Panic during compilation if function returns structure with unset slice

[alexvanin]

I run this code:

package foo

type Foo struct {
	x []int
}

func NewFoo() Foo {
	return Foo{}
}

func Main() int {
	foo := NewFoo()
	if foo.x == nil {
		return 1
	}

	return 0
}

I expect to get 1 but got panic during compilation. If I use return Foo{x:nil} panic does not occur and I got correct result.

Panic message:

panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x8098fb]

goroutine 19 [running]:
testing.tRunner.func1.1(0x891a80, 0xcd5eb0)
	/snap/go/current/src/testing/testing.go:940 +0x2f5
testing.tRunner.func1(0xc0000d37a0)
	/snap/go/current/src/testing/testing.go:943 +0x3f9
panic(0x891a80, 0xcd5eb0)
	/snap/go/current/src/runtime/panic.go:969 +0x166
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).emitLoadConst(0xc0000e9e00, 0x0, 0x0, 0x0, 0x0, 0x0)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/codegen.go:115 +0x4b
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).convertStruct(0xc0000e9e00, 0xc0000acc80)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/codegen.go:1211 +0x25a
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).Visit(0xc0000e9e00, 0x9c4be0, 0xc0000acc80, 0x0, 0x0)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/codegen.go:568 +0x1382
go/ast.Walk(0x9c1780, 0xc0000e9e00, 0x9c4be0, 0xc0000acc80)
	/snap/go/current/src/go/ast/walk.go:52 +0x66
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).Visit(0xc0000e9e00, 0x9c52a0, 0xc0000b7060, 0xc000099660, 0x0)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/codegen.go:437 +0x33cf
go/ast.Walk(0x9c1780, 0xc0000e9e00, 0x9c52a0, 0xc0000b7060)
	/snap/go/current/src/go/ast/walk.go:52 +0x66
go/ast.walkStmtList(0x9c1780, 0xc0000e9e00, 0xc000099410, 0x1, 0x1)
	/snap/go/current/src/go/ast/walk.go:32 +0x9e
go/ast.Walk(0x9c1780, 0xc0000e9e00, 0x9c49e0, 0xc00009de00)
	/snap/go/current/src/go/ast/walk.go:224 +0x1adf
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).convertFuncDecl(0xc0000e9e00, 0x9c4de0, 0xc0000ee180, 0xc00009de30)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/codegen.go:263 +0x542
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).compile(0xc0000e9e00, 0xc0000b73a0, 0xc0000c0370, 0xc0000a5230, 0x0)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/codegen.go:1317 +0x490
github.com/nspcc-dev/neo-go/pkg/compiler.CodeGen(0xc0000b73a0, 0xc0000b6f20, 0xc0000b73a0, 0x0, 0x0, 0xc00009dc01, 0xc0000b6f20)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/codegen.go:1345 +0x289
github.com/nspcc-dev/neo-go/pkg/compiler.CompileWithDebugInfo(0x9c1d60, 0xc0000b6f20, 0x7f8a774707d0, 0x0, 0x40e0e6, 0xc0000b6ee0, 0x20, 0x20)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/compiler.go:78 +0x90
github.com/nspcc-dev/neo-go/pkg/compiler.Compile(...)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/compiler.go:64
github.com/nspcc-dev/neo-go/pkg/compiler_test.vmAndCompileInterop(0xc0000d37a0, 0x92f6bc, 0xae, 0xc0000a5150, 0xc000044738)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/vm_test.go:66 +0x10b
github.com/nspcc-dev/neo-go/pkg/compiler_test.vmAndCompile(...)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/vm_test.go:56
github.com/nspcc-dev/neo-go/pkg/compiler_test.eval(0xc0000d37a0, 0x92f6bc, 0xae, 0x90bb00, 0xc0000b6ee0)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/vm_test.go:33 +0x49
github.com/nspcc-dev/neo-go/pkg/compiler_test.TestForLoopRangeGlobalIndex1(0xc0000d37a0)
	/home/alexvanin/Project/Neo/neo-go/pkg/compiler/for_test.go:486 +0x7d
testing.tRunner(0xc0000d37a0, 0x936d68)
	/snap/go/current/src/testing/testing.go:991 +0xdc
created by testing.(*T).Run
	/snap/go/current/src/testing/testing.go:1042 +0x357

[alexvanin]

branch: master-2.x
version: 0.74.1-pre-156-gc85e77e1

[fyrchik]

See my first comment to #952.

[fyrchik]

Fixed via #952 .