Merge pull request scala#3237 from xeno-by/topic/macrodef-returntype-inference

deprecates macro def return type inference

Author: retronym

src/compiler/scala/reflect/macros/compiler/Validators.scala

@@ -155,7 +155,7 @@ trait Validators {
         else mmap(macroDdef.vparamss)(param)
       val macroDefRet =
         if (!macroDdef.tpt.isEmpty) typer.typedType(macroDdef.tpt).tpe
-        else computeMacroDefTypeFromMacroImplRef(macroDdef, macroImplRef)
+        else computeMacroDefTypeFromMacroImplRef(macroDdef, macroImplRef) orElse AnyTpe
       val implReturnType = sigma(increaseMetalevel(ctxPrefix, macroDefRet))
 
       object SigmaTypeMap extends TypeMap {

src/compiler/scala/reflect/macros/util/Helpers.scala

@@ -77,7 +77,8 @@ trait Helpers {
 
   /** Decreases metalevel of the type, i.e. transforms:
    *    * c.Expr[T] to T
-   *    * Anything else to Any
+   *    * Nothing to Nothing
+   *    * Anything else to NoType
    *
    *  @see Metalevels.scala for more information and examples about metalevels
    */
@@ -86,7 +87,10 @@ trait Helpers {
     import runDefinitions._
     transparentShallowTransform(RepeatedParamClass, tp) {
       case ExprClassOf(runtimeType) => runtimeType
-      case _ => AnyTpe // so that macro impls with rhs = ??? don't screw up our inference
+      // special-casing Nothing here is a useful convention
+      // that enables no-hassle prototyping with `macro ???` and `macro { ...; ??? }`
+      case nothing if nothing =:= NothingTpe => NothingTpe
+      case _ => NoType
     }
   }
 }

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -5517,7 +5517,23 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
 
       val isMacroBodyOkay = !tree.symbol.isErroneous && !(tree1 exists (_.isErroneous)) && tree1 != EmptyTree
       val shouldInheritMacroImplReturnType = ddef.tpt.isEmpty
-      if (isMacroBodyOkay && shouldInheritMacroImplReturnType) computeMacroDefTypeFromMacroImplRef(ddef, tree1) else AnyTpe
+      if (isMacroBodyOkay && shouldInheritMacroImplReturnType) {
+        val commonMessage = "macro defs must have explicitly specified return types"
+        def reportFailure() = {
+          ddef.symbol.setFlag(IS_ERROR)
+          unit.error(ddef.pos, commonMessage)
+        }
+        def reportWarning(inferredType: Type) = {
+          val explanation = s"inference of $inferredType from macro impl's c.Expr[$inferredType] is deprecated and is going to stop working in 2.12"
+          unit.deprecationWarning(ddef.pos, s"$commonMessage ($explanation)")
+        }
+        computeMacroDefTypeFromMacroImplRef(ddef, tree1) match {
+          case ErrorType => ErrorType
+          case NothingTpe => NothingTpe
+          case NoType => reportFailure(); AnyTpe
+          case tpe => reportWarning(tpe); tpe
+        }
+      } else AnyTpe
     }
 
     def transformedOr(tree: Tree, op: => Tree): Tree = transformed remove tree match {

test/files/neg/macro-blackbox-extractor/Macros_1.scala

@@ -2,7 +2,7 @@ import scala.reflect.macros.BlackboxContext
 import language.experimental.macros
 
 object Extractor {
-  def unapply(x: Int) = macro Macros.unapplyImpl
+  def unapply(x: Int): Any = macro Macros.unapplyImpl
 }
 
 object Macros {

test/files/neg/macro-blackbox-structural/Impls_Macros_1.scala

@@ -11,5 +11,5 @@ object Macros {
     """
   }
 
-  def foo = macro impl
+  def foo: Any = macro impl
 }

test/files/neg/macro-bundle-object.check

@@ -1,5 +1,5 @@
 macro-bundle-object.scala:10: error: macro implementation has incompatible shape:
- required: (c: scala.reflect.macros.BlackboxContext): c.Expr[Any]
+ required: (c: scala.reflect.macros.BlackboxContext): c.Expr[Nothing]
  or      : (c: scala.reflect.macros.BlackboxContext): c.Tree
  found   : : Nothing
 number of parameter sections differ

test/files/neg/macro-invalidret.check

@@ -12,4 +12,24 @@ Macros_Test_2.scala:3: error: macro implementation has incompatible shape:
 type mismatch for return type: reflect.runtime.universe.Literal does not conform to c.Expr[Any]
   def foo2 = macro Impls.foo2
                          ^
-two errors found
+Macros_Test_2.scala:6: error: macro defs must have explicitly specified return types
+  def foo5 = macro Impls.foo5
+      ^
+Macros_Test_2.scala:7: warning: macro defs must have explicitly specified return types (inference of Int from macro impl's c.Expr[Int] is deprecated and is going to stop working in 2.12)
+  def foo6 = macro Impls.foo6
+      ^
+Macros_Test_2.scala:14: error: exception during macro expansion:
+scala.NotImplementedError: an implementation is missing
+	at scala.Predef$.$qmark$qmark$qmark(Predef.scala:227)
+	at Impls$.foo3(Impls_1.scala:7)
+
+  foo3
+  ^
+Macros_Test_2.scala:15: error: macro implementation is missing
+  foo4
+  ^
+Macros_Test_2.scala:17: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+  foo6
+  ^
+two warnings found
+5 errors found

test/files/neg/macro-invalidret.flags

@@ -1 +1,3 @@
--language:experimental.macros
+-language:experimental.macros
+-Xfatal-warnings
+-deprecation

test/files/neg/macro-invalidret/Impls_1.scala

@@ -4,4 +4,7 @@ import scala.reflect.runtime.{universe => ru}
 object Impls {
   def foo1(c: BlackboxContext) = 2
   def foo2(c: BlackboxContext) = ru.Literal(ru.Constant(42))
+  def foo3(c: BlackboxContext) = ???
+  def foo5(c: BlackboxContext) = c.universe.Literal(c.universe.Constant(42))
+  def foo6(c: BlackboxContext) = c.Expr[Int](c.universe.Literal(c.universe.Constant(42)))
 }

test/files/neg/macro-invalidret/Macros_Test_2.scala

@@ -1,10 +1,18 @@
 object Macros {
   def foo1 = macro Impls.foo1
   def foo2 = macro Impls.foo2
+  def foo3 = macro Impls.foo3
+  def foo4 = macro ???
+  def foo5 = macro Impls.foo5
+  def foo6 = macro Impls.foo6
 }
 
 object Test extends App {
   import Macros._
   foo1
   foo2
+  foo3
+  foo4
+  foo5
+  foo6
 }

test/files/neg/macro-invalidsig-params-badtype.check

@@ -1,5 +1,5 @@
 Impls_Macros_1.scala:8: error: macro implementation has incompatible shape:
- required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Int]): c.Expr[Any]
+ required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Int]): c.Expr[Nothing]
  or      : (c: scala.reflect.macros.BlackboxContext)(x: c.Tree): c.Tree
  found   : (c: scala.reflect.macros.BlackboxContext)(x: Int): Nothing
 type mismatch for parameter x: c.Expr[Int] does not conform to Int

test/files/neg/macro-invalidsig.check

@@ -1,29 +1,29 @@
 Macros_Test_2.scala:2: error: macro implementations cannot have implicit parameters other than WeakTypeTag evidences
-  def foo[U] = macro Impls1.foo[U]
-                            ^
+  def foo[U]: Int = macro Impls1.foo[U]
+                                 ^
 Macros_Test_2.scala:6: error: macro implementation has incompatible shape:
- required: (c: scala.reflect.macros.BlackboxContext): c.Expr[Any]
+ required: (c: scala.reflect.macros.BlackboxContext): c.Expr[Nothing]
  or      : (c: scala.reflect.macros.BlackboxContext): c.Tree
  found   : : Nothing
 number of parameter sections differ
   def foo = macro Impls2.foo
                          ^
 Macros_Test_2.scala:10: error: macro implementation has incompatible shape:
- required: (c: scala.reflect.macros.BlackboxContext): c.Expr[Any]
+ required: (c: scala.reflect.macros.BlackboxContext): c.Expr[Nothing]
  or      : (c: scala.reflect.macros.BlackboxContext): c.Tree
  found   : (c: scala.reflect.api.Universe): Nothing
 type mismatch for parameter c: scala.reflect.macros.BlackboxContext does not conform to scala.reflect.api.Universe
   def foo = macro Impls3.foo
                          ^
 Macros_Test_2.scala:14: error: macro implementation has incompatible shape:
- required: (c: scala.reflect.macros.BlackboxContext): c.Expr[Any]
+ required: (c: scala.reflect.macros.BlackboxContext): c.Expr[Nothing]
  or      : (c: scala.reflect.macros.BlackboxContext): c.Tree
  found   : (cs: scala.reflect.macros.BlackboxContext*): Nothing
 types incompatible for parameter cs: corresponding is not a vararg parameter
   def foo = macro Impls4.foo
                          ^
 Macros_Test_2.scala:18: error: macro implementation has incompatible shape:
- required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Any]): c.Expr[Any]
+ required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Any]): c.Expr[Nothing]
  or      : (c: scala.reflect.macros.BlackboxContext)(x: c.Tree): c.Tree
  found   : (c: scala.reflect.macros.BlackboxContext): Nothing
 number of parameter sections differ
@@ -33,35 +33,35 @@ Macros_Test_2.scala:22: error: macro implementations cannot have implicit parame
   def foo[U](x: Int) = macro Impls6.foo[T, U]
                                     ^
 Macros_Test_2.scala:26: error: macro implementation has incompatible shape:
- required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Int]): c.Expr[Any]
+ required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Int]): c.Expr[Nothing]
  or      : (c: scala.reflect.macros.BlackboxContext)(x: c.Tree): c.Tree
  found   : (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Int], y: c.Expr[Int]): Nothing
 parameter lists have different length, found extra parameter y: c.Expr[Int]
   def foo(x: Int) = macro Impls7.foo
                                  ^
 Macros_Test_2.scala:30: error: macro implementation has incompatible shape:
- required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Int]): c.Expr[Any]
+ required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Int]): c.Expr[Nothing]
  or      : (c: scala.reflect.macros.BlackboxContext)(x: c.Tree): c.Tree
  found   : (c: scala.reflect.macros.BlackboxContext)(x: c.universe.Symbol): Nothing
 type mismatch for parameter x: c.Expr[Int] does not conform to c.universe.Symbol
   def foo(x: Int) = macro Impls8.foo
                                  ^
 Macros_Test_2.scala:34: error: macro implementation has incompatible shape:
- required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Int], y: c.Expr[Int]): c.Expr[Any]
+ required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Int], y: c.Expr[Int]): c.Expr[Nothing]
  or      : (c: scala.reflect.macros.BlackboxContext)(x: c.Tree, y: c.Tree): c.Tree
  found   : (c: scala.reflect.macros.BlackboxContext)(xs: c.Expr[Int]*): Nothing
 parameter lists have different length, required extra parameter y: c.Expr[Int]
   def foo(x: Int, y: Int) = macro Impls9.foo
                                          ^
 Macros_Test_2.scala:38: error: macro implementation has incompatible shape:
- required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Int], y: c.Expr[Int]): c.Expr[Any]
+ required: (c: scala.reflect.macros.BlackboxContext)(x: c.Expr[Int], y: c.Expr[Int]): c.Expr[Nothing]
  or      : (c: scala.reflect.macros.BlackboxContext)(x: c.Tree, y: c.Tree): c.Tree
  found   : (c: scala.reflect.macros.BlackboxContext)(y: c.Expr[Int], x: c.Expr[Int]): Nothing
 parameter names differ: x != y
   def foo(x: Int, y: Int) = macro Impls10.foo
                                           ^
 Macros_Test_2.scala:42: error: macro implementation has incompatible shape:
- required: (c: scala.reflect.macros.BlackboxContext): c.Expr[Any]
+ required: (c: scala.reflect.macros.BlackboxContext): c.Expr[Nothing]
  or      : (c: scala.reflect.macros.BlackboxContext): c.Tree
  found   : (c: scala.reflect.macros.BlackboxContext)(U: c.universe.Type): Nothing
 number of parameter sections differ
@@ -77,9 +77,9 @@ Macros_Test_2.scala:54: error: macro implementation reference has too few type a
   def foo = macro Impls14.foo
                           ^
 Macros_Test_2.scala:59: error: macro implementation reference has too few type arguments for method foo: [T, U, V](c: scala.reflect.macros.BlackboxContext)(implicit evidence$5: c.WeakTypeTag[T], implicit evidence$6: c.WeakTypeTag[U], implicit V: c.WeakTypeTag[V])c.Expr[Unit]
-    def foo15[V] = macro Impls15.foo
-                                 ^
+    def foo15[V]: Unit = macro Impls15.foo
+                                       ^
 Macros_Test_2.scala:60: error: wrong number of type parameters for method foo: [T, U, V](c: scala.reflect.macros.BlackboxContext)(implicit evidence$7: c.WeakTypeTag[T], implicit evidence$8: c.WeakTypeTag[U], implicit V: c.WeakTypeTag[V])c.Expr[Unit]
-    def foo16[V] = macro Impls16.foo[V]
-                                    ^
+    def foo16[V]: Unit = macro Impls16.foo[V]
+                                          ^
 16 errors found

test/files/neg/macro-invalidsig/Macros_Test_2.scala

@@ -1,5 +1,5 @@
 object Macros1 {
-  def foo[U] = macro Impls1.foo[U]
+  def foo[U]: Int = macro Impls1.foo[U]
 }
 
 object Macros2 {
@@ -56,8 +56,8 @@ object Macros14 {
 
 class D[T] {
   class C[U] {
-    def foo15[V] = macro Impls15.foo
-    def foo16[V] = macro Impls16.foo[V]
+    def foo15[V]: Unit = macro Impls15.foo
+    def foo16[V]: Unit = macro Impls16.foo[V]
   }
 }
 

test/files/neg/macro-invalidusage-badargs/Macros_Test_2.scala

@@ -1,4 +1,4 @@
-object Macros { def foo(x: Int) = macro Impls.foo }
+object Macros { def foo(x: Int): Int = macro Impls.foo }
 import Macros._
 
 object Test extends App {

test/files/neg/macro-invalidusage-badbounds/Macros_Test_2.scala

@@ -1,5 +1,5 @@
 object Macros {
-  def foo[U <: String] = macro Impls.foo[U]
+  def foo[U <: String]: Unit = macro Impls.foo[U]
 }
 
 object Test extends App {

test/files/neg/macro-invalidusage-badtargs.check

@@ -1,16 +1,16 @@
-Macros_Test_2.scala:11: error: macro method foo1: (x: Int)Int does not take type parameters.
+Macros_Test_2.scala:13: error: macro method foo1: (x: Int)Int does not take type parameters.
   foo1[String](42)
       ^
-Macros_Test_2.scala:12: error: wrong number of type parameters for macro method foo2: [T](x: Int)Int
+Macros_Test_2.scala:14: error: wrong number of type parameters for macro method foo2: [T](x: Int)Int
   foo2[String, String](42)
       ^
-Macros_Test_2.scala:13: error: wrong number of type parameters for macro method foo3: [T, U](x: Int)Int
+Macros_Test_2.scala:15: error: wrong number of type parameters for macro method foo3: [T, U](x: Int)Int
   foo3[String](42)
       ^
-Macros_Test_2.scala:14: error: String takes no type parameters, expected: one
+Macros_Test_2.scala:16: error: String takes no type parameters, expected: one
   foo4[String](42)
        ^
-Macros_Test_2.scala:15: error: kinds of the type arguments (List) do not conform to the expected kinds of the type parameters (type T).
+Macros_Test_2.scala:17: error: kinds of the type arguments (List) do not conform to the expected kinds of the type parameters (type T).
 List's type parameters do not match type T's expected parameters:
 type A has no type parameters, but type U has one
   foo5[List](42)

test/files/neg/macro-invalidusage-badtargs/Macros_Test_2.scala

@@ -1,9 +1,11 @@
+import scala.language.higherKinds
+
 object Macros {
-  def foo1(x: Int) = macro Impls.foo
-  def foo2[T](x: Int) = macro Impls.foo
-  def foo3[T, U](x: Int) = macro Impls.foo
-  def foo4[T[_]](x: Int) = macro Impls.foo
-  def foo5[T[U[_]]](x: Int) = macro Impls.foo
+  def foo1(x: Int): Int = macro Impls.foo
+  def foo2[T](x: Int): Int = macro Impls.foo
+  def foo3[T, U](x: Int): Int = macro Impls.foo
+  def foo4[T[_]](x: Int): Int = macro Impls.foo
+  def foo5[T[U[_]]](x: Int): Int = macro Impls.foo
 }
 
 object Test extends App {

test/files/neg/macro-invalidusage-methodvaluesyntax/Macros_Test_2.scala

@@ -1,5 +1,5 @@
 object Macros {
-  def foo = macro Impls.foo
+  def foo: Unit = macro Impls.foo
 }
 
 object Test extends App {

test/files/neg/macro-override-macro-overrides-abstract-method-a.check

@@ -1,5 +1,5 @@
 Impls_Macros_1.scala:12: error: overriding method foo in trait Foo of type (x: Int)Int;
  macro method foo cannot be used here - term macros cannot override abstract methods
-  def foo(x: Int) = macro Impls.impl
+  def foo(x: Int): Int = macro Impls.impl
       ^
 one error found

test/files/neg/macro-override-macro-overrides-abstract-method-a/Impls_Macros_1.scala

@@ -9,5 +9,5 @@ trait Foo {
 }
 
 object Macros extends Foo {
-  def foo(x: Int) = macro Impls.impl
+  def foo(x: Int): Int = macro Impls.impl
 }

test/files/neg/macro-override-method-overrides-macro.check

@@ -1,5 +1,5 @@
 Macros_Test_2.scala:8: error: overriding macro method foo in class B of type (x: String)Unit;
  method foo cannot be used here - only term macros can override term macros
-  override def foo(x: String) = println("fooDString")
+  override def foo(x: String): Unit = println("fooDString")
                ^
 one error found

test/files/neg/macro-override-method-overrides-macro/Macros_Test_2.scala

@@ -1,15 +1,15 @@
 class B {
-  def foo(x: String) = macro Impls.fooBString
-  def foo(x: Int) = macro Impls.fooBInt
-  def foo(x: Boolean) = println("fooBBoolean")
+  def foo(x: String): Unit = macro Impls.fooBString
+  def foo(x: Int): Unit = macro Impls.fooBInt
+  def foo(x: Boolean): Unit = println("fooBBoolean")
 }
 
 class D extends B {
-  override def foo(x: String) = println("fooDString")
-  override def foo(x: Int) = macro Impls.fooDInt
+  override def foo(x: String): Unit = println("fooDString")
+  override def foo(x: Int): Unit = macro Impls.fooDInt
 }
 
 class Z extends D {
-  override def foo(x: String) = macro Impls.fooZString
-  override def foo(x: Boolean) = println("fooZBoolean")
+  override def foo(x: String): Unit = macro Impls.fooZString
+  override def foo(x: Boolean): Unit = println("fooZBoolean")
 }

test/files/neg/macro-quasiquotes.check

@@ -1,8 +1,8 @@
 Macros_1.scala:14: error: macro implementation has incompatible shape:
- required: (x: Impls.this.c.Expr[Int]): Impls.this.c.Expr[Any]
+ required: (x: Impls.this.c.Expr[Int]): Impls.this.c.Expr[Unit]
  or      : (x: Impls.this.c.Tree): Impls.this.c.Tree
  found   : (x: Impls.this.c.universe.Block): Impls.this.c.Tree
 type mismatch for parameter x: Impls.this.c.Expr[Int] does not conform to Impls.this.c.universe.Block
-  def m3(x: Int) = macro Impls.impl3
-                               ^
+  def m3(x: Int): Unit = macro Impls.impl3
+                                     ^
 one error found

test/files/neg/macro-quasiquotes/Macros_1.scala

@@ -9,7 +9,7 @@ trait Impls extends BlackboxMacro {
 }
 
 object Macros {
-  def m1(x: Int) = macro Impls.impl1
-  def m2(x: Int) = macro Impls.impl2
-  def m3(x: Int) = macro Impls.impl3
+  def m1(x: Int): Unit = macro Impls.impl1
+  def m2(x: Int): Unit = macro Impls.impl2
+  def m3(x: Int): Unit = macro Impls.impl3
 }

test/files/neg/t5753/Impls_Macros_1.scala

@@ -1,6 +1,6 @@
 import scala.reflect.macros.{BlackboxContext => Ctx}
 
 trait Impls {
-def impl(c: Ctx)(x: c.Expr[Any]) = x
+  def impl(c: Ctx)(x: c.Expr[Any]) = x
 }