improvement: Support completions for implicit classes

mtags/src/main/scala-3/scala/meta/internal/pc/CompilerSearchVisitor.scala

@@ -10,6 +10,7 @@ import scala.meta.internal.metals.ReportContext
 import scala.meta.pc.*
 
 import dotty.tools.dotc.core.Contexts.*
+import dotty.tools.dotc.core.Flags
 import dotty.tools.dotc.core.Names.*
 import dotty.tools.dotc.core.Symbols.*
 
@@ -20,8 +21,15 @@ class CompilerSearchVisitor(
 
   val logger: Logger = Logger.getLogger(classOf[CompilerSearchVisitor].getName)
 
+  private def isAccessibleImplicitClass(sym: Symbol) =
+    val owner = sym.maybeOwner
+    owner != NoSymbol && owner.isClass &&
+    owner.is(Flags.Implicit) &&
+    owner.isStatic && owner.isPublic
+
   private def isAccessible(sym: Symbol): Boolean = try
-    sym != NoSymbol && sym.isPublic && sym.isStatic
+    sym != NoSymbol && sym.isPublic && sym.isStatic ||
+      isAccessibleImplicitClass(sym)
   catch
     case err: AssertionError =>
       logger.log(Level.WARNING, err.getMessage())

mtags/src/main/scala-3/scala/meta/internal/pc/SemanticdbSymbols.scala

@@ -48,7 +48,16 @@ object SemanticdbSymbols:
                   //   however in scalac this method is defined only in `module Files`
                   if typeSym.is(JavaDefined) then
                     typeSym :: owner.info.decl(termName(value)).symbol :: Nil
+                  /**
+                   * Looks like decl doesn't work for:
+                   *  package a:
+                   *   implicit class <<A>> (i: Int):
+                   *      def inc = i + 1
+                   */
+                  else if typeSym == NoSymbol then
+                    owner.info.member(typeName(value)).symbol :: Nil
                   else typeSym :: Nil
+                  end if
                 case Descriptor.Term(value) =>
                   val outSymbol = owner.info.decl(termName(value)).symbol
                   if outSymbol.exists
@@ -91,6 +100,8 @@ object SemanticdbSymbols:
                     .map(_.symbol)
                     .filter(sym => symbolName(sym) == s)
                     .toList
+          end match
+        end tryMember
 
         parentSymbol.flatMap(tryMember)
     try

mtags/src/main/scala-3/scala/meta/internal/pc/completions/CompletionProvider.scala

@@ -224,7 +224,7 @@ class CompletionProvider(
 
     def mkItemWithImports(
         v: CompletionValue.Workspace | CompletionValue.Extension |
-          CompletionValue.Interpolator
+          CompletionValue.Interpolator | CompletionValue.ImplicitClass
     ) =
       val sym = v.symbol
       path match
@@ -277,7 +277,8 @@ class CompletionProvider(
     end mkItemWithImports
 
     completion match
-      case v: (CompletionValue.Workspace | CompletionValue.Extension) =>
+      case v: (CompletionValue.Workspace | CompletionValue.Extension |
+            CompletionValue.ImplicitClass) =>
         mkItemWithImports(v)
       case v: CompletionValue.Interpolator if v.isWorkspace || v.isExtension =>
         mkItemWithImports(v)

mtags/src/main/scala-3/scala/meta/internal/pc/completions/CompletionValue.scala

@@ -130,6 +130,20 @@ object CompletionValue:
     override def description(printer: MetalsPrinter)(using Context): String =
       s"${printer.completionSymbol(symbol)} (extension)"
 
+  /**
+   * CompletionValue for old implicit classes methods via SymbolSearch
+   */
+  case class ImplicitClass(
+      label: String,
+      symbol: Symbol,
+      override val snippetSuffix: CompletionSuffix,
+      override val importSymbol: Symbol,
+  ) extends Symbolic:
+    override def completionItemKind(using Context): CompletionItemKind =
+      CompletionItemKind.Method
+    override def description(printer: MetalsPrinter)(using Context): String =
+      s"${printer.completionSymbol(symbol)} (implicit)"
+
   /**
    * @param shortenedNames shortened type names by `Printer`. This field should be used for autoImports
    * @param start Starting position of the completion

mtags/src/main/scala-3/scala/meta/internal/pc/completions/Completions.scala

@@ -595,14 +595,40 @@ class Completions(
         Some(search.search(query, buildTargetIdentifier, visitor))
       case CompletionKind.Members =>
         val visitor = new CompilerSearchVisitor(sym =>
-          if sym.is(ExtensionMethod) &&
+          def isExtensionMethod = sym.is(ExtensionMethod) &&
             qualType.widenDealias <:< sym.extensionParam.info.widenDealias
-          then
+
+          def isImplicitClass(owner: Symbol) =
+
+            val constructorParam =
+              owner.info
+                .membersBasedOnFlags(
+                  Flags.ParamAccessor,
+                  Flags.EmptyFlags,
+                )
+                .headOption
+                .map(_.info)
+            owner.isClass && owner.is(Flags.Implicit) &&
+            constructorParam.exists(p =>
+              qualType.widenDealias <:< p.widenDealias
+            )
+          end isImplicitClass
+
+          def isImplicitClassMethod = sym.is(Flags.Method) &&
+            isImplicitClass(sym.maybeOwner)
+
+          if isExtensionMethod then
             completionsWithSuffix(
               sym,
               sym.decodedName,
               CompletionValue.Extension(_, _, _),
             ).map(visit).forall(_ == true)
+          else if isImplicitClassMethod then
+            completionsWithSuffix(
+              sym,
+              sym.decodedName,
+              CompletionValue.ImplicitClass(_, _, _, sym.maybeOwner),
+            ).map(visit).forall(_ == true)
           else false,
         )
         Some(search.searchMethods(query, buildTargetIdentifier, visitor))