Force compile errors for missing implicits in `Discovered` materialization to point at their source methods, for easier fixing

4 files changed, 53 insertions, 9 deletions

diff --git a/core/src/main/scala/mill/discover/Discovered.scala b/core/src/main/scala/mill/discover/Discovered.scala
index 9d46f196..0f3ced4e 100644
--- a/core/src/main/scala/mill/discover/Discovered.scala
+++ b/core/src/main/scala/mill/discover/Discovered.scala
@@ -53,10 +53,13 @@ object Discovered {
            !m.name.toString.contains(' ')
       } yield {
         val x = Ident(TermName(c.freshName()))
-        q"""mill.discover.Mirror.makeTargetPoint(
+        val t = q"""mill.discover.Mirror.makeTargetPoint(
           ${m.name.toString},
           ($x: ${m.typeSignature.resultType}) => $x.${m.name.toTermName}
         )"""
+
+        c.internal.setPos(t, m.pos)
+        t
       }
 
 
diff --git a/core/src/main/scala/mill/discover/Router.scala b/core/src/main/scala/mill/discover/Router.scala
index 90e50075..dda682b2 100644
--- a/core/src/main/scala/mill/discover/Router.scala
+++ b/core/src/main/scala/mill/discover/Router.scala
@@ -2,6 +2,7 @@ package mill.discover
 
 import ammonite.main.Compat
 import mill.define.Task
+import mill.discover.Router.ArgSig
 import sourcecode.Compat.Context
 
 import scala.annotation.StaticAnnotation
@@ -237,7 +238,18 @@ object Router{
       Result.Success(rights)
     }
   }
+
+  def makeReadCall[T: scopt.Read](dict: Map[String, String],
+                                  default: => Option[Any],
+                                  arg: ArgSig[_]) = {
+    read[T](dict, default, arg, implicitly[scopt.Read[T]].reads(_))
+  }
+  def makeReadVarargsCall[T: scopt.Read](arg: ArgSig[_],
+                             values: Seq[String]) = {
+    readVarargs[T](arg, values, implicitly[scopt.Read[T]].reads(_))
+  }
 }
+
 class Router [C <: Context](val c: C) {
   import c.universe._
   def getValsOrMeths(curCls: Type): Iterable[MethodSymbol] = {
@@ -260,6 +272,8 @@ class Router [C <: Context](val c: C) {
     }
   }
 
+
+
   def extractMethod(meth: MethodSymbol, curCls: c.universe.Type): c.universe.Tree = {
     val flattenedArgLists = meth.paramss.flatten
     def hasDefault(i: Int) = {
@@ -334,19 +348,18 @@ class Router [C <: Context](val c: C) {
 
       val reader =
         if(vararg) q"""
-          mill.discover.Router.readVarargs[$docUnwrappedType](
+          mill.discover.Router.makeReadVarargsCall[$docUnwrappedType](
             $argSig,
-            $extrasSymbol,
-            implicitly[scopt.Read[$docUnwrappedType]].reads(_)
+            $extrasSymbol
           )
         """ else q"""
-        mill.discover.Router.read[$docUnwrappedType](
+        mill.discover.Router.makeReadCall[$docUnwrappedType](
           $argListSymbol,
           $default,
-          $argSig,
-          implicitly[scopt.Read[$docUnwrappedType]].reads(_)
+          $argSig
         )
         """
+      c.internal.setPos(reader, meth.pos)
       (reader, argSig, vararg)
     }
 
diff --git a/core/src/test/scala/mill/discover/DiscoveredTests.scala b/core/src/test/scala/mill/discover/DiscoveredTests.scala
index dae7ff1b..843ec474 100644
--- a/core/src/test/scala/mill/discover/DiscoveredTests.scala
+++ b/core/src/test/scala/mill/discover/DiscoveredTests.scala
@@ -1,7 +1,9 @@
 package mill.discover
 
+import java.io.InputStreamReader
+
 import utest._
-import mill.Module
+import mill.{Module, T}
 import mill.util.TestUtil.test
 object DiscoveredTests extends TestSuite{
 
@@ -48,5 +50,32 @@ object DiscoveredTests extends TestSuite{
       )
       assert(mapped.toSet == expected.toSet)
     }
+    'compileError - {
+      'unserializableTarget - {
+
+        object outer extends Module {
+          def single = mill.T{ new InputStreamReader(System.in) }
+        }
+
+        val error = compileError("Discovered[outer.type]")
+        assert(
+          error.msg.contains("could not find implicit value"),
+          error.pos.contains("def single = mill.T{ new InputStreamReader(System.in) }")
+        )
+      }
+
+      'unreadableCommand - {
+        object outer extends Module {
+          def single(in: InputStreamReader) = mill.T.command{ println(123) }
+        }
+
+        val error = compileError("Discovered[outer.type]")
+
+        assert(
+          error.msg.contains("could not find implicit value"),
+          error.pos.contains("def single(in: InputStreamReader) = mill.T.command{ println(123) }")
+        )
+      }
+    }
   }
 }
diff --git a/core/src/test/scala/mill/eval/EvaluationTests.scala b/core/src/test/scala/mill/eval/EvaluationTests.scala
index ccb476e7..9a177b58 100644
--- a/core/src/test/scala/mill/eval/EvaluationTests.scala
+++ b/core/src/test/scala/mill/eval/EvaluationTests.scala
@@ -5,7 +5,6 @@ import mill.util.TestUtil.{Test, test}
 import mill.define.{Target, Task}
 import mill.{Module, T}
 import mill.discover.Discovered
-import mill.eval.Evaluator
 import mill.util.{OSet, TestUtil}
 import utest._
 import utest.framework.TestPath