Miscompilation of assignment

[AndreasLoow]

Hi, the following code

{
let j = ref(0)

if Js.String.get("%", j.contents) == "%" {
 j := j.contents + 1
 j := j.contents + 1
} else {
 j := j.contents + 1
}

Console.log(j.contents)
}

is compiled into

var j = 0;

j = j + 1 | 0;

if ("%"[j] === "%") {
  j = j + 1 | 0;
}

console.log(j);

Note how the assignment of j is moved outside the if-expression despite the move changing the evaluation of the condition of the if-expression. The code without the surrounding { and } is compiled correctly.

[cristianoc]

Thanks for reporting.
This seems to be a long standing issue, that can be reproduced already on old versions of the compiler.
Seems to be triggered by not exporting variable j, by either putting the code into { ... } block or shadowing the variable.

[cristianoc]

This appears to be due to an optimisation for records with only one field, such as contents.
The optimisation should only affect the generated code, but in this case prematurely turning x.contents into x confuses the checker for side effects, which thinks there are none.