refactor: Use std::string_view for prop conversions

[Saadnajmi]

Summary:

As pointed out by @tido64 in one of my other PRs, we can be more efficient on prop conversions by using std::string_view instead of just casting to std::string, which may cause a copy. I thought I might as well do a Find+Replace for the whole codebase and see what breaks.

Changelog:

[GENERAL] [CHANGED] - Use std::string_view for prop conversions

Test Plan:

CI should pass

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	17,931,480	-8,206
android	hermes	armeabi-v7a	n/a	--
android	hermes	x86	n/a	--
android	hermes	x86_64	n/a	--
android	jsc	arm64-v8a	21,289,773	-8,208
android	jsc	armeabi-v7a	n/a	--
android	jsc	x86	n/a	--
android	jsc	x86_64	n/a	--

Base commit: 57ed0fb
Branch: main

[motiz88]

Hey @Saadnajmi! These all seem like instances of the same, sadly invalid, pattern - see my comment on the first one.

[motiz88]

Casting to string and then to string_view doesn't really make sense, I'm afraid. You're creating a temporary string (incurring the same copy as before btw), then effectively creating a dangling pointer to its contents. See proof by godbolt + asan.

I don't have enough context, but it might make sense to create a non-copying const string& / string_value accessor on RawValue, if we know the string is stored in some stable location that is safe to access for the life of our value reference.

[tido64]

Ah, that makes sense. I had assumed we were casting from an any-ish type and the conversion was "free". std::string_view accepts raw char*, would it be enough to drop the cast i.e., auto string = string_view{value};?

Edit: Nvm, it looks like the string conversion is handled by the underlying folly::dynamic instance. Implementing a RawValue::string_view method using its dynamic::c_str() seems possible? Sorry, on mobile so it's hard to do proper investigation.

[Saadnajmi]

TIL I learned about compiler explorer, pretty awesome!
OK, I'll keep this PR up a bit to explore an alternative path, but noted the current version is not what we want.

[Saadnajmi]

Closing as I don't expect to come back to this