PR feedback

Author: pmattos

Sources/SWBCore/SpecImplementations/Tools/SwiftCompiler.swift

@@ -3237,7 +3237,7 @@ public final class SwiftCompilerSpec : CompilerSpec, SpecIdentifierType, SwiftDi
             // See the related `previewXOJITThunkInfoResolvesSymlinkedSourcePath` test.
             func resolvedPath(_ path: Path) -> Path { (try? fs.realpath(path)) ?? path }
             let realSourceFile = resolvedPath(sourceFile)
-            selectedInputPath = originalInputs.first { resolvedPath($0) == realSourceFile } ?? sourceFile
+            selectedInputPath = originalInputs.only { resolvedPath($0) == realSourceFile } ?? sourceFile
 
             if let driverPayload = payload.driverPayload {
                 do {

Sources/SWBUtil/Collection.swift

@@ -17,11 +17,28 @@ public extension Collection {
     }
 
     /// Return the only element in the collection, if it has exactly one element.
-    /// - complexity: O(1).
+    ///
+    /// **Complexity**. O(1).
     var only: Iterator.Element? {
         return !isEmpty && index(after: startIndex) == endIndex ? self.first : nil
     }
 
+    /// Returns the single element of the sequence satisfying `predicate`,
+    /// or `nil`if no element — or more than one element — satisfies it.
+    ///
+    /// Unlike `first(where:)`, multiple matches yield `nil`;
+    /// iteration stops as soon as a second match is found.
+    ///
+    /// **Complexity**.  O(n), where n is the length of the sequence.
+    func only(where predicate: (Element) throws -> Bool) rethrows -> Element? {
+        var onlyMatch: Element?
+        for candidate in self where try predicate(candidate) {
+            guard onlyMatch == nil else { return nil }
+            onlyMatch = candidate
+        }
+        return onlyMatch
+    }
+
     /// Returns the elements of the sequence, sorted using the given key path as the comparison between elements.
     @inlinable func sorted<Value: Comparable>(by predicate: (Element) -> Value) -> [Element] {
         return sorted(<, by: predicate)