Task local to opt out of XCTModify exhaustivity. (#102)

Author: mbrandonw

Sources/CasePaths/XCTUnwrap.swift

@@ -67,7 +67,11 @@ public func XCTModify<Root, Case>(
     return
   }
 
-  if let isEqual = _isEqual(before, value), isEqual {
+  if
+    XCTModifyLocals.isExhaustive,
+    let isEqual = _isEqual(before, value),
+    isEqual
+  {
     XCTFail(
       """
       XCTModify failed: expected "\(Case.self)" value to be modified but it was unchanged.
@@ -77,4 +81,8 @@ public func XCTModify<Root, Case>(
   root = casePath.embed(value)
 }
 
+@_spi(Internals) public enum XCTModifyLocals {
+  @TaskLocal public static var isExhaustive = true
+}
+
 private struct UnwrappingCase: Error {}

Tests/CasePathsTests/XCTModifyTests.swift

@@ -1,5 +1,5 @@
 #if DEBUG && (os(iOS) || os(macOS) || os(tvOS) || os(watchOS))
-  import CasePaths
+  @_spi(Internals) import CasePaths
   import XCTest
 
   final class XCTModifyTests: XCTestCase {
@@ -117,6 +117,17 @@
       }
       XCTAssertEqual(result, .success(2))
     }
+
+    func testXCTModifyFailUnchangedEquatable_NonExhaustive() throws {
+      try XCTSkipIf(ProcessInfo.processInfo.environment["CI"] != nil)
+
+      var result = Result<Int, SomeError>.success(2)
+      XCTModifyLocals.$isExhaustive.withValue(false) {
+        XCTModify(&result, case: /Result.success) {
+          _ = $0
+        }}
+      XCTAssertEqual(result, .success(2))
+    }
   }
 
   private struct SomeError: Error, Equatable {}