Enable SE-0422 Expression macro as caller-side default argument

2025-12-14 20:36:38 +01:00 · 2024-02-14 17:49:26 -08:00
parent 0558bde15e
commit 9ccfb574fd
12 changed files with 39 additions and 54 deletions
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,33 @@
 > This is in reverse chronological order, so newer entries are added to the top.

 ## Swift 5.11
+* [SE-0422][]:
+  Non-built-in expression macros can now be used as default arguments that
+  expand at each call site. For example, a custom `#CurrentFile` macro used as
+  a default argument in 'Library.swift' won't be expanded to `"Library.swift"`:
+
+  ```swift
+  @freestanding(expression)
+  public macro CurrentFile() -> String = ...
+
+  public func currentFile(name: String = #CurrentFile) { name }
+  ```
+
+  Instead, it will be expanded at where the function is called:
+  
+  ```swift
+  print(currentFile())
+  // Prints "main.swift"
+  ```
+
+  The expanded code can also use declarations from the caller side context:
+
+  ```swift
+  var person = "client"
+  greetPerson(/* greeting: #informalGreeting */)
+  // Prints "Hi client" if macro expands to "Hi \(person)"
+  ```
+
 * [SE-0417][]:
  Tasks now gain the ability to respect Task Executor preference.
  This allows tasks executing default actors (which do not declare a custom executor),
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -7535,9 +7535,6 @@ ERROR(extension_macro_invalid_conformance,none,
 ERROR(macro_attached_to_invalid_decl,none,
      "'%0' macro cannot be attached to %1 (%base2)",
      (StringRef, DescriptiveDeclKind, const Decl *))
-ERROR(macro_as_default_argument, none,
-      "non-built-in macro cannot be used as default argument",
-      ())
 ERROR(conformance_macro,none,
      "conformance macros are replaced by extension macros",
      ())
--- a/include/swift/Basic/Features.def
+++ b/include/swift/Basic/Features.def
@@ -114,6 +114,7 @@ SUPPRESSIBLE_LANGUAGE_FEATURE(RetroactiveAttribute, 364, "@retroactive")
 SUPPRESSIBLE_LANGUAGE_FEATURE(ExtensionMacroAttr, 0, "@attached(extension)")
 LANGUAGE_FEATURE(TypedThrows, 413, "Typed throws")
 SUPPRESSIBLE_LANGUAGE_FEATURE(Extern, 0, "@_extern")
+LANGUAGE_FEATURE(ExpressionMacroDefaultArguments, 422, "Expression macro as caller-side default argument")

 UPCOMING_FEATURE(ConciseMagicFile, 274, 6)
 UPCOMING_FEATURE(ForwardTrailingClosures, 286, 6)
@@ -135,7 +136,6 @@ EXPERIMENTAL_FEATURE(NamedOpaqueTypes, false)
 EXPERIMENTAL_FEATURE(FlowSensitiveConcurrencyCaptures, false)
 EXPERIMENTAL_FEATURE(CodeItemMacros, false)
 EXPERIMENTAL_FEATURE(BodyMacros, true)
-EXPERIMENTAL_FEATURE(ExpressionMacroDefaultArguments, false)
 EXPERIMENTAL_FEATURE(TupleConformances, false)

 // Whether to enable @_used and @_section attributes
--- a/lib/Sema/TypeCheckDeclPrimary.cpp
+++ b/lib/Sema/TypeCheckDeclPrimary.cpp
@@ -1027,13 +1027,6 @@ static bool checkExpressionMacroDefaultValueRestrictions(ParamDecl *param) {
  auto *initExpr = param->getStructuralDefaultExpr();
  assert(initExpr);

-  // Prohibit default argument that is a non-built-in macro to avoid confusion,
-  // unless the experimental feature flag is set.
-  if (!ctx.LangOpts.hasFeature(Feature::ExpressionMacroDefaultArguments)) {
-    ctx.Diags.diagnose(initExpr->getLoc(), diag::macro_as_default_argument);
-    return false;
-  }
-
 #if SWIFT_BUILD_SWIFT_SYNTAX
  auto *DC = param->getInnermostDeclContext();
  const SourceFile *SF = DC->getParentSourceFile();
--- a/test/Macros/macro_default_argument.swift
+++ b/test/Macros/macro_default_argument.swift
@@ -1,32 +0,0 @@
-// REQUIRES: swift_swift_parser
-
-// RUN: %empty-directory(%t)
-// RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/syntax_macro_definitions.swift -g -no-toolchain-stdlib-rpath
-
-// RUN: %target-typecheck-verify-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s
-
-@freestanding(expression)
-macro MagicLine() -> Int = #externalMacro(module: "MacroDefinition", type: "MagicLineMacro")
-
-struct LineContainer {
-    let line: Int
-}
-
-func partOfDefaultArgumentOkay(container: LineContainer = .init(line: #MagicLine)) {
-    print(container.line)
-}
-
-func parenthesizedExpansionAtDeclOkay(line: Int = (#MagicLine)) {
-    print(line)
-}
-
-func builtInOkay(line: Int = #line) {
-    print(line)
-}
-
-// expected-error@+1{{non-built-in macro cannot be used as default argument}}
-func asDefaultArgument(line: Int = #MagicLine) {
-    print(line)
-}
-
-asDefaultArgument()
--- a/test/Macros/macro_default_argument_access_level.swift
+++ b/test/Macros/macro_default_argument_access_level.swift
@@ -3,7 +3,7 @@
 // RUN: %empty-directory(%t)
 // RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/syntax_macro_definitions.swift -g -no-toolchain-stdlib-rpath

-// RUN: %target-typecheck-verify-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -enable-experimental-feature ExpressionMacroDefaultArguments
+// RUN: %target-typecheck-verify-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s

 public typealias Stringified<T> = (T, String)

--- a/test/Macros/macro_default_argument_diagnostics.swift
+++ b/test/Macros/macro_default_argument_diagnostics.swift
@@ -3,7 +3,7 @@
 // RUN: %empty-directory(%t)
 // RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/syntax_macro_definitions.swift -g -no-toolchain-stdlib-rpath

-// RUN: %target-typecheck-verify-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -enable-experimental-feature ExpressionMacroDefaultArguments -enable-bare-slash-regex
+// RUN: %target-typecheck-verify-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -enable-bare-slash-regex

 public typealias Stringified<T> = (T, String)

--- a/test/Macros/macro_default_argument_library.swift
+++ b/test/Macros/macro_default_argument_library.swift
@@ -4,7 +4,7 @@

 // RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/syntax_macro_definitions.swift -g -no-toolchain-stdlib-rpath

-// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %s -module-name CheckInterface -load-plugin-library %t/%target-library-name(MacroDefinition) -enable-experimental-feature ExpressionMacroDefaultArguments -I %t
+// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %s -module-name CheckInterface -load-plugin-library %t/%target-library-name(MacroDefinition) -I %t
 // RUN: %target-swift-typecheck-module-from-interface(%t.swiftinterface) -module-name CheckInterface -load-plugin-library %t/%target-library-name(MacroDefinition) -I %t

 // RUN: %FileCheck %s < %t.swiftinterface
--- a/test/Macros/macro_default_argument_serialized.swift
+++ b/test/Macros/macro_default_argument_serialized.swift
@@ -5,9 +5,9 @@

 // RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/syntax_macro_definitions.swift -g -no-toolchain-stdlib-rpath

-// RUN: %target-build-swift-dylib(%t/%target-library-name(Serialized)) %S/macro_default_argument_library.swift -module-name Serialized -emit-module -emit-module-path %t/Serialized.swiftmodule -load-plugin-library %t/%target-library-name(MacroDefinition) -enable-experimental-feature ExpressionMacroDefaultArguments -I %t -swift-version 5
+// RUN: %target-build-swift-dylib(%t/%target-library-name(Serialized)) %S/macro_default_argument_library.swift -module-name Serialized -emit-module -emit-module-path %t/Serialized.swiftmodule -load-plugin-library %t/%target-library-name(MacroDefinition) -I %t -swift-version 5

-// RUN: %target-build-swift -enable-experimental-feature ExpressionMacroDefaultArguments -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -o %t/main -module-name MacroUser -emit-tbd -emit-tbd-path %t/MacroUser.tbd -I %t -L %t %target-rpath(%t) -lSerialized
+// RUN: %target-build-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -o %t/main -module-name MacroUser -emit-tbd -emit-tbd-path %t/MacroUser.tbd -I %t -L %t %target-rpath(%t) -lSerialized
 // RUN: %target-codesign %t/main
 // RUN: %target-run %t/main | %FileCheck %s

--- a/test/Macros/macro_default_argument_source_location.swift
+++ b/test/Macros/macro_default_argument_source_location.swift
@@ -5,11 +5,11 @@

 // RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/syntax_macro_definitions.swift -g -no-toolchain-stdlib-rpath

-// RUN: %target-build-swift-dylib(%t/%target-library-name(WithMacroDefaultArg)) %S/Inputs/with_macro_default_arg_module.swift -module-name WithMacroDefaultArg -emit-module -emit-module-path %t/WithMacroDefaultArg.swiftmodule -load-plugin-library %t/%target-library-name(MacroDefinition) -enable-experimental-feature ExpressionMacroDefaultArguments -I %t -swift-version 5
+// RUN: %target-build-swift-dylib(%t/%target-library-name(WithMacroDefaultArg)) %S/Inputs/with_macro_default_arg_module.swift -module-name WithMacroDefaultArg -emit-module -emit-module-path %t/WithMacroDefaultArg.swiftmodule -load-plugin-library %t/%target-library-name(MacroDefinition) -I %t -swift-version 5

-// RUN: %target-build-swift-dylib(%t/%target-library-name(WithMacroDefaultArgInterface)) %S/Inputs/with_macro_default_arg_interface.swift -module-name WithMacroDefaultArgInterface -enable-library-evolution -emit-module-interface-path %t/WithMacroDefaultArgInterface.swiftinterface -load-plugin-library %t/%target-library-name(MacroDefinition) -enable-experimental-feature ExpressionMacroDefaultArguments -I %t -swift-version 5
+// RUN: %target-build-swift-dylib(%t/%target-library-name(WithMacroDefaultArgInterface)) %S/Inputs/with_macro_default_arg_interface.swift -module-name WithMacroDefaultArgInterface -enable-library-evolution -emit-module-interface-path %t/WithMacroDefaultArgInterface.swiftinterface -load-plugin-library %t/%target-library-name(MacroDefinition) -I %t -swift-version 5

-// RUN: %target-build-swift -enable-experimental-feature ExpressionMacroDefaultArguments -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %S/Inputs/with_macro_default_arg_same_module.swift %s -o %t/main -module-name MacroUser -emit-tbd -emit-tbd-path %t/MacroUser.tbd -I %t -L %t %target-rpath(%t) -lWithMacroDefaultArg -lWithMacroDefaultArgInterface
+// RUN: %target-build-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %S/Inputs/with_macro_default_arg_same_module.swift %s -o %t/main -module-name MacroUser -emit-tbd -emit-tbd-path %t/MacroUser.tbd -I %t -L %t %target-rpath(%t) -lWithMacroDefaultArg -lWithMacroDefaultArgInterface
 // RUN: %target-codesign %t/main
 // RUN: %target-run %t/main | %FileCheck %s

--- a/test/Macros/macro_default_argument_swiftinterface.swift
+++ b/test/Macros/macro_default_argument_swiftinterface.swift
@@ -5,9 +5,9 @@

 // RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/syntax_macro_definitions.swift -g -no-toolchain-stdlib-rpath

-// RUN: %target-build-swift-dylib(%t/%target-library-name(Interface)) %S/macro_default_argument_library.swift -module-name Interface -enable-library-evolution -emit-module-interface-path %t/Interface.swiftinterface -load-plugin-library %t/%target-library-name(MacroDefinition) -enable-experimental-feature ExpressionMacroDefaultArguments -I %t -swift-version 5
+// RUN: %target-build-swift-dylib(%t/%target-library-name(Interface)) %S/macro_default_argument_library.swift -module-name Interface -enable-library-evolution -emit-module-interface-path %t/Interface.swiftinterface -load-plugin-library %t/%target-library-name(MacroDefinition) -I %t -swift-version 5

-// RUN: %target-build-swift -enable-experimental-feature ExpressionMacroDefaultArguments -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -o %t/main -module-name MacroUser -emit-tbd -emit-tbd-path %t/MacroUser.tbd -I %t -L %t %target-rpath(%t) -lInterface
+// RUN: %target-build-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -o %t/main -module-name MacroUser -emit-tbd -emit-tbd-path %t/MacroUser.tbd -I %t -L %t %target-rpath(%t) -lInterface
 // RUN: %target-codesign %t/main
 // RUN: %target-run %t/main | %FileCheck %s

--- a/test/ModuleInterface/unbuildable.swift
+++ b/test/ModuleInterface/unbuildable.swift
@@ -22,7 +22,7 @@
 // RUN: not %target-swift-frontend -typecheck-module-from-interface %t/UnbuildableCurrent.swiftinterface 2>&1 | %FileCheck -check-prefixes=ALL,CURRENT-VERIFY %s
 // RUN: not %target-swift-frontend -typecheck-module-from-interface %t/UnbuildableFuture.swiftinterface 2>&1 | %FileCheck -check-prefixes=ALL,FUTURE-VERIFY %s

-// ALL: Unbuildable{{[^.]+}}.swiftinterface:{{[0-9]+}}:{{[0-9]+}}: error: non-built-in macro cannot be used as default argument
+// ALL: Unbuildable{{[^.]+}}.swiftinterface:{{[0-9]+}}:{{[0-9]+}}: error: no macro named 'somethingYouveNeverHeardOf'

 #if CURRENT
 import UnbuildableCurrent