Replace rethrows with typed throws in Graph (#662)

This replaces usage of `rethrows` with [typed
throws](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0413-typed-throws.md)
in the internal-only `Graph` support type.

### Motivation:

It's now
[recommended](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0413-typed-throws.md#when-to-use-typed-throws)
to use typed throws in generic code that never produces its own errors,
but only passes through errors that come from callers. And adopting
typed throws in more places will reduce barriers to eventually
supporting Embedded Swift.

### Modifications:

- Replace all usage of `rethrows` with the analogous typed throws
declaration in `Graph`.

### Result:

No behavioral/runtime change.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: stmontgomery

Sources/Testing/Support/Graph.swift

@@ -393,7 +393,7 @@ extension Graph {
   ///     path and leaf value of each node are passed to the closure.
   ///
   /// - Throws: Whatever is thrown by `body`.
-  private func _forEach(keyPath: [K], _ body: (Element) throws -> Void) rethrows -> Void {
+  private func _forEach<E>(keyPath: [K], _ body: (Element) throws(E) -> Void) throws(E) {
     try body((keyPath, value))
     for (key, child) in children {
       var childKeyPath = keyPath
@@ -411,7 +411,7 @@ extension Graph {
   ///     key path and leaf value of each node are passed to the closure.
   ///
   /// - Throws: Whatever is thrown by `body`.
-  private func _forEach(keyPath: [K], _ body: (Element) async throws -> Void) async rethrows -> Void {
+  private func _forEach<E>(keyPath: [K], _ body: (Element) async throws(E) -> Void) async throws(E) {
     try await body((keyPath, value))
     for (key, child) in children {
       var childKeyPath = keyPath
@@ -429,9 +429,9 @@ extension Graph {
   /// - Throws: Whatever is thrown by `body`.
   ///
   /// This function iterates depth-first.
-  func forEach(_ body: (Element) throws -> Void) rethrows -> Void {
-    try _forEach(keyPath: []) {
-      try body(($0, $1))
+  func forEach<E>(_ body: (Element) throws(E) -> Void) throws(E) {
+    try _forEach(keyPath: []) { (element) throws(E) in
+      try body(element)
     }
   }
 
@@ -444,9 +444,9 @@ extension Graph {
   /// - Throws: Whatever is thrown by `body`.
   ///
   /// This function iterates depth-first.
-  func forEach(_ body: (Element) async throws -> Void) async rethrows -> Void {
-    try await _forEach(keyPath: []) {
-      try await body(($0, $1))
+  func forEach<E>(_ body: (Element) async throws(E) -> Void) async throws(E) {
+    try await _forEach(keyPath: []) { (element) async throws(E) in
+      try await body(element)
     }
   }
 
@@ -496,9 +496,9 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func compactMapValues<U>(_ transform: (Element) throws -> U?) rethrows -> Graph<K, U>? {
-    try compactMapValues {
-      try transform($0).map { ($0, false) }
+  func compactMapValues<U, E>(_ transform: (Element) throws(E) -> U?) throws(E) -> Graph<K, U>? {
+    try compactMapValues { (element) throws(E) in
+      try transform(element).map { ($0, false) }
     }
   }
 
@@ -518,9 +518,9 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func compactMapValues<U>(_ transform: (Element) async throws -> U?) async rethrows -> Graph<K, U>? {
-    try await compactMapValues {
-      try await transform($0).map { ($0, false) }
+  func compactMapValues<U, E>(_ transform: (Element) async throws(E) -> U?) async throws(E) -> Graph<K, U>? {
+    try await compactMapValues { (element) async throws(E) in
+      try await transform(element).map { ($0, false) }
     }
   }
 
@@ -543,9 +543,9 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func compactMapValues<U>(_ transform: (Element) throws -> (U, recursivelyApply: Bool)?) rethrows -> Graph<K, U>? {
-    try _compactMapValues(keyPath: []) {
-      try transform(($0, $1))
+  func compactMapValues<U, E>(_ transform: (Element) throws(E) -> (U, recursivelyApply: Bool)?) throws(E) -> Graph<K, U>? {
+    try _compactMapValues(keyPath: []) { (element) throws(E) in
+      try transform(element)
     }
   }
 
@@ -563,7 +563,7 @@ extension Graph {
   ///     child nodes are omitted from the new graph.
   ///
   /// - Throws: Whatever is thrown by `transform`.
-  private func _compactMapValues<U>(keyPath: [K], _ transform: (Element) throws -> (U, recursivelyApply: Bool)?) rethrows -> Graph<K, U>? {
+  private func _compactMapValues<U, E>(keyPath: [K], _ transform: (Element) throws(E) -> (U, recursivelyApply: Bool)?) throws(E) -> Graph<K, U>? {
     guard let (newValue, recursivelyApply) = try transform((keyPath, value)) else {
       return nil
     }
@@ -603,9 +603,9 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func compactMapValues<U>(_ transform: (Element) async throws -> (U, recursivelyApply: Bool)?) async rethrows -> Graph<K, U>? {
-    try await _compactMapValues(keyPath: []) {
-      try await transform(($0, $1))
+  func compactMapValues<U, E>(_ transform: (Element) async throws(E) -> (U, recursivelyApply: Bool)?) async throws(E) -> Graph<K, U>? {
+    try await _compactMapValues(keyPath: []) { (element) async throws(E) in
+      try await transform(element)
     }
   }
 
@@ -623,7 +623,7 @@ extension Graph {
   ///     child nodes are omitted from the new graph.
   ///
   /// - Throws: Whatever is thrown by `transform`.
-  private func _compactMapValues<U>(keyPath: [K], _ transform: (Element) async throws -> (U, recursivelyApply: Bool)?) async rethrows -> Graph<K, U>? {
+  private func _compactMapValues<U, E>(keyPath: [K], _ transform: (Element) async throws(E) -> (U, recursivelyApply: Bool)?) async throws(E) -> Graph<K, U>? {
     guard let (newValue, recursivelyApply) = try await transform((keyPath, value)) else {
       return nil
     }
@@ -658,7 +658,7 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func mapValues<U>(_ transform: (Element) throws -> U) rethrows -> Graph<K, U> {
+  func mapValues<U, E>(_ transform: (Element) throws(E) -> U) throws(E) -> Graph<K, U> {
     try compactMapValues(transform)!
   }
 
@@ -676,7 +676,7 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func mapValues<U>(_ transform: (Element) async throws -> U) async rethrows -> Graph<K, U> {
+  func mapValues<U, E>(_ transform: (Element) async throws(E) -> U) async throws(E) -> Graph<K, U> {
     try await compactMapValues(transform)!
   }
 
@@ -698,7 +698,7 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func mapValues<U>(_ transform: (Element) throws -> (U, recursivelyApply: Bool)) rethrows -> Graph<K, U> {
+  func mapValues<U, E>(_ transform: (Element) throws(E) -> (U, recursivelyApply: Bool)) throws(E) -> Graph<K, U> {
     try compactMapValues(transform)!
   }
 
@@ -720,7 +720,7 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func mapValues<U>(_ transform: (Element) async throws -> (U, recursivelyApply: Bool)) async rethrows -> Graph<K, U> {
+  func mapValues<U, E>(_ transform: (Element) async throws(E) -> (U, recursivelyApply: Bool)) async throws(E) -> Graph<K, U> {
     try await compactMapValues(transform)!
   }
 
@@ -738,7 +738,7 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func map<U>(_ transform: (Element) throws -> U) rethrows -> [U] {
+  func map<U, E>(_ transform: (Element) throws(E) -> U) throws(E) -> [U] {
     try compactMap(transform)
   }
 
@@ -756,7 +756,7 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func map<U>(_ transform: (Element) async throws -> U) async rethrows -> [U] {
+  func map<U, E>(_ transform: (Element) async throws(E) -> U) async throws(E) -> [U] {
     try await compactMap(transform)
   }
 
@@ -776,10 +776,10 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func compactMap<U>(_ transform: (Element) throws -> U?) rethrows -> [U] {
+  func compactMap<U, E>(_ transform: (Element) throws(E) -> U?) throws(E) -> [U] {
     var result = [U]()
 
-    try forEach { keyPath, value in
+    try forEach { (keyPath, value) throws(E) in
       if let newValue = try transform((keyPath, value)) {
         result.append(newValue)
       }
@@ -804,10 +804,10 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func compactMap<U>(_ transform: (Element) async throws -> U?) async rethrows -> [U] {
+  func compactMap<U, E>(_ transform: (Element) async throws(E) -> U?) async throws(E) -> [U] {
     var result = [U]()
 
-    try await forEach { keyPath, value in
+    try await forEach { (keyPath, value) async throws(E) in
       if let newValue = try await transform((keyPath, value)) {
         result.append(newValue)
       }
@@ -829,7 +829,7 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func flatMap<S>(_ transform: (Element) throws -> S) rethrows -> [S.Element] where S: Sequence {
+  func flatMap<S, E>(_ transform: (Element) throws(E) -> S) throws(E) -> [S.Element] where S: Sequence {
     try map(transform).flatMap { $0 }
   }
 
@@ -846,7 +846,7 @@ extension Graph {
   /// - Throws: Whatever is thrown by `transform`.
   ///
   /// This function iterates depth-first.
-  func flatMap<S>(_ transform: (Element) async throws -> S) async rethrows -> [S.Element] where S: Sequence {
+  func flatMap<S, E>(_ transform: (Element) async throws(E) -> S) async throws(E) -> [S.Element] where S: Sequence {
     try await map(transform).flatMap { $0 }
   }
 }