Use the presentation compiler to drive REPL tab completion

The old implementation is still avaiable under a flag, but we'll
remove it in due course.

Design goal:

  - Push as much code in src/interactive as possible to enable reuse
    outside of the REPL
  - Don't entangle the REPL completion with JLine. The enclosed test
    case drives the REPL and autocompletion programatically.
  - Don't hard code UI choices, like how to render symbols or
    how to filter candidates.

When completion is requested, we wrap the entered code into the
same "interpreter wrapper" synthetic code as is done for regular
execution. We then start a throwaway instance of the presentation
compiler, which takes this as its one and only source file, and
has a classpath formed from the REPL's classpath and the REPL's
output directory (by default, this is in memory).

We can then typecheck the tree, and find the position in the synthetic
source corresponding to the cursor location. This is enough to use
the new completion APIs in the presentation compiler to prepare
a list of candidates.

We go to extra lengths to allow completion of partially typed
identifiers that appear to be keywords, e.g `global.def` should offer
`definitions`.

Two secret handshakes are included; move the the end of the line,
type `// print<TAB>` and you'll see the post-typer tree.
`// typeAt 4 6<TAB>` shows the type of the range position within
the buffer.

The enclosed unit test exercises most of the new functionality.

1 files changed, 29 insertions, 18 deletions

diff --git a/src/repl/scala/tools/nsc/interpreter/IMain.scala b/src/repl/scala/tools/nsc/interpreter/IMain.scala
index 3b54f5274e..2085fd4e50 100644
--- a/src/repl/scala/tools/nsc/interpreter/IMain.scala
+++ b/src/repl/scala/tools/nsc/interpreter/IMain.scala
@@ -15,10 +15,13 @@ import scala.concurrent.{ Future, ExecutionContext }
 import scala.reflect.runtime.{ universe => ru }
 import scala.reflect.{ ClassTag, classTag }
 import scala.reflect.internal.util.{ BatchSourceFile, SourceFile }
+import scala.tools.nsc.interactive
+import scala.tools.nsc.reporters.StoreReporter
+import scala.tools.nsc.util.ClassPath.DefaultJavaContext
 import scala.tools.util.PathResolverFactory
 import scala.tools.nsc.io.AbstractFile
 import scala.tools.nsc.typechecker.{ TypeStrings, StructuredTypeStrings }
-import scala.tools.nsc.util.{ ScalaClassLoader, stringFromReader, stringFromWriter, StackTraceOps, ClassPath, MergedClassPath }
+import scala.tools.nsc.util._
 import ScalaClassLoader.URLClassLoader
 import scala.tools.nsc.util.Exceptional.unwrap
 import scala.tools.nsc.backend.JavaPlatform
@@ -58,7 +61,7 @@ import java.io.File
  *  @author Moez A. Abdel-Gawad
  *  @author Lex Spoon
  */
-class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Settings, protected val out: JPrintWriter) extends AbstractScriptEngine with Compilable with Imports {
+class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Settings, protected val out: JPrintWriter) extends AbstractScriptEngine with Compilable with Imports with PresentationCompilation {
   imain =>
 
   setBindings(createBindings, ScriptContext.ENGINE_SCOPE)
@@ -446,7 +449,7 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
 
   /** Build a request from the user. `trees` is `line` after being parsed.
    */
-  private def buildRequest(line: String, trees: List[Tree]): Request = {
+  private[interpreter] def buildRequest(line: String, trees: List[Tree]): Request = {
     executingRequest = new Request(line, trees)
     executingRequest
   }
@@ -465,11 +468,12 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
     pos
   }
 
-  private def requestFromLine(line: String, synthetic: Boolean): Either[IR.Result, Request] = {
-    val content = line  //indentCode(line)
-    val trees = parse(content) match {
-      case parse.Incomplete     => return Left(IR.Incomplete)
-      case parse.Error          => return Left(IR.Error)
+  private[interpreter] def requestFromLine(line: String, synthetic: Boolean): Either[IR.Result, Request] = {
+    val content = line
+
+    val trees: List[global.Tree] = parse(content) match {
+      case parse.Incomplete(_)     => return Left(IR.Incomplete)
+      case parse.Error(_)          => return Left(IR.Error)
       case parse.Success(trees) => trees
     }
     repltrace(
@@ -854,7 +858,7 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
   }
 
   /** One line of code submitted by the user for interpretation */
-  class Request(val line: String, val trees: List[Tree]) {
+  class Request(val line: String, val trees: List[Tree], generousImports: Boolean = false) {
     def defines    = defHandlers flatMap (_.definedSymbols)
     def imports    = importedSymbols
     def value      = Some(handlers.last) filter (h => h.definesValue) map (h => definedSymbols(h.definesTerm.get)) getOrElse NoSymbol
@@ -888,7 +892,7 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
       * append to objectName to access anything bound by request.
       */
     lazy val ComputedImports(headerPreamble, importsPreamble, importsTrailer, accessPath) =
-      exitingTyper(importsCode(referencedNames.toSet, ObjectSourceCode, definesClass))
+      exitingTyper(importsCode(referencedNames.toSet, ObjectSourceCode, definesClass, generousImports))
 
     /** the line of code to compute */
     def toCompute = line
@@ -915,6 +919,7 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
         |${envLines mkString ("  ", ";\n  ", ";\n")}
         |$importsPreamble
         |${indentCode(toCompute)}""".stripMargin
+      def preambleLength = preamble.length - toCompute.length - 1
 
       val generate = (m: MemberHandler) => m extraCodeToEvaluate Request.this
 
@@ -954,7 +959,7 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
       def postwrap = s"}\nval $iw = new $iw\n"
     }
 
-    private lazy val ObjectSourceCode: Wrapper =
+    private[interpreter] lazy val ObjectSourceCode: Wrapper =
       if (isClassBased) new ClassBasedWrapper else new ObjectBasedWrapper
 
     private object ResultObjectSourceCode extends IMain.CodeAssembler[MemberHandler] {
@@ -1015,6 +1020,7 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
     }
 
     lazy val resultSymbol = lineRep.resolvePathToSymbol(fullAccessPath)
+
     def applyToResultMember[T](name: Name, f: Symbol => T) = exitingTyper(f(resultSymbol.info.nonPrivateDecl(name)))
 
     /* typeOf lookup with encoding */
@@ -1168,20 +1174,22 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
 
   /** Parse a line into and return parsing result (error, incomplete or success with list of trees) */
   object parse {
-    abstract sealed class Result
-    case object Error extends Result
-    case object Incomplete extends Result
+    abstract sealed class Result { def trees: List[Tree] }
+    case class Error(trees: List[Tree]) extends Result
+    case class Incomplete(trees: List[Tree]) extends Result
     case class Success(trees: List[Tree]) extends Result
 
-    def apply(line: String): Result = debugging(s"""parse("$line")""")  {
+    def apply(line: String, forPresentation: Boolean = false): Result = debugging(s"""parse("$line")""")  {
       var isIncomplete = false
-      currentRun.parsing.withIncompleteHandler((_, _) => isIncomplete = true) {
+      def parse = {
         reporter.reset()
         val trees = newUnitParser(line).parseStats()
-        if (reporter.hasErrors) Error
-        else if (isIncomplete) Incomplete
+        if (reporter.hasErrors) Error(trees)
+        else if (isIncomplete) Incomplete(trees)
         else Success(trees)
       }
+      currentRun.parsing.withIncompleteHandler((_, _) => isIncomplete = true) {parse}
+
     }
   }
 
@@ -1264,6 +1272,8 @@ class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Set
 /** Utility methods for the Interpreter. */
 object IMain {
   import java.util.Arrays.{ asList => asJavaList }
+  /** Dummy identifier fragement inserted at the cursor before presentation compilation. Needed to support completion of `global.def<TAB>` */
+  val DummyCursorFragment = "_CURSOR_"
 
   class Factory extends ScriptEngineFactory {
     @BeanProperty
@@ -1361,3 +1371,4 @@ object IMain {
     def stripImpl(str: String): String = naming.unmangle(str)
   }
 }
+