SI-5923 adapt macros when they are deferred

Amazingly enough, the fix for the "macro not expanded" problem was super
easy. (And I remember spending a day or two trying to find a quick fix
somewhen around Scala Days 2012!)

The problem was in the implementation of the macro expansion trigger,
which was buried in a chain of if-elif-elif. This meant that macro
expansion was mutually exclusive with a lot of important adaptations, e.g.
with `instantiate`.

More precisely, if an expandee contains an undetparam, its expansion
should be delayed until all its undetparams are inferred and then retried
later. Sometimes such inference can only happen upon a call to instantiate
in one of the elif's coming after the macro expansion elif. However this
elif would never be called for expandees, because control flow would always
enter the macro expansion branch preceding the inference branch.

Consequences of this fix are vast. First of all, we can get rid of the
"type parameter must be specified" hack. Secondly and most importantly,
we can now remove the `materializeImplicit` method from Implicits and
rely on implicit macros to materialize tags for us. (This is a tricky
change, and I'll do it later after we merge as much of my pending work
as possible). Finally, we learn that the current scheme of interaction
between macros, type inference and implicits is, in principle, sound!

11 files changed, 6 insertions, 8 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/classfile/Pickler.scala b/src/compiler/scala/tools/nsc/symtab/classfile/Pickler.scala
index efe7519d5e..c8b7fcee8f 100644
--- a/src/compiler/scala/tools/nsc/symtab/classfile/Pickler.scala
+++ b/src/compiler/scala/tools/nsc/symtab/classfile/Pickler.scala
@@ -77,11 +77,7 @@ abstract class Pickler extends SubComponent {
         }
 
         if (!t.isDef && t.hasSymbolField && t.symbol.isTermMacro) {
-          unit.error(t.pos, t.symbol.typeParams.length match {
-            case 0 => "macro has not been expanded"
-            case 1 => "this type parameter must be specified"
-            case _ => "these type parameters must be specified"
-          })
+          unit.error(t.pos, "macro has not been expanded")
           return
         }
       }
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index a9e2d479db..b0b1341a07 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -1061,6 +1061,7 @@ trait Typers extends Modes with Adaptations with Tags {
           instantiateToMethodType(mt)
 
         case _ =>
+        def vanillaAdapt(tree: Tree) = {
           def shouldInsertApply(tree: Tree) = inAllModes(mode, EXPRmode | FUNmode) && (tree.tpe match {
             case _: MethodType | _: OverloadedType | _: PolyType => false
             case _                                               => applyPossible
@@ -1076,8 +1077,6 @@ trait Typers extends Modes with Adaptations with Tags {
           }
           if (tree.isType)
             adaptType()
-          else if (inExprModeButNot(mode, FUNmode) && treeInfo.isMacroApplication(tree))
-            macroExpandApply(this, tree, mode, pt)
           else if (inAllModes(mode, PATTERNmode | FUNmode))
             adaptConstrPattern()
           else if (shouldInsertApply(tree))
@@ -1206,6 +1205,9 @@ trait Typers extends Modes with Adaptations with Tags {
             }
             fallBack
           }
+        }
+        val tree1 = if (inExprModeButNot(mode, FUNmode) && treeInfo.isMacroApplication(tree)) macroExpandApply(this, tree, mode, pt) else tree
+        if (tree == tree1) vanillaAdapt(tree1) else tree1
       }
     }
 
diff --git a/test/files/neg/t5353.check b/test/files/neg/t5353.check
index 75e2435600..bc3f77a4d6 100644
--- a/test/files/neg/t5353.check
+++ b/test/files/neg/t5353.check
@@ -1,4 +1,4 @@
-t5353.scala:2: error: this type parameter must be specified
+t5353.scala:2: error: macro has not been expanded
   def f(x: Boolean) = if (x) Array("abc") else Array()
                                                     ^
 one error found
diff --git a/test/files/neg/t5692a.check b/test/files/pos/t5692a.check
index 7fbfb5dba7..7fbfb5dba7 100644
--- a/test/files/neg/t5692a.check
+++ b/test/files/pos/t5692a.check
diff --git a/test/files/neg/t5692a.flags b/test/files/pos/t5692a.flags
index cd66464f2f..cd66464f2f 100644
--- a/test/files/neg/t5692a.flags
+++ b/test/files/pos/t5692a.flags
diff --git a/test/files/neg/t5692a/Macros_1.scala b/test/files/pos/t5692a/Macros_1.scala
index 06b5a3de36..06b5a3de36 100644
--- a/test/files/neg/t5692a/Macros_1.scala
+++ b/test/files/pos/t5692a/Macros_1.scala
diff --git a/test/files/neg/t5692a/Test_2.scala b/test/files/pos/t5692a/Test_2.scala
index 08d510cc6f..08d510cc6f 100644
--- a/test/files/neg/t5692a/Test_2.scala
+++ b/test/files/pos/t5692a/Test_2.scala
diff --git a/test/files/neg/t5692b.check b/test/files/pos/t5692b.check
index 16796826b4..16796826b4 100644
--- a/test/files/neg/t5692b.check
+++ b/test/files/pos/t5692b.check
diff --git a/test/files/neg/t5692b.flags b/test/files/pos/t5692b.flags
index cd66464f2f..cd66464f2f 100644
--- a/test/files/neg/t5692b.flags
+++ b/test/files/pos/t5692b.flags
diff --git a/test/files/neg/t5692b/Macros_1.scala b/test/files/pos/t5692b/Macros_1.scala
index b28d19f903..b28d19f903 100644
--- a/test/files/neg/t5692b/Macros_1.scala
+++ b/test/files/pos/t5692b/Macros_1.scala
diff --git a/test/files/neg/t5692b/Test_2.scala b/test/files/pos/t5692b/Test_2.scala
index 08d510cc6f..08d510cc6f 100644
--- a/test/files/neg/t5692b/Test_2.scala
+++ b/test/files/pos/t5692b/Test_2.scala