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Kristiyan Kostadinov 9cc0cbed0c refactor(compiler): generate if block instructions (#51380 )

Adds the logic to generate the instructions for `if` blocks. There are two primary use cases we need to account for:

A conditional that doesn't use the `as` parameter of the `if` block. To support it we generate a nested ternary expression that evaluates to the index of the template whose condition is truthy. If the block doesn't have an `else` branch, we pass in a special `-1` value which means that no view will be rendered.

Example with an `else`:
```ts
// {#if expr}
//   ...
//   {:else if otherExpr} ...
//   {:else} ...
// {/if}

if (rf & 1) {
  ɵɵtemplate(0, App_Conditional_0_Template, 0, 0);
  ɵɵtemplate(1, App_Conditional_1_Template, 0, 0);
  ɵɵtemplate(2, App_Conditional_2_Template, 0, 0);
}
if (rf & 2) {
  ɵɵconditional(0, ctx.expr ? 0 : ctx.otherExpr ? 1 : 2);
}
```

Example without an `else`:
```ts
// {#if expr}
//   ...
//   {:else if otherExpr} ...
// {/if}

if (rf & 1) {
  ɵɵtemplate(0, App_Conditional_0_Template, 0, 0);
  ɵɵtemplate(1, App_Conditional_1_Template, 0, 0);
}
if (rf & 2) {
  ɵɵconditional(0, ctx.expr ? 0 : ctx.otherExpr ? 1 : -1);
}
```

If a conditional captures it's value in an alias (e.g. `{#if expr; as foo}`) we need to assign the value to a temporary variable before passing it along to `conditional`.

```ts
// {#if expr; as alias}...{/if}
if (rf & 1) {
  ɵɵtemplate(0, App_Conditional_0_Template, 1, 0);
}
if (rf & 2) {
  let App_contFlowTmp;
  ɵɵconditional(0, (App_contFlowTmp = ctx.expr) ? 0 : -1, App_contFlowTmp);
}
```

PR Close #51380

2023-08-18 10:01:02 -07:00