if without braces in switch case is parsed weirdly

[ghost]

I'm not really sure what the parser is trying to do here. I think this should work. I don't think the comma is overloaded that much in Zig so I don't see any ambiguity.

pub fn main() void {
    var blah = false;
    var x = false;

    switch (x) {
        false => if (blah) x = true,
        true => if (blah) x = false,
    }
}

Semantic Analysis [719/735] /home/dbandstra/host/asdf.zig:6:18: error: incompatible types: '*bool' and 'void'
        false => if (blah) x = true,
                 ^
/home/dbandstra/host/asdf.zig:6:28: note: type '*bool' here
        false => if (blah) x = true,
                           ^
/home/dbandstra/host/asdf.zig:6:18: note: type 'void' here
        false => if (blah) x = true,
                 ^

It works if I add curly braces to the if's.

        false => if (blah) { x = true; },

And this:

pub fn main() void {
    var blah = false;
    var x = false;

    switch (x) {
        false => if (blah) x = true else x = false,
        true => if (blah) x = false else x = true,
    }
}

Yields this:

/home/dbandstra/host/asdf.zig:6:37: error: expected token '}', found 'else'
        false => if (blah) x = true else x = false,
                                    ^

[mikdusan]

also works:

pub fn main() void {
    var blah = false;
    var x = false;

    switch (x) {
        false => { if (blah) x = true; },
        true => { if (blah) x = false; },
    }
}

[fengb]

I'm guessing that without braces, the switch is looking for a return value and convinces the if to be an expression instead of a statement.

[ghost]

This works fine, so maybe the problem is limited to when you have an assignment in the if clause?

fn func() void {
    var x = false;
}

pub fn main() void {
    var blah = false;
    var x = false;

    switch (x) {
        false => if (blah) func(),
        true => if (blah) func() else func(),
    }
}

[Vexu]

Related #5731.

[mrjbq7]

I humbly suggest that if without braces should not be allowed.

It's one of the biggest footguns in C where the first line is in the if statement and the second line is not.

if (true)
    std.debug.writeAll("it's true!\n")
    std.debug.writeAll("no really, it's true\n")

[SpexGuy]

@mrjbq7 We are already planning to make that a compile error, but through a different mechanism: #35

Edit: We've also previously rejected the idea of requiring braces on if statements in #4294

[Vexu]

Self-hosted gives a nicer error for this:

error: invalid left-hand side to assignment
        false => if (blah) x = true,
                 ^~~~~~~~~~~

Proposal to change the grammar in #5731