better error for external rules ran with old scalafix-cli version

metaconfig-pprint brought by metaconfig 0.10.0 will not be available to
external rules when classloaded by an old scalafix-cli version as
the runtime scalafix-core and its dependencies are driven by
scalafix-cli dependencies, not the rule dependencies.

We obviously have no control over old scalafix-cli versions, but since
the reference to the potentially-missing type is from a macro-generated
block, this wraps it to provide a more actionnable error message.

scalafix-core/src/main/scala-2.12/scalafix/util/metaconfig/generic/package.scala

@@ -0,0 +1,21 @@
+package metaconfig
+
+import metaconfig.internal.ScalafixHijackMacros
+
+import scala.language.experimental.macros
+
+// shadows https://github.com/scalameta/metaconfig/blob/v0.10.0/metaconfig-core/shared/src/main/scala-2/metaconfig/generic/package.scala
+package object generic {
+  def deriveSurface[T]: Surface[T] =
+    macro ScalafixHijackMacros.deriveSurfaceImpl[T]
+  def deriveDecoder[T](default: T): ConfDecoder[T] =
+    macro metaconfig.internal.Macros.deriveConfDecoderImpl[T]
+  def deriveEncoder[T]: ConfEncoder[T] =
+    macro metaconfig.internal.Macros.deriveConfEncoderImpl[T]
+  def deriveCodec[T](default: T): ConfCodec[T] =
+    macro metaconfig.internal.Macros.deriveConfCodecImpl[T]
+  def deriveDecoderEx[T](default: T): ConfDecoderEx[T] =
+    macro metaconfig.internal.Macros.deriveConfDecoderExImpl[T]
+  def deriveCodecEx[T](default: T): ConfCodecEx[T] =
+    macro metaconfig.internal.Macros.deriveConfCodecExImpl[T]
+}

scalafix-core/src/main/scala-2.13/metaconfig/generic/package.scala

@@ -0,0 +1,21 @@
+package metaconfig
+
+import metaconfig.internal.ScalafixHijackMacros
+
+import scala.language.experimental.macros
+
+// shadows https://github.com/scalameta/metaconfig/blob/v0.10.0/metaconfig-core/shared/src/main/scala-2/metaconfig/generic/package.scala
+package object generic {
+  def deriveSurface[T]: Surface[T] =
+    macro ScalafixHijackMacros.deriveSurfaceImpl[T]
+  def deriveDecoder[T](default: T): ConfDecoder[T] =
+    macro metaconfig.internal.Macros.deriveConfDecoderImpl[T]
+  def deriveEncoder[T]: ConfEncoder[T] =
+    macro metaconfig.internal.Macros.deriveConfEncoderImpl[T]
+  def deriveCodec[T](default: T): ConfCodec[T] =
+    macro metaconfig.internal.Macros.deriveConfCodecImpl[T]
+  def deriveDecoderEx[T](default: T): ConfDecoderEx[T] =
+    macro metaconfig.internal.Macros.deriveConfDecoderExImpl[T]
+  def deriveCodecEx[T](default: T): ConfCodecEx[T] =
+    macro metaconfig.internal.Macros.deriveConfCodecExImpl[T]
+}

scalafix-core/src/main/scala/scalafix/internal/config/ConfigRulePatches.scala

@@ -3,6 +3,7 @@ package scalafix.internal.config
 import metaconfig.ConfDecoder
 import metaconfig.generic
 import metaconfig.generic.Surface
+import scalafix.internal.util.MetaconfigCompatMacros
 import scalafix.patch.Patch
 import scalafix.patch.Patch.internal._
 
@@ -17,7 +18,7 @@ case class ConfigRulePatches(
 
 object ConfigRulePatches {
   implicit val surface: Surface[ConfigRulePatches] =
-    generic.deriveSurface[ConfigRulePatches]
+    MetaconfigCompatMacros.deriveSurfaceOrig[ConfigRulePatches]
   val default: ConfigRulePatches = ConfigRulePatches()
   implicit val configRuleDecoder: ConfDecoder[ConfigRulePatches] =
     generic.deriveDecoder[ConfigRulePatches](default)

scalafix-core/src/main/scala/scalafix/internal/config/DebugConfig.scala

@@ -3,13 +3,14 @@ package scalafix.internal.config
 import metaconfig.ConfDecoder
 import metaconfig.generic
 import metaconfig.generic.Surface
+import scalafix.internal.util.MetaconfigCompatMacros
 
 case class DebugConfig(
     printSymbols: Boolean = false
 )
 object DebugConfig {
   implicit val surface: Surface[DebugConfig] =
-    generic.deriveSurface[DebugConfig]
+    MetaconfigCompatMacros.deriveSurfaceOrig[DebugConfig]
   val default: DebugConfig = DebugConfig()
   implicit val decoder: ConfDecoder[DebugConfig] =
     generic.deriveDecoder[DebugConfig](default)

scalafix-core/src/main/scala/scalafix/internal/config/LintConfig.scala

@@ -3,6 +3,7 @@ package scalafix.internal.config
 import metaconfig.ConfDecoder
 import metaconfig.generic
 import metaconfig.generic.Surface
+import scalafix.internal.util.MetaconfigCompatMacros
 import scalafix.lint.LintSeverity
 
 case class LintConfig(
@@ -21,7 +22,8 @@ case class LintConfig(
 }
 
 object LintConfig {
-  implicit val surface: Surface[LintConfig] = generic.deriveSurface[LintConfig]
+  implicit val surface: Surface[LintConfig] =
+    MetaconfigCompatMacros.deriveSurfaceOrig[LintConfig]
   lazy val default: LintConfig = LintConfig()
   implicit val decoder: ConfDecoder[LintConfig] =
     generic.deriveDecoder[LintConfig](default)

scalafix-core/src/main/scala/scalafix/internal/config/ScalafixConfig.scala

@@ -4,6 +4,7 @@ import scala.meta._
 
 import metaconfig._
 import metaconfig.generic.Surface
+import scalafix.internal.util.MetaconfigCompatMacros
 import scalafix.Versions
 import scalafix.internal.config.ScalafixConfig._
 
@@ -38,7 +39,7 @@ object ScalafixConfig {
   def decoder(default: ScalafixConfig): ConfDecoder[ScalafixConfig] =
     generic.deriveDecoder[ScalafixConfig](default)
   implicit lazy val surface: Surface[ScalafixConfig] =
-    generic.deriveSurface[ScalafixConfig]
+    MetaconfigCompatMacros.deriveSurfaceOrig[ScalafixConfig]
   implicit lazy val ScalafixConfigDecoder: ConfDecoder[ScalafixConfig] =
     decoder(default)
 

scalafix-core/src/main/scala/scalafix/internal/util/MetaconfigCompatMacros.scala

@@ -0,0 +1,40 @@
+package scalafix.internal.util
+
+import scala.language.experimental.macros
+import scala.reflect.macros.blackbox
+
+object MetaconfigCompatMacros {
+  // metaconfig.generic.deriveSurface cannot be used within scalafix-core as macro implementations cannot
+  // be used in the same compilation run that defines them
+  def deriveSurfaceOrig[T]: metaconfig.generic.Surface[T] =
+    macro metaconfig.internal.Macros.deriveSurfaceImpl[T]
+}
+
+class MetaconfigCompatMacros(override val c: blackbox.Context)
+    extends metaconfig.internal.Macros(c) {
+
+  import c.universe._
+
+  // Provide an actionnable error in case of linking issue, see https://github.com/scalacenter/scalafix/pull/1530#issuecomment-1061174301
+  override def deriveSurfaceImpl[T: c.WeakTypeTag]: Tree = {
+    val unsafeTree = super.deriveSurfaceImpl[T]
+
+    val buildVersion = scalafix.Versions.nightly
+    q"""
+      val runtimeVersion = _root_.scalafix.Versions.nightly
+      try {
+        new java.util.concurrent.Callable[${weakTypeOf[metaconfig.generic.Surface[T]]}] {
+          // Since the unsafeTree gets lifted into a static block, we wrap its execution
+          // inside a nested class to be able to intercept the NoClassDefFoundError
+          override def call: ${weakTypeOf[metaconfig.generic.Surface[T]]} = $unsafeTree
+        }.call
+      } catch {
+        case e: NoClassDefFoundError =>
+          throw new RuntimeException(
+            "Scalafix version " + runtimeVersion + " detected. Please upgrade to " + $buildVersion + " or later",
+            e
+          )
+      }
+    """
+  }
+}