Limit @Init(default:) to single variable bindings

Amidst tradeoffs needing careful consideration, I opted to restrict `@Init(default:)` to single variable bindings. Enabling it for multiple bindings in the future would be non-breaking. (Removing it in the future would be a breaking change.)
gohanlon · Dec 4, 2023 · b058368 · b058368
1 parent 537d967
commit b058368
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Showing 3 changed files with 122 additions and 53 deletions.
diff --git a/Sources/MemberwiseInitMacros/Macros/MemberwiseInitMacro.swift b/Sources/MemberwiseInitMacros/Macros/MemberwiseInitMacro.swift
@@ -174,16 +174,22 @@ public struct MemberwiseInitMacro: MemberMacro {
 
  var diagnostics = [Diagnostic]()
 
- if let customSettings, customSettings.label?.isInvalidSwiftLabel ?? false {
- diagnostics.append(customSettings.diagnosticOnLabelValue(message: .invalidSwiftLabel))
- } else if let customSettings,
- let label = customSettings.label,
- label != "_",
- variable.bindings.count > 1
- {
- diagnostics.append(
- customSettings.diagnosticOnLabel(message: .labelAppliedToMultipleBindings)
- )
+ if let customSettings = customSettings {
+ if customSettings.label?.isInvalidSwiftLabel ?? false {
+ diagnostics.append(customSettings.diagnosticOnLabelValue(message: .invalidSwiftLabel))
+ } else if let label = customSettings.label,
+ label != "_",
+ variable.bindings.count > 1
+ {
+ diagnostics.append(
+ customSettings.diagnosticOnLabel(message: .labelAppliedToMultipleBindings))
+ }
+
+ if customSettings.defaultValue != nil, variable.bindings.count > 1 {
+ diagnostics.append(
+ customSettings.diagnosticOnDefault(message: .defaultAppliedToMultipleBindings)
+ )
+ }
  }
 
  // TODO: repetition of logic for custom configuration logic
@@ -489,6 +495,15 @@ private struct VariableCustomSettings: Equatable {
  let type: TypeSyntax?
  let _syntaxNode: AttributeSyntax
 
+ func diagnosticOnDefault(message: MemberwiseInitMacroDiagnostic) -> Diagnostic {
+ let labelNode = self._syntaxNode
+ .arguments?
+ .as(LabeledExprListSyntax.self)?
+ .firstWhereLabel("default")
+
+ return diagnostic(node: labelNode ?? self._syntaxNode, message: message)
+ }
+
  func diagnosticOnLabel(message: MemberwiseInitMacroDiagnostic) -> Diagnostic {
  let labelNode = self._syntaxNode
  .arguments?

diff --git a/Sources/MemberwiseInitMacros/Macros/Support/Diagnostics.swift b/Sources/MemberwiseInitMacros/Macros/Support/Diagnostics.swift
@@ -2,6 +2,7 @@ import SwiftDiagnostics
 import SwiftSyntax
 
 enum MemberwiseInitMacroDiagnostic: Error, DiagnosticMessage {
+ case defaultAppliedToMultipleBindings
  case labelAppliedToMultipleBindings
  case labelConflictsWithProperty(String)
  case labelConflictsWithAnotherLabel(String)
@@ -12,6 +13,9 @@ enum MemberwiseInitMacroDiagnostic: Error, DiagnosticMessage {
 
  private var rawValue: String {
  switch self {
+ case .defaultAppliedToMultipleBindings:
+ ".defaultAppliedToMultipleBindings"
+
  case .labelAppliedToMultipleBindings:
  ".labelAppliedToMultipleBindings"
 
@@ -39,6 +43,9 @@ enum MemberwiseInitMacroDiagnostic: Error, DiagnosticMessage {
 
  var message: String {
  switch self {
+ case .defaultAppliedToMultipleBindings:
+ return "Custom 'default' can't be applied to multiple bindings"
+
  case .labelAppliedToMultipleBindings:
  return """
  Custom 'label' can't be applied to multiple bindings

diff --git a/Tests/MemberwiseInitTests/CustomInitDefaultTests.swift b/Tests/MemberwiseInitTests/CustomInitDefaultTests.swift
@@ -2,6 +2,8 @@ import MacroTesting
 import MemberwiseInitMacros
 import XCTest
 
+// TODO: Carefully consider whether to allow @Init(default:) to be applied to multiple bindings
+
 final class CustomInitDefaultTests: XCTestCase {
  override func invokeTest() {
  // NB: Waiting for swift-macro-testing PR to support explicit indentationWidth: https://github.com/pointfreeco/swift-macro-testing/pull/8
@@ -114,21 +116,30 @@ final class CustomInitDefaultTests: XCTestCase {
  @Init(default: 42) let x, y: Int
  }
  """
- } expansion: {
+ } diagnostics: {
  """
+ @MemberwiseInit
  struct S {
  @Init(default: 42) let x, y: Int
-
- internal init(
- x: Int = 42,
- y: Int = 42
- ) {
- self.x = x
- self.y = y
- }
+ ┬──────────
+ ╰─ 🛑 Custom 'default' can't be applied to multiple bindings
  }
  """
  }
+ // } expansion: {
+ // """
+ // struct S {
+ // @Init(default: 42) let x, y: Int
+ //
+ // internal init(
+ // x: Int = 42,
+ // y: Int = 42
+ // ) {
+ // self.x = x
+ // self.y = y
+ // }
+ // }
+ // """
  }
 
  func testVarWithMultipleBindings() {
@@ -139,21 +150,30 @@ final class CustomInitDefaultTests: XCTestCase {
  @Init(default: 42) var x, y: Int
  }
  """
- } expansion: {
+ } diagnostics: {
  """
+ @MemberwiseInit
  struct S {
  @Init(default: 42) var x, y: Int
-
- internal init(
- x: Int = 42,
- y: Int = 42
- ) {
- self.x = x
- self.y = y
- }
+ ┬──────────
+ ╰─ 🛑 Custom 'default' can't be applied to multiple bindings
  }
  """
  }
+ // } expansion: {
+ // """
+ // struct S {
+ // @Init(default: 42) var x, y: Int
+ //
+ // internal init(
+ // x: Int = 42,
+ // y: Int = 42
+ // ) {
+ // self.x = x
+ // self.y = y
+ // }
+ // }
+ // """
  }
 
  func testLetWithFirstBindingInitialized() {
@@ -164,19 +184,28 @@ final class CustomInitDefaultTests: XCTestCase {
  @Init(default: 42) let x = 0, y: Int
  }
  """
- } expansion: {
+ } diagnostics: {
  """
+ @MemberwiseInit
  struct S {
  @Init(default: 42) let x = 0, y: Int
-
- internal init(
- y: Int = 42
- ) {
- self.y = y
- }
+ ┬──────────
+ ╰─ 🛑 Custom 'default' can't be applied to multiple bindings
  }
  """
  }
+ // } expansion: {
+ // """
+ // struct S {
+ // @Init(default: 42) let x = 0, y: Int
+ //
+ // internal init(
+ // y: Int = 42
+ // ) {
+ // self.y = y
+ // }
+ // }
+ // """
  }
 
  func testVarWithFirstBindingInitialized() {
@@ -187,21 +216,30 @@ final class CustomInitDefaultTests: XCTestCase {
  @Init(default: 42) var x = 0, y: Int
  }
  """
- } expansion: {
+ } diagnostics: {
  """
+ @MemberwiseInit
  struct S {
  @Init(default: 42) var x = 0, y: Int
-
- internal init(
- x: Int = 0,
- y: Int = 42
- ) {
- self.x = x
- self.y = y
- }
+ ┬──────────
+ ╰─ 🛑 Custom 'default' can't be applied to multiple bindings
  }
  """
  }
+ // } expansion: {
+ // """
+ // struct S {
+ // @Init(default: 42) var x = 0, y: Int
+ //
+ // internal init(
+ // x: Int = 0,
+ // y: Int = 42
+ // ) {
+ // self.x = x
+ // self.y = y
+ // }
+ // }
+ // """
  }
 
  func testLetWithRaggedBindings_SucceedsWithInvalidCode() {
@@ -212,20 +250,29 @@ final class CustomInitDefaultTests: XCTestCase {
  @Init(default: 42) let x: Int, isOn: Bool
  }
  """
- } expansion: {
+ } diagnostics: {
  """
+ @MemberwiseInit
  struct S {
  @Init(default: 42) let x: Int, isOn: Bool
-
- internal init(
- x: Int = 42,
- isOn: Bool = 42
- ) {
- self.x = x
- self.isOn = isOn
- }
+ ┬──────────
+ ╰─ 🛑 Custom 'default' can't be applied to multiple bindings
  }
  """
  }
+ // } expansion: {
+ // """
+ // struct S {
+ // @Init(default: 42) let x: Int, isOn: Bool
+ //
+ // internal init(
+ // x: Int = 42,
+ // isOn: Bool = 42
+ // ) {
+ // self.x = x
+ // self.isOn = isOn
+ // }
+ // }
+ // """
  }
 }