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cmd/go2go: unexpected type parameter panic in translator #39953

griesemer opened this issue Jun 30, 2020 · 2 comments

cmd/go2go: unexpected type parameter panic in translator #39953

griesemer opened this issue Jun 30, 2020 · 2 comments


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@griesemer griesemer commented Jun 30, 2020

Extracted from #39758: The following program

package main

type top(type T, T2) struct {
	p *parent(T, T2)

type parent(type T, T2) struct {
	(child(T, T2))

type child(type T, T2) struct {

func (d *top(T, T2)) foo() *T {
	// panic: internal error: receiver type parameter inference failed
	// t, _ := 

	// panic: -: unexpected type string character '₇' in "T₇"
	t, _ :=
	return t

func (rb *child(T, T2)) foo() (*T, bool) {
	return nil, true

func main() {
	var _ top(int, int)

type-checks ok but the translator reports

$ go tool go2go run main.go2 
panic: unexpected type parameter

goroutine 1 [running]:
go/go2go.(*translator).typeToAST(0xc0001a5678, 0x12e40a0, 0xc00012ae80, 0xc00011d6e0, 0xc0001a4c78)
	/Users/gri/go/src/go/go2go/types.go:596 +0x1725
go/go2go.(*translator).typeListToASTList(0xc0001a5678, 0xc00011cf80, 0x2, 0x2, 0x0, 0x0, 0xc0001241f8, 0xc0001a4b68, 0x1003598, 0x12570c0)
	/Users/gri/go/src/go/go2go/rewrite.go:1175 +0xe5
go/go2go.(*translator).lookupInstantiatedType(0xc0001a5678, 0xc0001366c0, 0x0, 0x0, 0x0)
	/Users/gri/go/src/go/go2go/rewrite.go:1095 +0x2b6
go/go2go.(*translator).translateSelectorExpr(0xc0001a5678, 0xc00011c780)
	/Users/gri/go/src/go/go2go/rewrite.go:804 +0x5b1
go/go2go.(*translator).translateExpr(0xc0001a5678, 0xc00011c780)
	/Users/gri/go/src/go/go2go/rewrite.go:666 +0x4ba
go/go2go.(*translator).translateSelectorExpr(0xc0001a5678, 0xc00012a800)
	/Users/gri/go/src/go/go2go/rewrite.go:756 +0x71
go/go2go.(*translator).translateExpr(0xc0001a5678, 0xc00012a800)
	/Users/gri/go/src/go/go2go/rewrite.go:666 +0x4ba
go/go2go.(*translator).translateExpr(0xc0001a5678, 0xc0001046c0)
	/Users/gri/go/src/go/go2go/rewrite.go:685 +0x385
go/go2go.(*translator).translateExprList(0xc0001a5678, 0xc0001046c0, 0x1, 0x1)
	/Users/gri/go/src/go/go2go/rewrite.go:852 +0x46
go/go2go.(*translator).translateStmt(0xc0001a5678, 0xc00011c7e0)
	/Users/gri/go/src/go/go2go/rewrite.go:583 +0x29d
go/go2go.(*translator).translateBlockStmt(0xc0001a5678, 0xc000106de0)
	/Users/gri/go/src/go/go2go/rewrite.go:544 +0x57
go/go2go.(*translator).translateFuncDecl(0xc0001a5678, 0xc00011d5b0)
	/Users/gri/go/src/go/go2go/rewrite.go:534 +0xc5
go/go2go.(*translator).translate(0xc0001a5678, 0xc000140280)
	/Users/gri/go/src/go/go2go/rewrite.go:461 +0x391
go/go2go.rewriteAST(0xc00012a240, 0xc000126360, 0x0, 0x0, 0xc000101770, 0xc000140280, 0x2583701, 0xc00012a5c0, 0x14197e0)
	/Users/gri/go/src/go/go2go/rewrite.go:257 +0xe5
go/go2go.rewriteFile(0xc00017a0a0, 0x43, 0xc00012a240, 0xc000126360, 0x0, 0x0, 0xc000101770, 0xc00017a230, 0x4c, 0xc000140280, ...)
	/Users/gri/go/src/go/go2go/rewrite.go:221 +0xb8
go/go2go.rewriteFilesInPath(0xc000126360, 0x0, 0x0, 0xc00017a0a0, 0x43, 0xc000104480, 0x1, 0x1, 0x0, 0x0, ...)
	/Users/gri/go/src/go/go2go/go2go.go:114 +0xc5c
go/go2go.rewriteToPkgs(0xc000126360, 0x0, 0x0, 0xc00017a0a0, 0x43, 0xc0001061a0, 0xc00017a0a0, 0x43, 0x7ffeefbffa96, 0x8)
	/Users/gri/go/src/go/go2go/go2go.go:46 +0x165
main.translate(0xc000126360, 0xc00017a0a0, 0x43)
	/Users/gri/go/src/cmd/go2go/translate.go:15 +0x47
	/Users/gri/go/src/cmd/go2go/main.go:54 +0xb25
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@gopherbot gopherbot commented Jun 30, 2020

Change mentions this issue: [dev.go2go] go/go2go: instantiate embedded field when needed

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@ianlancetaylor ianlancetaylor commented Jun 30, 2020

Thanks, fixed on dev.go2go branch.

gopherbot pushed a commit that referenced this issue Jun 30, 2020
If an embedded field is an instantiated type, we need to instantiate
it when instantiating the whole type, in case the type arguments
themselves need instantiation.

Fixes #39953

Change-Id: I80b57456aa4f8e8b2eff82359066c37a9c2a40f5
Reviewed-by: Ian Lance Taylor <>
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