Add a new non_optional_string_data_conversion rule (#5264)

CHANGELOG.md

@@ -42,6 +42,11 @@
   [leonardosrodrigues0](https://github.com/leonardosrodrigues0)
   [#5265](https://github.com/realm/SwiftLint/issues/5265)
 
+* Add new `non_optional_string_data_conversion` rule to enforce 
+  non-failable conversions of UTF-8 `String` <-> `Data`.    
+  [Ben P](https://github.com/ben-p-commits)
+  [#5263](https://github.com/realm/SwiftLint/issues/5263)
+
 #### Bug Fixes
 
 * Fix some false positives in the `opening_brace` rule.  

Source/SwiftLintBuiltInRules/Models/BuiltInRules.swift

@@ -130,6 +130,7 @@ public let builtInRules: [any Rule.Type] = [
     NoGroupingExtensionRule.self,
     NoMagicNumbersRule.self,
     NoSpaceInMethodCallRule.self,
+    NonOptionalStringDataConversionRule.self,
     NonOverridableClassDeclarationRule.self,
     NotificationCenterDetachmentRule.self,
     NumberSeparatorRule.self,

Source/SwiftLintBuiltInRules/Rules/Lint/NonOptionalStringDataConversionRule.swift

@@ -0,0 +1,50 @@
+import SwiftSyntax
+
+@SwiftSyntaxRule
+struct NonOptionalStringDataConversionRule: Rule {
+    var configuration = SeverityConfiguration<Self>(.warning)
+    static let description = RuleDescription(
+        identifier: "non_optional_string_data_conversion",
+        name: "Non-Optional String <-> Data Conversion",
+        description: "Prefer using UTF-8 encoded strings when converting between `String` and `Data`",
+        kind: .lint,
+        nonTriggeringExamples: [
+            Example("Data(\"foo\".utf8)"),
+            Example("String(decoding: data, as: UTF8.self)")
+        ],
+        triggeringExamples: [
+            Example("\"foo\".data(using: .utf8)"),
+            Example("String(data: data, encoding: .utf8)")
+        ]
+    )
+}
+
+private extension NonOptionalStringDataConversionRule {
+    final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> {
+        override func visitPost(_ node: MemberAccessExprSyntax) {
+            if node.base?.is(StringLiteralExprSyntax.self) == true,
+               node.declName.baseName.text == "data",
+               let parent = node.parent?.as(FunctionCallExprSyntax.self),
+               let argument = parent.arguments.onlyElement,
+               argument.label?.text == "using",
+               argument.expression.as(MemberAccessExprSyntax.self)?.isUTF8 == true {
+                violations.append(node.positionAfterSkippingLeadingTrivia)
+            }
+        }
+
+        override func visitPost(_ node: DeclReferenceExprSyntax) {
+            if node.baseName.text == "String",
+               let parent = node.parent?.as(FunctionCallExprSyntax.self),
+               parent.arguments.map({ $0.label?.text }) == ["data", "encoding"],
+               parent.arguments.last?.expression.as(MemberAccessExprSyntax.self)?.isUTF8 == true {
+                violations.append(node.positionAfterSkippingLeadingTrivia)
+            }
+        }
+    }
+}
+
+private extension MemberAccessExprSyntax {
+    var isUTF8: Bool {
+        declName.baseName.text == "utf8"
+    }
+}

Source/SwiftLintCore/Extensions/Configuration+Remote.swift

@@ -94,7 +94,7 @@ internal extension Configuration.FileGraph.FilePath {
             guard
                 taskResult.2 == nil, // No error
                 (taskResult.1 as? HTTPURLResponse)?.statusCode == 200,
-                let configStr = (taskResult.0.flatMap { String(data: $0, encoding: .utf8) })
+                let configStr = (taskResult.0.flatMap { String(decoding: $0, as: UTF8.self) })
             else {
                 return try handleWrongData(
                     urlString: urlString,

Source/SwiftLintCore/RuleConfigurations/RegexConfiguration.swift

@@ -36,9 +36,8 @@ public struct RegexConfiguration<Parent: Rule>: SeverityBasedRuleConfiguration,
                 .map({ $0.rawValue }).sorted(by: <).joined(separator: ","),
             severity.rawValue
         ]
-        if let jsonData = try? JSONSerialization.data(withJSONObject: jsonObject),
-          let jsonString = String(data: jsonData, encoding: .utf8) {
-              return jsonString
+        if let jsonData = try? JSONSerialization.data(withJSONObject: jsonObject) {
+            return String(decoding: jsonData, as: UTF8.self)
         }
         queuedFatalError("Could not serialize regex configuration for cache")
     }

Source/swiftlint/Extensions/Configuration+CommandLine.swift

@@ -213,10 +213,8 @@ extension Configuration {
     fileprivate func getFiles(with visitor: LintableFilesVisitor) async throws -> [SwiftLintFile] {
         if visitor.useSTDIN {
             let stdinData = FileHandle.standardInput.readDataToEndOfFile()
-            if let stdinString = String(data: stdinData, encoding: .utf8) {
-                return [SwiftLintFile(contents: stdinString)]
-            }
-            throw SwiftLintError.usageError(description: "stdin isn't a UTF8-encoded string")
+            let stdinString = String(decoding: stdinData, as: UTF8.self)
+            return [SwiftLintFile(contents: stdinString)]
         } else if visitor.useScriptInputFiles {
             let files = try scriptInputFiles()
             guard visitor.forceExclude else {

Source/swiftlint/Helpers/LintableFilesVisitor.swift

@@ -178,8 +178,8 @@ struct LintableFilesVisitor {
     }
 
     private static func loadLogCompilerInvocations(_ path: String) -> [[String]]? {
-        if let data = FileManager.default.contents(atPath: path),
-            let logContents = String(data: data, encoding: .utf8) {
+        if let data = FileManager.default.contents(atPath: path) {
+            let logContents = String(decoding: data, as: UTF8.self)
             if logContents.isEmpty {
                 return nil
             }

Source/swiftlint/Helpers/SwiftPMCompilationDB.swift

@@ -37,7 +37,7 @@ struct SwiftPMCompilationDB: Codable {
             let pathToReplace = Array(nodes.nodes.keys.filter({ node in
                 node.hasSuffix(suffix)
             }))[0].dropLast(suffix.count - 1)
-            let stringFileContents = String(data: yaml, encoding: .utf8)!
+            let stringFileContents = String(decoding: yaml, as: UTF8.self)
                 .replacingOccurrences(of: pathToReplace, with: "")
             compilationDB = try decoder.decode(Self.self, from: stringFileContents)
         } else {

Tests/GeneratedTests/GeneratedTests.swift

@@ -770,6 +770,12 @@ class NoSpaceInMethodCallRuleGeneratedTests: SwiftLintTestCase {
     }
 }
 
+class NonOptionalStringDataConversionRuleGeneratedTests: SwiftLintTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(NonOptionalStringDataConversionRule.description)
+    }
+}
+
 class NonOverridableClassDeclarationRuleGeneratedTests: SwiftLintTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(NonOverridableClassDeclarationRule.description)

Tests/IntegrationTests/IntegrationTests.swift

@@ -172,8 +172,8 @@ private func execute(_ args: [String],
     queue.async(group: group) { stderrData = stderrPipe.fileHandleForReading.readDataToEndOfFile() }
     process.waitUntilExit()
     group.wait()
-    let stdout = stdoutData.flatMap { String(data: $0, encoding: .utf8) } ?? ""
-    let stderr = stderrData.flatMap { String(data: $0, encoding: .utf8) } ?? ""
+    let stdout = stdoutData.map { String(decoding: $0, as: UTF8.self) } ?? ""
+    let stderr = stderrData.map { String(decoding: $0, as: UTF8.self) } ?? ""
     return (process.terminationStatus, stdout, stderr)
 }
 

Tests/SwiftLintFrameworkTests/SwiftLintFileTests.swift

@@ -6,7 +6,7 @@ class SwiftLintFileTests: SwiftLintTestCase {
 
     override func setUp() async throws {
         try await super.setUp()
-        try "let i = 2".data(using: .utf8)!.write(to: tempFile)
+        try Data("let i = 2".utf8).write(to: tempFile)
     }
 
     override func tearDown() async throws {
@@ -40,12 +40,12 @@ class SwiftLintFileTests: SwiftLintTestCase {
         file.write("let j = 2")
 
         XCTAssertEqual(file.contents, "let j = 2")
-        XCTAssertEqual(FileManager.default.contents(atPath: tempFile.path), "let j = 2".data(using: .utf8))
+        XCTAssertEqual(FileManager.default.contents(atPath: tempFile.path), Data("let j = 2".utf8))
 
         file.append("2")
 
         XCTAssertEqual(file.contents, "let j = 22")
-        XCTAssertEqual(FileManager.default.contents(atPath: tempFile.path), "let j = 22".data(using: .utf8))
+        XCTAssertEqual(FileManager.default.contents(atPath: tempFile.path), Data("let j = 22".utf8))
     }
 
     func testFileNotTouchedIfNothingAppended() throws {