From bd5dc8d332eeb3fbfcec59cf713369b13dbbc76c Mon Sep 17 00:00:00 2001
From: Mateus Rodrigues <mateus.fr26@gmail.com>
Date: Wed, 11 Sep 2024 14:33:10 -0300
Subject: [PATCH 1/2] Add `buildFinalResult` to `CodeBlockItemListBuilder` to
 ensure newline between expressions

---
 .../ResultBuilderExtensions.swift             | 12 +++++++++
 .../CollectionNodeFlatteningTests.swift       | 27 +++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/Sources/SwiftSyntaxBuilder/ResultBuilderExtensions.swift b/Sources/SwiftSyntaxBuilder/ResultBuilderExtensions.swift
index cdd7f591342..237dec791a3 100644
--- a/Sources/SwiftSyntaxBuilder/ResultBuilderExtensions.swift
+++ b/Sources/SwiftSyntaxBuilder/ResultBuilderExtensions.swift
@@ -40,6 +40,18 @@ extension CodeBlockItemListBuilder {
   public static func buildExpression(_ expression: some Sequence<DeclSyntaxProtocol>) -> Component {
     buildExpression(expression.map { CodeBlockItemSyntax(item: .decl(DeclSyntax($0))) })
   }
+
+  public static func buildFinalResult(_ component: Component) -> CodeBlockItemListSyntax {
+    .init(
+      component.enumerated().map { (index, expression) in
+        if index > component.startIndex, !expression.leadingTrivia.contains(where: \.isNewline) {
+          return expression.with(\.leadingTrivia, .newline.merging(expression.leadingTrivia))
+        } else {
+          return expression
+        }
+      }
+    )
+  }
 }
 
 extension ConditionElementListBuilder {
diff --git a/Tests/SwiftSyntaxBuilderTest/CollectionNodeFlatteningTests.swift b/Tests/SwiftSyntaxBuilderTest/CollectionNodeFlatteningTests.swift
index e54c06ac721..a1e9c9a5cda 100644
--- a/Tests/SwiftSyntaxBuilderTest/CollectionNodeFlatteningTests.swift
+++ b/Tests/SwiftSyntaxBuilderTest/CollectionNodeFlatteningTests.swift
@@ -75,4 +75,31 @@ final class CollectionNodeFlatteningTests: XCTestCase {
       """
     )
   }
+
+  func test_FlattenCodeBlockItemListWithCodeBlockInterpolated() {
+    let block = CodeBlockItemListSyntax {
+      "let a = 1"
+      "let b = 2"
+      "let c = 3"
+    }
+
+    let buildable = CodeBlockItemListSyntax {
+      "let one = object.methodOne()"
+      "let two = object.methodTwo()"
+      "let three = {\(block)}()"
+    }
+
+    assertBuildResult(
+      buildable,
+      """
+      let one = object.methodOne()
+      let two = object.methodTwo()
+      let three = {
+          let a = 1
+          let b = 2
+          let c = 3
+      }()
+      """
+    )
+  }
 }

From 95f5aa69e87264e4881cddee0099b6670c474b89 Mon Sep 17 00:00:00 2001
From: Mateus Rodrigues <mateus.fr26@gmail.com>
Date: Wed, 11 Sep 2024 14:33:52 -0300
Subject: [PATCH 2/2] Replace `joined(separator:)` in `collapse` with custom
 logic to avoid adding unnecessary separators

---
 .../SwiftSyntaxMacroExpansion/MacroExpansion.swift   | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/Sources/SwiftSyntaxMacroExpansion/MacroExpansion.swift b/Sources/SwiftSyntaxMacroExpansion/MacroExpansion.swift
index b2f9d6bfa82..b3cd0d25e0a 100644
--- a/Sources/SwiftSyntaxMacroExpansion/MacroExpansion.swift
+++ b/Sources/SwiftSyntaxMacroExpansion/MacroExpansion.swift
@@ -528,5 +528,15 @@ public func collapse<Node: SyntaxProtocol>(
     break
   }
 
-  return expansions.joined(separator: separator)
+  // Join the expansions ensuring `separator` between them.
+  var collapsed = ""
+  for expansion in expansions {
+    if collapsed.isEmpty || expansion.hasPrefix(separator) {
+      collapsed.append(expansion)
+    } else {
+      collapsed.append(separator + expansion)
+    }
+  }
+
+  return collapsed
 }