Exclude constant variables from struct members

Author: Alexander Schmutz

Sources/StructBuilderClient/main.swift

@@ -50,3 +50,9 @@ class MyClass {
         self.m1 = m1
     }
 }
+
+@Buildable
+struct MyStruct {
+    let m1: String
+    let fix: String = ""
+}

Sources/StructBuilderMacro/StructAndClass/Helper/ExtractMembers.swift

@@ -13,6 +13,7 @@ func extractMembersFrom(_ memberBlockItemList: MemberBlockItemListSyntax) -> [St
         .filter(\.isStoredProperty)
         .filter { !hasStaticModifier($0) }
         .filter { !hasPrivateModifier($0) }
+        .filter { !isConstant($0) }
         .compactMap {
             guard let patternBinding = $0.bindings.first else { return nil }
             guard let identifier = getIdentifierFromMember(patternBinding) else { return nil }
@@ -37,6 +38,11 @@ private func hasPrivateModifier(_ variable: VariableDeclSyntax) -> Bool {
     variable.modifiers.contains(where: { $0.name.text.contains("private") })
 }
 
+private func isConstant(_ variable: VariableDeclSyntax) -> Bool {
+    variable.bindingSpecifier.text == "let"
+        && variable.bindings.first?.initializer != nil
+}
+
 // SOURCE: https://github.com/apple/swift-syntax/tree/main/Examples
 private extension VariableDeclSyntax {
     /// Determine whether this variable has the syntax of a stored property.

Tests/StructBuilderMacroTests/BuildableStructTests.swift

@@ -285,6 +285,36 @@ class BuildableStructTests: XCTestCase {
         )
     }
 
+    func test_should_ignore_constant_variables() {
+        assertMacroExpansion(
+            """
+            @Buildable
+            struct MyObject {
+                let m1: String?
+                let myConstant: String = ""
+            }
+            """,
+            expandedSource: """
+
+            struct MyObject {
+                let m1: String?
+                let myConstant: String = ""
+            }
+
+            struct MyObjectBuilder {
+                var m1: String?
+
+                func build() -> MyObject {
+                    return MyObject(
+                        m1: m1
+                    )
+                }
+            }
+            """,
+            macros: testMacros
+        )
+    }
+
     func test_should_set_correct_default_values_for_defined_types() {
         assertMacroExpansion(
             """