Disfavor the TestPredicate-returning == overloads

CHANGELOG.md

@@ -10,6 +10,8 @@ All notable changes are documented here. The format follows [Keep a Changelog](h
 
 - **A user `onCancel` handler that started new work during a sealed model's teardown drain was silently dropped.** `AnyContext.onRemoval` seals a model's `Cancellations` store, then drains it synchronously via `cancelAll()`/`cancelAll(for:)`. If one of the drained `onCancel` closures itself called `node.task { }`, a nested `node.onCancel { }`, or `forEach`, that registration landed on the already-sealed store: `Cancellations.register` cancelled it immediately before its body ever ran, with no signal — indistinguishable from the expected-silent case of a registration racing teardown from a different thread. `Cancellations.register` now checks a thread-local, `threadLocals.isDrainingCancellations`, set only around the synchronous drain in `cancelAll()`/`cancelAll(for:)`, and calls `reportIssue` (outside the lock) when a same-thread registration lands on a store sealed by the drain it's running inside of. A cross-thread race against teardown still stays silent, as intended — including a `Task { }` spawned from an `onCancel` handler that registers later: a thread-local, unlike a `@TaskLocal`, isn't inherited by that task. `OnCancelDuringTeardownRegistrationTests` is the regression coverage.
 
+- **SwiftModel's `==` overloads that return `TestPredicate` no longer hijack plain comparisons in app code.** The two public `==` operators behind `expect { a == b }` (which let a failure print both sides) were visible to every file that imports SwiftModel, and outside a builder they could win: `let immediate = self.outcome == .needsNewPlayer` in non-test code inferred `TestPredicate` rather than `Bool`, and needed an explicit `: Bool`. Both operators are now `@_disfavoredOverload`, so an untyped comparison infers `Bool` again. Disfavoring them alone would have cost `expect { }` its diffs: the builder's `Bool` `buildExpression` was already disfavored, so each path carried one disfavored declaration and the solver broke the tie toward the concrete `==` (`expect { model.outcome == .needsNewPlayer }` degraded from the `− .needsNewPlayer / + .pending` diff to a bare "Expectation not met"). `AssertBuilder.buildExpression(Bool)` is therefore removed. A plain `Bool` now reaches the existing `buildExpression(Bool?)` through a value-to-optional conversion, and that extra cost keeps the tie going to `TestPredicate`. Builder failure output for optional and enum implicit-member comparisons is byte-identical to before on Swift 6.3 and 6.4. Two new `builder … == …` snapshots in `OutputSnapshotTests` now pin it, where before only an explicitly `TestPredicate`-annotated predicate was covered. Comparisons like `expect { model.count == 99 }`, where a concrete `==` exists, now also show the diff on Swift 6.3, where they previously printed just `count == 3`. On 6.4 they print what they did before. `TestPredicateOverloadTests` (plain `import SwiftModel`) is the regression test for inference outside a builder, and it fails to compile without the fix.
+
 ---
 
 ## [1.0.21] — Write-lock holder resolves through read probes (AB-BA deadlock fix)

Sources/SwiftModel/Testing/ModelTester.swift

@@ -386,11 +386,14 @@ public extension AssertBuilder {
         layers.flatMap { $0 }
     }
 
-    @_disfavoredOverload
-    static func buildExpression(_ predicate: @autoclosure @escaping @Sendable () -> Bool, fileID: StaticString = #fileID, filePath: StaticString = #filePath, line: UInt = #line, column: UInt = #column) -> Result {
-        [Predicate(predicate: predicate, fileAndLine: FileAndLine(fileID: fileID, filePath: filePath, line: line, column: column))]
-    }
-
+    // Overload resolution inside the builder: the `==` overloads below that return
+    // `TestPredicate` are `@_disfavoredOverload` (so plain code outside a builder infers `Bool`),
+    // and so is this one. That leaves the `TestPredicate` path (rich lhs/rhs failure diff) and
+    // the plain `Bool ==` path tied on disfavored overloads, and the tie must go to
+    // `TestPredicate`. There is deliberately no `buildExpression(Bool)`: a plain `Bool` reaches
+    // this `Bool?` overload through a value-to-optional conversion, and that extra cost is what
+    // breaks the tie. Adding a `Bool` overload back makes `expect { model.outcome == .x }` lose
+    // its diff (pinned by the `builder … == …` snapshots in `OutputSnapshotTests`).
     @_disfavoredOverload
     static func buildExpression(_ predicate: @autoclosure @escaping @Sendable () -> Bool?, fileID: StaticString = #fileID, filePath: StaticString = #filePath, line: UInt = #line, column: UInt = #column) -> Result {
         [Predicate(predicate: { predicate() == true }, fileAndLine: FileAndLine(fileID: fileID, filePath: filePath, line: line, column: column))]
@@ -412,10 +415,14 @@ public struct TestPredicate: Sendable {
     var values: @Sendable () -> (Any, Any)? = { nil }
 }
 
+// `==` returning `TestPredicate`, for `expect { a == b }` failures that show both sides. Disfavored
+// so they never win outside the `AssertBuilder`: `let b = x == y` in app code must infer `Bool`.
+@_disfavoredOverload
 public func == <T: Equatable&Sendable>(lhs: @escaping @Sendable @autoclosure () -> T, rhs: @escaping @Sendable @autoclosure () -> T) -> TestPredicate {
     TestPredicate(predicate: { lhs() == rhs() }, values: { (lhs(), rhs()) })
 }
 
+@_disfavoredOverload
 public func == <T: Equatable&Sendable>(lhs: @escaping @Sendable @autoclosure () -> T?, rhs: @escaping @Sendable @autoclosure () -> T) -> TestPredicate {
     TestPredicate(predicate: { lhs() == rhs() }, values: { (lhs() as Any, rhs() as Any) })
 }

Tests/SwiftModelSnapshotTests/OutputSnapshotTests.swift

@@ -23,6 +23,23 @@ private struct SimpleCounter {
     var count: Int = 0
 }
 
+// A model with an optional property, for the `T? == T` builder overload.
+@Model
+private struct OptionalCounter {
+    var count: Int? = nil
+}
+
+private enum Outcome: Equatable, Sendable {
+    case pending
+    case needsNewPlayer
+}
+
+// A model with an enum property, for builder `==` against an implicit member.
+@Model
+private struct OutcomeHolder {
+    var outcome: Outcome = .pending
+}
+
 // A parent model that holds a child model, for testing how replacement diffs look
 @Model
 private struct ItemHolder {
@@ -257,6 +274,57 @@ struct TesterAssertOutputTests {
         }
     }
 
+    // The `==` overloads returning `TestPredicate` are `@_disfavoredOverload` (so a plain
+    // `let b = x == y` outside a builder infers `Bool`), and so is the builder's `Bool?`
+    // `buildExpression`; the tie must still go to the `TestPredicate` path so both sides print.
+    // These pin that with no type annotation, for shapes that have no concrete `Bool ==` shortcut
+    // (optional vs. value, enum vs. implicit member — the latter is the shape that regressed when
+    // only the operators were disfavored). Shapes like `Int == literal` resolve toolchain-
+    // dependently (Swift 6.3 takes the `TestPredicate` path, 6.4 the concrete `Int.==`), so they
+    // are deliberately not snapshotted here.
+    @Test("builder optional == predicate failure shows lhs/rhs diff")
+    func builderOptionalEqualityFailureMessage() async {
+        await TestAccessOverrides.$hardCapNanoseconds.withValue(50_000_000) {
+            await assertIssueSnapshot {
+                await withModelTesting(exhaustivity: .off) {
+                    let model = OptionalCounter().withAnchor()
+                    model.count = 3
+                    await expect { model.count == 99 }
+                }
+            } matches: {
+                """
+                Expectation not met: OptionalCounter.count: …
+
+                    − 99
+                    + 3
+
+                (Expected: −, Actual: +)
+                """
+            }
+        }
+    }
+
+    @Test("builder enum == implicit member failure shows lhs/rhs diff")
+    func builderEnumEqualityFailureMessage() async {
+        await TestAccessOverrides.$hardCapNanoseconds.withValue(50_000_000) {
+            await assertIssueSnapshot {
+                await withModelTesting(exhaustivity: .off) {
+                    let model = OutcomeHolder().withAnchor()
+                    await expect { model.outcome == .needsNewPlayer }
+                }
+            } matches: {
+                """
+                Expectation not met: OutcomeHolder.outcome: …
+
+                    − Outcome.needsNewPlayer
+                    + Outcome.pending
+
+                (Expected: −, Actual: +)
+                """
+            }
+        }
+    }
+
     @Test("passing assertion emits no issues")
     func passingAssertionNoIssues() async {
         await assertIssueSnapshot {

Tests/SwiftModelTests/TestPredicateOverloadTests.swift

@@ -0,0 +1,53 @@
+import Testing
+import SwiftModel // plain import, like a downstream app: sees only the public `==` overloads
+
+// SwiftModel's public `==` overloads returning `TestPredicate` exist for the `expect { a == b }`
+// builder, so failures can print both sides. They're `@_disfavoredOverload`, so ordinary code
+// outside a builder must keep inferring `Bool`. (The builder side is pinned by the
+// `builder … == …` snapshots in `SwiftModelSnapshotTests/OutputSnapshotTests.swift`.)
+
+private enum Outcome: Equatable, Sendable {
+    case pending
+    case needsNewPlayer
+}
+
+private struct Wrapper: Equatable, Sendable {
+    var value: Int
+}
+
+/// Only accepts `Bool`: passing an untyped `let` here fails to compile if it inferred `TestPredicate`.
+private func requireBool(_ value: Bool) -> Bool { value }
+
+private func genericEquals<T: Equatable & Sendable>(_ lhs: T, _ rhs: T) -> Bool {
+    let result = lhs == rhs
+    return requireBool(result)
+}
+
+struct TestPredicateOverloadTests {
+    @Test func equalityOutsideBuilderInfersBool() {
+        let outcome = Outcome.pending
+        let immediate = outcome == .needsNewPlayer
+        #expect(type(of: immediate) == Bool.self)
+        #expect(requireBool(immediate) == false)
+    }
+
+    @Test func optionalEqualityOutsideBuilderInfersBool() {
+        let count: Int? = 3
+        let matches = count == 3
+        #expect(type(of: matches) == Bool.self)
+        #expect(requireBool(matches))
+    }
+
+    @Test func structEqualityOutsideBuilderInfersBool() {
+        let a = Wrapper(value: 1)
+        let b = Wrapper(value: 2)
+        let same = a == b
+        #expect(type(of: same) == Bool.self)
+        #expect(requireBool(same) == false)
+    }
+
+    @Test func genericEqualityOutsideBuilderInfersBool() {
+        #expect(genericEquals(Outcome.needsNewPlayer, .needsNewPlayer))
+        #expect(genericEquals(Wrapper(value: 1), Wrapper(value: 2)) == false)
+    }
+}