Parentheses with comma operator in #if causes "Expression expected"

[Th0rN13]

Describe the bug
Comma operator in parentheses causes the error "Expression expected"
I found it in {#if }, but there may be similar behavior in other places.
It not very usable, but can be used for debug

To Reproduce
Steps to reproduce the behavior:

{#if (true, false)}
  content
{/if}

Expected behavior
No error

System (please complete the following information):

• OS: Windows
• IDE: VSCode
• Plugin/Package: Svelte Beta

[jasonlyu123]

Something the error is compile errors from svelte compiler. Do you found any problems like this but has no problems building? Or did I misunderstand what you mean? Because these examples are not valid syntax.

[Th0rN13]

This is valid syntax, and compiles without errors, and works as expected

[jasonlyu123]

Sorry I must have miss something when checking if it could compile earlier. I honestly doesn't know what this syntax can do lol.

[Th0rN13]

Do you mean any expression with parentheses and comma, like a function call?

No, i mean this syntax - comma operator. I wrap condition in parentheses

If i use

{#if prop === propCompare}
  content
{/if}

and want to temporarily change condition to true, but don't want fully remove condition, i use

{#if (prop === propCompare, true)}
  content
{/if}

This calculate conditions and use last operand in comma operator

Yes, i can use this without parentheses, like {#if prop === propCompare, true}, and it works good, but i use parentheses for visibility to me.

[jasonlyu123]

Thanks for pointing that out. Learned something. We must check this in various transformation in sveltetsx.

[jasonlyu123]

Await block also has this. but in both cases, the problem is not with comma but the extra parentheses

[arpitkalla]

Hey, I was looking into this issue and identified the problem was with appendLeft-ing the extra parenthesis as opposed to overwriting. I pointed it in the PR but my patch removes extra parenthesis around the guard. The "Expression expected" error should be removed, will test that out too.

[jasonlyu123]

language-tools/packages/svelte2tsx/src/htmlxtojsx.ts

Line 503 in 1bcd66d

str.overwrite(awaitBlock.start, awaitBlock.expression.start, '{() => {let _$$p = (');

language-tools/packages/svelte2tsx/src/htmlxtojsx.ts

Line 87 in 1bcd66d

str.overwrite(attr.start, attr.expression.start, `{...__sveltets_ensureType(Boolean, !!(`);

These two also has similar problem