Draft fixes

Author: Szymon Rodziewicz

compiler/src/dotty/tools/dotc/typer/Implicits.scala

@@ -559,7 +559,7 @@ object Implicits:
       else 
         reasons.mkString
 
-    def explanation(using Context) = em"Failed to synthesize implicit of type ${clarify(expectedType)}: ${formatReasons}"
+    def explanation(using Context) = em"Failed to synthesize an instance of type ${clarify(expectedType)}: ${formatReasons}"
 
 end Implicits
 

compiler/src/dotty/tools/dotc/typer/Synthesizer.scala

@@ -17,20 +17,12 @@ import transform.SyntheticMembers._
 import util.Property
 import ast.Trees.genericEmptyTree
 import annotation.{tailrec, constructorOnly}
+import ast.tpd._
+import Synthesizer._
 
 /** Synthesize terms for special classes */
 class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
-  import ast.tpd._
 
-  /** Tuple used to store the synthesis result with a list of errors */ 
-  private type TreeWithErrors = (Tree, List[String])
-  private def withNoErrors(tree: Tree): TreeWithErrors = (tree, List.empty)
-
-  private val EmptyTreeNoError: TreeWithErrors = withNoErrors(EmptyTree)
-  private def orElse(treeWithErrors1: TreeWithErrors, treeWithErrors2: => TreeWithErrors): TreeWithErrors = treeWithErrors1 match
-    case (tree, errors) if tree eq genericEmptyTree => (treeWithErrors2._1, treeWithErrors2._2 ::: errors)
-    case _                                          => treeWithErrors1
-      
   /** Handlers to synthesize implicits for special types */
   type SpecialHandler = (Type, Span) => Context ?=> TreeWithErrors
   private type SpecialHandlers = List[(ClassSymbol, SpecialHandler)]
@@ -620,3 +612,15 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
     recur(specialHandlers)
 
 end Synthesizer
+
+object Synthesizer:
+
+  /** Tuple used to store the synthesis result with a list of errors */ 
+  type TreeWithErrors = (Tree, List[String])
+  private def withNoErrors(tree: Tree): TreeWithErrors = (tree, List.empty)
+
+  private val EmptyTreeNoError: TreeWithErrors = withNoErrors(EmptyTree)
+  private def orElse(treeWithErrors1: TreeWithErrors, treeWithErrors2: => TreeWithErrors): TreeWithErrors = treeWithErrors1 match
+    case (tree, errors) if tree eq genericEmptyTree => (treeWithErrors2._1, treeWithErrors2._2 ::: errors)
+    case _                                          => treeWithErrors1
+end Synthesizer

tests/neg/i14432.check

@@ -1,4 +1,4 @@
 -- Error: tests/neg/i14432.scala:13:33 ---------------------------------------------------------------------------------
 13 |val mFoo = summon[Mirror.Of[Foo]] // error: no mirror found
    |                                 ^
-   |No given instance of type deriving.Mirror.Of[example.Foo] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[example.Foo]: Constructor of class Foo is unnaccessible from the calling scope.
+   |No given instance of type deriving.Mirror.Of[example.Foo] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[example.Foo]: Constructor of class Foo is unnaccessible from the calling scope.

tests/neg/i14432a.check

@@ -1,4 +1,4 @@
 -- Error: tests/neg/i14432a.scala:14:43 --------------------------------------------------------------------------------
 14 |  val mFoo = summon[Mirror.Of[example.Foo]] // error: no mirror found
    |                                           ^
-   |No given instance of type deriving.Mirror.Of[example.Foo] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[example.Foo]: Constructor of class Foo is unnaccessible from the calling scope.
+   |No given instance of type deriving.Mirror.Of[example.Foo] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[example.Foo]: Constructor of class Foo is unnaccessible from the calling scope.

tests/neg/i14432b.check

@@ -1,4 +1,4 @@
 -- Error: tests/neg/i14432b.scala:15:43 --------------------------------------------------------------------------------
 15 |  val mFoo = summon[Mirror.Of[example.Foo]] // error: no mirror found
    |                                           ^
-   |No given instance of type deriving.Mirror.Of[example.Foo] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[example.Foo]: Constructor of class Foo is unnaccessible from the calling scope.
+   |No given instance of type deriving.Mirror.Of[example.Foo] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[example.Foo]: Constructor of class Foo is unnaccessible from the calling scope.

tests/neg/i14432c.check

@@ -9,4 +9,4 @@
 -- Error: tests/neg/i14432c.scala:16:43 --------------------------------------------------------------------------------
 16 |  val mFoo = summon[Mirror.Of[example.Foo]] // error: no mirror
    |                                           ^
-   |No given instance of type deriving.Mirror.Of[example.Foo] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[example.Foo]: Constructor of class Foo is unnaccessible from the calling scope.
+   |No given instance of type deriving.Mirror.Of[example.Foo] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[example.Foo]: Constructor of class Foo is unnaccessible from the calling scope.

tests/neg/i14432d.check

@@ -1,4 +1,4 @@
 -- Error: tests/neg/i14432d.scala:17:45 --------------------------------------------------------------------------------
 17 |    val mFoo = summon[Mirror.Of[example.Foo]] // error
    |                                             ^
-   |No given instance of type deriving.Mirror.Of[example.Foo] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[example.Foo]: Constructor of class Foo is unnaccessible from the calling scope.
+   |No given instance of type deriving.Mirror.Of[example.Foo] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[example.Foo]: Constructor of class Foo is unnaccessible from the calling scope.

tests/neg/mirror-synthesis-errors.check

@@ -1,28 +1,28 @@
 -- Error: tests/neg/mirror-synthesis-errors.scala:21:32 ----------------------------------------------------------------
 21 |val testA = summon[Mirror.Of[A]] // error: Not a sealed trait
    |                                ^
-   |No given instance of type deriving.Mirror.Of[A] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[A]: trait A is not a sealed trait
+   |No given instance of type deriving.Mirror.Of[A] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[A]: trait A is not a sealed trait
 -- Error: tests/neg/mirror-synthesis-errors.scala:22:32 ----------------------------------------------------------------
 22 |val testC = summon[Mirror.Of[C]] // error: Does not have subclasses
    |                                ^
-   |No given instance of type deriving.Mirror.Of[C] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[C]: trait C does not have subclasses
+   |No given instance of type deriving.Mirror.Of[C] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[C]: trait C does not have subclasses
 -- Error: tests/neg/mirror-synthesis-errors.scala:23:32 ----------------------------------------------------------------
 23 |val testD = summon[Mirror.Of[D]] // error: child SubD takes more than one parameter list
    |                                ^
-   |No given instance of type deriving.Mirror.Of[D] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[D]: class D's child class SubD is not a generic product because class SubD takes more than one parameter list
+   |No given instance of type deriving.Mirror.Of[D] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[D]: class D's child class SubD is not a generic product because class SubD takes more than one parameter list
 -- Error: tests/neg/mirror-synthesis-errors.scala:24:38 ----------------------------------------------------------------
 24 |val testSubD = summon[Mirror.Of[SubD]] // error: takes more than one parameter list
    |                                      ^
-   |No given instance of type deriving.Mirror.Of[SubD] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[SubD]: class SubD is not a sealed class
+   |No given instance of type deriving.Mirror.Of[SubD] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[SubD]: class SubD is not a sealed class
 -- Error: tests/neg/mirror-synthesis-errors.scala:25:32 ----------------------------------------------------------------
 25 |val testE = summon[Mirror.Of[E]] // error: Not an abstract class
    |                                ^
-   |No given instance of type deriving.Mirror.Of[E] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[E]: class E is not an abstract class
+   |No given instance of type deriving.Mirror.Of[E] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[E]: class E is not an abstract class
 -- Error: tests/neg/mirror-synthesis-errors.scala:26:32 ----------------------------------------------------------------
 26 |val testF = summon[Mirror.Of[F]] // error: No children
    |                                ^
-   |No given instance of type deriving.Mirror.Of[F] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[F]: trait F does not have subclasses
+   |No given instance of type deriving.Mirror.Of[F] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[F]: trait F does not have subclasses
 -- Error: tests/neg/mirror-synthesis-errors.scala:27:36 ----------------------------------------------------------------
 27 |val testG = summon[Mirror.Of[Foo.G]] // error: Has anonymous subclasses
    |                                    ^
-   |No given instance of type deriving.Mirror.Of[Foo.G] was found for parameter x of method summon in object Predef. Failed to synthesize implicit of type deriving.Mirror.Of[Foo.G]: trait G has anonymous or inaccessible subclasses
+   |No given instance of type deriving.Mirror.Of[Foo.G] was found for parameter x of method summon in object Predef. Failed to synthesize an instance of type deriving.Mirror.Of[Foo.G]: trait G has anonymous or inaccessible subclasses