Implement never use force try (swiftlang#56)

Author: LaurenWhite

Sources/Rules/NeverUseForceTry.swift

@@ -4,16 +4,30 @@ import SwiftSyntax
 
 /// Force-try (`try!`) is forbidden.
 ///
-/// This rule does not apply to test code, defined as code which matches one or more of:
-///   * Parent directory named "Tests"
+/// This rule does not apply to test code, defined as code which:
 ///   * Contains the line `import XCTest`
 ///
 /// Lint: Using `try!` results in a lint error.
 ///
-/// Format: The use of `try!` is replaced with a `try`...`catch` block where the `catch` block
-///         contains `fatalError("TODO(<username>): document before submitting")`
+/// TODO: Create exception for NSRegularExpression
 ///
 /// - SeeAlso: https://google.github.io/swift#error-types
-public final class NeverUseForceTry: SyntaxFormatRule {
+public final class NeverUseForceTry: SyntaxLintRule {
 
+  public override func visit(_ node: SourceFileSyntax) {
+    setImportsXCTest(context: context, sourceFile: node)
+    super.visit(node)
+  }
+
+  public override func visit(_ node: TryExprSyntax) {
+    guard !context.importsXCTest else { return }
+    guard let mark = node.questionOrExclamationMark else { return }
+    if mark.tokenKind == .exclamationMark {
+      diagnose(.doNotForceTry, on: node.tryKeyword)
+    }
+  }
+}
+
+extension Diagnostic.Message {
+  static let doNotForceTry = Diagnostic.Message(.warning, "do not use force try")
 }

Tests/SwiftFormatTests/NeverUseForceTryTests.swift

@@ -0,0 +1,32 @@
+import Foundation
+import XCTest
+import SwiftSyntax
+
+@testable import Rules
+
+public class NeverUseForceTryTests: DiagnosingTestCase {
+  public func testInvalidTryExpression() {
+    let input =
+      """
+      let document = try! Document(path: "important.data")
+      let document = try Document(path: "important.data")
+      let x = try! someThrowingFunction()
+      if let data = try? fetchDataFromDisk() { return data }
+      """
+    performLint(NeverUseForceTry.self, input: input)
+    XCTAssertDiagnosed(.doNotForceTry)
+    XCTAssertDiagnosed(.doNotForceTry)
+    XCTAssertNotDiagnosed(.doNotForceTry)
+  }
+
+  public func testAllowForceTryInTestCode() {
+    let input =
+      """
+      import XCTest
+
+      let document = try! Document(path: "important.data")
+      """
+    performLint(NeverUseForceTry.self, input: input)
+    XCTAssertNotDiagnosed(.doNotForceTry)
+  }
+}