Warn about forgotten string interpolators.

In the compiler sources this arrives with a number of false
positives, because we frequently work with strings containing
$foo where foo is an in-scope identifier. I think in normal
source code this will be less of a problem, or none at all;
but to be conservative the warning is born under -Xlint.

5 files changed, 42 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Macros.scala b/src/compiler/scala/tools/nsc/typechecker/Macros.scala
index 91ebd798e1..2dbfa1d0d3 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Macros.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Macros.scala
@@ -189,7 +189,7 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
       val payload = pickledPayload.map{ case Assign(k, v) => (unpickleAtom(k), unpickleAtom(v)) }.toMap
 
       val pickleVersionFormat = payload("versionFormat").asInstanceOf[Int]
-      if (versionFormat != pickleVersionFormat) throw new Error("macro impl binding format mismatch: expected $versionFormat, actual $pickleVersionFormat")
+      if (versionFormat != pickleVersionFormat) throw new Error(s"macro impl binding format mismatch: expected $versionFormat, actual $pickleVersionFormat")
 
       val className = payload("className").asInstanceOf[String]
       val methodName = payload("methodName").asInstanceOf[String]
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index eaf57cd39c..33f1ed3386 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -86,6 +86,9 @@ trait Typers extends Adaptations with Tags {
   // that are turned private by typedBlock
   private final val SYNTHETIC_PRIVATE = TRANS_FLAG
 
+  private final val InterpolatorCodeRegex  = """\$\{.*?\}""".r
+  private final val InterpolatorIdentRegex = """\$\w+""".r
+
   // To enable decent error messages when the typer crashes.
   // TODO - this only catches trees which go through def typed,
   // but there are all kinds of back ways - typedClassDef, etc. etc.
@@ -5151,6 +5154,19 @@ trait Typers extends Adaptations with Tags {
 
       def typedLiteral(tree: Literal) = {
         val value = tree.value
+        // Warn about likely interpolated strings which are missing their interpolators
+        if (settings.lint.value) value match {
+          case Constant(s: String) =>
+            def names = InterpolatorIdentRegex findAllIn s map (n => newTermName(n stripPrefix "$"))
+            val shouldWarn = (
+                 (InterpolatorCodeRegex findFirstIn s).nonEmpty
+              || (names exists (n => context.lookupSymbol(n, _ => true).symbol.exists))
+            )
+            if (shouldWarn)
+              unit.warning(tree.pos, "looks like an interpolated String; did you forget the interpolator?")
+          case _ =>
+        }
+
         tree setType (
           if (value.tag == UnitTag) UnitClass.tpe
           else ConstantType(value))
diff --git a/test/files/neg/forgot-interpolator.check b/test/files/neg/forgot-interpolator.check
new file mode 100644
index 0000000000..f6de4d7b3a
--- /dev/null
+++ b/test/files/neg/forgot-interpolator.check
@@ -0,0 +1,9 @@
+forgot-interpolator.scala:4: warning: looks like an interpolated String; did you forget the interpolator?
+  def f = "Put the $bippy in the $bippy!" // warn
+          ^
+forgot-interpolator.scala:14: warning: looks like an interpolated String; did you forget the interpolator?
+  def f = """Put the ${println("bippy")} in the bippy!""" // warn
+          ^
+error: No warnings can be incurred under -Xfatal-warnings.
+two warnings found
+one error found
diff --git a/test/files/neg/forgot-interpolator.flags b/test/files/neg/forgot-interpolator.flags
new file mode 100644
index 0000000000..7949c2afa2
--- /dev/null
+++ b/test/files/neg/forgot-interpolator.flags
@@ -0,0 +1 @@
+-Xlint -Xfatal-warnings
diff --git a/test/files/neg/forgot-interpolator.scala b/test/files/neg/forgot-interpolator.scala
new file mode 100644
index 0000000000..d67db82643
--- /dev/null
+++ b/test/files/neg/forgot-interpolator.scala
@@ -0,0 +1,15 @@
+class A {
+  val bippy = 123
+
+  def f = "Put the $bippy in the $bippy!" // warn
+}
+
+class B {
+  val dingus = 123
+
+  def f = "Put the $bippy in the $bippy!" // no warn
+}
+
+class C {
+  def f = """Put the ${println("bippy")} in the bippy!""" // warn
+}