Implemented a file parser. Added SourceOfExamples for lazy example listing (especially useful when lazily searching for files that match a certain prefix).

util/complete/src/main/scala/sbt/complete/Parser.scala

@@ -70,7 +70,7 @@ sealed trait RichParser[A]
 	/** If an exception is thrown by the original Parser,
 	* capture it and fail locally instead of allowing the exception to propagate up and terminate parsing.*/
 	def failOnException: Parser[A]
-	
+
 	@deprecated("Use `not` and explicitly provide the failure message", "0.12.2")
 	def unary_- : Parser[Unit]
 
@@ -87,6 +87,9 @@ sealed trait RichParser[A]
 	/** Explicitly defines the completions for the original Parser.*/
 	def examples(s: Set[String], check: Boolean = false): Parser[A]
 
+	/** Explicitly defines the completions for the original Parser.*/
+	def examples(s: SourceOfExamples, maxNumberOfExamples: Int): Parser[A]
+
 	/** Converts a Parser returning a Char sequence to a Parser returning a String.*/
 	def string(implicit ev: A <:< Seq[Char]): Parser[String]
 
@@ -239,7 +242,7 @@ object Parser extends ParserMain
 						case None => if(max.isZero) success(revAcc.reverse) else new Repeat(partial, repeated, min, max, revAcc)
 					}
 			}
-		
+
 		partial match
 		{
 			case Some(part) =>
@@ -285,6 +288,7 @@ trait ParserMain
 		def - (o: Parser[_]) = sub(a, o)
 		def examples(s: String*): Parser[A] = examples(s.toSet)
 		def examples(s: Set[String], check: Boolean = false): Parser[A] = Parser.examples(a, s, check)
+		def examples(s: SourceOfExamples, maxNumberOfExamples: Int): Parser[A] = Parser.examples(a, s, maxNumberOfExamples)
 		def filter(f: A => Boolean, msg: String => String): Parser[A] = filterParser(a, f, "", msg)
 		def string(implicit ev: A <:< Seq[Char]): Parser[String] = map(_.mkString)
 		def flatMap[B](f: A => Parser[B]) = bindParser(a, f)
@@ -295,7 +299,7 @@ trait ParserMain
 
 	/** Construct a parser that is valid, but has no valid result.  This is used as a way
 	* to provide a definitive Failure when a parser doesn't match empty input.  For example,
-	* in `softFailure(...) | p`, if `p` doesn't match the empty sequence, the failure will come 
+	* in `softFailure(...) | p`, if `p` doesn't match the empty sequence, the failure will come
 	* from the Parser constructed by the `softFailure` method. */
 	private[sbt] def softFailure(msg: => String, definitive: Boolean = false): Parser[Nothing] =
 		SoftInvalid( mkFailures(msg :: Nil, definitive) )
@@ -430,6 +434,17 @@ trait ParserMain
 		}
 		else a
 
+	def examples[A](a: Parser[A], completions: SourceOfExamples, maxNumberOfExamples: Int): Parser[A] =
+		if(a.valid) {
+			a.result match
+			{
+				case Some(av) => success( av )
+				case None =>
+					new DynamicExamples(a, completions, maxNumberOfExamples)
+			}
+		}
+		else a
+
 	def matched(t: Parser[_], seen: Vector[Char] = Vector.empty, partial: Boolean = false): Parser[String] =
 		t match
 		{
@@ -442,7 +457,7 @@ trait ParserMain
 		}
 
 	/** Establishes delegate parser `t` as a single token of tab completion.
-	* When tab completion of part of this token is requested, the completions provided by the delegate `t` or a later derivative are appended to 
+	* When tab completion of part of this token is requested, the completions provided by the delegate `t` or a later derivative are appended to
 	* the prefix String already seen by this parser. */
 	def token[T](t: Parser[T]): Parser[T] = token(t, TokenCompletions.default)
 
@@ -703,6 +718,26 @@ private final class Examples[T](delegate: Parser[T], fixed: Set[String]) extends
 			Completions(fixed map(f => Completion.suggestion(f)) )
 	override def toString = "examples(" + delegate + ", " + fixed.take(2) + ")"
 }
+abstract class SourceOfExamples
+{
+	def apply(): Iterable[String]
+	def withAddedPrefix(addedPrefix: String): SourceOfExamples
+}
+private final class DynamicExamples[T](delegate: Parser[T], sourceOfExamples: SourceOfExamples, maxNumberOfExamples: Int = 10) extends ValidParser[T]
+{
+	def derive(c: Char) = examples(delegate derive c, sourceOfExamples.withAddedPrefix(c.toString), maxNumberOfExamples)
+	def result = delegate.result
+	lazy val resultEmpty = delegate.resultEmpty
+	def completions(level: Int) = {
+		if(sourceOfExamples().isEmpty)
+			if(resultEmpty.isValid) Completions.nil else Completions.empty
+		else {
+			val examplesBasedOnTheResult = sourceOfExamples().take(maxNumberOfExamples).toSet
+			Completions(examplesBasedOnTheResult.map(ex => Completion.suggestion(ex)))
+		}
+	}
+	override def toString = "examples(" + delegate + ", " + sourceOfExamples().take(2).toList + ")"
+}
 private final class StringLiteral(str: String, start: Int) extends ValidParser[String]
 {
 	assert(0 <= start && start < str.length)

util/complete/src/main/scala/sbt/complete/Parsers.scala

@@ -7,6 +7,7 @@ package sbt.complete
 	import java.io.File
 	import java.net.URI
 	import java.lang.Character.{getType, MATH_SYMBOL, OTHER_SYMBOL, DASH_PUNCTUATION, OTHER_PUNCTUATION, MODIFIER_SYMBOL, CURRENCY_SYMBOL}
+    import java.nio.file.{Files, Path}
 
 /** Provides standard implementations of commonly useful [[Parser]]s. */
 trait Parsers
@@ -78,7 +79,7 @@ trait Parsers
 	def isScalaIDChar(c: Char) = c.isLetterOrDigit || c == '_'
 
 	def isDelimiter(c: Char) = c match { case '`' | '\'' | '\"' | /*';' | */',' | '.' => true ; case _ => false }
-	
+
 	/** Matches a single character that is not a whitespace character. */
 	lazy val NotSpaceClass = charClass(!_.isWhitespace, "non-whitespace character")
 
@@ -128,8 +129,32 @@ trait Parsers
 	/** Returns true if `c` is an ASCII letter or digit. */
 	def alphanum(c: Char) = ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || ('0' <= c && c <= '9')
 
-	// TODO: implement
+	class FileExamples(base: Path, prefix: String = "") extends SourceOfExamples {
-	def fileParser(base: File): Parser[File] = token(mapOrFail(NotSpace)(s => new File(s.mkString)), "<file>")
+		private val prefixPath: String = "." + File.separator + prefix
+
+		override def apply(): Iterable[String] = files(base).map(base.relativize).map(_.toString.substring(prefix.length))
+
+		override def withAddedPrefix(addedPrefix: String): FileExamples = new FileExamples(base, prefix + addedPrefix)
+
+		protected def fileStartsWithPrefix(path: Path): Boolean = path.toString.startsWith(prefixPath)
+
+		protected def directoryStartsWithPrefix(path: Path): Boolean = {
+			val pathString = path.toString
+			pathString.startsWith(prefixPath) || prefixPath.startsWith(pathString)
+		}
+
+		protected def files(directory: Path): Iterable[Path] = {
+			import scala.collection.JavaConversions._
+			val subPathStream = Files.newDirectoryStream(directory).toStream
+			val (subDirectories, filesOnly) = subPathStream.partition(path => Files.isDirectory(path))
+			filesOnly.filter(fileStartsWithPrefix) ++ subDirectories.filter(directoryStartsWithPrefix).flatMap(files)
+		}
+	}
+
+	def fileParser(base: File, maxNumberOfExamples: Int = 25): Parser[File] =
+		OptSpace ~> StringBasic
+			.examples(new FileExamples(base.toPath), maxNumberOfExamples)
+			.map(new File(_))
 
 	/** Parses a port number.  Currently, this accepts any integer and presents a tab completion suggestion of `<port>`. */
 	lazy val Port = token(IntBasic, "<port>")
@@ -153,7 +178,7 @@ trait Parsers
 	/** Parses a verbatim quoted String value, discarding the quotes in the result.  This kind of quoted text starts with triple quotes `"""`
 	* and ends at the next triple quotes and may contain any character in between. */
 	lazy val StringVerbatim: Parser[String] = VerbatimDQuotes ~>
-		any.+.string.filter(!_.contains(VerbatimDQuotes), _ => "Invalid verbatim string") <~ 
+		any.+.string.filter(!_.contains(VerbatimDQuotes), _ => "Invalid verbatim string") <~
 		VerbatimDQuotes
 
 	/** Parses a string value, interpreting escapes and discarding the surrounding quotes in the result.
@@ -168,7 +193,7 @@ trait Parsers
 	  BackslashChar ~> ('b' ^^^ '\b' | 't' ^^^ '\t' | 'n' ^^^ '\n' | 'f' ^^^ '\f' | 'r' ^^^ '\r' |
 	  '\"' ^^^ '\"' | '\'' ^^^ '\'' | '\\' ^^^ '\\' | UnicodeEscape)
 
-	/** Parses a single unicode escape sequence into the represented Char. 
+	/** Parses a single unicode escape sequence into the represented Char.
 	* A unicode escape begins with a backslash, followed by a `u` and 4 hexadecimal digits representing the unicode value. */
 	lazy val UnicodeEscape: Parser[Char] =
 	  ("u" ~> repeat(HexDigit, 4, 4)) map { seq => Integer.parseInt(seq.mkString, 16).toChar }