Merge pull request swiftlang#15 from rintaro/completion-adjustlocation-fix

[Completion] Fix crash for completion on identifier at the start of file

Author: benlangmuir

Sources/SourceKit/sourcekitd/SwiftLanguageServer.swift

@@ -300,7 +300,11 @@ extension SwiftLanguageServer {
       return
     }
 
-    let completionPos = adjustCompletionLocation(req.params.position, in: snapshot)
+    guard let completionPos = adjustCompletionLocation(req.params.position, in: snapshot) else {
+      log("invalid completion position \(req.params.position)")
+      req.reply(CompletionList(isIncomplete: true, items: []))
+      return
+    }
 
     guard let offset = snapshot.utf8Offset(of: completionPos) else {
       log("invalid completion position \(req.params.position) (adjusted: \(completionPos)")
@@ -387,29 +391,35 @@ extension SwiftLanguageServer {
     return result
   }
 
-  func adjustCompletionLocation(_ pos: Position, in snapshot: DocumentSnapshot) -> Position {
-    guard let requestedLoc = snapshot.index(of: pos), requestedLoc != snapshot.text.startIndex else {
-      return pos
+  /// Adjust completion position to the start of identifier characters.
+  func adjustCompletionLocation(_ pos: Position, in snapshot: DocumentSnapshot) -> Position? {
+    guard pos.line < snapshot.lineTable.count else {
+      // Line out of range.
+      return nil
     }
+    let lineSlice = snapshot.lineTable[pos.line]
+    let startIndex = lineSlice.startIndex
 
     let identifierChars = CharacterSet.alphanumerics.union(CharacterSet(charactersIn: "_"))
 
-    var prev = requestedLoc
-    var loc = snapshot.text.index(before: requestedLoc)
-    while identifierChars.contains(snapshot.text[loc].unicodeScalars.first!) {
-      prev = loc
-      loc = snapshot.text.index(before: loc)
+    guard var loc = lineSlice.utf16.index(startIndex, offsetBy: pos.utf16index, limitedBy: lineSlice.endIndex) else {
+      // Column out of range.
+      return nil
+    }
+    while loc != startIndex {
+      let prev = lineSlice.index(before: loc)
+      if !identifierChars.contains(lineSlice.unicodeScalars[prev]) {
+        break
+      }
+      loc = prev
     }
 
-    // #aabccccccdddddd
-    // ^^- prev  ^-requestedLoc
-    // `- loc
-    //
-    // We offset the column by (requestedLoc - prev), which must be >=0 and on the same line.
-
-    let delta = requestedLoc.encodedOffset - prev.encodedOffset
+    // ###aabccccccdddddd
+    // ^  ^- loc  ^-requestedLoc
+    // `- startIndex
 
-    return Position(line: pos.line, utf16index: pos.utf16index - delta)
+    let adjustedOffset = lineSlice.utf16.distance(from: startIndex, to: loc)
+    return Position(line: pos.line, utf16index: adjustedOffset)
   }
 
   func hover(_ req: Request<HoverRequest>) {

Tests/SourceKitTests/LocalSwiftTests.swift

@@ -220,6 +220,35 @@ final class LocalSwiftTests: XCTestCase {
     XCTAssertNotEqual(after, selfDot)
   }
 
+  func testCompletionPosition() {
+    let url = URL(fileURLWithPath: "/a.swift")
+    sk.allowUnexpectedNotification = true
+
+    sk.send(DidOpenTextDocument(textDocument: TextDocumentItem(
+      url: url,
+      language: .swift,
+      version: 12,
+      text: "foo")))
+
+    for col in 0 ... 3 {
+      let inOrAfterFoo = try! sk.sendSync(CompletionRequest(
+        textDocument: TextDocumentIdentifier(url),
+        position: Position(line: 0, utf16index: col)))
+      XCTAssertFalse(inOrAfterFoo.isIncomplete)
+      XCTAssertFalse(inOrAfterFoo.items.isEmpty)
+    }
+
+    let outOfRange1 = try! sk.sendSync(CompletionRequest(
+      textDocument: TextDocumentIdentifier(url),
+      position: Position(line: 0, utf16index: 4)))
+    XCTAssertTrue(outOfRange1.isIncomplete)
+
+    let outOfRange2 = try! sk.sendSync(CompletionRequest(
+      textDocument: TextDocumentIdentifier(url),
+      position: Position(line: 1, utf16index: 0)))
+    XCTAssertTrue(outOfRange2.isIncomplete)
+  }
+
   func testXMLToMarkdownDeclaration() {
     XCTAssertEqual(try! xmlDocumentationToMarkdown("""
       <Declaration>func foo(_ bar: <Type usr="fake">Baz</Type>)</Declaration>

Tests/SourceKitTests/XCTestManifests.swift

@@ -29,6 +29,7 @@ extension LocalSwiftTests {
     // to regenerate.
     static let __allTests__LocalSwiftTests = [
         ("testCompletion", testCompletion),
+        ("testCompletionPosition", testCompletionPosition),
         ("testDocumentSymbolHighlight", testDocumentSymbolHighlight),
         ("testEditing", testEditing),
         ("testHover", testHover),