Fix #4986: Support implicitNotFound on parameters

Also fixes some complex cases of resolving type variables in `implicitNotFound` message for annotations put on type definitions

Author: prolativ

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -2447,8 +2447,8 @@ import transform.SymUtils._
 
   class InvalidReferenceInImplicitNotFoundAnnotation(typeVar: String, owner: String)(using Context)
     extends ReferenceMsg(InvalidReferenceInImplicitNotFoundAnnotationID) {
-    def msg = em"""|Invalid reference to a type variable "${hl(typeVar)}" found in the annotation argument.
-                   |The variable does not occur in the signature of ${hl(owner)}.
+    def msg = em"""|Invalid reference to a type variable ${hl(typeVar)} found in the annotation argument.
+                   |The variable does not occur as a parameter in the scope of ${hl(owner)}.
                    |""".stripMargin
     def explain = ""
   }

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

@@ -6,12 +6,16 @@ import ast._
 import core._
 import Types._, ProtoTypes._, Contexts._, Decorators._, Denotations._, Symbols._
 import Implicits._, Flags._, Constants.Constant
+import Trees._
+import NameOps._
 import util.Spans._
 import util.SrcPos
 import config.Feature
 import java.util.regex.Matcher.quoteReplacement
 import reporting._
 
+import scala.util.matching.Regex
+
 object ErrorReporting {
 
   import tpd._
@@ -131,14 +135,6 @@ object ErrorReporting {
      *  all occurrences of `${X}` where `X` is in `paramNames` with the
      *  corresponding shown type in `args`.
      */
-    def userDefinedErrorString(raw: String, paramNames: List[String], args: List[Type]): String = {
-      def translate(name: String): Option[String] = {
-        assert(paramNames.length == args.length)
-        val idx = paramNames.indexOf(name)
-        if (idx >= 0) Some(quoteReplacement(ex"${args(idx)}")) else None
-      }
-      """\$\{\w*\}""".r.replaceSomeIn(raw, m => translate(m.matched.drop(2).init))
-    }
 
     def rewriteNotice: String =
       if Feature.migrateTo3 then "\nThis patch can be inserted automatically under -rewrite."
@@ -180,9 +176,189 @@ object ErrorReporting {
     end selectErrorAddendum
   }
 
+  def substitutableTypeSymbolsInScope(sym: Symbol)(using Context): List[Symbol] =
+    sym.ownersIterator.takeWhile(!_.is(Flags.Package)).flatMap { ownerSym =>
+      ownerSym.paramSymss.flatten.filter(_.isType) ++
+      ownerSym.typeRef.nonClassTypeMembers.map(_.symbol)
+    }.toList
+
   def dependentStr =
     """Term-dependent types are experimental,
       |they must be enabled with a `experimental.dependent` language import or setting""".stripMargin
 
   def err(using Context): Errors = new Errors
 }
+
+
+class ImplicitSearchError(
+  arg: tpd.Tree,
+  pt: Type,
+  where: String,
+  paramSymWithMethodCallTree: Option[(Symbol, tpd.Tree)] = None,
+  ignoredInstanceNormalImport: => Option[SearchSuccess],
+  importSuggestionAddendum: => String
+)(using ctx: Context) {
+  def missingArgMsg = arg.tpe match {
+    case ambi: AmbiguousImplicits =>
+      (ambi.alt1, ambi.alt2) match {
+        case (alt @ AmbiguousImplicitMsg(msg), _) =>
+          userDefinedAmbiguousImplicitMsg(alt, msg)
+        case (_, alt @ AmbiguousImplicitMsg(msg)) =>
+          userDefinedAmbiguousImplicitMsg(alt, msg)
+        case _ =>
+          defaultAmbiguousImplicitMsg(ambi)
+      }
+    case _ =>
+      val shortMessage = userDefinedImplicitNotFoundParamMessage
+        .orElse(userDefinedImplicitNotFoundTypeMessage)
+        .getOrElse(defaultImplicitNotFoundMessage)
+      formatMsg(shortMessage)() ++ hiddenImplicitsAddendum
+  }
+
+  private def formatMsg(shortForm: String)(headline: String = shortForm) = arg match {
+    case arg: Trees.SearchFailureIdent[?] =>
+      shortForm
+    case _ =>
+      arg.tpe match {
+        case tpe: SearchFailureType =>
+          val original = arg match
+            case Inlined(call, _, _) => call
+            case _ => arg
+
+          i"""$headline.
+            |I found:
+            |
+            |    ${original.show.replace("\n", "\n    ")}
+            |
+            |But ${tpe.explanation}."""
+      }
+  }
+
+  private def userDefinedErrorString(raw: String, paramNames: List[String], args: List[Type]): String = {
+    def translate(name: String): Option[String] = {
+      val idx = paramNames.indexOf(name)
+      if (idx >= 0) Some(ex"${args(idx)}") else None
+    }
+
+    """\$\{\s*([^}\s]+)\s*\}""".r.replaceAllIn(raw, (_: Regex.Match) match {
+      case Regex.Groups(v) => quoteReplacement(translate(v).getOrElse(""))
+    })
+  }
+
+  /** Extract a user defined error message from a symbol `sym`
+   *  with an annotation matching the given class symbol `cls`.
+   */
+  private def userDefinedMsg(sym: Symbol, cls: Symbol) = for {
+    ann <- sym.getAnnotation(cls)
+    Trees.Literal(Constant(msg: String)) <- ann.argument(0)
+  } yield msg
+
+  private def location(preposition: String) = if (where.isEmpty) "" else s" $preposition $where"
+
+  private def defaultAmbiguousImplicitMsg(ambi: AmbiguousImplicits) = {
+    formatMsg(s"ambiguous implicit arguments: ${ambi.explanation}${location("of")}")(
+      s"ambiguous implicit arguments of type ${pt.show} found${location("for")}"
+    )
+  }
+
+  private def defaultImplicitNotFoundMessage = {
+    em"no implicit argument of type $pt was found${location("for")}"
+  }
+
+  /** Construct a custom error message given an ambiguous implicit
+   *  candidate `alt` and a user defined message `raw`.
+   */
+  private def userDefinedAmbiguousImplicitMsg(alt: SearchSuccess, raw: String) = {
+    val params = alt.ref.underlying match {
+      case p: PolyType => p.paramNames.map(_.toString)
+      case _           => Nil
+    }
+    def resolveTypes(targs: List[tpd.Tree])(using Context) =
+      targs.map(a => Inferencing.fullyDefinedType(a.tpe, "type argument", a.span))
+
+    // We can extract type arguments from:
+    //   - a function call:
+    //     @implicitAmbiguous("msg A=${A}")
+    //     implicit def f[A](): String = ...
+    //     implicitly[String] // found: f[Any]()
+    //
+    //   - an eta-expanded function:
+    //     @implicitAmbiguous("msg A=${A}")
+    //     implicit def f[A](x: Int): String = ...
+    //     implicitly[Int => String] // found: x => f[Any](x)
+
+    val call = tpd.closureBody(alt.tree) // the tree itself if not a closure
+    val (_, targs, _) = tpd.decomposeCall(call)
+    val args = resolveTypes(targs)(using ctx.fresh.setTyperState(alt.tstate))
+    userDefinedErrorString(raw, params, args)
+  }
+
+  /** @param rawMsg           Message template with variables, e.g. "Variable A is ${A}"
+   *  @param sym              Symbol of the annotated type or of the method whose parameter was annotated
+   *  @param substituteType   Function substituting specific types for abstract types associated with variables, e.g A -> Int
+   */
+  private def formatAnnotationMessage(rawMsg: String, sym: Symbol, substituteType: Type => Type): String = {
+    val substitutableTypesSymbols = ErrorReporting.substitutableTypeSymbolsInScope(sym)
+
+    userDefinedErrorString(
+      rawMsg,
+      paramNames = substitutableTypesSymbols.map(_.name.unexpandedName.toString),
+      args = substitutableTypesSymbols.map(_.typeRef).map(substituteType)
+    )
+  }
+
+  /** Extracting the message from a method parameter, e.g. in
+   *
+   *  trait Foo
+   *
+   *  def foo(implicit @annotation.implicitNotFound("Foo is missing") foo: Foo): Any = ???
+   */
+  private def userDefinedImplicitNotFoundParamMessage = paramSymWithMethodCallTree.flatMap { (sym, applTree) =>
+    userDefinedMsg(sym, defn.ImplicitNotFoundAnnot).map { rawMsg =>
+      val methodOwner = applTree.symbol.owner
+      val methodOwnerType: Type = applTree match {
+        case Select(qual, _) => qual.tpe
+        case TypeApply(Select(qual, _), _) => qual.tpe
+        case _ => methodOwner.typeRef
+      }
+      val substituteTypesFromMethodOwner = (_: Type).asSeenFrom(methodOwnerType, methodOwner)
+      val substituteMethodTypeParams: Type => Type = applTree match {
+        case TypeApply(_, targs) =>
+          val methodTypeParams = applTree.symbol.paramSymss.flatten.filter(_.isType)
+          val methodTypeArgs = targs.map(_.tpe)
+          _.subst(methodTypeParams, methodTypeArgs)
+        case _ =>
+          identity
+      }
+
+      val substituteType = substituteTypesFromMethodOwner andThen substituteMethodTypeParams
+      formatAnnotationMessage(rawMsg, sym.owner, substituteType)
+    }
+  }
+
+  /** Extracting the message from a type, e.g. in
+   *
+   *  @annotation.implicitNotFound("Foo is missing")
+   *  trait Foo
+   *
+   *  def foo(implicit foo: Foo): Any = ???
+   */
+  private def userDefinedImplicitNotFoundTypeMessage = userDefinedMsg(pt.typeSymbol, defn.ImplicitNotFoundAnnot).map { rawMsg =>
+    val substituteType = (_: Type).asSeenFrom(pt, pt.typeSymbol)
+    formatAnnotationMessage(rawMsg, pt.typeSymbol, substituteType)
+  }
+
+  private def hiddenImplicitsAddendum: String =
+    def hiddenImplicitNote(s: SearchSuccess) =
+      em"\n\nNote: given instance ${s.ref.symbol.showLocated} was not considered because it was not imported with `import given`."
+
+    val normalImports = ignoredInstanceNormalImport.map(hiddenImplicitNote)
+
+    normalImports.getOrElse(importSuggestionAddendum)
+  end hiddenImplicitsAddendum
+
+  private object AmbiguousImplicitMsg {
+    def unapply(search: SearchSuccess): Option[String] =
+      userDefinedMsg(search.ref.symbol, defn.ImplicitAmbiguousAnnot)
+  }
+}

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

@@ -82,6 +82,7 @@ object Implicits:
   def strictEquality(using Context): Boolean =
     ctx.mode.is(Mode.StrictEquality) || Feature.enabled(nme.strictEquality)
 
+
   /** A common base class of contextual implicits and of-type implicits which
    *  represents a set of references to implicit definitions.
    */
@@ -832,126 +833,40 @@ trait Implicits:
     arg
   }
 
-  def missingArgMsg(arg: Tree, pt: Type, where: String)(using Context): String = {
-
-    def msg(shortForm: String)(headline: String = shortForm) = arg match {
-      case arg: Trees.SearchFailureIdent[?] =>
-        shortForm
-      case _ =>
-        arg.tpe match {
-          case tpe: SearchFailureType =>
-            val original = arg match
-              case Inlined(call, _, _) => call
-              case _ => arg
-
-            i"""$headline.
-              |I found:
-              |
-              |    ${original.show.replace("\n", "\n    ")}
-              |
-              |But ${tpe.explanation}."""
-        }
-    }
-
-    def location(preposition: String) = if (where.isEmpty) "" else s" $preposition $where"
-
-    /** Extract a user defined error message from a symbol `sym`
-     *  with an annotation matching the given class symbol `cls`.
-     */
-    def userDefinedMsg(sym: Symbol, cls: Symbol) = for {
-      ann <- sym.getAnnotation(cls)
-      Trees.Literal(Constant(msg: String)) <- ann.argument(0)
-    }
-    yield msg
-
-
-    arg.tpe match {
-      case ambi: AmbiguousImplicits =>
-        object AmbiguousImplicitMsg {
-          def unapply(search: SearchSuccess): Option[String] =
-            userDefinedMsg(search.ref.symbol, defn.ImplicitAmbiguousAnnot)
-        }
-
-        /** Construct a custom error message given an ambiguous implicit
-         *  candidate `alt` and a user defined message `raw`.
-         */
-        def userDefinedAmbiguousImplicitMsg(alt: SearchSuccess, raw: String) = {
-          val params = alt.ref.underlying match {
-            case p: PolyType => p.paramNames.map(_.toString)
-            case _           => Nil
+  /** @param arg                          Tree representing a failed result of implicit search
+   *  @param pt                           Type for which an implicit value was searched
+   *  @param where                        Description of where the search was performed. Might be empty
+   *  @param paramSymWithMethodCallTree   Symbol of the parameter for which the implicit was searched and tree of the method call that triggered the implicit search
+   */
+  def missingArgMsg(
+    arg: Tree,
+    pt: Type,
+    where: String,
+    paramSymWithMethodCallTree: Option[(Symbol, Tree)] = None
+  )(using Context): String = {
+    def findHiddenImplicitsCtx(c: Context): Context =
+      if c == NoContext then c
+      else c.freshOver(findHiddenImplicitsCtx(c.outer)).addMode(Mode.FindHiddenImplicits)
+
+    def ignoredInstanceNormalImport = arg.tpe match
+      case fail: SearchFailureType =>
+        if (fail.expectedType eq pt) || isFullyDefined(fail.expectedType, ForceDegree.none) then
+          inferImplicit(fail.expectedType, fail.argument, arg.span) match {
+            case s: SearchSuccess => Some(s)
+            case f: SearchFailure =>
+              f.reason match {
+                case ambi: AmbiguousImplicits => Some(ambi.alt1)
+                case r => None
+              }
           }
-          def resolveTypes(targs: List[Tree])(using Context) =
-            targs.map(a => fullyDefinedType(a.tpe, "type argument", a.span))
-
-          // We can extract type arguments from:
-          //   - a function call:
-          //     @implicitAmbiguous("msg A=${A}")
-          //     implicit def f[A](): String = ...
-          //     implicitly[String] // found: f[Any]()
-          //
-          //   - an eta-expanded function:
-          //     @implicitAmbiguous("msg A=${A}")
-          //     implicit def f[A](x: Int): String = ...
-          //     implicitly[Int => String] // found: x => f[Any](x)
-
-          val call = closureBody(alt.tree) // the tree itself if not a closure
-          val (_, targs, _) = decomposeCall(call)
-          val args = resolveTypes(targs)(using ctx.fresh.setTyperState(alt.tstate))
-          err.userDefinedErrorString(raw, params, args)
-        }
-
-        (ambi.alt1, ambi.alt2) match {
-          case (alt @ AmbiguousImplicitMsg(msg), _) =>
-            userDefinedAmbiguousImplicitMsg(alt, msg)
-          case (_, alt @ AmbiguousImplicitMsg(msg)) =>
-            userDefinedAmbiguousImplicitMsg(alt, msg)
-          case _ =>
-            msg(s"ambiguous implicit arguments: ${ambi.explanation}${location("of")}")(
-                s"ambiguous implicit arguments of type ${pt.show} found${location("for")}")
-        }
+        else
+          // It's unsafe to search for parts of the expected type if they are not fully defined,
+          // since these come with nested contexts that are lost at this point. See #7249 for an
+          // example where searching for a nested type causes an infinite loop.
+          None
 
-      case _ =>
-        val userDefined = userDefinedMsg(pt.typeSymbol, defn.ImplicitNotFoundAnnot).map(raw =>
-          err.userDefinedErrorString(
-            raw,
-            pt.typeSymbol.typeParams.map(_.name.unexpandedName.toString),
-            pt.widenExpr.dropDependentRefinement.argInfos))
-
-        def hiddenImplicitsAddendum: String =
-
-          def hiddenImplicitNote(s: SearchSuccess) =
-            em"\n\nNote: given instance ${s.ref.symbol.showLocated} was not considered because it was not imported with `import given`."
-
-          def findHiddenImplicitsCtx(c: Context): Context =
-            if c == NoContext then c
-            else c.freshOver(findHiddenImplicitsCtx(c.outer)).addMode(Mode.FindHiddenImplicits)
-
-          val normalImports = arg.tpe match
-            case fail: SearchFailureType =>
-              if (fail.expectedType eq pt) || isFullyDefined(fail.expectedType, ForceDegree.none) then
-                inferImplicit(fail.expectedType, fail.argument, arg.span)(
-                  using findHiddenImplicitsCtx(ctx)) match {
-                  case s: SearchSuccess => hiddenImplicitNote(s)
-                  case f: SearchFailure =>
-                    f.reason match {
-                      case ambi: AmbiguousImplicits => hiddenImplicitNote(ambi.alt1)
-                      case r => ""
-                    }
-                }
-              else
-                // It's unsafe to search for parts of the expected type if they are not fully defined,
-                // since these come with nested contexts that are lost at this point. See #7249 for an
-                // example where searching for a nested type causes an infinite loop.
-                ""
-
-          def suggestedImports = importSuggestionAddendum(pt)
-          if normalImports.isEmpty then suggestedImports else normalImports
-        end hiddenImplicitsAddendum
-
-        msg(userDefined.getOrElse(
-          em"no implicit argument of type $pt was found${location("for")}"))() ++
-        hiddenImplicitsAddendum
-    }
+    val error = new ImplicitSearchError(arg, pt, where, paramSymWithMethodCallTree, ignoredInstanceNormalImport, importSuggestionAddendum(pt))
+    error.missingArgMsg
   }
 
   /** A string indicating the formal parameter corresponding to a  missing argument */