Detect when a syntax error could be remedied

by adding more input to the end of a compilation unit. This is intended
for use by the interpreter, so that it knows to keep reading more lines
of input.

5 files changed, 117 insertions, 62 deletions

diff --git a/src/compiler/scala/tools/nsc/CompilationUnits.scala b/src/compiler/scala/tools/nsc/CompilationUnits.scala
index 8e2f9f14b7..4f2752b738 100644
--- a/src/compiler/scala/tools/nsc/CompilationUnits.scala
+++ b/src/compiler/scala/tools/nsc/CompilationUnits.scala
@@ -12,6 +12,9 @@ import scala.collection.mutable.HashSet
 
 trait CompilationUnits requires Global {
 
+  /** One unit of compilation that has been submitted to the compiler.
+    * It typically corresponds to a single file of source code.  It includes
+    * error-reporting hooks.  */
   class CompilationUnit(val source: SourceFile) {
 
     /** the fresh name creator */
@@ -42,6 +45,12 @@ trait CompilationUnits requires Global {
       if (settings.unchecked.value) reporter.warning(position(pos), msg)
       else currentRun.uncheckedWarnings = true
 
+    def incompleteInputError(pos:int, msg:String) =
+      if (!(errorPositions contains pos)) {
+        errorPositions += pos
+        reporter.incompleteInputError(position(pos), msg)
+      }
+
     override def toString() = source.toString()
 
     def clear() = {
diff --git a/src/compiler/scala/tools/nsc/Interpreter.scala b/src/compiler/scala/tools/nsc/Interpreter.scala
index aeb23ef8a5..e4dd4b8d6e 100644
--- a/src/compiler/scala/tools/nsc/Interpreter.scala
+++ b/src/compiler/scala/tools/nsc/Interpreter.scala
@@ -119,7 +119,7 @@ class Interpreter(val settings: Settings, reporter: Reporter, out: PrintWriter)
                           parentClassLoader)
 
   /** XXX Let's get rid of this.  I believe the Eclipse plugin is
-    * the only user of it.   */
+    * the only user of it, so this should be doable.  */
   protected def parentClassLoader: ClassLoader = null
 
   /** the previous requests this interpreter has processed */
@@ -161,39 +161,41 @@ class Interpreter(val settings: Settings, reporter: Reporter, out: PrintWriter)
     stringWriter.toString
   }
 
-  /** Parse a line into a sequence of trees.
-   *
-   *  @param line ...
-   *  @return     ...
-   */
+  /** Parse a line into a sequence of trees. */
   private def parse(line: String): List[Tree] = {
-    // simple parse: just parse it, nothing else
-    def simpleParse(code: String): List[Tree] = {
-      val unit =
-        new CompilationUnit(
-          new SourceFile("<console>", code.toCharArray()))
-
-      new compiler.syntaxAnalyzer.Parser(unit).templateStatSeq
-    }
+    var justNeedsMore = false
+    reporter.withIncompleteHandler((pos,msg) => {justNeedsMore = true}) {
+//reporter.incompleteInputError = (pos,msg) => {justNeedsMore = true}
+      // simple parse: just parse it, nothing else
+      def simpleParse(code: String): List[Tree] = {
+        val unit =
+          new CompilationUnit(
+            new SourceFile("<console>", code.toCharArray()))
+        new compiler.syntaxAnalyzer.Parser(unit).templateStatSeq
+      }
 
-    // parse the main code along with the imports
-    reporter.reset
-    val trees = simpleParse(codeForImports + line)
-    if (reporter.hasErrors)
-      Nil // the result did not parse, so stop
-    else {
-      // parse the imports alone
-      val importTrees = simpleParse(codeForImports)
-
-      // return just the new trees, not the import trees
-      trees.drop(importTrees.length)
+      // parse the main code along with the imports
+      reporter.reset
+      val trees = simpleParse(codeForImports + line)
+      if (justNeedsMore) {
+        reporter.error(
+            null,
+            "Input truncated.  Interpreted expressions must fit on one line.")
+        // XXX should accept more lines of input
+        Nil
+      } else if (reporter.hasErrors)
+        Nil // the result did not parse, so stop
+      else {
+        // parse the imports alone
+        val importTrees = simpleParse(codeForImports)
+
+        // return just the new trees, not the import trees
+        trees.drop(importTrees.length)
+      }
     }
   }
 
-  /** Compile one source file.
-   *
-   *  @param filename
-   */
+  /** Compile one source file. */
   def compileFile(filename: String): Unit = {
     val jfile = new File(filename)
     if (!jfile.exists) {
@@ -207,9 +209,6 @@ class Interpreter(val settings: Settings, reporter: Reporter, out: PrintWriter)
 
   /** Compile an nsc SourceFile.  Returns true if there are
    *  no compilation errors, or false othrewise.
-   *
-   *  @param sources ...
-   *  @return        ...
    */
   def compileSources(sources: List[SourceFile]): Boolean = {
     val cr = new compiler.Run
@@ -220,20 +219,11 @@ class Interpreter(val settings: Settings, reporter: Reporter, out: PrintWriter)
 
   /** Compile a string.  Returns true if there are no
    *  compilation errors, or false otherwise.
-   *
-   *  @param code ...
-   *  @return     ...
    */
   def compileString(code: String): Boolean =
     compileSources(List(new SourceFile("<script>", code.toCharArray)))
 
-  /** build a request from the user.  "tree" is "line" after being parsed.
-   *
-   *  @param trees    ...
-   *  @param line     ...
-   *  @param lineName ...
-   *  @return         ...
-   */
+  /** build a request from the user.  "trees" is "line" after being parsed. */
   private def buildRequest(trees: List[Tree], line: String, lineName: String): Request =
     trees match {
       /* This case for assignments is more specialized than desirable: it only
@@ -252,7 +242,6 @@ class Interpreter(val settings: Settings, reporter: Reporter, out: PrintWriter)
       case List(_:AliasTypeDef) => new TypeAliasReq(line, lineName)
       case List(_:Import) => new ImportReq(line, lineName)
       case _ => {
-        //reporter.error(null, trees.toString)
         reporter.error(null, "That kind of statement combination is not supported by the interpreter.")
         null
       }
diff --git a/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala b/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
index d8ca5d73a1..f0a3808c01 100644
--- a/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
+++ b/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
@@ -137,14 +137,44 @@ trait Parsers requires SyntaxAnalyzer {
         in.errpos = in.currentPos
       }
 
+    def incompleteInputError(pos: int, msg: String): unit = {
+      if (pos != in.errpos) {
+        unit.incompleteInputError(pos, msg)
+        in.errpos = pos
+      }
+    }
+
+    def incompleteInputError(msg: String): unit =
+      incompleteInputError(in.currentPos, msg)  // in.currentPos should be at the EOF
+
+    def syntaxErrorOrIncomplete(msg: String, skipIt: Boolean): unit = {
+      if(in.token == EOF)
+        incompleteInputError(msg)
+      else
+        syntaxError(in.currentPos, msg, skipIt)
+    }
+
+    /** Consume one token of the specified type, or
+      * signal an error if it is not there.
+      */
     def accept(token: int): int = {
       val pos = in.currentPos
-      if (in.token != token)
-        syntaxError(
-          if (Position.line(unit.source, in.currentPos) > Position.line(unit.source, in.lastPos)) in.lastPos
-          else in.currentPos,
+      if (in.token != token) {
+        val posToReport =
+          if (Position.line(unit.source, in.currentPos) >
+              Position.line(unit.source, in.lastPos))
+            in.lastPos
+          else
+            in.currentPos
+        val msg =
           in.token2string(token) + " expected but " +
-            in.token2string(in.token) + " found.", true)
+          in.token2string(in.token) + " found."
+
+        if(in.token == EOF)
+          incompleteInputError(posToReport, msg)
+        else
+          syntaxError(posToReport, msg, true)
+      }
       if (in.token == token) in.nextToken()
       pos
     }
@@ -465,7 +495,7 @@ trait Parsers requires SyntaxAnalyzer {
             case NULL =>
               Constant(null)
             case _ =>
-              syntaxError("illegal literal", true)
+              syntaxErrorOrIncomplete("illegal literal", true)
               null
           })
       }
@@ -879,7 +909,7 @@ trait Parsers requires SyntaxAnalyzer {
             liftingScope(makeClosure(simpleExpr()))
             // Note: makeClosure does some special treatment of liftedGenerators
           } else {
-            syntaxError("identifier expected", true)
+            syntaxErrorOrIncomplete("identifier expected", true)
             errorTermTree
           }
         }
@@ -901,9 +931,9 @@ trait Parsers requires SyntaxAnalyzer {
                 Typed(t, atPos(pos1) { Ident(nme.WILDCARD_STAR.toTypeName) })
               }
               if (in.token != RPAREN)
-                syntaxError(in.currentPos, "`)' expected", false)
+                syntaxErrorOrIncomplete("`)' expected", false)
             } else {
-              syntaxError(in.currentPos, "`*' expected", true)
+              syntaxErrorOrIncomplete("`*' expected", true)
             }
           } else {
             t = atPos(pos) {
@@ -1032,6 +1062,8 @@ trait Parsers requires SyntaxAnalyzer {
                 t = atPos(pos) {
                   Function(ts.toList map convertToParam, TypeTree())
                 }
+              } else if(in.token == EOF) {
+                incompleteInputError("`=>' expected")
               } else {
                 syntaxError(commapos, "`)' expected", false)
               }
@@ -1063,7 +1095,7 @@ trait Parsers requires SyntaxAnalyzer {
             else if (in.token == REQUIRES || in.token == IMPLICIT)
               syntaxErrorMigrate(""+in+" is now a reserved word; cannot be used as identifier")
           }
-          syntaxError("illegal start of simple expression", true)
+          syntaxErrorOrIncomplete("illegal start of simple expression", true)
           t = errorTermTree
       }
       simpleExprRest(t, isNew)
@@ -1338,7 +1370,7 @@ trait Parsers requires SyntaxAnalyzer {
         if (settings.migrate.value &&
             in.token == MATCH || in.token == REQUIRES || in.token == IMPLICIT)
           syntaxErrorMigrate(""+in+" is now a reserved word; cannot be used as identifier")
-        syntaxError("illegal start of simple pattern", true)
+        syntaxErrorOrIncomplete("illegal start of simple pattern", true)
         errorPatternTree
     }
 
@@ -1515,6 +1547,8 @@ trait Parsers requires SyntaxAnalyzer {
            (!result.head.isEmpty && result.head.head.mods.hasFlag(Flags.IMPLICIT))))
         if (in.token == LBRACKET)
           syntaxError(pos, "no type parameters allowed here", false)
+        else if(in.token == EOF)
+          incompleteInputError(pos, "auxiliary constructor needs non-implicit parameter list")
         else
           syntaxError(pos, "auxiliary constructor needs non-implicit parameter list", false)
       addImplicitViews(owner, result, implicitViews)
@@ -1847,7 +1881,7 @@ trait Parsers requires SyntaxAnalyzer {
           case SUPERTYPE | SUBTYPE | SEMI | NEWLINE | COMMA | RBRACE =>
             typeBounds(mods | Flags.DEFERRED, name)
           case _ =>
-            syntaxError("`=', `>:', or `<:' expected", true)
+            syntaxErrorOrIncomplete("`=', `>:', or `<:' expected", true)
             EmptyTree
         }
       }
@@ -1868,7 +1902,7 @@ trait Parsers requires SyntaxAnalyzer {
       case CASEOBJECT =>
         objectDef(mods | Flags.CASE)
       case _ =>
-        syntaxError("illegal start of definition", true)
+        syntaxErrorOrIncomplete("expected start of definition", true)
         EmptyTree
     }
 
@@ -2011,7 +2045,7 @@ trait Parsers requires SyntaxAnalyzer {
           (stats ++
              joinAttributes(attrs, joinComment(List(tmplDef(modifiers()/*| mixinAttribute(attrs)*/)))))
         } else if (in.token != SEMI && in.token != NEWLINE) {
-          syntaxError("illegal start of class or object definition", true)
+          syntaxErrorOrIncomplete("expected class or object definition", true)
         }
         if (in.token != RBRACE && in.token != EOF) acceptStatSep()
       }
@@ -2037,7 +2071,7 @@ trait Parsers requires SyntaxAnalyzer {
           (stats ++
              joinAttributes(attrs, joinComment(defOrDcl(modifiers()/*| mixinAttribute(attrs)*/))))
         } else if (in.token != SEMI && in.token != NEWLINE) {
-          syntaxError("illegal start of definition", true)
+          syntaxErrorOrIncomplete("illegal start of definition", true)
         }
         if (in.token != RBRACE && in.token != EOF) acceptStatSep()
       }
@@ -2124,7 +2158,7 @@ trait Parsers requires SyntaxAnalyzer {
         if (isDclIntro) {
           stats ++= joinComment(defOrDcl(NoMods))
         } else if (in.token != SEMI && in.token != NEWLINE) {
-          syntaxError("illegal start of declaration", true)
+          syntaxErrorOrIncomplete("illegal start of declaration", true)
         }
         if (in.token != RBRACE) acceptStatSep()
       }
@@ -2183,7 +2217,7 @@ trait Parsers requires SyntaxAnalyzer {
         } else if (in.token == SEMI || in.token == NEWLINE) {
           in.nextToken()
         } else {
-          syntaxError("illegal start of statement", true)
+          syntaxErrorOrIncomplete("illegal start of statement", true)
         }
       }
       stats.toList
diff --git a/src/compiler/scala/tools/nsc/ast/parser/Scanners.scala b/src/compiler/scala/tools/nsc/ast/parser/Scanners.scala
index d612148cfc..a1ed4b088d 100644
--- a/src/compiler/scala/tools/nsc/ast/parser/Scanners.scala
+++ b/src/compiler/scala/tools/nsc/ast/parser/Scanners.scala
@@ -440,7 +440,7 @@ trait Scanners requires SyntaxAnalyzer {
             }
           } while (in.ch != '/' && in.ch != SU)
           if (in.ch == '/') in.next
-          else syntaxError("unclosed comment")
+          else incompleteInputError("unclosed comment")
           openComments = openComments - 1
         }
         true
@@ -606,7 +606,7 @@ trait Scanners requires SyntaxAnalyzer {
           getMultiLineStringLit
         }
       } else if (in.ch == SU) {
-        syntaxError("unclosed multi-line string literal")
+        incompleteInputError("unclosed multi-line string literal")
       } else {
         putChar(in.ch)
         in.next
@@ -808,6 +808,13 @@ trait Scanners requires SyntaxAnalyzer {
     */
     def syntaxError(msg: String): unit = syntaxError(pos, msg)
 
+    /** signal an error where the input ended in the middle of a token */
+    def incompleteInputError(msg: String): unit = {
+      unit.incompleteInputError(pos, msg)
+      token = EOF
+      errpos = pos
+    }
+
 // Keywords -----------------------------------------------------------------
 
     /** Keyword array; maps from name indices to tokens */
diff --git a/src/compiler/scala/tools/nsc/reporters/Reporter.scala b/src/compiler/scala/tools/nsc/reporters/Reporter.scala
index b75a75f565..cbfab874e4 100644
--- a/src/compiler/scala/tools/nsc/reporters/Reporter.scala
+++ b/src/compiler/scala/tools/nsc/reporters/Reporter.scala
@@ -47,4 +47,20 @@ abstract class Reporter {
   def    info(pos : Position, msg : String, force : Boolean) : Unit = info0(pos, msg, INFO   , force);
   def warning(pos : Position, msg : String                 ) : Unit = info0(pos, msg, WARNING, false);
   def   error(pos : Position, msg : String                 ) : Unit = info0(pos, msg,   ERROR, false);
+
+  /** An error that could possibly be fixed if the unit were longer.
+     * This is used, for example, when the interpreter tries
+     * to distinguish fatal errors from those that are due to
+     * needing more lines of input from the user. */
+  var incompleteInputError: ((Position,String) => Unit) = error
+
+  def withIncompleteHandler[T](handler: ((Position,String) => Unit))(thunk: =>T) = {
+    val savedHandler = incompleteInputError
+    try {
+      incompleteInputError = handler
+      thunk
+    } finally {
+      incompleteInputError = savedHandler
+    }
+  }
 }