Change 'unsafeDowncast' to 'as!' (#52)

glbrntt · web-flow · commit 9bf4c712ad79 · 2024-07-24T12:31:27.000-07:00
Motivation:

The 'unsafeDowncast' can cause a miscompile leading to unexpected
runtime behaviour.

Modifications:

- Use 'as!' instead

Result:

No miscompiles on 5.10
diff --git a/Sources/OpenAPIURLSession/BufferedStream/Lock.swift b/Sources/OpenAPIURLSession/BufferedStream/Lock.swift
@@ -111,7 +111,8 @@ final class LockStorage<Value>: ManagedBuffer<Value, LockPrimitive> {
     let buffer = Self.create(minimumCapacity: 1) { _ in
       return value
     }
-    let storage = unsafeDowncast(buffer, to: Self.self)
+    // Avoid 'unsafeDowncast' as there is a miscompilation on 5.10.
+    let storage = buffer as! Self
 
     storage.withUnsafeMutablePointers { _, lockPtr in
       LockOperations.create(lockPtr)

Original file line number	Diff line number	Diff line change
`@@ -111,7 +111,8 @@ final class LockStorage<Value>: ManagedBuffer<Value, LockPrimitive> {`
`111`	`111`	`let buffer = Self.create(minimumCapacity: 1) { _ in`
`112`	`112`	`return value`
`113`	`113`	`}`
`114`		`- let storage = unsafeDowncast(buffer, to: Self.self)`
	`114`	`+ // Avoid 'unsafeDowncast' as there is a miscompilation on 5.10.`
	`115`	`+ let storage = buffer as! Self`
`115`	`116`
`116`	`117`	`storage.withUnsafeMutablePointers { _, lockPtr in`
`117`	`118`	`LockOperations.create(lockPtr)`