feat: static template expression evaluation

[Ocean-OS]

This optimizes the compiled output by using static analysis to evaluate some nonreactive template expressions.
For example, this component

<script>
let a = 1;
let b = 2;
</script>
<p>{a} + {b} = {a + b}</p>

would have its template expression compiled to:

p.textContent = `1 + 2 = 3`;

However, this:

<script>
let a = 1;
let b = 2;
a++;
</script>
<p>{a} + {b} = {a + b}</p>

would get compiled to:

$.template_effect(() => $.set_text(text, `${$.get(a) ?? ''} + 2 = ${$.get(a) + b ?? ''}`));

I think the end goal (that would be achieved either here or another PR) would be inlining this in the template, so that the top example would end up having its template look like this:

let root = $.template(`<p>1 + 2 = 3</p>`);

...which removes the (albeit small) overhead of locating the <p> element and creating an effect to update it.

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• Run the tests with pnpm test and lint the project with pnpm lint

[changeset-bot]

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Latest commit: 9907cbc

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[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@15374

[Ocean-OS]

ok there appear to be some tests that need to be changed as well...

[Ocean-OS]

once tests are implemented for the client, I will work on adding this to the server version.

[paoloricciuti]

We tried inlining constant values before and it ended up in such a hassle that we reverted it...there are a thousands things to keep track of for every non trivial example. If you succeed big props to you, just wanted to warn you 😄

[Ocean-OS]

We tried inlining constant values before and it ended up in such a hassle that we reverted it...there are a thousands things to keep track of for every non trivial example. If you succeed big props to you, just wanted to warn you 😄

If I'm correct in assuming you're referring to #10015, this should work, since that appears to hoist constant variables for optimization, so for example:

<script>
let name = 'world';
</script>
<h1>Hello, {name}!</h1>

would become something like this:

let name = 'world';
let root = $.template(`<h1>Hello, ${name}!</h1>`);
function Component() {
  //...
}

This instead takes a more direct approach, by replacing constant primitive variables with their value, like so:

//...
function Component() {
  //...
  let name = 'world';
  h1.textContent = `Hello, world!`;
  //...
}

Additionally, this PR is not only limited to variables; most expressions consisting of literal primitives (and/or those variables) will be evaluated as well.
So, if only the variables part isn't working, then those ~10 lines of code could just be fixed or removed, and there'd still be some (albeit small) optimizations happening without the variables part.