014?, 0xc000116b90?}, 0xc000381540, 0xc000620180, {0x0, 0x0})
	/home/joe/sdk/go1.21.0/src/go/types/stmt.go:44 +0x345
go/types.(*Checker).funcDecl.func1()
	/home/joe/sdk/go1.21.0/src/go/types/decl.go:826 +0x39
go/types.(*Checker).processDelayed(0xc0002c05a0, 0x0)
	/home/joe/sdk/go1.21.0/src/go/types/check.go:439 +0x15c
go/types.(*Checker).checkFiles(0xc0002c05a0, {0xc0000b6418, 0x1, 0x1})
	/home/joe/sdk/go1.21.0/src/go/types/check.go:383 +0x245
go/types.(*Checker).Files(...)
	/home/joe/sdk/go1.21.0/src/go/types/check.go:341
golang.org/x/tools/gopls/internal/lsp/cache.doTypeCheck({0x116d688, 0xc00058ef30}, 0xc00052c240, {{0xc0008826f6, 0xa}, {0xc0008826f6, 0xa}, {0xc000882710, 0x4}, {0xc0001a21f0, ...}, ...})
	/home/joe/tools/gopls/internal/lsp/cache/check.go:1561 +0x8a5
golang.org/x/tools/gopls/internal/lsp/cache.typeCheckImpl({0x116d688, 0xc00058edb0}, 0x2?, {{0xc0008826f6, 0xa}, {0xc0008826f6, 0xa}, {0xc000882710, 0x4}, {0xc0001a21f0, ...}, ...})
	/home/joe/tools/gopls/internal/lsp/cache/check.go:1420 +0x205
golang.org/x/tools/gopls/internal/lsp/cache.(*typeCheckBatch).checkPackage(0xc0000c3ed8?, {0x116d688, 0xc00058e480}, 0xc000592240)
	/home/joe/tools/gopls/internal/lsp/cache/check.go:674 +0x245
golang.org/x/tools/gopls/internal/lsp/cache.(*typeCheckBatch).handleSyntaxPackage(0xc00052c240, {0x116d688, 0xc00058e480}, 0xc0006c5860?, {0xc0008826f6, 0xa})
	/home/joe/tools/gopls/internal/lsp/cache/check.go:532 +0x42a
golang.org/x/tools/gopls/internal/lsp/cache.(*snapshot).forEachPackageInternal.func2()
	/home/joe/tools/gopls/internal/lsp/cache/check.go:394 +0x2b
golang.org/x/sync/errgroup.(*Group).Go.func1()
	/home/joe/go/pkg/mod/golang.org/x/sync@v0.3.0/errgroup/errgroup.go:75 +0x56
created by golang.org/x/sync/errgroup.(*Group).Go in goroutine 158
	/home/joe/go/pkg/mod/golang.org/x/sync@v0.3.0/errgroup/errgroup.go:72 +0x96

Here is a minimal program that can reproduce the bug. Deleting the last ')' on line 8 will cause gopls to crash.

package main

func A[T any](func(T) T, ...any) {}
func B[T any](t T) T { return t }
func C(args ...func(any)) any { return nil }

func main() {
	A[any](B, C(func(any) {})) // Delete the last ) on this line
}

[findleyr]

Thanks very much for the repro! This appears to be a type-checker bug.

[findleyr]

@gopherbot please backport this to 1.21; it is a type checker and compiler panic.

[gopherbot]

Backport issue(s) opened: #61932 (for 1.21).

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

[findleyr]

Bisected to https://go.dev/cl/495395

[griesemer]

Simpler reproducer (for go/types):

package p

func A(func(any), ...any) {}
func B[T any](T)          {}

func _() {
	A(B, nil
}

Run as testdata/manual.go with go test -run Manual.

[griesemer]

The optimization "Optimization: Only if the callee's parameter list was adjusted do we need to..." in call.go seems incorrect. If we always do it, the crash disappears. Investigating.