Implement never force unwrap (swiftlang#77)

Author: LaurenWhite

Diff for: Sources/Rules/NeverForceUnwrap.swift

@@ -8,5 +8,29 @@ import SwiftSyntax
 ///
 /// - SeeAlso: https://google.github.io/swift#force-unwrapping-and-force-casts
 public final class NeverForceUnwrap: SyntaxLintRule {
+  
+  // Checks if "XCTest" is an import statement
+  public override func visit(_ node: SourceFileSyntax) {
+    setImportsXCTest(context: context, sourceFile: node)
+    super.visit(node)
+  }
+  
+  public override func visit(_ node: ForcedValueExprSyntax) {
+    guard !context.importsXCTest else { return }
+    diagnose(.doNotForceUnwrap(name: node.expression.description), on: node)
+  }
+  
+  public override func visit(_ node: AsExprSyntax) {
+    guard !context.importsXCTest else { return }
+    diagnose(.doNotForceCast(name: node.typeName.description), on: node)
+  }
+}
 
+extension Diagnostic.Message {
+  static func doNotForceUnwrap(name: String) -> Diagnostic.Message {
+    return .init(.warning, "do not force unwrap '\(name)'")
+  }
+  static func doNotForceCast(name: String) -> Diagnostic.Message {
+    return .init(.warning, "do not force cast to '\(name)'")
+  }
 }

Diff for: Tests/SwiftFormatTests/NeverForceUnwrapTests.swift

@@ -0,0 +1,46 @@
+import Foundation
+import SwiftSyntax
+import XCTest
+
+@testable import Rules
+
+public class NeverForceUnwrapTests: DiagnosingTestCase {
+  public func testUnsafeUnwrap() {
+    let input =
+    """
+    func someFunc() -> Int {
+      var a = getInt()
+      var b = a as! Int
+      let c = (someValue())!
+      let d = String(a)!
+      let regex = try! NSRegularExpression(pattern: "a*b+c?")
+      return a!
+    }
+    """
+    performLint(NeverForceUnwrap.self, input: input)
+    XCTAssertDiagnosed(.doNotForceCast(name: "Int"))
+    XCTAssertDiagnosed(.doNotForceUnwrap(name: "(someValue())"))
+    XCTAssertDiagnosed(.doNotForceUnwrap(name: "String(a)"))
+    XCTAssertNotDiagnosed(.doNotForceCast(name: "try"))
+    XCTAssertNotDiagnosed(.doNotForceUnwrap(name: "try"))
+    XCTAssertDiagnosed(.doNotForceUnwrap(name: "a"))
+  }
+  public func testIgnoreTestCode() {
+    let input =
+    """
+      import XCTest
+
+      var b = a as! Int
+      """
+    performLint(NeverUseImplicitlyUnwrappedOptionals.self, input: input)
+    XCTAssertNotDiagnosed(.doNotForceCast(name: "Int"))
+  }
+  
+  #if !os(macOS)
+  static let allTests = [
+    NeverForceUnwrapTests.testUnsafeUnwrap,
+    ]
+  #endif
+}
+
+