[SR-10794] Close option suggestions (#2144)

* Suggest Close Options [SR-10794]

* Add Test for Suggestion

* Added a comment about #available requirement, and some additional test cases

* Add `bestMatch` function and clean up description

* Tweak comment

Author: EPage-Ed

Sources/Basic/EditDistance.swift

@@ -13,6 +13,8 @@
 /// - Complexity: O(_n*m_), where *n* is the length of the first String and
 ///   *m* is the length of the second one.
 public func editDistance(_ first: String, _ second: String) -> Int {
+    // FIXME: We should use the new `CollectionDifference` API once the
+    // deployment target is bumped.
     let a = Array(first.utf16)
     let b = Array(second.utf16)
     var distance = [[Int]](repeating: [Int](repeating: 0, count: b.count + 1), count: a.count + 1)
@@ -34,3 +36,21 @@ public func editDistance(_ first: String, _ second: String) -> Int {
     }
     return distance[a.count][b.count]
 }
+
+/// Finds the "best" match for a `String` from an array of possible options.
+///
+/// - Parameters:
+///     - input: The input `String` to match.
+///     - options: The available options for `input`.
+///
+/// - Returns: The best match from the given `options`, or `nil` if none were sufficiently close.
+public func bestMatch(for input: String, from options: [String]) -> String? {
+    return options
+        .map { ($0, editDistance(input, $0)) }
+        // Filter out unreasonable edit distances. Based on:
+        // https://github.com/apple/swift/blob/37daa03b7dc8fb3c4d91dc560a9e0e631c980326/lib/Sema/TypeCheckNameLookup.cpp#L606
+        .filter { $0.1 <= ($0.0.count + 2) / 3 }
+        // Sort by edit distance
+        .sorted { $0.1 < $1.1 }
+        .first?.0
+}

Sources/SPMUtility/ArgumentParser.swift

@@ -16,7 +16,7 @@ import func SPMLibc.exit
 public enum ArgumentParserError: Swift.Error {
 
     /// An unknown option is encountered.
-    case unknownOption(String)
+    case unknownOption(String, suggestion: String?)
 
     /// The value of an argument is invalid.
     case invalidValue(argument: String, error: ArgumentConversionError)
@@ -43,8 +43,12 @@ extension ArgumentParserError: LocalizedError {
 extension ArgumentParserError: CustomStringConvertible {
     public var description: String {
         switch self {
-        case .unknownOption(let option):
-            return "unknown option \(option); use --help to list available options"
+        case .unknownOption(let option, let suggestion):
+            var desc = "unknown option \(option); use --help to list available options"
+            if let suggestion = suggestion {
+                desc += "\nDid you mean \(suggestion)?"
+            }
+            return desc
         case .invalidValue(let argument, let error):
             return "\(error) for argument \(argument); use --help to print usage"
         case .expectedValue(let option):
@@ -847,7 +851,8 @@ public final class ArgumentParser {
                 let (argumentString, value) = argumentString.spm_split(around: "=")
                 // Get the corresponding option for the option argument.
                 guard let optionArgument = optionsMap[argumentString] else {
-                    throw ArgumentParserError.unknownOption(argumentString)
+                    let suggestion = bestMatch(for: argumentString, from: Array(optionsMap.keys))
+                    throw ArgumentParserError.unknownOption(argumentString, suggestion: suggestion)
                 }
 
                 argument = optionArgument

Tests/UtilityTests/ArgumentParserTests.swift

@@ -120,8 +120,24 @@ class ArgumentParserTests: XCTestCase {
         do {
             _ = try parser.parse(["foo", "--bar"])
             XCTFail("unexpected success")
-        } catch ArgumentParserError.unknownOption(let option) {
+        } catch ArgumentParserError.unknownOption(let option, let suggestion) {
             XCTAssertEqual(option, "--bar")
+            XCTAssertNil(suggestion)
+        }
+
+        do {
+            _ = try parser.parse(["--food"])
+            XCTFail("unexpected success")
+        } catch ArgumentParserError.unknownOption(let option, let suggestion) {
+            XCTAssertEqual(option, "--food")
+            XCTAssertEqual(suggestion, "--foo")
+        }
+        do {
+            _ = try parser.parse(["--verb"])
+            XCTFail("unexpected success")
+        } catch ArgumentParserError.unknownOption(let option, let suggestion) {
+            XCTAssertEqual(option, "--verb")
+            XCTAssertNil(suggestion)
         }
 
         do {
@@ -286,19 +302,19 @@ class ArgumentParserTests: XCTestCase {
 
         do {
             args = try parser.parse(["--foo", "foo", "b", "--no-fly", "--branch", "bugfix"])
-        } catch ArgumentParserError.unknownOption(let arg) {
+        } catch ArgumentParserError.unknownOption(let arg, _) {
             XCTAssertEqual(arg, "--branch")
         }
 
         do {
             args = try parser.parse(["--foo", "foo", "a", "--branch", "bugfix", "--no-fly"])
-        } catch ArgumentParserError.unknownOption(let arg) {
+        } catch ArgumentParserError.unknownOption(let arg, _) {
             XCTAssertEqual(arg, "--no-fly")
         }
 
         do {
             args = try parser.parse(["a", "--branch", "bugfix", "--foo"])
-        } catch ArgumentParserError.unknownOption(let arg) {
+        } catch ArgumentParserError.unknownOption(let arg, _) {
             XCTAssertEqual(arg, "--foo")
         }
 
@@ -374,7 +390,7 @@ class ArgumentParserTests: XCTestCase {
 
         do {
             args = try parser.parse(["foo", "bar", "--no-fly"])
-        } catch ArgumentParserError.unknownOption(let arg) {
+        } catch ArgumentParserError.unknownOption(let arg, _) {
             XCTAssertEqual(arg, "--no-fly")
         }
     }
@@ -717,7 +733,7 @@ class ArgumentParserTests: XCTestCase {
         do {
             _ = try parser.parse(["-18"])
             XCTFail("unexpected success")
-        } catch ArgumentParserError.unknownOption(let option) {
+        } catch ArgumentParserError.unknownOption(let option, _) {
             XCTAssertEqual(option, "-18")
         }