Emit return type for closures to help with type checking a bit

Author: grynspan

Sources/Testing/Expectations/Expectation+Macro.swift

@@ -69,7 +69,7 @@
   _ optionalValue: consuming T?,
   _ comment: @autoclosure () -> Comment? = nil,
   sourceLocation: SourceLocation = #_sourceLocation
-) -> T = #externalMacro(module: "TestingMacros", type: "RequireMacro") where T: ~Copyable
+) -> T = #externalMacro(module: "TestingMacros", type: "UnwrapMacro") where T: ~Copyable
 
 /// Unwrap an optional boolean value or, if it is `nil`, fail and throw an
 /// error.

Sources/TestingMacros/ConditionMacro.swift

@@ -39,6 +39,12 @@ public import SwiftSyntaxMacros
 public protocol ConditionMacro: ExpressionMacro, Sendable {
   /// Whether or not the macro's expansion may throw an error.
   static var isThrowing: Bool { get }
+
+  /// The return type of the expansion's closure, if it can be statically
+  /// determined.
+  ///
+  /// This property is ignored when a condition macro is closure-based.
+  static var returnType: TypeSyntax? { get }
 }
 
 // MARK: -
@@ -67,6 +73,15 @@ extension ConditionMacro {
     .disabled
   }
 
+  public static var returnType: TypeSyntax? {
+    TypeSyntax(
+      MemberTypeSyntax(
+        baseType: IdentifierTypeSyntax(name: .identifier("Swift")),
+        name: .identifier("Bool")
+      )
+    )
+  }
+
   /// Perform the expansion of this condition macro.
   ///
   /// - Parameters:
@@ -179,6 +194,7 @@ extension ConditionMacro {
             for: macro,
             rootedAt: originalArgumentExpr,
             effectKeywordsToApply: effectKeywordsToApply,
+            returnType: returnType,
             in: context
           )
           checkArguments.append(Argument(expression: closureExpr))
@@ -316,6 +332,25 @@ public struct RequireMacro: ConditionMacro {
   }
 }
 
+/// A type describing the expansion of the `#require()` macro when it produces
+/// an optional value.
+public struct UnwrapMacro: ConditionMacro {
+  public static var isThrowing: Bool {
+    true
+  }
+
+  public static var returnType: TypeSyntax? {
+    TypeSyntax(
+      MemberTypeSyntax(
+        baseType: IdentifierTypeSyntax(name: .identifier("Swift")),
+        name: .identifier("Optional")
+      )
+    )
+  }
+}
+
+// MARK: - Refined condition macros
+
 /// A protocol that can be used to create a condition macro that refines the
 /// behavior of another previously-defined condition macro.
 public protocol RefinedConditionMacro: ConditionMacro {
@@ -326,6 +361,10 @@ extension RefinedConditionMacro {
   public static var isThrowing: Bool {
     Base.isThrowing
   }
+
+  public static var returnType: TypeSyntax? {
+    Base.returnType
+  }
 }
 
 // MARK: - Diagnostics-emitting condition macros
@@ -335,7 +374,7 @@ extension RefinedConditionMacro {
 ///
 /// This type is otherwise exactly equivalent to ``RequireMacro``.
 public struct AmbiguousRequireMacro: RefinedConditionMacro {
-  public typealias Base = RequireMacro
+  public typealias Base = UnwrapMacro
 
   public static func expansion(
     of macro: some FreestandingMacroExpansionSyntax,
@@ -346,7 +385,7 @@ public struct AmbiguousRequireMacro: RefinedConditionMacro {
     }
 
     // Perform the normal macro expansion for #require().
-    return try RequireMacro.expansion(of: macro, in: context)
+    return try Base.expansion(of: macro, in: context)
   }
 
   /// Check for an ambiguous argument to the `#require()` macro and emit the
@@ -378,7 +417,7 @@ public struct AmbiguousRequireMacro: RefinedConditionMacro {
 ///
 /// This type is otherwise exactly equivalent to ``RequireMacro``.
 public struct NonOptionalRequireMacro: RefinedConditionMacro {
-  public typealias Base = RequireMacro
+  public typealias Base = UnwrapMacro
 
   public static func expansion(
     of macro: some FreestandingMacroExpansionSyntax,
@@ -389,7 +428,7 @@ public struct NonOptionalRequireMacro: RefinedConditionMacro {
     }
 
     // Perform the normal macro expansion for #require().
-    return try RequireMacro.expansion(of: macro, in: context)
+    return try Base.expansion(of: macro, in: context)
   }
 }
 
@@ -418,7 +457,7 @@ public struct RequireThrowsMacro: RefinedConditionMacro {
     }
 
     // Perform the normal macro expansion for #require().
-    return try RequireMacro.expansion(of: macro, in: context)
+    return try Base.expansion(of: macro, in: context)
   }
 }
 
@@ -438,7 +477,7 @@ public struct RequireThrowsNeverMacro: RefinedConditionMacro {
     }
 
     // Perform the normal macro expansion for #require().
-    return try RequireMacro.expansion(of: macro, in: context)
+    return try Base.expansion(of: macro, in: context)
   }
 }
 

Sources/TestingMacros/Support/ConditionArgumentParsing.swift

@@ -614,6 +614,8 @@ extension ConditionMacro {
   ///     for the purposes of generating expression ID values.
   ///   - effectKeywordsToApply: The set of effect keywords in the expanded
   ///     expression or its lexical context that may apply to `node`.
+  ///   - returnType: The return type of the expanded closure, if statically
+  ///     known at macro expansion time.
   ///   - context: The macro context in which the expression is being parsed.
   ///
   /// - Returns: A tuple containing the rewritten copy of `node`, a list of all
@@ -626,6 +628,7 @@ extension ConditionMacro {
     for macro: some FreestandingMacroExpansionSyntax,
     rootedAt effectiveRootNode: some SyntaxProtocol,
     effectKeywordsToApply: Set<Keyword>,
+    returnType: (some TypeSyntaxProtocol)?,
     in context: some MacroExpansionContext
   ) -> (ClosureExprSyntax, rewrittenNodes: Set<Syntax>) {
     _diagnoseTrivialBooleanValue(from: ExprSyntax(node), for: macro, in: context)
@@ -713,6 +716,11 @@ extension ConditionMacro {
             }
           )
         ),
+        returnClause: returnType.map { returnType in
+          ReturnClauseSyntax(
+            type: returnType.with(\.leadingTrivia, .space)
+          ).with(\.leadingTrivia, .space)
+        },
         inKeyword: .keyword(.in)
           .with(\.leadingTrivia, .space)
           .with(\.trailingTrivia, .newline)

Sources/TestingMacros/TestingMacrosMain.swift

@@ -22,6 +22,7 @@ struct TestingMacrosMain: CompilerPlugin {
       TestDeclarationMacro.self,
       ExpectMacro.self,
       RequireMacro.self,
+      UnwrapMacro.self,
       AmbiguousRequireMacro.self,
       NonOptionalRequireMacro.self,
       RequireThrowsMacro.self,

Tests/SubexpressionShowcase/SubexpressionShowcase.swift

@@ -110,6 +110,7 @@ func subexpressionShowcase() async throws {
   #expect(m(123 == 456))
 #endif
 
+  try #require(x == x)
   _ = try #require(.some(Int32.Magnitude(1)))
 
   let n = 1 as Any