Indirectly changing values within switch cases causes an 'unintentional comparison' error

[ephf]

🔎 Search Terms

switch, case, indirect, unintentional, comparison, change, equality, update, modify, if

🕗 Version & Regression Information

This is the behavior in every version I tried, and I could not find FAQ entries related to the issue.

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.7.0-beta#code/DYUwLgBAHhC8EFYDcAoAZgVwHYGMwEsB7LCHACwEMsBzEAfSgAoBKCAb2jggEYAmJCAF8UKAM4B3fGHKMorNighLSFUSEQAuRcp3kqtBi1TadS-Gllx4feRAD0AKggA6VxAd2hKQUA

💻 Code

let x = 5;
function change_x() { x = 12; }

switch(x) {
    case 5:
        change_x();

        if(x == 12) { /* ... */ }
}

🙁 Actual behavior

bug.ts:8:12 - error TS2367: This comparison appears to be unintentional because the types '5' and '12' have no overlap.

8         if(x == 12) { /* ... */ }
             ~~~~~~~

This error should not show when compiling as x is set to 12 when calling the change_x function.

🙂 Expected behavior

It is expected that there is no error given when compiling.

Additional information about the issue

This can be navigated around by introducing a second variable before the switch statement.

let x = 5;
function change_x() { x = 12; }

let y = x; // here
switch(y) {
    case 5:
        change_x();

        if(x == 12) { /* ... */ }
}

This code no longer produces an error in the latest version

see playground

[MartinJohns]

Duplicate of #9998.

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.