dev.go2go: assertion fails when type parameter is specified for non-generic function call

[tdakkota]

What version of Go are you using (go version)?

$ go version
go version devel +2298dab082 Thu Oct 22 00:19:08 2020 +0000 windows/amd64

Does this issue reproduce with the latest release?

n/a

What operating system and processor architecture are you using (go env)?

• go2go playground
• windows/amd64

What did you do?

https://go2goplay.golang.org/p/2GM38sBGtph

What did you expect to see?

An error like 'function A is not generic'.

What did you see instead?

Panic due to failed assertion.

Stack trace

panic: assertion failed [recovered]
	panic: assertion failed [recovered]
	panic: assertion failed

goroutine 1 [running]:
go/types.(*Checker).handleBailout(0xc000116280, 0xc000143be0)
	/usr/local/go-faketime/src/go/types/check.go:252 +0x9b
panic(0x64e940, 0x6e0db0)
	/usr/local/go-faketime/src/runtime/panic.go:969 +0x175
go/types.(*Checker).stmt.func1(0xc000116280, 0xc000055720)
	/usr/local/go-faketime/src/go/types/stmt.go:307 +0x85
panic(0x64e940, 0x6e0db0)
	/usr/local/go-faketime/src/runtime/panic.go:975 +0x3e9
go/types.assert(...)
	/usr/local/go-faketime/src/go/types/errors.go:19
go/types.(*Checker).call(0xc000116280, 0xc000072300, 0xc0000557c0, 0x6e90c0, 0xc000010c90, 0x0)
	/usr/local/go-faketime/src/go/types/call.go:188 +0x17cf
go/types.(*Checker).exprInternal(0xc000116280, 0xc000072300, 0x6e90c0, 0xc000010c90, 0x0, 0x0, 0x0)
	/usr/local/go-faketime/src/go/types/expr.go:1349 +0x2b75
go/types.(*Checker).rawExpr(0xc000116280, 0xc000072300, 0x6e90c0, 0xc000010c90, 0x0, 0x0, 0x0)
	/usr/local/go-faketime/src/go/types/expr.go:1033 +0xc5
go/types.(*Checker).exprOrType(0xc000116280, 0xc000072300, 0x6e90c0, 0xc000010c90)
	/usr/local/go-faketime/src/go/types/expr.go:1748 +0x55
go/types.(*Checker).call(0xc000116280, 0xc000072300, 0xc000055450, 0x6e8bc0, 0xc000055450, 0x0)
	/usr/local/go-faketime/src/go/types/call.go:21 +0xbf
go/types.(*Checker).exprInternal(0xc000116280, 0xc000072300, 0x6e8bc0, 0xc000055450, 0x0, 0x0, 0x38)
	/usr/local/go-faketime/src/go/types/expr.go:1600 +0x1dba
go/types.(*Checker).rawExpr(0xc000116280, 0xc000072300, 0x6e8bc0, 0xc000055450, 0x0, 0x0, 0x0)
	/usr/local/go-faketime/src/go/types/expr.go:1033 +0xc5
go/types.(*Checker).stmt(0xc000116280, 0x0, 0x6e8e00, 0xc00001c540)
	/usr/local/go-faketime/src/go/types/stmt.go:333 +0x3e9b
go/types.(*Checker).stmtList(0xc000116280, 0x0, 0xc00001c550, 0x1, 0x1)
	/usr/local/go-faketime/src/go/types/stmt.go:125 +0xd1
go/types.(*Checker).funcBody(0xc000116280, 0xc00004a540, 0xc00001a3ec, 0x4, 0xc00004a600, 0xc000010cc0, 0x0, 0x0)
	/usr/local/go-faketime/src/go/types/stmt.go:42 +0x257
go/types.(*Checker).funcDecl.func1()
	/usr/local/go-faketime/src/go/types/decl.go:813 +0x67
go/types.(*Checker).processDelayed(0xc000116280, 0x0)
	/usr/local/go-faketime/src/go/types/check.go:327 +0x3e
go/types.(*Checker).checkFiles(0xc000116280, 0xc00003dcb8, 0x1, 0x1, 0x0, 0x0)
	/usr/local/go-faketime/src/go/types/check.go:295 +0x205
go/types.(*Checker).Files(...)
	/usr/local/go-faketime/src/go/types/check.go:257
go/types.(*Config).Check(0xc0000722c0, 0xc00001a3e0, 0x4, 0xc000072280, 0xc00003dcb8, 0x1, 0x1, 0xc0000553b0, 0x0, 0x4b70cf, ...)
	/usr/local/go-faketime/src/go/types/api.go:392 +0x188
go/go2go.RewriteBuffer(0xc00004a3c0, 0x7ffdc74c2dec, 0x1e, 0xc00013a000, 0x36, 0x236, 0x0, 0xc000010a80, 0xc000010a50, 0xc000010a20, ...)
	/usr/local/go-faketime/src/go/go2go/go2go.go:139 +0x257
main.translateFile(0xc00004a3c0, 0x7ffdc74c2dec, 0x1e)
	/usr/local/go-faketime/src/cmd/go2go/translate.go:26 +0xa9
main.main()
	/usr/local/go-faketime/src/cmd/go2go/main.go:74 +0x309

[griesemer]

This is fixed in cmd/compile/internal/types2, the version of go/types based on top of the compiler's internal syntax package (dev.go2go branch):

$ go test -run Check$ -files $HOME/tmp/x.go -errlist
--- FAIL: TestCheck (0.00s)
    check_test.go:116: /Users/gri/tmp/x.go:7:2: invalid operation: cannot index A (value of type func())
FAIL

(with x.go containing the offending source per this report). This will need to be back-ported at some point.

As we are starting to focus on a real (non-prototype) implementation to explore a full implementation in the compiler, future fixes will be made in the dev.typeparams branch. We are not going to spend a lot of energy fixing minor errors in the dev.go2go branch.

Leaving open so that we can make sure this will be fixed in a future dev.typeparams go/types version.

cc: @findleyr

[griesemer]

This is working as expected with the correct error message in Go 1.18.