gnovm: values defined in structure after an anonymous structure field panics

[paulogarithm]

Invalid struct parsing after anonymous struct field

Description

When you create a structure, then you define an anonymous field and try to create a variable out of it, the parsing fails and it says "the variable after your anonymous field does not exist", like for example:

type Foo struct {
	Anon struct { Value int }
	Hello int
}

will say:

struct type struct{Anon struct{Value int}; Hello int} has no field Hello [recovered]

(the full example bellow)

Your environment

go version go1.24.1 linux/amd64
gno version: master.2244+84e53f51

Steps to reproduce

Here is a code snippet

package main

type Foo struct {
	Anon struct { Value int }
	Hello int
}

func main() {
	x := Foo{
		Anon: struct{Value int}{ Value: 42 },
		Hello: 80,
	}
	_=x
}

Expected behaviour

using golang:

$ go run a.go
$ echo $?
0
$ 

Actual behaviour

using gno

$ gno run a.go
panic: struct type struct{Anon struct{Value int}; Hello int} has no field Hello [recovered]
# ... more logs bellow
$ echo $?
2

Logs

here are the full logs after gno run a.go command:

panic: struct type struct{Anon struct{Value int}; Hello int} has no field Hello [recovered]
        panic: main/a.go:11:3: struct type struct{Anon struct{Value int}; Hello int} has no field Hello:
        --- preprocess stack ---
        stack 2: func main() { x<!VPBlock(1,0)> := Foo<VPBlock(3,0)>{Anon<VPField(0,0,Anon)>: struct { Value (const-type int) }{Value<VPField(0,0,Value)>: (const (42 int))}, Hello<VPUverse(0)>: 80}; _<VPUverse(0)> = x<VPUverse(0)> }
        stack 1: file{ package main; type Foo (const-type main.Foo); func main() { x<!VPBlock(1,0)> := Foo<VPBlock(3,0)>{Anon<VPField(0,0,Anon)>: struct { Value (const-type int) }{Value<VPField(0,0,Value)>: (const (42 int))}, Hello<VPUverse(0)>: 80}; _<VPUverse(0)> = x<VPUverse(0)> } }
        stack 0: package(main)
        ------------------------

goroutine 1 [running]:
github.com/gnolang/gno/gnovm/pkg/gnolang.doRecover({0xc00001b200, 0x3, 0x20}, {0x124fdc0, 0xc0004367e0})
        /home/pol/gno/gnovm/pkg/gnolang/preprocess.go:401 +0x37e
panic({0xdf5780?, 0xc000498a40?})
        /usr/local/go/src/runtime/panic.go:792 +0x132
github.com/gnolang/gno/gnovm/pkg/gnolang.(*StructType).GetPathForName(0xc0003ef980, {0xc000198620, 0x5})
        /home/pol/gno/gnovm/pkg/gnolang/types.go:801 +0x1d9
github.com/gnolang/gno/gnovm/pkg/gnolang.preprocess1.func1({0xc00001b400, 0x4, 0x20}, 0x12, 0x1, {0x124fdc0, 0xc0004367e0}, 0x3)
        /home/pol/gno/gnovm/pkg/gnolang/preprocess.go:986 +0xe37
github.com/gnolang/gno/gnovm/pkg/gnolang.transcribe(0xc000125728, {0xc00001b400, 0x4, 0x20}, 0x12, 0x1, {0x124fdc0, 0xc0004367e0}, 0xc000124bbf)
        /home/pol/gno/gnovm/pkg/gnolang/transcribe.go:696 +0x1c48
github.com/gnolang/gno/gnovm/pkg/gnolang.transcribe(0xc000125728, {0xc00001b400, 0x3, 0x20}, 0x25, 0x0, {0x124fa40, 0xc000494820}, 0xc000124e5f)
        /home/pol/gno/gnovm/pkg/gnolang/transcribe.go:244 +0x63b0
github.com/gnolang/gno/gnovm/pkg/gnolang.transcribe(0xc000125728, {0xc00001b400, 0x2, 0x20}, 0x46, 0x0, {0x124f7c0, 0xc000436840}, 0xc0001250ff)
        /home/pol/gno/gnovm/pkg/gnolang/transcribe.go:359 +0x5290
github.com/gnolang/gno/gnovm/pkg/gnolang.transcribe(0xc000125728, {0xc00001b400, 0x1, 0x20}, 0x4e, 0x1, {0x1250fc0, 0xc0003f1208}, 0xc00012539f)
        /home/pol/gno/gnovm/pkg/gnolang/transcribe.go:640 +0x77de
github.com/gnolang/gno/gnovm/pkg/gnolang.transcribe(0xc000125728, {0xc00001b400, 0x0, 0x20}, 0x0, 0x0, {0x1251140, 0xc0004a0708}, 0xc00012563f)
        /home/pol/gno/gnovm/pkg/gnolang/transcribe.go:678 +0x9f88
github.com/gnolang/gno/gnovm/pkg/gnolang.Transcribe({0x1251140, 0xc0004a0708}, 0xc000125728)
        /home/pol/gno/gnovm/pkg/gnolang/transcribe.go:132 +0xb6
github.com/gnolang/gno/gnovm/pkg/gnolang.preprocess1({0x125a540, 0xc00045e000}, {0x125d9f0, 0xc0004a0a88}, {0x1251140, 0xc0004a0708?})
        /home/pol/gno/gnovm/pkg/gnolang/preprocess.go:503 +0x2f6
github.com/gnolang/gno/gnovm/pkg/gnolang.Preprocess({0x125a540, 0xc00045e000}, {0x125d9f0, 0xc0004a0a88}, {0x1251140, 0xc0004a0708})
        /home/pol/gno/gnovm/pkg/gnolang/preprocess.go:451 +0xac
github.com/gnolang/gno/gnovm/pkg/gnolang.(*Machine).runFileDecls(0xc000422008, 0x1, {0xc00008c098, 0x1, 0x1})
        /home/pol/gno/gnovm/pkg/gnolang/machine.go:539 +0x38b
github.com/gnolang/gno/gnovm/pkg/gnolang.(*Machine).RunFiles(0xc000422008, {0xc00008c098, 0x1, 0x1})
        /home/pol/gno/gnovm/pkg/gnolang/machine.go:427 +0x173
main.execRun(0xc0000d3740, {0xc0004984f0, 0x1, 0x1}, {0x1254170, 0xc0004943c0})
        /home/pol/gno/gnovm/cmd/gno/run.go:135 +0x48a
main.newRunCmd.func1({0xe8b180?, 0xc00018c4d0?}, {0xc0004984f0?, 0xc0004362a0?, 0x0?})
        /home/pol/gno/gnovm/cmd/gno/run.go:39 +0x30
github.com/gnolang/gno/tm2/pkg/commands.(*Command).Run(0xb?, {0x1245520?, 0x19ae7c0?})
        /home/pol/gno/tm2/pkg/commands/command.go:265 +0x192
github.com/gnolang/gno/tm2/pkg/commands.(*Command).Run(0xc0001d0000?, {0x1245520?, 0x19ae7c0?})
        /home/pol/gno/tm2/pkg/commands/command.go:269 +0x13e
github.com/gnolang/gno/tm2/pkg/commands.(*Command).ParseAndRun(0xc0001d0000, {0x1245520, 0x19ae7c0}, {0xc00018c4c0?, 0xc0001d06c0?, 0xc0001d0780?})
        /home/pol/gno/tm2/pkg/commands/command.go:150 +0x49
github.com/gnolang/gno/tm2/pkg/commands.(*Command).Execute(0x1254170?, {0x1245520?, 0x19ae7c0?}, {0xc00018c4c0?, 0x18f4c68?, 0xc000002380?})
        /home/pol/gno/tm2/pkg/commands/command.go:127 +0x2c
main.main()
        /home/pol/gno/gnovm/cmd/gno/main.go:13 +0x5f

Proposed solution

ig its just a parsing typo somewhere in the code

this is what i found tho, it does skip somewhere in the GetPathForName, see bellow

// gnovm/pkg/gnolang/preprocess.go:986

					case *StructType:
						n.Path = bt.GetPathForName(n.Name) // here, bt.Fields have all the fields !
						return n, TRANS_CONTINUE

i checked doing that:

					case *StructType:
						println("fields in structure:")
						for _, v := range bt.Fields {
							println("-", v.String())
						}
						println("field to check for:")
						println(n.Name, "\n")
						n.Path = bt.GetPathForName(n.Name)

// Outputs:
// fields in structure:
// - Anon struct{Value int}
// - Hello int
// field to check for:
// Hello

so it is included well in the parsing, but the error is just bellow here:

// gnovm/pkg/gnolang/types.go:785

func (st *StructType) GetPathForName(n Name) ValuePath {
	for i := 0; i < len(st.Fields); i++ { // it itters through the fields
		ft := st.Fields[i]
		if ft.Name == n {
			if i > 2<<16-1 {
				panic("too many fields")
			}
			return NewValuePathField(0, uint16(i), n)
		}
		if st, ok := ft.Type.(*StructType); ok { // if its anon struct it just skips... the number of fields IN the anon struct... but skips them in the parent struct ? why ?
			if ft.Name != "" {
				// skip fields not promoted. (this comment is not from me, its from the code)
				i += len(st.Fields)
			}
		}
	}
	panic(fmt.Sprintf("struct type %s has no field %s",
		st.String(), n))
}

so for me the fix would be to get rid of the condition like that:

func (st *StructType) GetPathForName(n Name) ValuePath {
	for i := 0; i < len(st.Fields); i++ {
		ft := st.Fields[i]
		if ft.Name == n {
			if i > 2<<16-1 {
				panic("too many fields")
			}
			return NewValuePathField(0, uint16(i), n)
		}
-		if st, ok := ft.Type.(*StructType); ok {
-			if ft.Name != "" {
-				// skip fields not promoted.
-				i += len(st.Fields)
-			}
-		}
	}
	panic(fmt.Sprintf("struct type %s has no field %s",
		st.String(), n))
}

but this may be really usefull for something else, but i dont see why tho... ?

Note

removing the condition make the code works, but idk if it break everything

TL;DR

there is a condition when checking fields that just skips the fields in anon structure in gnovm/pkg/gnolang/types.go:794 and it seems useless, but im too scared to remove it because maybe it will break everything

[paulogarithm]

here is the line i talked about:

https://github.com/gnolang/gno/blob/master/gnovm/pkg/gnolang/types.go#L794

[ltzmaxwell]

Thank you for spotting this.

It seems buggy — you can probably just remove it. Then run make test in gnovm/Makefile, (maybe also examples/Makefile, gno.land/Makefile) to verify that everything still works.