refactor: move the SemanticDB to binary name conversion onto Symbol

metals/src/main/scala/scala/meta/internal/metals/mbt/VirtualTextDocument.scala

@@ -6,6 +6,7 @@ import javax.tools.JavaFileObject.Kind
 import javax.tools.SimpleJavaFileObject
 
 import scala.meta.internal.metals.MetalsEnrichments._
+import scala.meta.internal.mtags.Symbol
 import scala.meta.internal.{semanticdb => s}
 import scala.meta.pc
 import scala.meta.pc.SemanticdbCompilationUnit
@@ -32,7 +33,7 @@ final case class VirtualTextDocument(
       case None =>
         pkg.replace('/', '.')
       case Some(sym) =>
-        sym.stripSuffix("#").stripSuffix(".").replace('/', '.')
+        Symbol(sym).toplevelClassName
     }
   }
   override def getName(): String = uri.toString

mtags/src/main/scala/scala/meta/internal/mtags/ClasspathDefinitionIndex.scala

@@ -117,8 +117,7 @@ class ClasspathDefinitionIndex(mtags: () => Mtags, dialect: Dialect) {
       symbol: Symbol
   ): Option[String] = {
     val jar = new JarFile(module.jar.toFile)
-    val classfileName =
-      s"${symbol.toplevel.value.stripSuffix("#").stripSuffix(".")}.class"
+    val classfileName = s"${symbol.toplevelBinaryName}.class"
     try {
       val entry = jar.getEntry(classfileName)
       if (entry != null) {

mtags/src/main/scala/scala/meta/internal/mtags/Symbol.scala

@@ -57,6 +57,22 @@ final class Symbol private (val value: String) {
     !value.isPackage &&
     value.owner.isPackage
   }
+
+  /**
+   * The JVMS 4.2.1 binary name of the toplevel class this symbol belongs to,
+   * for example `scala/Option#get().` becomes `scala/Option`. Toplevel, because
+   * a nested class is `Outer$Inner` in a binary name but `Outer#Inner#` here.
+   */
+  def toplevelBinaryName: String =
+    toplevel.value.stripSuffix("#").stripSuffix(".")
+
+  /**
+   * [[toplevelBinaryName]] with `.` between package parts, the form
+   * `Class.forName` expects: `scala/Option#get().` becomes `scala.Option`.
+   */
+  def toplevelClassName: String =
+    toplevelBinaryName.replace('/', '.')
+
   def asNonEmpty: Option[Symbol] =
     if (isNone) None
     else Some(this)
@@ -86,6 +102,15 @@ object Symbol {
     else new Symbol(sym)
   }
 
+  /**
+   * The symbol of a toplevel class named the way `Class.forName` names it, the
+   * inverse of [[Symbol.toplevelClassName]]: `scala.Option` becomes
+   * `scala/Option#`. Toplevel, since a nested class is `Outer.Inner` there but
+   * `Outer#Inner#` here.
+   */
+  def fromToplevelClassName(className: String): Symbol =
+    Symbol(className.replace('.', '/') + "#")
+
   def validated(sym: String): Either[String, Symbol] = {
     // NOTE(olafur): this validation method is hacky, we should write a proper
     // parser that reports positioned error messages with actionable feedback

mtags/src/main/scala/scala/meta/internal/mtags/SymbolIndexBucket.scala

@@ -373,7 +373,7 @@ class SymbolIndexBucket(
   // Output: scala/collection/immutable/List.scala
   //         scala/collection/immutable/List.java
   private def trivialPaths(toplevel: Symbol): List[String] = {
-    val noExtension = toplevel.value.stripSuffix(".").stripSuffix("#")
+    val noExtension = toplevel.toplevelBinaryName
     List(
       noExtension + ".scala",
       noExtension + ".java"
@@ -382,8 +382,8 @@ class SymbolIndexBucket(
 
   private def modulePaths(toplevel: Symbol): List[String] = {
     if (Properties.isJavaAtLeast("9")) {
-      val noExtension = toplevel.value.stripSuffix(".").stripSuffix("#")
-      val javaSymbol = noExtension.replace("/", ".")
+      val noExtension = toplevel.toplevelBinaryName
+      val javaSymbol = toplevel.toplevelClassName
       for {
         cls <- sourceJars.loadClassSafe(javaSymbol).toList
         // note(@tgodzik) Modules are only available in Java 9+, so we need to invoke this reflectively