Add XCTFailContext task local (#68)

* Add XCTFailContext task local

* wip

* wip

Author: stephencelis

.github/workflows/ci.yml

@@ -30,7 +30,7 @@ jobs:
       run: make test-linux
 
   wasm:
-     name: SwiftWASM
+     name: Wasm
      runs-on: ubuntu-latest
      strategy:
        matrix:

Sources/XCTestDynamicOverlay/XCTFail.swift

@@ -1,5 +1,17 @@
 import Foundation
 
+public struct XCTFailContext {
+  @TaskLocal public static var current: Self?
+
+  public var file: StaticString
+  public var line: UInt
+
+  public init(file: StaticString, line: UInt) {
+    self.file = file
+    self.line = line
+  }
+}
+
 #if DEBUG
   #if canImport(ObjectiveC)
     /// This function generates a failure immediately and unconditionally.
@@ -12,6 +24,10 @@ import Foundation
     ///   results.
     @_disfavoredOverload
     public func XCTFail(_ message: String = "") {
+      if let context = XCTFailContext.current {
+        XCTFail(message, file: context.file, line: context.line)
+        return
+      }
       var message = message
       attachHostApplicationWarningIfNeeded(&message)
       guard

Tests/XCTestDynamicOverlayTests/XCTContextTests.swift

@@ -0,0 +1,17 @@
+#if !os(Linux)
+  import XCTest
+  import XCTestDynamicOverlay
+
+  public final class XCTContextTests: XCTestCase {
+    func testContext() {
+      XCTExpectFailure {
+        $0.compactDescription == "Failed"
+          && $0.sourceCodeContext.location
+            == XCTSourceCodeLocation(filePath: "unknown", lineNumber: 1)
+      }
+      XCTFailContext.$current.withValue(XCTFailContext(file: "unknown", line: 1)) {
+        XCTestDynamicOverlay.XCTFail("Failed")
+      }
+    }
+  }
+#endif