Replace all runtime platform checks with linktime conditions

[armanbilge]

No reason to pay a performance penalty at runtime when we can elide the useless code at linking time.

[LeeTibbert]

It may be possible to remove the include of Platform.
I was moving quickly, but I did not see any other uses of it in the this new file.

[LeeTibbert]

This PR is a public service, thank you. It eliminates some artifacts of Evolution.

I looked at the network related files. A quick scan for concept, not character by character.
All looked good.

I did not see any edits to Platform.scala. Should the isLinux etc methods there be removed altogether?

[armanbilge]

Thank you for the review!

I did not see any edits to Platform.scala. Should the isLinux etc methods there be removed altogether?

This is a good question. These are public APIs and they are implemented slightly differently than LinktimeInfo. However I am not sure in which situations they would be useful now, if at all. I'd be happy to see them removed to avoid having too many ways to do similar things.

[LeeTibbert]

I think the APIs are public in the sense of "having been in SN variants released to the wild" not public
in the "This is in Java or ScalaJVM". If I am wrong and the latter is true, the story changes.
V5.0 is the time to break API, especially those with which we will have to live for awhile.

Please double check my thinking, too easy to throw the baby out with the bath water.
Someone starting a process on one OS and migrating it to another OS might have a situation
where the Runtime runtime hardware architecture differs from the linktime architecture.

There might be C code backing the Platform isLinux etc. methods. That can probably
be deleted also.

I'd be happy to see them removed to avoid having too many ways to do similar things.

Yes, I myself have been left pondering when to use Platform and when to use LinkTimeInfo and
getting tangled up. Probably why you see Platform in the network code.

I am a big fan of the Python "one way to do things" concept.

[armanbilge]

I think the APIs are public in the sense of "having been in SN variants released to the wild"

This is correct, these are Native lib APIs that are not private to Scala Native.

---

Someone starting a process on one OS and migrating it to another OS might have a situation
where the Runtime runtime hardware architecture differs from the linktime architecture.

Well, there is some nuance here 😅

I described the Platform checks as having a runtime penalty. What I meant by this, is that they compile to a function call. This is different from LinktimeInfo checks which are constants that exist only at linking-time and are used to eagerly perform dead-code-elimination of branches in the logic.

However, even though the Platform checks are function calls, what they return may be compile-time constants.

scala-native/nativelib/src/main/resources/scala-native/platform/platform.c

Lines 15 to 37 in 26830d4

	int scalanative_platform_is_freebsd() {
	#if defined(__FreeBSD__)
	return 1;
	#else
	return 0;
	#endif
	}
	int scalanative_platform_is_linux() {
	#ifdef __linux__
	return 1;
	#else
	return 0;
	#endif
	}
	int scalanative_platform_is_mac() {
	#ifdef __APPLE__
	return 1;
	#else
	return 0;
	#endif
	}

Although in other instances they may also do runtime checks e.g.

scala-native/nativelib/src/main/resources/scala-native/platform/platform.c

Lines 49 to 56 in 26830d4

	int scalanative_platform_probe_mac_x8664_is_arm64() {
	int translated = 0;
	#ifdef __APPLE__
	size_t translatedLen = sizeof(translated);
	int ret = sysctlbyname("sysctl.proc_translated", &translated,
	&translatedLen, NULL, 0);

In any case, at least for the current checks we have in Platform, I cannot imagine a viable program where the check would evaluate differently at compile/linking-time and runtime.

[LeeTibbert]

OK, I think I have found a counter example which argues for keeping Platform, probably with
a comment recommending using LinkTimeInfo equivalent.

printf(s"Running on Linux: ${Platform.isLinux()}\n That is, the isFoo() occurs outside an if,
Yes, the code can be converted by adding a `if (LinkTimeInfo.isLinux) printf ("Running on Linux\n")

At first blush, it looks like some Platform.c code could be eliminated and Platform.scala
converted to use if (ifLinkTimeInfo.isFoo) true else false. However the Platform object is extern`. I at one point there was some work to remove the restriction that all methods
in an extern object needed to be extern. I do not know if that work has ever been merged.

So, leaving the .c code, possibly with a comment in Platform.scala might defer diving
into a time suck with poor benefit/cost ratio.

[LeeTibbert]

Upon further investigation: Rationalizing/unifying Platform is probably a task for the next person who
messes up badly. There are various "Platform.scalas. The ones in scripted-testsrefer back to theruntime` Platform (which I had proposed to eliminate). Some of the Platforms use direct Java os properties
(probably for good reason).

I hereby withdraw my proposal to rationalize Platform and pray that I am not the next one to mess up
badly enough to get thrown into that pit of misery.

[WojciechMazur]

You can rebase it on top of #3337 when it's merge to get rid of failing tests in tools/test