Why adding to a nested `if` expression causes a compilation error?

[JalonSolov]

Discussed in #26864

^{Originally posted by programandala-net April 12, 2026}
i have found out a curious issue about nested if expressions; i have isolated it in this example code:

import rand

fn chance() bool {
	return rand.i8() >= 0
}

fn main() {
	// these nested `if` expressions are compiled fine
	// (note a literal is added to the *outer* `if` expression):

	_ := if chance() {  0  } else { if chance() {  2  } else {  3  } } + 5
	_ := if chance() { 'a' } else { if chance() { 'c' } else { 'd' } } + 'f'

	// but when something is added to the *inner* `if` expression, the compilation
	// fails:

	// XXX compilation error: mismatched types `void` and `int literal`:
	// _ := if chance() {  0  } else { if chance() {  2  } else {  3  } +  4 } + 5

	// XXX compilation error: mismatched types `void` and `string`:
	// _ := if chance() { 'a' } else { if chance() { 'c' } else { 'd' } + 'e'} + 'f'

	// and when the inner `if` expression is added to something, the
	// compilation works:

	_ := if chance() {  0  } else {  1  + if chance() {  2  } else {  3  } +  4 } + 5
	_ := if chance() { 'a' } else { 'b' + if chance() { 'c' } else { 'd' } + 'e'} + 'f'

}

i have searched the documentation, the github issues and the github discussions but found nothing related.

it seems a bug, but perhaps i am neglecting something, so i prefer to ask here first, before opening an issue.

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[JalonSolov]

Simplest reproduction:

fn main() {
        // XXX compilation error: mismatched types `void` and `int literal`:
        _ := { if true {  2  } else {  3  } +  4 } + 5

        // XXX compilation error: mismatched types `void` and `string`:
        _ := { if true { 'c' } else { 'd' } + 'e'} + 'f'
}

give this output:

x.v:3:43: error: unexpected token `}`, expecting `:`
    1 | fn main() {
    2 |     // XXX compilation error: mismatched types `void` and `int literal`:
    3 |     _ := { if true {  2  } else {  3  } +  4 } + 5
      |                                              ^
    4 | 
    5 |     // XXX compilation error: mismatched types `void` and `string`: