De-dupe locations returned from the defintions request

We might end up with duplicate locations when performing a definition request on eg. `MyStruct()` when no explicit initializer is declared. In this case we get two symbol infos, one for the declaration of the `MyStruct` type and one for the initializer, which is implicit and thus has the location of  the `MyStruct` declaration itself.

rdar://123036565
Fixes #1055

Author: ahoppen

Sources/SourceKitLSP/SourceKitServer.swift

@@ -1818,7 +1818,7 @@ extension SourceKitServer {
         position: req.position
       )
     )
-    return try await symbols.asyncMap { (symbol) -> [Location] in
+    let locations = try await symbols.asyncMap { (symbol) -> [Location] in
       if symbol.bestLocalDeclaration != nil && !(symbol.isDynamic ?? true)
         && symbol.usr?.hasPrefix("s:") ?? false /* Swift symbols have USRs starting with s: */
       {
@@ -1830,6 +1830,11 @@ extension SourceKitServer {
       }
       return try await self.definitionLocations(for: symbol, in: req.textDocument.uri, languageService: languageService)
     }.flatMap { $0 }
+    // Remove any duplicate locations. We might end up with duplicate locations when performing a definition request
+    // on eg. `MyStruct()` when no explicit initializer is declared. In this case we get two symbol infos, one for the
+    // declaration of the `MyStruct` type and one for the initializer, which is implicit and thus has the location of
+    // the `MyStruct` declaration itself.
+    return locations.unique
   }
 
   func definition(
@@ -2374,3 +2379,11 @@ fileprivate extension RequestID {
     }
   }
 }
+
+fileprivate extension Sequence where Element: Hashable {
+  /// Removes all duplicate elements from the sequence, maintaining order.
+  var unique: [Element] {
+    var set = Set<Element>()
+    return self.filter { set.insert($0).inserted }
+  }
+}

Tests/SourceKitLSPTests/DefinitionTests.swift

@@ -362,4 +362,32 @@ class DefinitionTests: XCTestCase {
       )
     )
   }
+
+  func testDefinitionOfImplicitInitializer() async throws {
+    let testClient = try await TestSourceKitLSPClient()
+    let uri = DocumentURI.for(.swift)
+
+    let positions = testClient.openDocument(
+      """
+      class 1️⃣Foo {}
+
+      func test() {
+        2️⃣Foo()
+      }
+      """,
+      uri: uri
+    )
+
+    let response = try await testClient.send(
+      DefinitionRequest(textDocument: TextDocumentIdentifier(uri), position: positions["2️⃣"])
+    )
+    guard case .locations(let locations) = response else {
+      XCTFail("Expected locations response")
+      return
+    }
+    XCTAssertEqual(
+      locations,
+      [Location(uri: uri, range: Range(positions["1️⃣"]))]
+    )
+  }
 }