Show Implicit Candidate & RefAndLevel

Author: dwijnand

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -640,6 +640,13 @@ class PlainPrinter(_ctx: Context) extends Printer {
     else if (pos.source.exists) s"${pos.source.file.name}:${pos.line + 1}"
     else s"(no source file, offset = ${pos.span.point})"
 
+  def toText(cand: Candidate): Text =
+    "Cand("
+      ~ toTextRef(cand.ref)
+      ~ (if cand.isConversion then " conv" else "")
+      ~ (if cand.isExtension then " ext" else "")
+      ~ Str(" L" + cand.level) ~ ")"
+
   def toText(result: SearchResult): Text = result match {
     case result: SearchSuccess =>
       "SearchSuccess: " ~ toText(result.ref) ~ " via " ~ toText(result.tree)

compiler/src/dotty/tools/dotc/printing/Printer.scala

@@ -7,7 +7,7 @@ import Texts._, ast.Trees._
 import Types.{Type, SingletonType, LambdaParam},
        Symbols.Symbol, Scopes.Scope, Constants.Constant,
        Names.Name, Denotations._, Annotations.Annotation, Contexts.Context
-import typer.Implicits.SearchResult
+import typer.Implicits.*
 import util.SourcePosition
 import typer.ImportInfo
 
@@ -153,6 +153,9 @@ abstract class Printer {
   /** Textual representation of source position */
   def toText(pos: SourcePosition): Text
 
+  /** Textual representation of implicit candidates. */
+  def toText(cand: Candidate): Text
+
   /** Textual representation of implicit search result */
   def toText(result: SearchResult): Text
 

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

@@ -49,17 +49,19 @@ object Implicits:
   }
 
   /** Both search candidates and successes are references with a specific nesting level. */
-  sealed trait RefAndLevel {
+  sealed trait RefAndLevel extends Showable {
     def ref: TermRef
     def level: Int
   }
 
   /** An eligible implicit candidate, consisting of an implicit reference and a nesting level */
-  case class Candidate(implicitRef: ImplicitRef, kind: Candidate.Kind, level: Int) extends RefAndLevel {
+  case class Candidate(implicitRef: ImplicitRef, kind: Candidate.Kind, level: Int) extends RefAndLevel with Showable {
     def ref: TermRef = implicitRef.underlyingRef
 
     def isExtension = (kind & Candidate.Extension) != 0
     def isConversion = (kind & Candidate.Conversion) != 0
+
+    def toText(printer: Printer): Text = printer.toText(this)
   }
   object Candidate {
     type Kind = Int