Support completion in erroneous string interpolation.

In the code:

```
s"${fooo<CURSOR"
```

The parser treats `fooo` as a interpolator ID for the quote that
we actually intend to end the interpolated string.

Inserting a space (in addition to `__CURSOR__` that we already
patch in to avoid parsing a partial identifier as a keyword),
solves this problem.

2 files changed, 9 insertions, 1 deletions

diff --git a/src/repl/scala/tools/nsc/interpreter/PresentationCompilerCompleter.scala b/src/repl/scala/tools/nsc/interpreter/PresentationCompilerCompleter.scala
index 0fb3236966..4b0330aaf7 100644
--- a/src/repl/scala/tools/nsc/interpreter/PresentationCompilerCompleter.scala
+++ b/src/repl/scala/tools/nsc/interpreter/PresentationCompilerCompleter.scala
@@ -36,7 +36,7 @@ class PresentationCompilerCompleter(intp: IMain) extends Completion with ScalaCo
     // secret handshakes
     val slashPrint  = """.*// *print *""".r
     val slashTypeAt = """.*// *typeAt *(\d+) *(\d+) *""".r
-    val Cursor = IMain.DummyCursorFragment
+    val Cursor = IMain.DummyCursorFragment + " "
 
     def print(result: Result) = {
       val offset = result.preambleLength
diff --git a/test/junit/scala/tools/nsc/interpreter/CompletionTest.scala b/test/junit/scala/tools/nsc/interpreter/CompletionTest.scala
index 514f30571e..d00a9bf69a 100644
--- a/test/junit/scala/tools/nsc/interpreter/CompletionTest.scala
+++ b/test/junit/scala/tools/nsc/interpreter/CompletionTest.scala
@@ -52,6 +52,14 @@ class CompletionTest {
   }
 
   @Test
+  def incompleteStringInterpolation(): Unit = {
+    val intp = newIMain()
+    val completer = new PresentationCompilerCompleter(intp)
+    checkExact(completer, """val x_y_z = 1; s"${x_""", "}\"")("x_y_z")
+    checkExact(completer, """val x_y_z = 1; s"${x_""", "\"")("x_y_z")
+  }
+
+  @Test
   def symbolically(): Unit = {
     val intp = newIMain()
     val completer = new PresentationCompilerCompleter(intp)