Fix #5460: Improve completion of import nodes

compiler/src/dotty/tools/dotc/interactive/Completion.scala

@@ -0,0 +1,304 @@
+package dotty.tools.dotc.interactive
+
+import dotty.tools.dotc.ast.Trees._
+import dotty.tools.dotc.config.Printers.interactiv
+import dotty.tools.dotc.core.Contexts.{Context, NoContext}
+import dotty.tools.dotc.core.CheckRealizable
+import dotty.tools.dotc.core.Decorators.StringInterpolators
+import dotty.tools.dotc.core.Denotations.SingleDenotation
+import dotty.tools.dotc.core.Flags._
+import dotty.tools.dotc.core.Names.{Name, TermName}
+import dotty.tools.dotc.core.NameKinds.SimpleNameKind
+import dotty.tools.dotc.core.NameOps.NameDecorator
+import dotty.tools.dotc.core.Symbols.{defn, NoSymbol, Symbol}
+import dotty.tools.dotc.core.Scopes
+import dotty.tools.dotc.core.StdNames.{nme, tpnme}
+import dotty.tools.dotc.core.TypeError
+import dotty.tools.dotc.core.Types.{NamedType, Type, takeAllFilter}
+import dotty.tools.dotc.printing.Texts._
+import dotty.tools.dotc.util.{NoSourcePosition, SourcePosition}
+
+import scala.collection.mutable
+
+object Completion {
+
+  import dotty.tools.dotc.ast.tpd._
+
+  /** Get possible completions from tree at `pos`
+   *
+   *  @return offset and list of symbols for possible completions
+   */
+  def completions(pos: SourcePosition)(implicit ctx: Context): (Int, List[Symbol]) = {
+    val path = Interactive.pathTo(ctx.compilationUnit.tpdTree, pos.pos)
+    computeCompletions(pos, path)(Interactive.contextOfPath(path))
+  }
+
+  /**
+   * Inspect `path` to determine what kinds of symbols should be considered.
+   *
+   * If the path starts with:
+   *  - a `RefTree`, then accept symbols of the same kind as its name;
+   *  - a renaming import, and the cursor is on the renamee, accept both terms and types;
+   *  - an import, accept both terms and types;
+   *
+   * Otherwise, provide no completion suggestion.
+   */
+  private def completionMode(path: List[Tree], pos: SourcePosition): Mode = {
+    path match {
+      case (ref: RefTree) :: _ =>
+        if (ref.name.isTermName) Mode.Term
+        else if (ref.name.isTypeName) Mode.Type
+        else Mode.None
+
+      case Thicket(name :: _ :: Nil) :: (_: Import) :: _ =>
+        if (name.pos.contains(pos.pos)) Mode.Import
+        else Mode.None // Can't help completing the renaming
+
+      case Import(_, _) :: _ =>
+        Mode.Import
+
+      case _ =>
+        Mode.None
+    }
+  }
+
+  /**
+   * Inspect `path` to determine the completion prefix. Only symbols whose name start with the
+   * returned prefix should be considered.
+   */
+  private def completionPrefix(path: List[Tree], pos: SourcePosition): String = {
+    path match {
+      case Thicket(name :: _ :: Nil) :: (_: Import) :: _ =>
+        completionPrefix(name :: Nil, pos)
+
+      case Import(expr, selectors) :: _ =>
+        selectors.find(_.pos.contains(pos.pos)).map { selector =>
+          completionPrefix(selector.asInstanceOf[Tree] :: Nil, pos)
+        }.getOrElse("")
+
+      case (ref: RefTree) :: _ =>
+        if (ref.name == nme.ERROR) ""
+        else ref.name.toString.take(pos.pos.point - ref.pos.point)
+
+      case _ =>
+        ""
+    }
+  }
+
+  /** Inspect `path` to determine the offset where the completion result should be inserted. */
+  private def completionOffset(path: List[Tree]): Int = {
+    path match {
+      case (ref: RefTree) :: _ => ref.pos.point
+      case _ => 0
+    }
+  }
+
+  /** Create a new `CompletionBuffer` for completing at `pos`. */
+  private def completionBuffer(path: List[Tree], pos: SourcePosition): CompletionBuffer = {
+    val mode = completionMode(path, pos)
+    val prefix = completionPrefix(path, pos)
+    new CompletionBuffer(mode, prefix, pos)
+  }
+
+  private def computeCompletions(pos: SourcePosition, path: List[Tree])(implicit ctx: Context): (Int, List[Symbol]) = {
+
+    val offset = completionOffset(path)
+    val buffer = completionBuffer(path, pos)
+
+    if (buffer.mode != Mode.None) {
+      path match {
+        case Select(qual, _) :: _                 => buffer.addMemberCompletions(qual)
+        case Import(expr, _) :: _                 => buffer.addMemberCompletions(expr)
+        case (_: Thicket) :: Import(expr, _) :: _ => buffer.addMemberCompletions(expr)
+        case _                                    => buffer.addScopeCompletions
+      }
+    }
+
+    val completionList = buffer.getCompletions
+
+    interactiv.println(i"""completion with pos     = $pos,
+                          |                prefix  = ${buffer.prefix},
+                          |                term    = ${buffer.mode.is(Mode.Term)},
+                          |                type    = ${buffer.mode.is(Mode.Type)}
+                          |                results = $completionList%, %""")
+    (offset, completionList)
+  }
+
+  private class CompletionBuffer(val mode: Mode, val prefix: String, pos: SourcePosition) {
+
+    private[this] val completions = Scopes.newScope.openForMutations
+
+    /**
+     * Return the list of symbols that shoudl be included in completion results.
+     *
+     * If the mode is `Import` and several symbols share the same name, the type symbols are
+     * preferred over term symbols.
+     */
+    def getCompletions(implicit ctx: Context): List[Symbol] = {
+      // Show only the type symbols when there are multiple options with the same name
+      completions.toList.groupBy(_.name.stripModuleClassSuffix.toSimpleName).mapValues {
+        case sym :: Nil => sym :: Nil
+        case syms => syms.filter(_.isType)
+      }.values.flatten.toList
+    }
+
+    /**
+     * Add symbols that are currently in scope to `info`: the members of the current class and the
+     * symbols that have been imported.
+     */
+    def addScopeCompletions(implicit ctx: Context): Unit = {
+      if (ctx.owner.isClass) {
+        addAccessibleMembers(ctx.owner.thisType)
+        ctx.owner.asClass.classInfo.selfInfo match {
+          case selfSym: Symbol => add(selfSym)
+          case _ =>
+        }
+      }
+      else if (ctx.scope != null) ctx.scope.foreach(add)
+
+      addImportCompletions
+
+      var outer = ctx.outer
+      while ((outer.owner `eq` ctx.owner) && (outer.scope `eq` ctx.scope)) {
+        addImportCompletions(outer)
+        outer = outer.outer
+      }
+      if (outer `ne` NoContext) addScopeCompletions(outer)
+    }
+
+    /**
+     * Find all the members of `qual` and add the ones that pass the include filters to `info`.
+     *
+     * If `info.mode` is `Import`, the members added via implicit conversion on `qual` are not
+     * considered.
+     */
+    def addMemberCompletions(qual: Tree)(implicit ctx: Context): Unit = {
+      addAccessibleMembers(qual.tpe)
+      if (!mode.is(Mode.Import)) {
+        // Implicit conversions do not kick in when importing
+        implicitConversionTargets(qual)(ctx.fresh.setExploreTyperState())
+          .foreach(addAccessibleMembers)
+      }
+    }
+
+    /**
+     * If `sym` exists, no symbol with the same name is already included, and it satisfies the
+     * inclusion filter, then add it to the completions.
+     */
+    private def add(sym: Symbol)(implicit ctx: Context) =
+      if (sym.exists && !completions.lookup(sym.name).exists && include(sym)) {
+        completions.enter(sym)
+      }
+
+    /** Lookup members `name` from `site`, and try to add them to the completion list. */
+    private def addMember(site: Type, name: Name)(implicit ctx: Context) =
+      if (!completions.lookup(name).exists)
+        for (alt <- site.member(name).alternatives) add(alt.symbol)
+
+    /** Include in completion sets only symbols that
+     *   1. start with given name prefix, and
+     *   2. do not contain '$' except in prefix where it is explicitly written by user, and
+     *   3. are not a primary constructor,
+     *   4. are the module class in case of packages,
+     *   5. are mutable accessors, to exclude setters for `var`,
+     *   6. have same term/type kind as name prefix given so far
+     *
+     *  The reason for (2) is that we do not want to present compiler-synthesized identifiers
+     *  as completion results. However, if a user explicitly writes all '$' characters in an
+     *  identifier, we should complete the rest.
+     */
+    private def include(sym: Symbol)(implicit ctx: Context): Boolean =
+      sym.name.startsWith(prefix) &&
+      !sym.name.toString.drop(prefix.length).contains('$') &&
+      !sym.isPrimaryConstructor &&
+      (!sym.is(Package) || !sym.moduleClass.exists) &&
+      !sym.is(allOf(Mutable, Accessor)) &&
+      (
+           (mode.is(Mode.Term) && sym.isTerm)
+        || (mode.is(Mode.Type) && (sym.isType || sym.isStable))
+      )
+
+    /**
+     * Find all the members of `site` that are accessible and which should be included in `info`.
+     *
+     * @param site The type to inspect.
+     * @return The members of `site` that are accessible and pass the include filter of `info`.
+     */
+    private def accessibleMembers(site: Type)(implicit ctx: Context): Seq[Symbol] = site match {
+      case site: NamedType if site.symbol.is(Package) =>
+        site.decls.toList.filter(include) // Don't look inside package members -- it's too expensive.
+      case _ =>
+        def appendMemberSyms(name: Name, buf: mutable.Buffer[SingleDenotation]): Unit =
+          try buf ++= site.member(name).alternatives
+          catch { case ex: TypeError => }
+        site.memberDenots(takeAllFilter, appendMemberSyms).collect {
+          case mbr if include(mbr.symbol) => mbr.accessibleFrom(site, superAccess = true).symbol
+          case _ => NoSymbol
+        }.filter(_.exists)
+    }
+
+    /** Add all the accessible members of `site` in `info`. */
+    private def addAccessibleMembers(site: Type)(implicit ctx: Context): Unit =
+      for (mbr <- accessibleMembers(site)) addMember(site, mbr.name)
+
+    /**
+     * Add in `info` the symbols that are imported by `ctx.importInfo`. If this is a wildcard import,
+     * all the accessible members of the import's `site` are included.
+     */
+    private def addImportCompletions(implicit ctx: Context): Unit = {
+      val imp = ctx.importInfo
+      if (imp != null) {
+        def addImport(name: TermName) = {
+          addMember(imp.site, name)
+          addMember(imp.site, name.toTypeName)
+        }
+        // FIXME: We need to also take renamed items into account for completions,
+        // That means we have to return list of a pairs (Name, Symbol) instead of a list
+        // of symbols from `completions`.!=
+        for (imported <- imp.originals if !imp.excluded.contains(imported)) addImport(imported)
+        if (imp.isWildcardImport)
+          for (mbr <- accessibleMembers(imp.site) if !imp.excluded.contains(mbr.name.toTermName))
+            addMember(imp.site, mbr.name)
+      }
+    }
+
+    /**
+     * Given `qual` of type T, finds all the types S such that there exists an implicit conversion
+     * from T to S.
+     *
+     * @param qual The argument to which the implicit conversion should be applied.
+     * @return The set of types that `qual` can be converted to.
+     */
+    private def implicitConversionTargets(qual: Tree)(implicit ctx: Context): Set[Type] = {
+      val typer = ctx.typer
+      val conversions = new typer.ImplicitSearch(defn.AnyType, qual, pos.pos).allImplicits
+      val targets = conversions.map(_.widen.finalResultType)
+      interactiv.println(i"implicit conversion targets considered: ${targets.toList}%, %")
+      targets
+    }
+
+  }
+
+  /**
+   * The completion mode: defines what kinds of symbols should be included in the completion
+   * results.
+   */
+  private class Mode(val bits: Int) extends AnyVal {
+    def is(other: Mode): Boolean = (bits & other.bits) == other.bits
+    def |(other: Mode): Mode = new Mode(bits | other.bits)
+  }
+  private object Mode {
+    /** No symbol should be included */
+    val None: Mode = new Mode(0)
+
+    /** Term symbols are allowed */
+    val Term: Mode = new Mode(1)
+
+    /** Type and stable term symbols are allowed */
+    val Type: Mode = new Mode(2)
+
+    /** Both term and type symbols are allowed */
+    val Import: Mode = new Mode(4) | Term | Type
+  }
+
+}