**Description:**
This issue is more severe than I originally thought. It raises not in
array indexing, but in function calls and property mutation. We should
treat all function arguments as potentially be property mutated,
otherwise following example
```js
class A {
a = 1
toString() {
return this.a
}
}
const a = new A()
function foo(x) {
x.a++
}
const b = a + 1
foo(a)
console.log(b)
```
would be error(It should log 2, but logs 3 after compress).
As the result, massive regressions is unavoidable, since some of these
optimizations may indeed cause error. Part of them can be mitigated with
following optimization -- allow inline of ident even if its original
value is mutated. Consider
```js
export function foo(x) {
const y = x
x.a = 1
y.b = 2
}
```
If x is a primitive value, all mutations to its properties are ignored;
if x is a object, then y refers to the same object no matter what
mutation is performed.
And there's still room for more, currently following code
```js
export function foo(x) {
const y = Math.floor(x);
g(y);
}
```
But I'd rather do it in a separate PR.
**Related issue:**
- Closes#7402.
**Description:**
This PR improves the alias analyzer by distinguishing call and reference, thus reducing the number of identifiers.
---
Co-authored-by: Justin Ridgewell <justin@ridgewell.name>
**Description:**
We had two passes for joining variables. This PR removes one in the full optimizer, which is wrong.
**Related issue:**
- Closes https://github.com/swc-project/swc/issues/5989.
Safety:
For a function-local variable, an expression with side-effects would be a call, including an indirect one with a member expression.
- If the call is function-local, it will be analyzed by the analyzer and inliner will not work.
- If the call is not a function-local one, it cannot modify the local variable.
# API Changes
## `swc_ecma_utils`
### Renames
- `find_ids` => `find_pat_ids`
- `prepend` => `prepend_stmt`
- `as_bool` => `cast_to_bool`
- `as_number` => `as_pure_number`
- `as_string` => `cast_to_string`
- (`as_pure_bool`, `cast_to_number` is not renamed)
- `UsageFinder` => `IdentUsageFinder`.
- `IdentFinder` => `IdentRefFinder`.
## Changes
- Re-export of `HANDLER` from `swc_common::errors` is removed. Use `swc_common::error::HANDLER` instead.
- Re-export of `Id` from `swc_ecma_ast` is removed. Use `swc_ecma_ast::Id` instead.
- `ExprCtx` is used for apis related to `Expr`.
- `preserve_effects` is now a method of `ExprCtx`. It was a top-level function.
- `extract_side_effects_to` is now a method of `ExprCtx`. It was a top-level function.
- `IdentUsageFinder` (previously `UsageFinder`) now takes `Id` instead of `Ident`.
- `IdentRefFinder` (previously `IdentFinder`) now takes `Id` instead of `Ident`.
- `ExprExt::is_ident_ref_to` is removed.
- `Expr::is_global_ref_to` is added.
- `:🆔:id` is removed. Use `Ident::to_id()` instead.
