Option smartcast after non-option assignment

[quaesitor-scientiam]

V version: V 0.4.9 a6a8e4c, press to see full `v doctor` output

V full version	V 0.4.9 45fd7eb.a6a8e4c
OS	windows, Microsoft Windows 11 Pro 26100 64-bit
Processor	24 cpus, 64bit, little endian, AMD Ryzen 9 5900X 12-Core Processor
Memory	76.58GB/127.92GB
V executable	S:\repo\vlang\v.exe
V last modified time	2025-01-29 18:20:27
V home dir	OK, value: S:\repo\vlang
VMODULES	OK, value: C:\Users\john3.vmodules
VTMP	OK, value: C:\Users\john3\AppData\Local\Temp\v_0
Current working dir	OK, value: S:\vProjects\testit
Git version	git version 2.45.1.windows.1
V git status	weekly.2025.04-67-ga6a8e4c9
.git/config present	true
cc version	N/A
gcc version	gcc (MinGW-W64 x86_64-ucrt-posix-seh, built by Brecht Sanders, r2) 14.2.0
clang version	(built by Brecht Sanders, r2) clang version 19.1.1
msvc version	N/A
tcc version	tcc version 0.9.27 (x86_64 Windows)
tcc git status	thirdparty-windows-amd64 b425ac82
emcc version	N/A
glibc version	N/A

What did you do?
./v -g -o vdbg cmd/v && ./vdbg -cg testit.v && S:\vProjects\testit\testit.exe

module main

pub struct Foo {
	mut:
	test bool
}
pub fn Foo.init() Foo {
	return Foo{test: false}
}


fn what(mut foo ?Foo) {
	if foo == none {
		foo = Foo.init()
		foo.test = true
	}
}

fn main() {
	what(none)
}

What did you see?

testit.v:20:7: warning: automatic referencing/dereferencing is deprecated and will be removed soon (got: 0 references, expected: 1 references)
   18 | 
   19 | fn main() {
   20 |     what(none)
      |          ~~~~
   21 | }
testit.v:15:7: error: cannot access fields of an Option, handle the error with `or {...}` or propagate it with `?`
   13 |     if foo == none {
   14 |         foo = Foo.init()
   15 |         foo.test = true
      |             ~~~~
   16 |     }
   17 | }
testit.v:20:7: error: function `what` parameter `foo` is `mut`, so use `mut none` instead
   18 | 
   19 | fn main() {
   20 |     what(none)
      |          ~~~~
   21 | }

What did you expect to see?

clean build

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[huly-for-github]

Connected to Huly®: V_0.6-22036

[spytheman]

The what(none) errors are irrelevant to the problem.
Only this block is:

if foo == none {
		foo = Foo.init()
		foo.test = true
}

since after foo = Foo.init(), foo is guaranteed to be a Foo value, and in the lines that follow, its fields should be accessible.

[jorgeluismireles]

I only can get rid of warnings and errors until Foo was a member of another struct Bar:

pub struct Foo {
mut:
	test bool
}

struct Bar {
mut:
	foo ?Foo
}

fn (mut b Bar) what() {
	if b.foo != none { 
		b.foo.test = true
	}
}

fn main() {
	mut b1 := Bar{ } // foo remains none
	b1.what()
	println('${b1.foo}') // Option(none)
	mut b2 := Bar{ foo:Foo{} }
	b2.what()
	println('${b2.foo}') // Option(Foo{test:true})
}

[quaesitor-scientiam]

That doesn't solve the issue unfortunately

[JalonSolov]

No, it doesn't. That will have to be done with a bug fix.

The workaround, as @spytheman said yesterday in discord, would be to create a new variable, and assign that to foo at the end of the if statement:

if foo == none {
	mut newfoo := Foo.init()
	newfoo.test = true
	foo = newfoo
}