feat: scope checker and renamer

Merge request lab2425_spring/WACC_37!8

src/main/wacc/Error.scala

@@ -0,0 +1,8 @@
+package wacc
+
+enum Error {
+  case DuplicateDeclaration(ident: ast.Ident)
+  case UndefinedIdentifier(ident: ast.Ident, identType: renamer.IdentType)
+  case FunctionParamsMismatch(expected: Int, got: Int)
+  case TypeMismatch(expected: types.SemType, got: types.SemType)
+}

src/main/wacc/Main.scala

@@ -1,5 +1,6 @@
 package wacc
 
+import scala.collection.mutable
 import parsley.{Failure, Success}
 import scopt.OParser
 import java.io.File
@@ -32,8 +33,15 @@ val cliParser = {
 def compile(contents: String): Int = {
   parser.parse(contents) match {
     case Success(ast) =>
-      // TODO: Do semantics things
-      0
+      given errors: mutable.Builder[Error, List[Error]] = List.newBuilder
+      renamer.rename(ast)
+      // given ctx: types.TypeCheckerCtx[List[Error]] =
+      //   types.TypeCheckerCtx(names, errors)
+      // types.check(ast)
+      if (errors.result.nonEmpty) {
+        errors.result.foreach(println)
+        200
+      } else 0
     case Failure(msg) =>
       println(msg)
       100

src/main/wacc/ast.scala

@@ -27,9 +27,11 @@ object ast {
   case class StrLiter(v: String)(pos: Position) extends Expr6
   object StrLiter extends ParserBridgePos1[String, StrLiter]
   case class PairLiter()(pos: Position) extends Expr6
-  object PairLiter extends Expr6 with ParserBridgePos0[PairLiter]
-  case class Ident(v: String)(pos: Position) extends Expr6 with LValue
-  object Ident extends ParserBridgePos1[String, Ident]
+  object PairLiter extends ParserBridgePos0[PairLiter]
+  case class Ident(v: String, var uid: Int = -1)(pos: Position) extends Expr6 with LValue
+  object Ident extends ParserBridgePos1[String, Ident] {
+    def apply(v: String)(pos: Position): Ident = new Ident(v)(pos)
+  }
   case class ArrayElem(name: Ident, indices: NonEmptyList[Expr])(pos: Position)
       extends Expr6
       with LValue

src/main/wacc/renamer.scala

@@ -0,0 +1,215 @@
+package wacc
+
+import scala.collection.mutable
+
+object renamer {
+  import ast._
+  import types._
+
+  enum IdentType {
+    case Func
+    case Var
+  }
+
+  private case class Scope(
+      current: mutable.Map[(String, IdentType), Ident],
+      parent: Map[(String, IdentType), Ident]
+  ) {
+
+    /** Create a new scope with the current scope as its parent.
+      *
+      * @return
+      *   A new scope with an empty current scope, and this scope flattened into the parent scope.
+      */
+    def subscope: Scope =
+      Scope(mutable.Map.empty, Map.empty.withDefault(current.withDefault(parent)))
+
+    /** Attempt to add a new identifier to the current scope. If the identifier already exists in
+      * the current scope, add an error to the error list.
+      *
+      * @param semType
+      *   The semantic type of the identifier.
+      * @param name
+      *   The name of the identifier.
+      * @param identType
+      *   The identifier type (function or variable).
+      * @param globalNames
+      *   The global map of identifiers to semantic types - the identifier will be added to this
+      *   map.
+      * @param globalNumbering
+      *   The global map of identifier names to the number of times they have been declared - will
+      *   used to rename this identifier, and will be incremented.
+      * @param errors
+      *   The list of errors to append to.
+      */
+    def add(semType: SemType, name: Ident, identType: IdentType)(using
+        globalNames: mutable.Map[Ident, SemType],
+        globalNumbering: mutable.Map[String, Int],
+        errors: mutable.Builder[Error, List[Error]]
+    ) = {
+      if (current.contains((name.v, identType))) {
+        errors += Error.DuplicateDeclaration(name)
+      } else {
+        val uid = globalNumbering.getOrElse(name.v, 0)
+        name.uid = uid
+        current((name.v, identType)) = name
+
+        globalNames(name) = semType
+        globalNumbering(name.v) = uid + 1
+      }
+    }
+  }
+
+  /** Check scoping of all variables and functions in the program. Also generate semantic types for
+    * all identifiers.
+    *
+    * @param prog
+    *   AST of the program
+    * @param errors
+    *   List of errors to append to
+    * @return
+    *   Map of all (renamed) identifies to their semantic types
+    */
+  def rename(prog: Program)(using
+      errors: mutable.Builder[Error, List[Error]]
+  ): Map[Ident, SemType] =
+    given globalNames: mutable.Map[Ident, SemType] = mutable.Map.empty
+    given globalNumbering: mutable.Map[String, Int] = mutable.Map.empty
+    val scope = Scope(mutable.Map.empty, Map.empty)
+    val Program(funcs, main) = prog
+    funcs
+      // First add all function declarations to the scope
+      .map { case FuncDecl(retType, name, params, body) =>
+        val paramTypes = params.map { param =>
+          val paramType = SemType(param.paramType)
+          paramType
+        }
+        scope.add(KnownType.Func(SemType(retType), paramTypes), name, IdentType.Func)
+        (params zip paramTypes, body)
+      }
+      // Only then rename the function bodies
+      // (functions can call one-another regardless of order of declaration)
+      .foreach { case (params, body) =>
+        val functionScope = scope.subscope
+        params.foreach { case (param, paramType) =>
+          functionScope.add(paramType, param.name, IdentType.Var)
+        }
+        body.toList.foreach(rename(functionScope.subscope)) // body can shadow function params
+      }
+    main.toList.foreach(rename(scope))
+    globalNames.toMap
+
+  /** Check scoping of all identifies in a given AST node.
+    *
+    * @param scope
+    *   The current scope and flattened parent scope.
+    * @param node
+    *   The AST node.
+    * @param globalNames
+    *   The global map of identifiers to semantic types - renamed identifiers will be added to this
+    *   map.
+    * @param globalNumbering
+    *   The global map of identifier names to the number of times they have been declared - used and
+    *   updated during identifier renaming.
+    * @param errors
+    */
+  private def rename(scope: Scope)(
+      node: Ident | Stmt | LValue | RValue | Expr
+  )(using
+      globalNames: mutable.Map[Ident, SemType],
+      globalNumbering: mutable.Map[String, Int],
+      errors: mutable.Builder[Error, List[Error]]
+  ): Unit = node match {
+    // These cases are more interesting because the involve making subscopes
+    // or modifying the current scope.
+    case VarDecl(synType, name, value) => {
+      // Order matters here. Variable isn't declared until after the value is evaluated.
+      rename(scope)(value)
+      // Attempt to add the new variable to the current scope.
+      scope.add(SemType(synType), name, IdentType.Var)
+    }
+    case If(cond, thenStmt, elseStmt) => {
+      rename(scope)(cond)
+      // then and else both have their own scopes
+      thenStmt.toList.foreach(rename(scope.subscope))
+      elseStmt.toList.foreach(rename(scope.subscope))
+    }
+    case While(cond, body) => {
+      rename(scope)(cond)
+      // while bodies have their own scopes
+      body.toList.foreach(rename(scope.subscope))
+    }
+    // begin-end blocks have their own scopes
+    case Block(body) => body.toList.foreach(rename(scope.subscope))
+
+    // These cases are simpler, mostly just recursive calls to rename()
+    case Assign(lhs, value) => {
+      // Variables may be reassigned with their value in the rhs, so order doesn't matter here.
+      rename(scope)(lhs)
+      rename(scope)(value)
+    }
+    case Read(lhs)      => rename(scope)(lhs)
+    case Free(expr)     => rename(scope)(expr)
+    case Return(expr)   => rename(scope)(expr)
+    case Exit(expr)     => rename(scope)(expr)
+    case Print(expr, _) => rename(scope)(expr)
+    case NewPair(fst, snd) => {
+      rename(scope)(fst)
+      rename(scope)(snd)
+    }
+    case Call(name, args) => {
+      renameIdent(scope, name, IdentType.Func)
+      args.foreach(rename(scope))
+    }
+    case Fst(elem)         => rename(scope)(elem)
+    case Snd(elem)         => rename(scope)(elem)
+    case ArrayLiter(elems) => elems.foreach(rename(scope))
+    case ArrayElem(name, indices) => {
+      rename(scope)(name)
+      indices.toList.foreach(rename(scope))
+    }
+    case Parens(expr) => rename(scope)(expr)
+    case op: UnaryOp  => rename(scope)(op.x)
+    case op: BinaryOp => {
+      rename(scope)(op.x)
+      rename(scope)(op.y)
+    }
+    // Default to variables. Only `call` uses IdentType.Func.
+    case id: Ident => renameIdent(scope, id, IdentType.Var)
+    // These literals cannot contain identifies, exit immediately.
+    case IntLiter(_) | BoolLiter(_) | CharLiter(_) | StrLiter(_) | PairLiter() | Skip() => ()
+  }
+
+  /** Lookup an identifier in the current scope and rename it. If the identifier is not found, add
+    * an error to the error list and add it to the current scope with an unknown type.
+    *
+    * @param scope
+    *   The current scope and flattened parent scope.
+    * @param ident
+    *   The identifier to rename.
+    * @param identType
+    *   The type of the identifier (function or variable).
+    * @param globalNames
+    *   Used to add not-found identifiers to scope.
+    * @param globalNumbering
+    *   Used to add not-found identifiers to scope.
+    * @param errors
+    *   The list of errors to append to.
+    */
+  private def renameIdent(scope: Scope, ident: Ident, identType: IdentType)(using
+      globalNames: mutable.Map[Ident, SemType],
+      globalNumbering: mutable.Map[String, Int],
+      errors: mutable.Builder[Error, List[Error]]
+  ): Unit = {
+    // Unfortunately map defaults only work with `.apply()`, which throws an error when the key is not found.
+    // Neither is there a way to check whether a default exists, so we have to use a try-catch.
+    try {
+      val Ident(_, uid) = scope.current.withDefault(scope.parent)((ident.v, identType))
+      ident.uid = uid
+    } catch {
+      case _: NoSuchElementException =>
+        errors += Error.UndefinedIdentifier(ident, identType)
+        scope.add(?, ident, identType)
+    }
+  }
+}

src/main/wacc/types.scala

@@ -0,0 +1,31 @@
+package wacc
+
+object types {
+  import ast._
+
+  sealed trait SemType
+  case object ? extends SemType
+  enum KnownType extends SemType {
+    case Int
+    case Bool
+    case Char
+    case String
+    case Array(elem: SemType)
+    case Pair(left: SemType, right: SemType)
+    case Func(ret: SemType, params: List[SemType])
+  }
+
+  object SemType {
+    def apply(synType: Type | PairElemType): KnownType = synType match {
+      case IntType()    => KnownType.Int
+      case BoolType()   => KnownType.Bool
+      case CharType()   => KnownType.Char
+      case StringType() => KnownType.String
+      // For semantic types it is easier to work with recursion rather than a fixed size
+      case ArrayType(elemType, dimension) =>
+        (0 until dimension).foldLeft(SemType(elemType))((acc, _) => KnownType.Array(acc))
+      case PairType(fst, snd) => KnownType.Pair(SemType(fst), SemType(snd))
+      case UntypedPairType()  => KnownType.Pair(?, ?)
+    }
+  }
+}