Return signature help parameter offsets as UTF-16 offsets

Author: a7medev

Sources/SwiftLanguageService/SignatureHelp.swift

@@ -17,20 +17,43 @@ import SourceKitD
 import SourceKitLSP
 import SwiftBasicFormat
 
+fileprivate extension String {
+  func utf16Offset(of utf8Offset: Int, callerFile: StaticString = #fileID, callerLine: UInt = #line) -> Int {
+    guard
+      let stringIndex = self.utf8.index(self.startIndex, offsetBy: utf8Offset, limitedBy: self.endIndex)
+    else {
+      logger.fault(
+        """
+        UTF-8 offset is past the end of the string while getting UTF-16 offset of \(utf8Offset) \
+        (\(callerFile, privacy: .public):\(callerLine, privacy: .public))
+        """
+      )
+      return self.utf16.count
+    }
+    return self.utf16.distance(from: self.startIndex, to: stringIndex)
+  }
+}
+
 fileprivate extension ParameterInformation {
-  init?(_ parameter: SKDResponseDictionary, _ keys: sourcekitd_api_keys) {
+  init?(_ parameter: SKDResponseDictionary, _ signatureLabel: String, _ keys: sourcekitd_api_keys) {
     guard let nameOffset = parameter[keys.nameOffset] as Int?,
       let nameLength = parameter[keys.nameLength] as Int?
     else {
       return nil
     }
 
-    let documentation = parameter[keys.docComment].map {
-      StringOrMarkupContent.markupContent(MarkupContent(kind: .markdown, value: $0))
-    }
+    let documentation: StringOrMarkupContent? =
+      if let docComment: String = parameter[keys.docComment] {
+        .markupContent(MarkupContent(kind: .markdown, value: docComment))
+      } else {
+        nil
+      }
+
+    let labelStart = signatureLabel.utf16Offset(of: nameOffset)
+    let labelEnd = signatureLabel.utf16Offset(of: nameOffset + nameLength)
 
     self.init(
-      label: .offsets(start: nameOffset, end: nameOffset + nameLength),
+      label: .offsets(start: labelStart, end: labelEnd),
       documentation: documentation
     )
   }
@@ -45,11 +68,14 @@ fileprivate extension SignatureInformation {
     }
 
     let activeParameter = signature[keys.activeParameter] as Int?
-    let parameters = skParameters.compactMap { ParameterInformation($0, keys) }
-
-    let documentation = signature[keys.docComment].map {
-      StringOrMarkupContent.markupContent(MarkupContent(kind: .markdown, value: $0))
-    }
+    let parameters = skParameters.compactMap { ParameterInformation($0, label, keys) }
+
+    let documentation: StringOrMarkupContent? =
+      if let docComment: String = signature[keys.docComment] {
+        .markupContent(MarkupContent(kind: .markdown, value: docComment))
+      } else {
+        nil
+      }
 
     self.init(
       label: label,

Tests/SourceKitLSPTests/SwiftSignatureHelpTests.swift

@@ -373,6 +373,48 @@ final class SwiftSignatureHelpTests: XCTestCase {
     )
   }
 
+  func testSignatureHelpNonASCII() async throws {
+    let testClient = try await TestSourceKitLSPClient()
+    let uri = DocumentURI(for: .swift)
+
+    let positions = testClient.openDocument(
+      """
+      /// This is a test function
+      func 🧑‍🧑‍🧒‍🧒🧑‍🧑‍🧒‍🧒(🧑🏽‍🚀🧑🏽‍🚀: Int, `🕵🏻‍♀️🕵🏻‍♀️`: String) -> Double { 0 }
+
+      func main() {
+        🧑‍🧑‍🧒‍🧒🧑‍🧑‍🧒‍🧒(🧑🏽‍🚀🧑🏽‍🚀: 1️⃣)
+      }
+      """,
+      uri: uri
+    )
+
+    let result = try await testClient.send(
+      SignatureHelpRequest(
+        textDocument: TextDocumentIdentifier(uri),
+        position: positions["1️⃣"]
+      )
+    )
+
+    let signatureHelp = try XCTUnwrap(result)
+    let signature = try XCTUnwrap(signatureHelp.signatures.only)
+
+    XCTAssertEqual(signatureHelp.activeSignature, 0)
+    XCTAssertEqual(signatureHelp.activeParameter, 0)
+    XCTAssertEqual(signature.label, "🧑‍🧑‍🧒‍🧒🧑‍🧑‍🧒‍🧒(🧑🏽‍🚀🧑🏽‍🚀: Int, `🕵🏻‍♀️🕵🏻‍♀️`: String) -> Double")
+    XCTAssertEqual(
+      signature.documentation,
+      .markupContent(MarkupContent(kind: .markdown, value: "This is a test function"))
+    )
+    XCTAssertEqual(
+      signature.parameters,
+      [
+        ParameterInformation(label: .offsets(start: 23, end: 42)),
+        ParameterInformation(label: .offsets(start: 44, end: 68)),
+      ]
+    )
+  }
+
   func testSignatureHelpSwiftPMProject() async throws {
     let project = try await SwiftPMTestProject(
       files: [