From ee0488baef8f497a7b7f2d17f58649c3e1cf33ea Mon Sep 17 00:00:00 2001
From: Lukas Pistrol <lukas@pistrol.com>
Date: Thu, 15 Jun 2023 08:52:58 +0200
Subject: [PATCH] add type validation and protocol conformance

---
 .../SFSymbolsDiagnostic.swift                 |  6 +++
 .../SFSymbolsMacroImpl/SFSymbolsMacro.swift   | 21 ++++++++-
 .../SFSymbolsMacroTests.swift                 | 44 +++++++++++++++++++
 3 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/Sources/SFSymbolsMacroImpl/SFSymbolsDiagnostic.swift b/Sources/SFSymbolsMacroImpl/SFSymbolsDiagnostic.swift
index b38b9ce..901672d 100644
--- a/Sources/SFSymbolsMacroImpl/SFSymbolsDiagnostic.swift
+++ b/Sources/SFSymbolsMacroImpl/SFSymbolsDiagnostic.swift
@@ -8,6 +8,8 @@
 import SwiftDiagnostics
 
 enum SFSymbolDiagnostic: DiagnosticMessage {
+    case notAnEnum
+    case missingStringProtocolConformance(symbol: String)
     case noValidSFSymbol(symbol: String)
 
     var severity: DiagnosticSeverity { return .error }
@@ -16,6 +18,10 @@ enum SFSymbolDiagnostic: DiagnosticMessage {
         switch self {
         case .noValidSFSymbol(let symbol):
             "\"\(symbol)\" is not a valid SF Symbol."
+        case .notAnEnum:
+            "Macro \"@SFSymbol\" can only be applied to enums."
+        case .missingStringProtocolConformance(let symbol):
+            "Enum \"\(symbol)\" needs conformance to String protocol."
         }
     }
 
diff --git a/Sources/SFSymbolsMacroImpl/SFSymbolsMacro.swift b/Sources/SFSymbolsMacroImpl/SFSymbolsMacro.swift
index 071d4c7..0cb5e7b 100644
--- a/Sources/SFSymbolsMacroImpl/SFSymbolsMacro.swift
+++ b/Sources/SFSymbolsMacroImpl/SFSymbolsMacro.swift
@@ -21,7 +21,7 @@ public struct SFSymbolMacro: MemberMacro {
         providingMembersOf declaration: Declaration,
         in context: Context
     ) throws -> [DeclSyntax] {
-        try validateSymbolName(declaration)
+        try validate(declaration)
         return [
             """
             var image: Image {
@@ -54,7 +54,8 @@ public struct SFSymbolMacro: MemberMacro {
 
     // MARK: Helper Methods
 
-    private static func validateSymbolName(_ declaration: DeclGroupSyntax) throws {
+    private static func validate(_ declaration: DeclGroupSyntax) throws {
+        try validateStringProtocolInheritance(declaration)
         let members = declaration.memberBlock.members
         let cases = members.compactMap { $0.decl.as(EnumCaseDeclSyntax.self) }
         let ids = getIdentifiers(from: cases)
@@ -63,6 +64,22 @@ public struct SFSymbolMacro: MemberMacro {
         }
     }
 
+    private static func validateStringProtocolInheritance(_ declaration: DeclGroupSyntax) throws {
+        guard let enumDecl = declaration.as(EnumDeclSyntax.self) else {
+            throw DiagnosticsError(diagnostics: [
+                .init(node: Syntax(declaration), message: SFSymbolDiagnostic.notAnEnum)
+            ])
+        }
+        let identifier = enumDecl.identifier
+        guard enumDecl.inheritanceClause?.inheritedTypeCollection.contains(where: {
+            $0.typeName.as(SimpleTypeIdentifierSyntax.self)?.name.text == "String"
+        }) ?? false else {
+            throw DiagnosticsError(diagnostics: [
+                .init(node: Syntax(identifier), message: SFSymbolDiagnostic.missingStringProtocolConformance(symbol: identifier.text))
+            ])
+        }
+    }
+
     /// Gets either the rawValue (if available) or the identifier of the enum case.
     private static func getIdentifiers(from cases: [EnumCaseDeclSyntax]) -> [SymbolPair] {
         return cases.flatMap { enumCase in
diff --git a/Tests/SFSymbolsMacroTests/SFSymbolsMacroTests.swift b/Tests/SFSymbolsMacroTests/SFSymbolsMacroTests.swift
index d791ebc..5c36914 100644
--- a/Tests/SFSymbolsMacroTests/SFSymbolsMacroTests.swift
+++ b/Tests/SFSymbolsMacroTests/SFSymbolsMacroTests.swift
@@ -91,4 +91,48 @@ final class SFSymbolsMacroTests: XCTestCase {
             macros: testMacros
         )
     }
+
+    func testInvalidEnum() {
+        assertMacroExpansion(
+            """
+            @SFSymbol
+            enum Symbols {
+                case globe
+            }
+            """,
+            expandedSource:
+            """
+
+            enum Symbols {
+                case globe
+            }
+            """,
+            diagnostics: [
+                .init(message: "Enum \"Symbols\" needs conformance to String protocol.", line: 2, column: 6)
+            ],
+            macros: testMacros
+        )
+    }
+
+    func testInvalidType() {
+        assertMacroExpansion(
+            """
+            @SFSymbol
+            struct Symbols {
+                let xyz = "xyz"
+            }
+            """,
+            expandedSource:
+            """
+
+            struct Symbols {
+                let xyz = "xyz"
+            }
+            """,
+            diagnostics: [
+                .init(message: "Macro \"@SFSymbol\" can only be applied to enums.", line: 1, column: 1)
+            ],
+            macros: testMacros
+        )
+    }
 }