Forward port CommandLineParser rewrite

Improvements on scala 2 were motivated by
exponential parsing costs:

scala/scala#6622
scala/scala#5882

Author: som-snytt

compiler/src/dotty/tools/dotc/config/CommandLineParser.scala

@@ -2,67 +2,100 @@ package dotty.tools.dotc
 package config
 
 import scala.annotation.tailrec
-import scala.annotation.internal.sharable
 
-/** A simple (overly so) command line parser.
- *  !!! This needs a thorough test suite to make sure quoting is
- *  done correctly and portably.
+/** A simple enough command line parser.
  */
 object CommandLineParser {
-  // splits a string into a quoted prefix and the rest of the string,
-  // taking escaping into account (using \)
-  // `"abc"def` will match as `DoubleQuoted(abc, def)`
-  private class QuotedExtractor(quote: Char) {
-    def unapply(in: String): Option[(String, String)] = {
-      val del = quote.toString
-      if (in startsWith del) {
-        var escaped = false
-        val (quoted, next) = (in substring 1) span {
-          case `quote` if !escaped => false
-          case '\\'    if !escaped => escaped = true; true
-          case _                   => escaped = false; true
+  private final val DQ = '"'
+  private final val SQ = '\''
+
+  /** Split the line into tokens separated by whitespace or quotes.
+   *
+   *  @return either an error message or reverse list of tokens
+   */
+  private def tokens(in: String) = {
+    import Character.isWhitespace
+    import java.lang.{StringBuilder => Builder}
+    import collection.mutable.ArrayBuffer
+
+    var accum: List[String] = Nil
+    var pos = 0
+    var start = 0
+    val qpos = new ArrayBuffer[Int](16)    // positions of paired quotes
+
+    def cur: Int  = if (done) -1 else in.charAt(pos)
+    def bump() = pos += 1
+    def done   = pos >= in.length
+
+    def skipToQuote(q: Int) = {
+      var escaped = false
+      def terminal = in.charAt(pos) match {
+        case _ if escaped => escaped = false ; false
+        case '\\'         => escaped = true ; false
+        case `q`          => true
+        case _            => false
+      }
+      while (!done && !terminal) pos += 1
+      !done
+    }
+    @tailrec
+    def skipToDelim(): Boolean =
+      cur match {
+        case q @ (DQ | SQ)        => { qpos += pos; bump(); skipToQuote(q) } && { qpos += pos; bump(); skipToDelim() }
+        case -1                   => true
+        case c if isWhitespace(c) => true
+        case _                    => bump(); skipToDelim()
+      }
+    def skipWhitespace() = while (isWhitespace(cur)) pos += 1
+    def copyText() = {
+      val buf = new Builder
+      var p = start
+      var i = 0
+      while (p < pos) {
+        if (i >= qpos.size) {
+          buf.append(in, p, pos)
+          p = pos
+        } else if (p == qpos(i)) {
+          buf.append(in, qpos(i)+1, qpos(i+1))
+          p = qpos(i+1)+1
+          i += 2
+        } else {
+          buf.append(in, p, qpos(i))
+          p = qpos(i)
         }
-        // the only way to get out of the above loop is with an empty next or !escaped
-        // require(next.isEmpty || !escaped)
-        if (next startsWith del) Some((quoted, next substring 1))
-        else None
       }
-      else None
+      buf.toString
     }
-  }
-  private object DoubleQuoted extends QuotedExtractor('"')
-  private object SingleQuoted extends QuotedExtractor('\'')
-  @sharable private val Word = """(\S+)(.*)""".r
-
-  // parse `in` for an argument, return it and the remainder of the input (or an error message)
-  // (argument may be in single/double quotes, taking escaping into account, quotes are stripped)
-  private def argument(in: String): Either[String, (String, String)] = in match {
-    case DoubleQuoted(arg, rest) => Right((arg, rest))
-    case SingleQuoted(arg, rest) => Right((arg, rest))
-    case Word(arg, rest)         => Right((arg, rest))
-    case _                       => Left(s"Illegal argument: $in")
-  }
+    def text() = {
+      val res =
+        if (qpos.isEmpty) in.substring(start, pos)
+        else if (qpos(0) == start && qpos(1) == pos) in.substring(start+1, pos-1)
+        else copyText()
+      qpos.clear()
+      res
+    }
+    def badquote = Left("Unmatched quote")
 
-  // parse a list of whitespace-separated arguments (ignoring whitespace in quoted arguments)
-  @tailrec private def commandLine(in: String, accum: List[String] = Nil): Either[String, (List[String], String)] = {
-    val trimmed = in.trim
-    if (trimmed.isEmpty) Right((accum.reverse, ""))
-    else argument(trimmed) match {
-      case Right((arg, next)) =>
-        (next span Character.isWhitespace) match {
-          case("", rest) if rest.nonEmpty => Left("Arguments should be separated by whitespace.") // TODO: can this happen?
-          case(ws, rest)                  => commandLine(rest, arg :: accum)
-        }
-      case Left(msg) => Left(msg)
+    @tailrec def loop(): Either[String, List[String]] = {
+      skipWhitespace()
+      start = pos
+      if (done) Right(accum)
+      else if (!skipToDelim()) badquote
+      else {
+        accum = text() :: accum
+        loop()
+      }
     }
+    loop()
   }
 
   class ParseException(msg: String) extends RuntimeException(msg)
 
-  def tokenize(line: String): List[String] = tokenize(line, x => throw new ParseException(x))
   def tokenize(line: String, errorFn: String => Unit): List[String] =
-    commandLine(line) match {
-      case Right((args, _)) => args
-      case Left(msg)        => errorFn(msg) ; Nil
+    tokens(line) match {
+      case Right(args) => args.reverse
+      case Left(msg)   => errorFn(msg) ; Nil
     }
+
+  def tokenize(line: String): List[String] = tokenize(line, x => throw new ParseException(x))
 }

compiler/test/dotty/tools/dotc/config/CommandLineParserTest.scala

@@ -0,0 +1,43 @@
+
+package dotty.tools.dotc.config
+
+import org.junit.Assert.{assertEquals, assertTrue}
+import org.junit.Test
+
+class CommandLineParserTest:
+  import CommandLineParser.{tokenize, ParseException}
+
+  private def check(tokens: String*)(input: String): Unit = assertEquals(tokens, tokenize(input))
+
+  private def checkFails(input: String): Unit =
+    var failed = false
+    val res = tokenize(input, _ => failed = true)
+    assertTrue(s"Expected bad tokenization for [$input] but result was [$res]", failed)
+
+  @Test def parserTokenizes() =
+    check()("")
+    check("x")("x")
+    check("x", "y")("x y")
+    check("x", "y", "z")("x y z")
+
+  @Test def parserTrims() =
+    check()(" ")
+    check("x")(" x ")
+    check("x")("\nx\n")
+    check("x", "y", "z")(" x y z ")
+
+  @Test def parserQuotes() =
+    check("x")("'x'")
+    check("x")(""""x"""")
+    check("x", "y", "z")("x 'y' z")
+    check("x", " y ", "z")("x ' y ' z")
+    check("x", "y", "z")("""x "y" z""")
+    check("x", " y ", "z")("""x " y " z""")
+    // interior quotes
+    check("x y z")("x' y 'z")   // was assertEquals(List("x'","y","'z"), tokenize("x' y 'z"))
+    check("x\ny\nz")("x'\ny\n'z")
+    check("x'y'z")("""x"'y'"z""")
+    check("abcxyz")(""""abc"xyz""")
+    // missing quotes
+    checkFails(""""x""")         // was assertEquals(List("\"x"), tokenize(""""x"""))
+    checkFails("""x'""")