fix(app): make MC <1.12.2 downloadable again (#4494)

PR #4270 modified the internal `fetch` function used by the application
to download version artifacts in a way that 4xx HTTP errors also caused
an abnormal return, instead of just 5xx errors. That was a good change,
but it had the unintended side effect of exposing our faulty logic
elsewhere of trying to download non-native JAR library artifacts when
only native artifacts are appropriate, at least according to the
PrismLauncher source code I've read. Such a download always returned a
404 error, but because such error was considered successful, a dummy
library file was still created and things worked seemingly fine.

These changes bring the Modrinth App behavior in this regard more in
line with PrismLauncher's, avoiding downloading non-native artifacts for
dependencies that have native artifacts available. (Reference:
8b5e91920d/launcher/minecraft/Library.cpp (L163))

I've tested these changes to work successfully with a variety of old
vanilla and modded Minecraft versions.

Fixes #4464.

packages/daedalus/src/minecraft.rs

@@ -179,6 +179,56 @@ pub enum Os {
     Unknown,
 }
 
+impl Os {
+    /// Returns the native OS of the build
+    pub fn native() -> Self {
+        match std::env::consts::OS {
+            "windows" => Self::Windows,
+            "macos" => Self::Osx,
+            "linux" => Self::Linux,
+            _ => Self::Unknown,
+        }
+    }
+
+    /// Returns the native OS variant of the build, taking into account the architecture of its Java runtime
+    pub fn native_arch(java_arch: &str) -> Self {
+        if std::env::consts::OS == "windows" {
+            if java_arch == "aarch64" {
+                Os::WindowsArm64
+            } else {
+                Os::Windows
+            }
+        } else if std::env::consts::OS == "linux" {
+            if java_arch == "aarch64" {
+                Os::LinuxArm64
+            } else if java_arch == "arm" {
+                Os::LinuxArm32
+            } else {
+                Os::Linux
+            }
+        } else if std::env::consts::OS == "macos" {
+            if java_arch == "aarch64" {
+                Os::OsxArm64
+            } else {
+                Os::Osx
+            }
+        } else {
+            Os::Unknown
+        }
+    }
+
+    /// Returns the base OS of a variant (e.g. OsxArm64 -> Osx)
+    pub fn get_os(&self) -> Self {
+        match self {
+            Os::OsxArm64 => Os::Osx,
+            Os::LinuxArm32 => Os::Linux,
+            Os::LinuxArm64 => Os::Linux,
+            Os::WindowsArm64 => Os::Windows,
+            _ => self.clone(),
+        }
+    }
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone)]
 /// A rule which depends on what OS the user is on
 pub struct OsRule {
@@ -277,6 +327,24 @@ pub struct Library {
     pub downloadable: bool,
 }
 
+impl Library {
+    /// Returns the OS key and classifiers for downloading natives, if applicable
+    pub fn natives_os_key_and_classifiers(
+        &self,
+        java_arch: &str,
+    ) -> Option<(&str, &HashMap<String, LibraryDownload>)> {
+        self.natives
+            .as_ref()
+            .and_then(|natives| natives.get(&Os::native_arch(java_arch)))
+            .and_then(|natives| {
+                self.downloads
+                    .as_ref()
+                    .and_then(|downloads| downloads.classifiers.as_ref())
+                    .map(|classifiers| (natives.as_str(), classifiers))
+            })
+    }
+}
+
 #[derive(Deserialize, Debug, Clone)]
 /// A partial library which should be merged with a full library
 pub struct PartialLibrary {