Improve diagnostics for macro annotated members

Sources/MMIO/Register.swift

@@ -12,7 +12,7 @@
 /// A container type referencing of a region of memory whose layout is defined
 /// by another type.
 public struct Register<Value> where Value: RegisterValue {
-  public let unsafeAddress: UInt
+  public var unsafeAddress: UInt
 
   #if FEATURE_INTERPOSABLE
   public var interposer: (any MMIOInterposer)?

Sources/MMIOMacros/SwiftSyntaxExtensions/Diagnostics/ErrorDiagnostic.swift

@@ -36,9 +36,4 @@ extension ErrorDiagnostic {
   static func internalError() -> Self {
     .init("'\(Macro.signature)' internal error. \(Self.internalErrorSuffix)")
   }
-
-  // Declaration Member Errors
-  static func onlyMemberVarDecls() -> Self {
-    .init("'\(Macro.signature)' type can only contain properties")
-  }
 }

Sources/MMIOMacros/SwiftSyntaxExtensions/Diagnostics/MacroContext.swift

@@ -38,6 +38,25 @@ where Macro: ParsableMacro, Context: MacroExpansionContext {
         fixIts: fixIts))
     return ExpansionError()
   }
+
+  func error(
+    at node: some SyntaxProtocol,
+    message: ErrorDiagnostic<Macro>,
+    highlights: [Syntax]? = nil,
+    notes: [Note] = [],
+    fixIts: [FixIt]
+  ) -> ExpansionError {
+    self.context.diagnose(
+      .init(
+        node: node,
+        position: nil,
+        message: message,
+        highlights: highlights,
+        notes: notes,
+        fixIts: fixIts))
+    return ExpansionError()
+  }
+
 }
 
 extension MacroContext where Context == SuppressionContext {

Sources/MMIOMacros/SwiftSyntaxExtensions/WithAttributesSyntax.swift

@@ -43,28 +43,37 @@ extension WithAttributesSyntax {
         matches.append(.init(attribute: attribute, macroType: macroType))
       }
     }
-    guard matches.count == 1 else {
-      switch macros.count {
-      case 1:
-        throw context.error(
-          at: self,
-          message: .expectedMemberAnnotatedWithMacro(macros),
-          fixIts: .insertMacro(node: self, macros[0]))
-      default:
-        throw context.error(
-          at: self,
-          message: .expectedMemberAnnotatedWithMacro(macros))
-      }
+
+    switch matches.count {
+    case 0:
+      throw context.error(
+        at: self,
+        message: .expectedMemberAnnotatedWithMacro(macros),
+        fixIts: macros.map { .insertMacro(node: self, $0) })
+    case 1:
+      return matches[0]
+    default:
+      throw context.error(
+        at: self,
+        message: .expectedMemberAnnotatedWithMacro(macros))
     }
-    return matches[0]
   }
 }
 
 extension ErrorDiagnostic {
   static func expectedMemberAnnotatedWithMacro(
     _ macros: [any (ParsableMacro.Type)]
   ) -> Self {
-    guard macros.count == 1 else {
+    switch macros.count {
+    case 0:
+      preconditionFailure("Expected at at least one macro")
+    case 1:
+      return .init(
+        """
+        '\(Macro.signature)' type member must be annotated with \
+        '\(macros[0].signature)'
+        """)
+    default:
       guard let last = macros.last else { fatalError() }
       let optionsPrefix =
         macros
@@ -75,15 +84,10 @@ extension ErrorDiagnostic {
 
       return .init(
         """
-        '\(Macro.signature)' type member must be annotated with exactly one \
-        macro of \(options)
+        '\(Macro.signature)' type member must be annotated with exactly one of \
+        \(options)
         """)
     }
-    return .init(
-      """
-      '\(Macro.signature)' type member must be annotated with \
-      '\(macros[0].signature)' macro
-      """)
   }
 }
 

Tests/MMIOMacrosTests/Macros/RegisterMacroTests.swift

@@ -105,17 +105,35 @@ final class RegisterMacroTests: XCTestCase {
           message: ErrorDiagnostic.expectedMemberAnnotatedWithMacro(bitFieldMacros).message,
           line: 3,
           column: 3,
-          highlight: "var v1: Int"),
+          highlight: "var v1: Int",
+          fixIts: [
+            .init(message: "Insert '@Reserved(bits:)' macro"),
+            .init(message: "Insert '@ReadWrite(bits:as:)' macro"),
+            .init(message: "Insert '@ReadOnly(bits:as:)' macro"),
+            .init(message: "Insert '@WriteOnly(bits:as:)' macro"),
+          ]),
         .init(
           message: ErrorDiagnostic.expectedMemberAnnotatedWithMacro(bitFieldMacros).message,
           line: 4,
           column: 3,
-          highlight: "@OtherAttribute var v2: Int"),
+          highlight: "@OtherAttribute var v2: Int",
+          fixIts: [
+            .init(message: "Insert '@Reserved(bits:)' macro"),
+            .init(message: "Insert '@ReadWrite(bits:as:)' macro"),
+            .init(message: "Insert '@ReadOnly(bits:as:)' macro"),
+            .init(message: "Insert '@WriteOnly(bits:as:)' macro"),
+          ]),
         .init(
           message: ErrorDiagnostic.expectedMemberAnnotatedWithMacro(bitFieldMacros).message,
           line: 5,
           column: 3,
-          highlight: "var v3: Int { willSet {} }"),
+          highlight: "var v3: Int { willSet {} }",
+          fixIts: [
+            .init(message: "Insert '@Reserved(bits:)' macro"),
+            .init(message: "Insert '@ReadWrite(bits:as:)' macro"),
+            .init(message: "Insert '@ReadOnly(bits:as:)' macro"),
+            .init(message: "Insert '@WriteOnly(bits:as:)' macro"),
+          ]),
       ],
       macros: Self.macros,
       indentationWidth: Self.indentationWidth)