[stdlib] Switch Int/Float inits + join to be on StringProtocol

stdlib/public/core/FloatingPointParsing.swift.gyb

@@ -123,7 +123,7 @@ extension ${Self} : LosslessStringConvertible {
   /// - Parameter text: The input string to convert to a `${Self}` instance. If
   ///   `text` has invalid characters or is in an invalid format, the result
   ///   is `nil`.
-  public init?(_ text: String) {
+  public init?<S: StringProtocol>(_ text: S) {
     let u16 = text.utf16
     func parseNTBS(_ chars: UnsafePointer<CChar>) -> (${Self}, Int) {
       var result: ${Self} = 0
@@ -133,7 +133,7 @@ extension ${Self} : LosslessStringConvertible {
       return (result, endPtr == nil ? 0 : endPtr! - chars)
     }
 
-    let (result, n) = text.withCString(parseNTBS)
+    let (result, n) = text._ephemeralString.withCString(parseNTBS)
 
     if n == 0 || n != u16.count
     || u16.contains(where: { $0 > 127 || _isspace_clocale($0) }) {

stdlib/public/core/IntegerParsing.swift

@@ -131,10 +131,10 @@ extension FixedWidthInteger {
   ///   - radix: The radix, or base, to use for converting `text` to an integer
   ///     value. `radix` must be in the range `2...36`. The default is 10.
   @_semantics("optimize.sil.specialize.generic.partial.never")
-  public init?/*<S : StringProtocol>*/(_ text: String, radix: Int = 10) {
+  public init?<S : StringProtocol>(_ text: S, radix: Int = 10) {
     _precondition(2...36 ~= radix, "Radix not in range 2...36")
     let r = Self(radix)
-    let s = text// ._ephemeralString
+    let s = text._ephemeralString
     defer { _fixLifetime(s) }
 
     let c = s._core

stdlib/public/core/String.swift

@@ -880,7 +880,7 @@ extension String {
   }
 }
 
-extension Sequence where Element == String {
+extension Sequence where Element: StringProtocol {
 
   /// Returns a new string by concatenating the elements of the sequence,
   /// adding the given separator between each element.
@@ -914,7 +914,7 @@ extension Sequence where Element == String {
       for chunk in self {
         // FIXME(performance): this code assumes UTF-16 in-memory representation.
         // It should be switched to low-level APIs.
-        r += separatorSize + chunk.utf16.count
+        r += separatorSize + chunk._ephemeralString.utf16.count
       }
       return r - separatorSize
     }
@@ -925,17 +925,17 @@ extension Sequence where Element == String {
 
     if separatorSize == 0 {
       for x in self {
-        result.append(x)
+        result.append(x._ephemeralString)
       }
       return result
     }
 
     var iter = makeIterator()
     if let first = iter.next() {
-      result.append(first)
+      result.append(first._ephemeralString)
       while let next = iter.next() {
         result.append(separator)
-        result.append(next)
+        result.append(next._ephemeralString)
       }
     }