The `modifierFlagsCache` property is among the top properties that cause
megamorphic stub cache misses when having `tsc` build itself. This is
because it's added sort of randomly to a whole lot of different objects,
at arbitrary points after their initialization.
This also means that `modifierFlagsCache` is often not present on the
instances, which means that when missing on the megamorphic stub cache,
Node/V8 has to compute `NonExistent` handlers for the relevant inline
caches.
It's a lot cheaper to just make sure that the property is always
existent on the instance, and ideally also at the same offset. This
change ensures exactly that.
Drive-by-fix: Also make sure that `transformFlags` (and `parent`)
is always at the same offset for `Node` objects.
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Fixes#29585.
#29314 and #29385 made it so their respective settings are only recognized when provided to the host as a whole.
This PR makes it so that the relevant settings for the preferences on the file override those of the preferences on the host.
* Add user preference to control renaming through exports
* Only impact renaming
* Update baselines
* Use flag to control all prefix and suffix text and imports
* [WIP] add tests
* Only skip export import specifier with flag
* [WIP] Update tests
* Update test
* Pick up preference from host and update test
* Shorten flag name
* Add missing utility function
* Update comment
* [WIP] rename flag and respond to cr
* [WIP] Add flag for forRelatedSymbol
* Use larger search symbol set for old-style rename
* Respond to CR
* Fix small error
* Fix type mismatch
* Update comment and remove unnecessary exprot
* Respond to CR
Starts on #29035 by creating a codefix to enable the `experimentalDecorators` setting in a user's config file, if one exists. The issue's discussion also mentions giving a more precise error message if the user has a jsconfig or tsconfig or creating one if not; I'd rather tackle those in separate PRs to keep this one small.
Doesn't create the code action if no config file is present. Otherwise keeps to the precedent of returning without action when the config file contents aren't the expected JSON structure (looking at `fixCannotFindModule.ts`). Moves a couple JSON helpers from that file into the sibling `helpers.ts` so both codefixes can use them.
