Adds a margin stripping string interpolator.

Currently only for compiler internal use.

Designed to avoid surprises if the interpolated values
themselves contain the margin delimiter.

Before:

    val bip = "\n  |.."

     s"""fooo
        |bar $bip
        |baz""".stripMargin

    "fooo
    bar
    ..
    baz"

After:

    sm"""fooo
        |bar $bip
        |baz"""

    "fooo
    bar
      |..
    baz"

4 files changed, 96 insertions, 0 deletions

diff --git a/src/reflect/scala/reflect/internal/SymbolTable.scala b/src/reflect/scala/reflect/internal/SymbolTable.scala
index 554acf9c0b..02ac59a461 100644
--- a/src/reflect/scala/reflect/internal/SymbolTable.scala
+++ b/src/reflect/scala/reflect/internal/SymbolTable.scala
@@ -345,6 +345,12 @@ abstract class SymbolTable extends macros.Universe
   /** Is this symbol table a part of a compiler universe?
    */
   def isCompilerUniverse = false
+
+  /**
+   * Adds the `sm` String interpolator to a [[scala.StringContext]].
+   */
+  implicit val StringContextStripMarginOps: StringContext => StringContextStripMarginOps = util.StringContextStripMarginOps
+
 }
 
 object SymbolTableStats {
diff --git a/src/reflect/scala/reflect/internal/util/StripMarginInterpolator.scala b/src/reflect/scala/reflect/internal/util/StripMarginInterpolator.scala
new file mode 100644
index 0000000000..e7579229b2
--- /dev/null
+++ b/src/reflect/scala/reflect/internal/util/StripMarginInterpolator.scala
@@ -0,0 +1,40 @@
+package scala.reflect
+package internal
+package util
+
+trait StripMarginInterpolator {
+  def stringContext: StringContext
+
+  /**
+   * A safe combination of `[[scala.collection.immutable.StringLike#stripMargin]]
+   * and [[scala.StringContext#raw]].
+   *
+   * The margin of each line is defined by whitespace leading up to a '|' character.
+   * This margin is stripped '''before''' the arguments are interpolated into to string.
+   *
+   * String escape sequences are '''not''' processed; this interpolater is designed to
+   * be used with triple quoted Strings.
+   *
+   * {{{
+   * scala> val foo = "f|o|o"
+   * foo: String = f|o|o
+   * scala> sm"""|${foo}
+   *             |"""
+   * res0: String =
+   * "f|o|o
+   * "
+   * }}}
+   */
+  final def sm(args: Any*): String = {
+    def isLineBreak(c: Char) = c == '\n' || c == '\f' // compatible with StringLike#isLineBreak
+    def stripTrailingPart(s: String) = {
+      val (pre, post) = s.span(c => !isLineBreak(c))
+      pre + post.stripMargin
+    }
+    val stripped: List[String] = stringContext.parts.toList match {
+      case head :: tail => head.stripMargin :: (tail map stripTrailingPart)
+      case Nil => Nil
+    }
+    new StringContext(stripped: _*).raw(args: _*)
+  }
+}
diff --git a/src/reflect/scala/reflect/internal/util/package.scala b/src/reflect/scala/reflect/internal/util/package.scala
new file mode 100644
index 0000000000..6d77235db6
--- /dev/null
+++ b/src/reflect/scala/reflect/internal/util/package.scala
@@ -0,0 +1,9 @@
+package scala.reflect
+package internal
+
+package object util {
+  /**
+   * Adds the `sm` String interpolator to a [[scala.StringContext]].
+   */
+  implicit class StringContextStripMarginOps(val stringContext: StringContext) extends StripMarginInterpolator
+}
diff --git a/test/files/run/sm-interpolator.scala b/test/files/run/sm-interpolator.scala
new file mode 100644
index 0000000000..7f7b9f061a
--- /dev/null
+++ b/test/files/run/sm-interpolator.scala
@@ -0,0 +1,41 @@
+object Test extends App {
+  import scala.reflect.internal.util.StringContextStripMarginOps
+  def check(actual: Any, expected: Any) = if (actual != expected) sys.error(s"expected: [$expected], actual: [$actual])")
+
+  val bar = "|\n ||"
+
+  check(
+    sm"""|ab  
+         |de
+         |${bar} | ${1}""",
+      "ab  \nde\n|\n || | 1")
+
+  check(
+    sm"|",
+      "")
+
+  check(
+    sm"${0}",
+      "0")
+
+  check(
+    sm"${0}",
+    "0")
+
+  check(
+    sm"""${0}|${1}
+     |""",
+      "0|1\n")
+
+  check(
+    sm"""   ||""",
+      "|")
+
+  check(
+    sm""" ${" "} ||""",
+      "   ||")
+
+  check(
+      sm"\n",
+     raw"\n".stripMargin)
+}