Add Inline temp variable code action

Sources/SwiftLanguageService/CodeActions/InlineTempVariable.swift

@@ -0,0 +1,215 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2026 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+@_spi(SourceKitLSP) import LanguageServerProtocol
+import SourceKitLSP
+import SwiftSyntax
+
+/// A code action that inlines a temporary variable by replacing all references
+/// to it with its initializer expression, then removing the declaration.
+///
+/// The action is offered when the cursor is on a `let` or `var` declaration
+/// with a single binding that has an initializer and no type annotation.
+///
+/// **Before:**
+/// ```swift
+/// let basePrice = item.price
+/// let total = basePrice * quantity
+/// ```
+///
+/// **After:**
+/// ```swift
+/// let total = item.price * quantity
+/// ```
+struct InlineTempVariable: SyntaxCodeActionProvider {
+  static func codeActions(in scope: SyntaxCodeActionScope) -> [CodeAction] {
+    // Find the variable declaration the cursor is on.
+    guard let varDecl = scope.innermostNodeContainingRange?.findParentOfSelf(
+      ofType: VariableDeclSyntax.self,
+      stoppingIf: { $0.is(CodeBlockSyntax.self) || $0.is(MemberBlockSyntax.self) }
+    ) else {
+      return []
+    }
+
+    // Only support single-binding declarations.
+    guard varDecl.bindings.count == 1, let binding = varDecl.bindings.first else {
+      return []
+    }
+
+    // Must have a simple identifier pattern and an initializer.
+    guard let pattern = binding.pattern.as(IdentifierPatternSyntax.self),
+      let initializer = binding.initializer?.value
+    else {
+      return []
+    }
+
+    // Don't inline if there's a type annotation — the user likely wants it explicit.
+    if binding.typeAnnotation != nil {
+      return []
+    }
+
+    let variableName = pattern.identifier.text
+
+    // Find the parent code block that contains this declaration.
+    guard let codeBlockItem = varDecl.parent?.as(CodeBlockItemSyntax.self),
+      let codeBlockItemList = codeBlockItem.parent?.as(CodeBlockItemListSyntax.self)
+    else {
+      return []
+    }
+
+    // Find the index of this declaration in the code block.
+    guard let declIndex = codeBlockItemList.firstIndex(where: { $0.id == codeBlockItem.id }) else {
+      return []
+    }
+
+    // Collect all statements after the declaration.
+    let subsequentStatements = codeBlockItemList[codeBlockItemList.index(after: declIndex)...]
+
+    // Find all references to the variable in subsequent statements.
+    let references = findReferences(to: variableName, in: Array(subsequentStatements))
+
+    // Only offer the action if the variable is actually used.
+    if references.isEmpty {
+      return []
+    }
+
+    // Don't inline if the variable is used as an inout argument or is reassigned.
+    for ref in references {
+      if isInoutArgument(ref) || isAssignmentTarget(ref) {
+        return []
+      }
+    }
+
+    // Build text edits: replace each reference with the initializer, then remove the declaration.
+    var textEdits: [TextEdit] = []
+
+    // For each reference, replace the identifier with the initializer expression.
+    let initializerText = initializer.description.trimmingCharacters(in: .whitespaces)
+
+    // Determine if we need parentheses around the inlined expression.
+    let needsParens = initializerNeedsParentheses(initializer)
+    let replacementText = needsParens ? "(\(initializerText))" : initializerText
+
+    for ref in references {
+      let startPos = scope.snapshot.position(of: ref.positionAfterSkippingLeadingTrivia)
+      let endPos = scope.snapshot.position(of: ref.endPositionBeforeTrailingTrivia)
+      textEdits.append(
+        TextEdit(
+          range: startPos..<endPos,
+          newText: replacementText
+        )
+      )
+    }
+
+    // Remove the entire declaration statement including trailing newline.
+    let declStart = scope.snapshot.position(of: codeBlockItem.positionAfterSkippingLeadingTrivia)
+    let declEnd: Position
+    let nextIndex = codeBlockItemList.index(after: declIndex)
+    if nextIndex < codeBlockItemList.endIndex {
+      declEnd = scope.snapshot.position(of: codeBlockItemList[nextIndex].positionAfterSkippingLeadingTrivia)
+    } else {
+      declEnd = scope.snapshot.position(of: codeBlockItem.endPositionBeforeTrailingTrivia)
+    }
+
+    textEdits.append(
+      TextEdit(
+        range: declStart..<declEnd,
+        newText: ""
+      )
+    )
+
+    return [
+      CodeAction(
+        title: "Inline '\(variableName)'",
+        kind: .refactorInline,
+        edit: WorkspaceEdit(
+          changes: [
+            scope.snapshot.uri: textEdits
+          ]
+        )
+      )
+    ]
+  }
+}
+
+// MARK: - Helpers
+
+/// Finds all `DeclReferenceExprSyntax` nodes that reference the given variable name.
+private func findReferences(
+  to variableName: String,
+  in statements: [CodeBlockItemSyntax]
+) -> [DeclReferenceExprSyntax] {
+  var references: [DeclReferenceExprSyntax] = []
+  for statement in statements {
+    let collector = ReferenceCollector(variableName: variableName)
+    collector.walk(statement)
+    references.append(contentsOf: collector.references)
+  }
+  return references
+}
+
+private class ReferenceCollector: SyntaxVisitor {
+  let variableName: String
+  var references: [DeclReferenceExprSyntax] = []
+
+  init(variableName: String) {
+    self.variableName = variableName
+    super.init(viewMode: .sourceAccurate)
+  }
+
+  override func visit(_ node: DeclReferenceExprSyntax) -> SyntaxVisitorContinueKind {
+    if node.baseName.text == variableName && node.argumentNames == nil {
+      references.append(node)
+    }
+    return .visitChildren
+  }
+}
+
+/// Checks if the given reference is used as an `&variable` inout argument.
+private func isInoutArgument(_ ref: DeclReferenceExprSyntax) -> Bool {
+  return ref.parent?.is(InOutExprSyntax.self) == true
+}
+
+/// Checks if the given reference is the target of an assignment.
+private func isAssignmentTarget(_ ref: DeclReferenceExprSyntax) -> Bool {
+  guard let infixExpr = ref.parent?.as(InfixOperatorExprSyntax.self) else {
+    return false
+  }
+  // Check if this ref is on the left side and the operator is assignment.
+  if infixExpr.leftOperand.as(DeclReferenceExprSyntax.self)?.id == ref.id,
+    infixExpr.operator.as(AssignmentExprSyntax.self) != nil
+  {
+    return true
+  }
+  return false
+}
+
+/// Determines if the initializer expression needs parentheses when inlined
+/// to avoid changing the meaning of the code.
+///
+/// For example, inlining `let x = a + b` into `x * c` should produce
+/// `(a + b) * c`, not `a + b * c`.
+private func initializerNeedsParentheses(_ expr: ExprSyntax) -> Bool {
+  // Binary operations, ternary expressions, try/await, and closures
+  // generally need parentheses when inlined.
+  if expr.is(InfixOperatorExprSyntax.self)
+    || expr.is(TernaryExprSyntax.self)
+    || expr.is(TryExprSyntax.self)
+    || expr.is(AwaitExprSyntax.self)
+    || expr.is(AsExprSyntax.self)
+    || expr.is(IsExprSyntax.self)
+  {
+    return true
+  }
+  return false
+}

Sources/SwiftLanguageService/CodeActions/SyntaxCodeActions.swift

@@ -21,6 +21,7 @@ let allSyntaxCodeActions: [any SyntaxCodeActionProvider.Type] = {
     ApplyDeMorganLaw.self,
     ConvertComputedPropertyToZeroParameterFunction.self,
     ConvertIfLetToGuard.self,
+    InlineTempVariable.self,
     ConvertIntegerLiteral.self,
     ConvertJSONToCodableStruct.self,
     ConvertStringConcatenationToStringInterpolation.self,

Tests/SourceKitLSPTests/CodeActionTests.swift

@@ -1835,6 +1835,88 @@ final class CodeActionTests: SourceKitLSPTestCase {
     }
   }
 
+  func testInlineTempVariable() async throws {
+    let testClient = try await TestSourceKitLSPClient(capabilities: clientCapabilitiesWithCodeActionSupport)
+    let uri = DocumentURI(for: .swift, testName: #function)
+    let positions = testClient.openDocument(
+      """
+      func example() {
+        1️⃣let basePrice = item.price
+        let total = basePrice * quantity
+      }
+      """,
+      uri: uri
+    )
+
+    let result = try await testClient.send(
+      CodeActionRequest(
+        range: Range(positions["1️⃣"]),
+        context: .init(),
+        textDocument: TextDocumentIdentifier(uri)
+      )
+    )
+    let codeActions = try XCTUnwrap(result?.codeActions)
+    let inlineAction = try XCTUnwrap(codeActions.first { $0.title == "Inline 'basePrice'" })
+    XCTAssertEqual(inlineAction.kind, .refactorInline)
+
+    // Verify the edit replaces the reference and removes the declaration.
+    let edits = try XCTUnwrap(inlineAction.edit?.changes?[uri])
+    XCTAssertEqual(edits.count, 2)
+    XCTAssert(edits.contains { $0.newText == "item.price" })
+    XCTAssert(edits.contains { $0.newText == "" })
+  }
+
+  func testInlineTempVariableWithParentheses() async throws {
+    let testClient = try await TestSourceKitLSPClient(capabilities: clientCapabilitiesWithCodeActionSupport)
+    let uri = DocumentURI(for: .swift, testName: #function)
+    let positions = testClient.openDocument(
+      """
+      func example() {
+        1️⃣let offset = a + b
+        let result = offset * c
+      }
+      """,
+      uri: uri
+    )
+
+    let result = try await testClient.send(
+      CodeActionRequest(
+        range: Range(positions["1️⃣"]),
+        context: .init(),
+        textDocument: TextDocumentIdentifier(uri)
+      )
+    )
+    let codeActions = try XCTUnwrap(result?.codeActions)
+    let inlineAction = try XCTUnwrap(codeActions.first { $0.title == "Inline 'offset'" })
+
+    let edits = try XCTUnwrap(inlineAction.edit?.changes?[uri])
+    XCTAssert(edits.contains { $0.newText == "(a + b)" })
+  }
+
+  func testInlineTempVariableNotOfferedForUnusedVariable() async throws {
+    let testClient = try await TestSourceKitLSPClient(capabilities: clientCapabilitiesWithCodeActionSupport)
+    let uri = DocumentURI(for: .swift, testName: #function)
+    let positions = testClient.openDocument(
+      """
+      func example() {
+        1️⃣let x = 42
+        print("hello")
+      }
+      """,
+      uri: uri
+    )
+
+    let result = try await testClient.send(
+      CodeActionRequest(
+        range: Range(positions["1️⃣"]),
+        context: .init(),
+        textDocument: TextDocumentIdentifier(uri)
+      )
+    )
+    let codeActions = try XCTUnwrap(result?.codeActions)
+    XCTAssertNil(codeActions.first { $0.title.starts(with: "Inline") })
+  }
+
   /// Retrieves the code action at a set of markers and asserts that it matches a list of expected code actions.
   ///
   /// - Parameters: