SI-9450 Fix triple quoted strings in REPL :power mode

Some extra synthetic code generated under this mode failed to escape
input before adding it to a literal string. It used to get away with
this most of the time by triple quoting the literal.

This commit reuses Scala string escaping logic buried in `Constant`
to do this properly. Actually, the proper approach would be to build
the synthetic code with trees and quasiquotes, and avoid the mess
of stringly-genererated code.

I threw in some defensive hygiene for the reference to `Nil` while
I was in the neighbourhood.

2 files changed, 7 insertions, 1 deletions

diff --git a/test/files/run/repl-power.check b/test/files/run/repl-power.check
index 2a7b7783d9..4e030bd9fa 100644
--- a/test/files/run/repl-power.check
+++ b/test/files/run/repl-power.check
@@ -25,4 +25,7 @@ m: $r.treedsl.global.Literal = 10
 scala> typed(m).tpe                              // typed is in scope
 res2: $r.treedsl.global.Type = Int(10)
 
+scala> """escaping is hard, m'kah"""
+res3: String = escaping is hard, m'kah
+
 scala> :quit
diff --git a/test/files/run/repl-power.scala b/test/files/run/repl-power.scala
index 4dfeb37885..5ecaad8723 100644
--- a/test/files/run/repl-power.scala
+++ b/test/files/run/repl-power.scala
@@ -1,7 +1,9 @@
 import scala.tools.partest.ReplTest
 
 object Test extends ReplTest {
-  def code = """
+  def tripleQuote(s: String) = "\"\"\"" + s + "\"\"\""
+
+  def code = s"""
 :power
 // guarding against "error: reference to global is ambiguous"
 global.emptyValDef  // "it is imported twice in the same scope by ..."
@@ -9,5 +11,6 @@ val tp = ArrayClass[scala.util.Random]    // magic with tags
 tp.memberType(Array_apply)                // evidence
 val m = LIT(10)                           // treedsl
 typed(m).tpe                              // typed is in scope
+${tripleQuote("escaping is hard, m'kah")}
   """.trim
 }