[stdlib] Replace precondition with the internal _precondition

stdlib/public/core/ArrayBuffer.swift

@@ -254,23 +254,29 @@ extension _ArrayBuffer {
   internal func _typeCheckSlowPath(_ index: Int) {
     if _fastPath(_isNative) {
       let element: AnyObject = cast(toBufferOf: AnyObject.self)._native[index]
-      precondition(
-        element is Element,
-        """
-        Down-casted Array element failed to match the target type
-        Expected \(Element.self) but found \(type(of: element))
-        """
-      )
+      guard element is Element else {
+        _assertionFailure(
+          "Fatal error",
+          """
+          Down-casted Array element failed to match the target type
+          Expected \(Element.self) but found \(type(of: element))
+          """,
+          flags: _fatalErrorFlags()
+        )
+      }
     }
     else {
       let element = _nonNative[index]
-      precondition(
-        element is Element,
-        """
-        NSArray element failed to match the Swift Array Element type
-        Expected \(Element.self) but found \(type(of: element))
-        """
-      )
+      guard element is Element else {
+        _assertionFailure(
+          "Fatal error",
+          """
+          NSArray element failed to match the Swift Array Element type
+          Expected \(Element.self) but found \(type(of: element))
+          """,
+          flags: _fatalErrorFlags()
+        )
+      }
     }
   }
 
@@ -505,23 +511,29 @@ extension _ArrayBuffer {
       _native._checkValidSubscript(i)
 
       element = cast(toBufferOf: AnyObject.self)._native[i]
-      precondition(
-        element is Element,
-        """
-        Down-casted Array element failed to match the target type
-        Expected \(Element.self) but found \(type(of: element))
-        """
-      )
+      guard element is Element else {
+        _assertionFailure(
+          "Fatal error",
+          """
+          Down-casted Array element failed to match the target type
+          Expected \(Element.self) but found \(type(of: element))
+          """,
+          flags: _fatalErrorFlags()
+        )
+      }
     } else {
       // ObjC arrays do their own subscript checking.
       element = _nonNative[i]
-      precondition(
-        element is Element,
-        """
-        NSArray element failed to match the Swift Array Element type
-        Expected \(Element.self) but found \(type(of: element))
-        """
-      )
+      guard element is Element else {
+        _assertionFailure(
+          "Fatal error",
+          """
+          NSArray element failed to match the Swift Array Element type
+          Expected \(Element.self) but found \(type(of: element))
+          """,
+          flags: _fatalErrorFlags()
+        )
+      }
     }
     return element
   }

stdlib/public/core/Misc.swift

@@ -81,7 +81,7 @@ func _mangledTypeName(_ type: Any.Type) -> String? {
   let (result, repairsMade) = String._fromUTF8Repairing(
       UnsafeBufferPointer(start: stringPtr, count: count))
 
-  precondition(!repairsMade, "repairs made to _mangledTypeName, this is not expected since names should be valid UTF-8")
+  _precondition(!repairsMade, "repairs made to _mangledTypeName, this is not expected since names should be valid UTF-8")
 
   return result
 }

stdlib/public/core/Sort.swift

@@ -696,6 +696,6 @@ extension UnsafeMutableBufferPointer {
     }
 
     // FIXME: Remove this, it works around rdar://problem/45044610
-    precondition(result)
+    _precondition(result)
   }
 }

stdlib/public/core/StringBridge.swift

@@ -481,7 +481,7 @@ private func getConstantTaggedCocoaContents(_ cocoaString: _CocoaString) ->
   let length = ivarPointer.pointee.length
   let isUTF16Mask:UInt = 0x0000_0000_0000_0004 //CFStringFlags bit 4: isUnicode
   let isASCII = ivarPointer.pointee.flags & isUTF16Mask == 0
-  precondition(isASCII) // we don't currently support non-ASCII here
+  _precondition(isASCII) // we don't currently support non-ASCII here
   let contentsPtr = ivarPointer.pointee.str
   return (
     utf16Length: Int(length),

stdlib/public/core/StringLegacy.swift

@@ -28,7 +28,7 @@ extension String {
   ///   - count: The number of times to repeat `repeatedValue` in the resulting
   ///     string.
   public init(repeating repeatedValue: String, count: Int) {
-    precondition(count >= 0, "Negative count not allowed")
+    _precondition(count >= 0, "Negative count not allowed")
     guard count > 1 else {
       self = count == 0 ? "" : repeatedValue
       return

stdlib/public/core/StringStorage.swift

@@ -445,7 +445,7 @@ extension __StringStorage {
 
   // @opaque
   fileprivate var _breadcrumbsAddress: UnsafeMutablePointer<_StringBreadcrumbs?> {
-    precondition(
+    _precondition(
       hasBreadcrumbs, "Internal error: string breadcrumbs not present")
     return UnsafeMutablePointer(_realCapacityEnd)
   }

stdlib/public/core/StringUTF16View.swift

@@ -158,7 +158,7 @@ extension String.UTF16View: BidirectionalCollection {
 
   @inlinable @inline(__always)
   public func index(before idx: Index) -> Index {
-    precondition(!idx.isZeroPosition)
+    _precondition(!idx.isZeroPosition)
     if _slowPath(_guts.isForeign) { return _foreignIndex(before: idx) }
     if _guts.isASCII { return idx.priorEncoded }
 

stdlib/public/core/StringUTF8View.swift

@@ -145,7 +145,7 @@ extension String.UTF8View: BidirectionalCollection {
 
   @inlinable @inline(__always)
   public func index(before i: Index) -> Index {
-    precondition(!i.isZeroPosition)
+    _precondition(!i.isZeroPosition)
     if _fastPath(_guts.isFastUTF8) {
       return i.strippingTranscoding.priorEncoded
     }

stdlib/public/core/StringUnicodeScalarView.swift

@@ -129,7 +129,7 @@ extension String.UnicodeScalarView: BidirectionalCollection {
   @inlinable @inline(__always)
   public func index(before i: Index) -> Index {
     let i = _guts.scalarAlign(i)
-    precondition(i._encodedOffset > 0)
+    _precondition(i._encodedOffset > 0)
     // TODO(String performance): isASCII fast-path
 
     if _fastPath(_guts.isFastUTF8) {