Remove use of deprecated String functions in StringExtension.

Remove some functions that are no longer used, and update the
rest to Swift 4's String API.  lastIndexOf changes to lastIndex(of: ),
matching the standard library naming conventions, and returns a
String.Index? instead of an Int.

Add an implementation of Substring.hasPrefix for Linux; this
is in the Apple standard library but not the Linux one.
https://bugs.swift.org/browse/SR-5627

Add unit tests for StringExtension.

Bump the Swift download for the Travis Linux tests from 4.0
to 4.0.2.  There is a bug in Substring.range(of:) in 4.0.0
(https://bugs.swift.org/browse/SR-5663) that we need to avoid.

.travis/run-tests-swift.sh

@@ -6,7 +6,7 @@ set -euo pipefail
 # here since environment variables doesn't pass
 # across scripts
 if [ $TRAVIS_OS_NAME == "linux" ]; then
-  export SWIFT_VERSION=swift-4.0
+  export SWIFT_VERSION=swift-4.0.2
   export SWIFT_HOME=$(pwd)/swift/$SWIFT_VERSION-RELEASE-ubuntu14.04/usr/bin/
   export PATH=$SWIFT_HOME:$PATH
 

runtime/Swift/Sources/Antlr4/ListTokenSource.swift

@@ -85,9 +85,8 @@ public class ListTokenSource: TokenSource {
             let lastToken = tokens[tokens.count - 1]
 
             if let tokenText = lastToken.getText() {
-                let lastNewLine = tokenText.lastIndexOf("\n")
-                if lastNewLine >= 0 {
-                    return tokenText.length - lastNewLine - 1
+                if let lastNewLine = tokenText.lastIndex(of: "\n") {
+                    return tokenText.distance(from: lastNewLine, to: tokenText.endIndex) - 1
                 }
             }
             return (lastToken.getCharPositionInLine() +

runtime/Swift/Sources/Antlr4/misc/extension/StringExtension.swift

@@ -6,62 +6,38 @@
 
 import Foundation
 
-//http://stackoverflow.com/questions/28182441/swift-how-to-get-substring-from-start-to-last-index-of-character
-//https://github.com/williamFalcon/Bolt_Swift/blob/master/Bolt/BoltLibrary/String/String.swift
-
 extension String {
-
-    var length: Int {
-        return self.characters.count
-    }
-
-    func indexOf(_ target: String) -> Int {
-        let range = self.range(of: target)
-        if let range = range {
-            return self.characters.distance(from: self.startIndex, to: range.lowerBound)
-
-        } else {
-            return -1
+    func lastIndex(of target: String) -> String.Index? {
+        if target.isEmpty {
+            return nil
         }
-    }
-
-    func indexOf(_ target: String, startIndex: Int) -> Int {
-
-        let startRange = self.characters.index(self.startIndex, offsetBy: startIndex)
-        let range = self.range(of: target, options: .literal, range: startRange..<self.endIndex)
-
-        if let range = range {
-
-            return self.characters.distance(from: self.startIndex, to: range.lowerBound)
-        } else {
-            return -1
-        }
-    }
-
-    func lastIndexOf(_ target: String) -> Int {
-        var index = -1
-        var stepIndex = self.indexOf(target)
-        while stepIndex > -1 {
-            index = stepIndex
-            if stepIndex + target.length < self.length {
-                stepIndex = indexOf(target, startIndex: stepIndex + target.length)
-            } else {
-                stepIndex = -1
+        var result: String.Index? = nil
+        var substring = self[...]
+        while true {
+            guard let targetRange = substring.range(of: target) else {
+                return result
             }
+            result = targetRange.lowerBound
+            let nextChar = substring.index(after: targetRange.lowerBound)
+            substring = self[nextChar...]
         }
-        return index
-    }
-
-    subscript(integerIndex: Int) -> Character {
-        let index = characters.index(startIndex, offsetBy: integerIndex)
-        return self[index]
     }
 
     subscript(integerRange: Range<Int>) -> String {
-        let start = characters.index(startIndex, offsetBy: integerRange.lowerBound)
-        let end = characters.index(startIndex, offsetBy: integerRange.upperBound)
+        let start = index(startIndex, offsetBy: integerRange.lowerBound)
+        let end = index(startIndex, offsetBy: integerRange.upperBound)
         let range = start ..< end
         return String(self[range])
     }
 }
 
+
+// Implement Substring.hasPrefix, which is not currently in the Linux stdlib.
+// https://bugs.swift.org/browse/SR-5627
+#if os(Linux)
+extension Substring {
+    func hasPrefix(_ prefix: String) -> Bool {
+        return String(self).hasPrefix(prefix)
+    }
+}
+#endif

runtime/Swift/Tests/Antlr4Tests/StringExtensionTests.swift

@@ -0,0 +1,31 @@
+/// Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
+/// Use of this file is governed by the BSD 3-clause license that
+/// can be found in the LICENSE.txt file in the project root.
+
+import Foundation
+import XCTest
+@testable import Antlr4
+
+class StringExtensionTests: XCTestCase {
+
+    func testLastIndex() {
+        doLastIndexTest("", "", nil)
+        doLastIndexTest("a", "", nil)
+        doLastIndexTest("a", "a", 0)
+        doLastIndexTest("aba", "a", 2)
+        doLastIndexTest("aba", "b", 1)
+        doLastIndexTest("abc", "d", nil)
+    }
+
+}
+
+private func doLastIndexTest(_ str: String, _ target: String, _ expectedOffset: Int?) {
+    let expectedIdx: String.Index?
+    if let expectedOffset = expectedOffset {
+        expectedIdx = str.index(str.startIndex, offsetBy: expectedOffset)
+    }
+    else {
+        expectedIdx = nil
+    }
+    XCTAssertEqual(str.lastIndex(of: target), expectedIdx)
+}