Merge pull request #5981 from eed3si9n/wip/pure-expression

Work around "a pure expression does nothing" warning

core-macros/src/main/scala/sbt/internal/util/appmacro/ContextUtil.scala

@@ -312,6 +312,17 @@ final class ContextUtil[C <: blackbox.Context](val ctx: C) {
               case Converted.Failure(p, m)       => ctx.abort(p, m)
               case _: Converted.NotApplicable[_] => super.transform(tree)
             }
+          // try to workaround https://github.com/scala/bug/issues/12112 by removing raw Ident(_) in blocks
+          case Block(stats0, expr0) =>
+            val stats = stats0 flatMap { stat0 =>
+              val stat = super.transform(stat0)
+              stat match {
+                case Typed(ident @ Ident(_), _) if ident.symbol.isSynthetic => None
+                case _                                                      => Some(stat)
+              }
+            }
+            val expr = super.transform(expr0)
+            Block(stats, expr).setType(expr.tpe)
           case _ => super.transform(tree)
         }
     }

sbt/src/sbt-test/project/setting-macro/project/PureExpressionPlugin.scala

@@ -0,0 +1,15 @@
+package pkgtest
+
+import sbt._, Keys._
+
+// https://github.com/scala/bug/issues/12112
+object PureExpressionPlugin extends AutoPlugin {
+  lazy val testPureExpression = taskKey[Unit]("")
+  override def projectSettings: Seq[Setting[_]] = {
+    testPureExpression := {
+      updateFull.value
+      (Compile / compile).value
+      (Test / test).value
+    }
+  }
+}

sbt/src/sbt-test/project/setting-macro/project/plugins.sbt

@@ -0,0 +1 @@
+Compile / scalacOptions += "-Xfatal-warnings"