Merge pull request #2187 from ahoppen/ahoppen/accessor-return-empty-array

Don’t add any accessors if accessor macro returned an empty array

Author: ahoppen

Sources/SwiftSyntaxMacroExpansion/MacroSystem.swift

@@ -267,7 +267,8 @@ private func expandAccessorMacroWithoutExistingAccessors(
       conformanceList: nil,
       in: context,
       indentationWidth: indentationWidth
-    )
+    ),
+    !expanded.isEmpty
   else {
     return nil
   }

Tests/SwiftSyntaxMacroExpansionTest/AccessorMacroTests.swift

@@ -18,7 +18,9 @@
 // macros are invoked.                                                      //
 //==========================================================================//
 
+import SwiftDiagnostics
 import SwiftSyntax
+import SwiftSyntaxMacroExpansion
 import SwiftSyntaxMacros
 import SwiftSyntaxMacrosTestSupport
 import XCTest
@@ -261,4 +263,61 @@ final class AccessorMacroTests: XCTestCase {
       indentationWidth: indentationWidth
     )
   }
+
+  func testEmpty() {
+    struct TestMacro: AccessorMacro {
+      static func expansion(
+        of node: AttributeSyntax,
+        providingAccessorsOf declaration: some DeclSyntaxProtocol,
+        in context: some MacroExpansionContext
+      ) throws -> [AccessorDeclSyntax] {
+        return []
+      }
+    }
+
+    // The compiler will reject this with
+    // 'Expansion of macro 'Test()' did not produce a non-observing accessor'
+    // We consider this a semantic error because swift-syntax doesn't have
+    // knowledge about which accessors are observing and which ones aren't.
+    assertMacroExpansion(
+      "@Test var x: Int",
+      expandedSource: "var x: Int",
+      macros: ["Test": TestMacro.self]
+    )
+
+    assertMacroExpansion(
+      "@Test var x: Int { 1 }",
+      expandedSource: "var x: Int { 1 }",
+      macros: ["Test": TestMacro.self]
+    )
+  }
+
+  func testEmitErrorFromMacro() {
+    struct TestMacro: AccessorMacro {
+      static func expansion(
+        of node: AttributeSyntax,
+        providingAccessorsOf declaration: some DeclSyntaxProtocol,
+        in context: some MacroExpansionContext
+      ) throws -> [AccessorDeclSyntax] {
+        context.diagnose(Diagnostic(node: node, message: MacroExpansionErrorMessage("test")))
+        return []
+      }
+    }
+
+    assertMacroExpansion(
+      "@Test var x: Int",
+      expandedSource: "var x: Int",
+      diagnostics: [
+        DiagnosticSpec(message: "test", line: 1, column: 1)
+      ],
+      macros: ["Test": TestMacro.self]
+    )
+
+    assertMacroExpansion(
+      "@Test var x: Int { 1 }",
+      expandedSource: "var x: Int { 1 }",
+      diagnostics: [DiagnosticSpec(message: "test", line: 1, column: 1)],
+      macros: ["Test": TestMacro.self]
+    )
+  }
 }

Tests/SwiftSyntaxMacroExpansionTest/CodeItemMacroTests.swift

@@ -133,4 +133,23 @@ final class CodeItemMacroTests: XCTestCase {
       indentationWidth: indentationWidth
     )
   }
+
+  func testEmpty() {
+    struct TestMacro: CodeItemMacro {
+      static func expansion(
+        of node: some FreestandingMacroExpansionSyntax,
+        in context: some MacroExpansionContext
+      ) throws -> [CodeBlockItemSyntax] {
+        return []
+      }
+    }
+
+    assertMacroExpansion(
+      "#test",
+      expandedSource: "",
+      macros: [
+        "test": TestMacro.self
+      ]
+    )
+  }
 }

Tests/SwiftSyntaxMacroExpansionTest/DeclarationMacroTests.swift

@@ -389,4 +389,22 @@ final class DeclarationMacroTests: XCTestCase {
     )
   }
 
+  func testEmpty() {
+    struct TestMacro: DeclarationMacro {
+      static func expansion(
+        of node: some FreestandingMacroExpansionSyntax,
+        in context: some MacroExpansionContext
+      ) throws -> [DeclSyntax] {
+        return []
+      }
+    }
+
+    assertMacroExpansion(
+      "#test",
+      expandedSource: "",
+      macros: [
+        "test": TestMacro.self
+      ]
+    )
+  }
 }

Tests/SwiftSyntaxMacroExpansionTest/ExtensionMacroTests.swift

@@ -106,4 +106,26 @@ final class ExtensionMacroTests: XCTestCase {
       indentationWidth: indentationWidth
     )
   }
+
+  func testEmpty() {
+    struct TestMacro: ExtensionMacro {
+      static func expansion(
+        of node: AttributeSyntax,
+        attachedTo declaration: some DeclGroupSyntax,
+        providingExtensionsOf type: some TypeSyntaxProtocol,
+        conformingTo protocols: [TypeSyntax],
+        in context: some MacroExpansionContext
+      ) throws -> [ExtensionDeclSyntax] {
+        return []
+      }
+    }
+
+    assertMacroExpansion(
+      "@Test struct Foo {}",
+      expandedSource: "struct Foo {}",
+      macros: [
+        "Test": TestMacro.self
+      ]
+    )
+  }
 }

Tests/SwiftSyntaxMacroExpansionTest/MemberAttributeMacroTests.swift

@@ -354,4 +354,48 @@ final class MemberAttributeMacroTests: XCTestCase {
     )
   }
 
+  func testEmpty() {
+    struct TestMacro: MemberAttributeMacro {
+      static func expansion(
+        of node: AttributeSyntax,
+        attachedTo declaration: some DeclGroupSyntax,
+        providingAttributesFor member: some DeclSyntaxProtocol,
+        in context: some MacroExpansionContext
+      ) throws -> [AttributeSyntax] {
+        return []
+      }
+    }
+
+    assertMacroExpansion(
+      """
+      @Test
+      struct Foo {
+        var x: Int
+      }
+      """,
+      expandedSource: """
+        struct Foo {
+          var x: Int
+        }
+        """,
+      macros: [
+        "Test": TestMacro.self
+      ]
+    )
+
+    assertMacroExpansion(
+      """
+      @Test
+      struct Foo {
+      }
+      """,
+      expandedSource: """
+        struct Foo {
+        }
+        """,
+      macros: [
+        "Test": TestMacro.self
+      ]
+    )
+  }
 }

Tests/SwiftSyntaxMacroExpansionTest/MemberMacroTests.swift

@@ -255,4 +255,48 @@ final class MemberMacroTests: XCTestCase {
     )
   }
 
+  func testEmpty() {
+    struct TestMacro: MemberMacro {
+      static func expansion(
+        of node: AttributeSyntax,
+        providingMembersOf declaration: some DeclGroupSyntax,
+        conformingTo protocols: [TypeSyntax],
+        in context: some MacroExpansionContext
+      ) throws -> [DeclSyntax] {
+        return []
+      }
+    }
+
+    assertMacroExpansion(
+      """
+      @Test
+      struct Foo {
+        var x: Int
+      }
+      """,
+      expandedSource: """
+        struct Foo {
+          var x: Int
+        }
+        """,
+      macros: [
+        "Test": TestMacro.self
+      ]
+    )
+
+    assertMacroExpansion(
+      """
+      @Test
+      struct Foo {
+      }
+      """,
+      expandedSource: """
+        struct Foo {
+        }
+        """,
+      macros: [
+        "Test": TestMacro.self
+      ]
+    )
+  }
 }

Tests/SwiftSyntaxMacroExpansionTest/PeerMacroTests.swift

@@ -173,4 +173,24 @@ final class PeerMacroTests: XCTestCase {
       macros: ["Test": TestMacro.self]
     )
   }
+
+  func testEmpty() {
+    struct TestMacro: PeerMacro {
+      static func expansion(
+        of node: AttributeSyntax,
+        providingPeersOf declaration: some DeclSyntaxProtocol,
+        in context: some MacroExpansionContext
+      ) throws -> [DeclSyntax] {
+        return []
+      }
+    }
+
+    assertMacroExpansion(
+      "@Test var x: Int",
+      expandedSource: "var x: Int",
+      macros: [
+        "Test": TestMacro.self
+      ]
+    )
+  }
 }