Assert the Linkage of SwiftSyntax and SwiftParser

Tests/SwiftParserTest/Linkage.swift

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+#if canImport(Darwin)
+import Darwin
+import XCTest
+
+final class LinkageTest: XCTestCase {
+  // Assert that SwiftSyntax and SwiftParser do not introduce more link-time
+  // dependencies than are strictly necessary. We want to minimize our link-time
+  // dependencies. If this set changes - in particular, if it grows - consult
+  // a SwiftSyntax maintainer to see if there's a way to avoid adding the
+  // dependency.
+  func testLinkage() throws {
+    guard let baseURL = try self.findEnclosingTestBundle() else {
+      XCTFail("Unable to determine path to enclosing xctest bundle")
+      return
+    }
+
+    try assertLinkage(of: "SwiftSyntax", in: baseURL, assertions: [
+      .library("-lobjc"),
+      .library("-lswiftCompatibility51", condition: .mayBeAbsent("Starting in Xcode 14 this library is not always autolinked")),
+      .library("-lswiftCompatibility56", condition: .mayBeAbsent("Starting in Xcode 14 this library is not always autolinked")),
+      .library("-lswiftCompatibilityConcurrency"),
+      .library("-lswiftCore"),
+      .library("-lswiftDarwin"),
+      .library("-lswiftSwiftOnoneSupport", condition: .when(configuration: .debug)),
+      .library("-lswift_Concurrency"),
+      .library("-lswift_StringProcessing", condition: .when(swiftVersionAtLeast: .v5_7)),
+    ])
+
+    try assertLinkage(of: "SwiftParser", in: baseURL, assertions: [
+      .library("-lobjc"),
+      .library("-lswiftCompatibility51", condition: .mayBeAbsent("Starting in Xcode 14 this library is not always autolinked")),
+      .library("-lswiftCompatibility56", condition: .mayBeAbsent("Starting in Xcode 14 this library is not always autolinked")),
+      .library("-lswiftCompatibilityConcurrency"),
+      .library("-lswiftCore"),
+      .library("-lswiftDarwin"),
+      .library("-lswiftSwiftOnoneSupport", condition: .when(configuration: .debug)),
+      .library("-lswift_Concurrency"),
+      .library("-lswift_StringProcessing", condition: .when(swiftVersionAtLeast: .v5_7)),
+    ])
+  }
+}
+
+extension LinkageTest {
+  public struct MachHeader {
+    var magic: UInt32
+    var cputype: UInt32
+    var cpusubtype: UInt32
+    var filetype: UInt32
+    var ncmds: UInt32
+    var sizeofcmds: UInt32
+    var flags: UInt32
+    var reserved: UInt32
+
+    public struct LoadCommand: OptionSet {
+      public var rawValue: UInt32
+
+      public init(rawValue: UInt32) {
+        self.rawValue = rawValue
+      }
+
+      /// A load command that defines a list of linker options strings embedded
+      /// directly into this file.
+      public static let linkerOption = Self(rawValue: 0x2D)
+    }
+  }
+
+  struct LoadCommand {
+    var cmd: MachHeader.LoadCommand
+    var cmdsize: UInt32
+  }
+
+  struct LinkerOptionCommand {
+    var cmd: MachHeader.LoadCommand
+    var cmdsize: UInt32
+    var count: UInt32
+    /* concatenation of zero terminated UTF8 strings.
+     Zero filled at end to align */
+  }
+}
+
+extension LinkageTest {
+  private func assertLinkage(
+    of library: String,
+    in bundle: EnclosingTestBundle,
+    assertions: [Linkage.Assertion]
+  ) throws {
+    let linkages = try bundle.objectFiles(for: library).reduce(into: []) { acc, next in
+      acc += try self.extractAutolinkingHints(in: next)
+    }
+
+    let sortedLinkages = Set(linkages).sorted()
+    var expectedLinkagesIdx = sortedLinkages.startIndex
+    var assertions = assertions.makeIterator()
+    while let assert = assertions.next() {
+      // Evaluate the condition first, if any.
+      if let condition = assert.condition, !condition.evaluate() {
+        continue
+      }
+
+      // Make sure there's a linkage to even assert against. If not, then we've
+      // got too many assertions and not enough link libraries. This isn't
+      // always a bad thing, but it's worth calling out so we document this
+      // with `.mayBeAbsent(...)`.
+      guard expectedLinkagesIdx < sortedLinkages.endIndex else {
+        XCTFail("Expected linkage was not present: \(assert.linkage)",
+                file: assert.file, line: assert.line)
+        continue
+      }
+
+      let linkage = sortedLinkages[expectedLinkagesIdx]
+
+      // Check the linkage assertion. If it doesn't hold, the real fun begins.
+      guard !assert.matches(linkage) else {
+        expectedLinkagesIdx += 1
+        continue
+      }
+
+      // Skip flaky linkages if they're absent.
+      if case .flaky = assert.condition {
+        continue
+      }
+
+      XCTFail("Expected linkage to \(assert.linkage), but recieved linkage to \(linkage.linkage); Perhaps linkage assertions are out of order?",
+              file: assert.file, line: assert.line)
+      expectedLinkagesIdx += 1
+    }
+
+    for superfluousLinkage in sortedLinkages[expectedLinkagesIdx..<sortedLinkages.endIndex] {
+      XCTFail("Found unasserted link-time dependency: \(superfluousLinkage.linkage)")
+    }
+  }
+
+  private enum EnclosingTestBundle {
+    case incremental(URL)
+    case unified(URL)
+
+    func objectFiles(for library: String) throws -> [URL] {
+      switch self {
+      case .incremental(let baseURL):
+        return [baseURL.appendingPathComponent(library + ".o")]
+      case .unified(let baseURL):
+        return try FileManager.default
+          .contentsOfDirectory(at: baseURL.appendingPathComponent(library + ".build"),
+                               includingPropertiesForKeys: nil)
+          .filter({ $0.pathExtension == "o" })
+      }
+    }
+  }
+
+  private func findEnclosingTestBundle() throws -> EnclosingTestBundle? {
+    for i in 0..<_dyld_image_count() {
+      let name = try XCTUnwrap(_dyld_get_image_name(i))
+      let path = String(cString: name)
+      // We can wind up in SwiftParserTest.xctest when built via the IDE or
+      // in SwiftSyntaxPackageTests.xctest when built at the command line
+      // via the package manager.
+      guard path.hasSuffix("SwiftParserTest") || path.hasSuffix("SwiftSyntaxPackageTests") else {
+        continue
+      }
+
+      var baseURL = URL(fileURLWithPath: path)
+      while !baseURL.pathComponents.isEmpty, baseURL.pathExtension != "xctest" {
+        baseURL = baseURL.deletingLastPathComponent()
+      }
+
+      if baseURL.pathComponents.isEmpty {
+        continue
+      }
+
+      let url = baseURL.deletingLastPathComponent()
+      if path.hasSuffix("SwiftParserTest") {
+        return .incremental(url)
+      } else {
+        return .unified(url)
+      }
+    }
+    return nil
+  }
+
+  private func extractAutolinkingHints(in object: URL) throws -> [Linkage] {
+    let data = try Data(contentsOf: object, options: .mappedIfSafe)
+    assert(data.starts(with: [0xcf,0xfa,0xed,0xfe]), "Not a mach object file?")
+    return data.withUnsafeBytes { (buf: UnsafeRawBufferPointer) -> [Linkage] in
+      var result = [Linkage]()
+      guard let base = buf.baseAddress else {
+        return []
+      }
+
+      let hdr = base.bindMemory(to: MachHeader.self, capacity: 1)
+
+      var commandStart = base + MemoryLayout<MachHeader>.size
+      for _ in 0..<Int(hdr.pointee.ncmds) {
+        let command = commandStart.load(as: LoadCommand.self)
+        defer {
+          commandStart = commandStart.advanced(by: Int(command.cmdsize))
+        }
+
+        switch command.cmd {
+        case .linkerOption:
+          let (namePtr, cmdCount) = commandStart.withMemoryRebound(to: LinkerOptionCommand.self, capacity: 1, { cmd in
+            return cmd.withMemoryRebound(to: CChar.self, capacity: 1) { p in
+              return (p.advanced(by: MemoryLayout<LinkerOptionCommand>.size), Int(cmd.pointee.count))
+            }
+          })
+          if cmdCount == 1 {
+            result.append(.library(String(cString: namePtr)))
+          } else if cmdCount == 2 {
+            guard String(cString: namePtr) == "-framework" else {
+              continue
+            }
+
+            let frameworkName = String(cString: namePtr.advanced(by: "-framework".utf8.count + 1))
+            result.append(.framework(frameworkName))
+          } else {
+            XCTFail("Unexpected number of linker options: \(cmdCount)")
+          }
+        default:
+          continue
+        }
+      }
+      return result
+    }
+  }
+}
+#endif
+
+fileprivate enum Linkage: Comparable, Hashable {
+  case library(String)
+  case framework(String)
+
+  var linkage: String {
+    switch self {
+    case .library(let s): return s
+    case .framework(let s): return s
+    }
+  }
+
+  func hasPrefix(_ prefix: String) -> Bool {
+    return self.linkage.hasPrefix(prefix)
+  }
+}
+
+extension Linkage {
+  fileprivate struct Assertion {
+    var linkage: Linkage
+    var condition: Condition?
+    var file: StaticString
+    var line: UInt
+
+    func matches(_ linkage: Linkage) -> Bool {
+      return self.linkage == linkage
+    }
+
+    static func library(_ linkage: String, condition: Condition? = nil, file: StaticString = #file, line: UInt = #line) -> Assertion {
+      return Linkage.Assertion(linkage: .library(linkage), condition: condition, file: file, line: line)
+    }
+
+    static func framework(_ linkage: String, condition: Condition? = nil, file: StaticString = #file, line: UInt = #line) -> Assertion {
+      return Linkage.Assertion(linkage: .framework(linkage), condition: condition, file: file, line: line)
+    }
+  }
+}
+
+extension Linkage.Assertion {
+  fileprivate enum Condition {
+    case swiftVersionAtLeast(versionBound: SwiftVersion)
+    case configuration(ProductConfiguration)
+    case flaky
+
+    enum SwiftVersion: Comparable {
+      case v5_5
+      case v5_6
+      case v5_7
+      // We don't support compiling with <=5.4
+    }
+
+    enum ProductConfiguration: Equatable {
+      case debug
+      case release
+    }
+
+    fileprivate static func when(swiftVersionAtLeast version: SwiftVersion) -> Condition {
+      return .swiftVersionAtLeast(versionBound: version)
+    }
+
+    fileprivate static func when(configuration: ProductConfiguration) -> Condition {
+      return .configuration(configuration)
+    }
+
+    fileprivate static func mayBeAbsent(_ reason: StaticString) -> Condition {
+      return .flaky
+    }
+
+    fileprivate func evaluate() -> Bool {
+      switch self {
+      case let .swiftVersionAtLeast(versionBound: bound):
+#if swift(>=5.7)
+        let version: SwiftVersion = .v5_7
+#elseif swift(>=5.6)
+        let version: SwiftVersion = .v5_6
+#elseif swift(>=5.5)
+        let version: SwiftVersion = .v5_5
+#else
+        #error("Swift version is too old!")
+#endif
+        return version >= bound
+      case let .configuration(expectation):
+#if DEBUG
+        let config: ProductConfiguration = .debug
+#else
+        let config: ProductConfiguration = .release
+#endif
+        return config == expectation
+      case .flaky:
+        return true
+      }
+    }
+  }
+}