Added testDefinitionInSystemModuleInterface

Use SwiftPMPackage test module
Added version of buildAndIndex that includes system symbols

Author: adam-fowler

Sources/SKTestSupport/INPUTS/SwiftPMPackage/Sources/lib/lib.swift

@@ -1,7 +1,11 @@
 public struct Lib {
+  let a: /*Lib.a.string*/String
+
   public func /*Lib.foo:def*/foo() {}
 
-  public init() {}
+  public init() {
+    self.a = "lib"
+  }
 }
 
 func topLevelFunction() {

Sources/SKTestSupport/SKSwiftPMTestWorkspace.swift

@@ -125,6 +125,11 @@ extension SKSwiftPMTestWorkspace {
     index.pollForUnitChangesAndWait()
   }
 
+  public func buildAndIndexWithSystemSymbols() throws {
+    try buildWithSystemSymbols()
+    index.pollForUnitChangesAndWait()
+  }
+
   func build() throws {
     try TSCBasic.Process.checkNonZeroExit(arguments: [
       toolchain.swift!.pathString,
@@ -135,6 +140,15 @@ extension SKSwiftPMTestWorkspace {
       "-Xcc", "-index-ignore-system-symbols",
     ])
   }
+
+  func buildWithSystemSymbols() throws {
+    try TSCBasic.Process.checkNonZeroExit(arguments: [
+      toolchain.swift!.pathString,
+      "build",
+      "--package-path", sources.rootDirectory.path,
+      "--scratch-path", buildDir.path,
+    ])
+  }
 }
 
 extension SKSwiftPMTestWorkspace {

Tests/SourceKitLSPTests/SwiftInterfaceTests.swift

@@ -14,6 +14,7 @@ import Foundation
 import LanguageServerProtocol
 import LSPTestSupport
 import LSPLogging
+import SKSupport
 import SKTestSupport
 import SourceKitLSP
 import XCTest
@@ -113,6 +114,27 @@ final class SwiftInterfaceTests: XCTestCase {
           """))
   }
 
+  func testDefinitionInSystemModuleInterface() throws {
+    guard let ws = try staticSourceKitSwiftPMWorkspace(name: "SwiftPMPackage") else { return }
+    try ws.buildAndIndexWithSystemSymbols()
+    let stringRef = ws.testLoc("Lib.a.string")
+    try ws.openDocument(stringRef.url, language: .swift)
+    let definition = try ws.sk.sendSync(DefinitionRequest(
+      textDocument: stringRef.docIdentifier,
+      position: stringRef.position))
+    guard case .locations(let jump) = definition else {
+      XCTFail("Response is not locations")
+      return
+    }
+    let location = try XCTUnwrap(jump.first)
+    XCTAssertTrue(location.uri.pseudoPath.hasSuffix("/Swift.String.swiftinterface"))
+    // load contents of swiftinterface
+    let contents = try XCTUnwrap(location.uri.fileURL.flatMap({ try String(contentsOf: $0, encoding: .utf8) }))
+    let lineTable = LineTable(contents)
+    let line = lineTable[location.range.lowerBound.line]
+    XCTAssert(line.hasPrefix("@frozen public struct String"))
+  }
+  
   func testSwiftInterfaceAcrossModules() throws {
     guard let ws = try staticSourceKitSwiftPMWorkspace(name: "SwiftPMPackage") else { return }
     try ws.buildAndIndex()