resolver.ts

/**
 * Resolve infrastructure to obtain types and elements.
 * @module resolver
 *//***/

import {
  DiagnosticEmitter,
  DiagnosticCode
} from "./diagnostics";

import {
  Program,
  ElementKind,
  OperatorKind,
  FlowFlags,

  Element,
  Class,
  ClassPrototype,
  Function,
  FunctionTarget,
  FunctionPrototype,
  VariableLikeElement,
  Property,
  DecoratorFlags,
  FieldPrototype,
  Field,
  Global
} from "./program";

import {
  SignatureNode,
  ParameterKind,
  CommonTypeNode,
  NodeKind,
  TypeNode,
  TypeParameterNode,
  Node,
  Range,
  IdentifierExpression,
  CallExpression,
  ElementAccessExpression,
  PropertyAccessExpression,
  LiteralExpression,
  LiteralKind,
  ParenthesizedExpression,
  AssertionExpression,
  Expression,
  IntegerLiteralExpression,
  UnaryPrefixExpression,
  UnaryPostfixExpression,
  AssertionKind
} from "./ast";

import {
  Type,
  Signature,
  typesToString,
  TypeKind,
  TypeFlags
} from "./types";

import {
  PATH_DELIMITER,
  INSTANCE_DELIMITER,
  CommonFlags
} from "./common";

import {
  makeMap
} from "./util";

import {
  Token
} from "./tokenizer";

/** Indicates whether errors are reported or not. */
export enum ReportMode {
  /** Report errors. */
  REPORT,
  /** Swallow errors. */
  SWALLOW
}

/** Provides tools to resolve types and expressions. */
export class Resolver extends DiagnosticEmitter {

  /** The program this resolver belongs to. */
  program: Program;

  /** Target expression of the previously resolved property or element access. */
  currentThisExpression: Expression | null = null;
  /** Element expression of the previously resolved element access. */
  currentElementExpression : Expression | null = null;

  /** Constructs the resolver for the specified program. */
  constructor(program: Program) {
    super(program.diagnostics);
    this.program = program;
  }

  /** Resolves a {@link CommonTypeNode} to a concrete {@link Type}. */
  resolveType(
    node: CommonTypeNode,
    contextualTypeArguments: Map<string,Type> | null = null,
    reportMode = ReportMode.REPORT
  ): Type | null {

    // handle signatures specifically
    if (node.kind == NodeKind.SIGNATURE) {
      let signature = this.resolveSignature(<SignatureNode>node, contextualTypeArguments, reportMode);
      if (!signature) return null;
      return node.isNullable ? signature.type.asNullable() : signature.type;
    }

    // now dealing with TypeNode
    assert(node.kind == NodeKind.TYPE);
    var typeNode = <TypeNode>node;
    var simpleName = typeNode.name.text;
    var globalName = simpleName;
    var localName = typeNode.range.source.internalPath + PATH_DELIMITER + simpleName; // TODO cache

    // check file-global / program-global enum or class
    {
      let elementsLookup = this.program.elementsLookup;
      let element: Element | null;
      if (
        (element = elementsLookup.get(localName)) || // file-global
        (element = elementsLookup.get(globalName))   // program-global
      ) {
        switch (element.kind) {
          case ElementKind.ENUM: {
            if (typeNode.typeArguments !== null && typeNode.typeArguments.length) {
              if (reportMode == ReportMode.REPORT) {
                this.error(
                  DiagnosticCode.Type_0_is_not_generic,
                  node.range, element.internalName
                );
              }
              return null;
            }
            return Type.i32;
          }
          case ElementKind.CLASS_PROTOTYPE: {
            let instance = this.resolveClassInclTypeArguments(
              <ClassPrototype>element,
              typeNode.typeArguments,
              makeMap<string,Type>(contextualTypeArguments),
              node
            ); // reports
            if (!instance) return null;
            return node.isNullable ? instance.type.asNullable() : instance.type;
          }
        }
      }
    }

    // check (global) type alias
    {
      let alias = this.program.typeAliases.get(simpleName);
      if (alias) return this.resolveType(alias.type, contextualTypeArguments, reportMode);
    }

    // resolve parameters
    var typeArgumentNodes = typeNode.typeArguments;
    var typeArguments: Type[] | null = null;
    if (typeArgumentNodes) {
      let numTypeArguments = typeArgumentNodes.length;
      typeArguments = new Array<Type>(numTypeArguments);
      for (let i = 0; i < numTypeArguments; ++i) {
        let paramType = this.resolveType( // reports
          typeArgumentNodes[i],
          contextualTypeArguments,
          reportMode
        );
        if (!paramType) return null;
        typeArguments[i] = paramType;
      }
      if (numTypeArguments) { // can't be a placeholder if it has parameters
        let instanceKey = typesToString(typeArguments);
        if (instanceKey.length) {
          localName += "<" + instanceKey + ">";
          globalName += "<" + instanceKey + ">";
        }
      } else if (contextualTypeArguments) {
        let placeholderType = contextualTypeArguments.get(globalName);
        if (placeholderType) return placeholderType;
      }
    }

    // check file-global / program-global type
    {
      let typesLookup = this.program.typesLookup;
      let type: Type | null;
      if (
        (type = typesLookup.get(localName)) ||
        (type = typesLookup.get(globalName))
      ) {
        return type;
      }
    }

    // check built-in macro types
    if (simpleName == "NATIVE") {
      if (!(typeArguments && typeArguments.length == 1)) {
        if (reportMode == ReportMode.REPORT) {
          this.error(
            DiagnosticCode.Expected_0_type_arguments_but_got_1,
            typeNode.range, "1", (typeArgumentNodes ? typeArgumentNodes.length : 1).toString(10)
          );
        }
        return null;
      }
      switch (typeArguments[0].kind) {
        case TypeKind.I8:
        case TypeKind.I16:
        case TypeKind.I32: return Type.i32;
        case TypeKind.ISIZE: if (!this.program.options.isWasm64) return Type.i32;
        case TypeKind.I64: return Type.i64;
        case TypeKind.U8:
        case TypeKind.U16:
        case TypeKind.U32:
        case TypeKind.BOOL: return Type.u32;
        case TypeKind.USIZE: if (!this.program.options.isWasm64) return Type.u32;
        case TypeKind.U64: return Type.u64;
        case TypeKind.F32: return Type.f32;
        case TypeKind.F64: return Type.f64;
        case TypeKind.VOID: return Type.void;
        default: assert(false);
      }
    }

    if (reportMode == ReportMode.REPORT) {
      this.error(
        DiagnosticCode.Cannot_find_name_0,
        typeNode.name.range, globalName
      );
    }
    return null;
  }

  /** Resolves a {@link SignatureNode} to a concrete {@link Signature}. */
  resolveSignature(
    node: SignatureNode,
    contextualTypeArguments: Map<string,Type> | null = null,
    reportMode: ReportMode = ReportMode.REPORT
  ): Signature | null {
    var explicitThisType = node.explicitThisType;
    var thisType: Type | null = null;
    if (explicitThisType) {
      thisType = this.resolveType(explicitThisType, contextualTypeArguments, reportMode);
      if (!thisType) return null;
    }
    var parameterTypeNodes = node.parameters;
    var numParameters = parameterTypeNodes.length;
    var parameterTypes = new Array<Type>(numParameters);
    var parameterNames = new Array<string>(numParameters);
    var requiredParameters = 0;
    var hasRest = false;
    for (let i = 0; i < numParameters; ++i) {
      let parameterTypeNode = parameterTypeNodes[i];
      switch (parameterTypeNode.parameterKind) {
        case ParameterKind.DEFAULT: {
          requiredParameters = i + 1;
          break;
        }
        case ParameterKind.REST: {
          assert(i == numParameters);
          hasRest = true;
          break;
        }
      }
      let parameterType = this.resolveType(
        assert(parameterTypeNode.type),
        contextualTypeArguments,
        reportMode
      );
      if (!parameterType) return null;
      parameterTypes[i] = parameterType;
      parameterNames[i] = parameterTypeNode.name.text;
    }
    var returnTypeNode = node.returnType;
    var returnType: Type | null;
    if (returnTypeNode) {
      returnType = this.resolveType(returnTypeNode, contextualTypeArguments, reportMode);
      if (!returnType) return null;
    } else {
      returnType = Type.void;
    }
    var signature = new Signature(parameterTypes, returnType, thisType);
    signature.parameterNames = parameterNames;
    signature.requiredParameters = requiredParameters;
    signature.hasRest = hasRest;
    return signature;
  }

  /** Resolves an array of type arguments to concrete types. */
  resolveTypeArguments(
    typeParameters: TypeParameterNode[],
    typeArgumentNodes: CommonTypeNode[] | null,
    contextualTypeArguments: Map<string,Type>,
    alternativeReportNode: Node | null = null,
    reportMode: ReportMode = ReportMode.REPORT
  ): Type[] | null {
    var minParameterCount = 0;
    var maxParameterCount = 0;
    for (let i = 0; i < typeParameters.length; ++i) {
      if (!typeParameters[i].defaultType) ++minParameterCount;
      ++maxParameterCount;
    }
    var argumentCount = typeArgumentNodes ? typeArgumentNodes.length : 0;
    if (argumentCount < minParameterCount || argumentCount > maxParameterCount) {
      this.error(
        DiagnosticCode.Expected_0_type_arguments_but_got_1,
        argumentCount
          ? Range.join(
              (<TypeNode[]>typeArgumentNodes)[0].range,
              (<TypeNode[]>typeArgumentNodes)[argumentCount - 1].range
            )
          : assert(alternativeReportNode).range.atEnd,
        (argumentCount < minParameterCount ? minParameterCount : maxParameterCount).toString(10),
        argumentCount.toString(10)
      );
      return null;
    }
    var typeArguments = new Array<Type>(maxParameterCount);
    for (let i = 0; i < maxParameterCount; ++i) {
      let type = i < argumentCount
        ? this.resolveType( // reports
            (<TypeNode[]>typeArgumentNodes)[i],
            contextualTypeArguments,
            reportMode
          )
        : this.resolveType( // reports
            assert(typeParameters[i].defaultType),
            contextualTypeArguments,
            reportMode
          );
      if (!type) return null;
      // TODO: check extendsType
      contextualTypeArguments.set(typeParameters[i].name.text, type);
      typeArguments[i] = type;
    }
    return typeArguments;
  }

  /** Resolves an identifier to the element it refers to. */
  resolveIdentifier(
    identifier: IdentifierExpression,
    context: Element | null,
    reportMode: ReportMode = ReportMode.REPORT
  ): Element | null {
    var name = identifier.text;
    var element: Element | null;

    if (context) {

      switch (context.kind) {
        case ElementKind.FUNCTION: { // search locals, use prototype
          element = (<Function>context).flow.getScopedLocal(name);
          if (element) {
            this.currentThisExpression = null;
            this.currentElementExpression = null;
            return element;
          }
          context = (<Function>context).prototype.parent;
          break;
        }
        case ElementKind.CLASS: { // use prototype
          context = (<Class>context).prototype.parent;
          break;
        }
      }

      // search context
      while (context) {
        let members = context.members;
        if (members) {
          if (element = members.get(name)) {
            this.currentThisExpression = null;
            this.currentElementExpression = null;
            return element;
          }
        }
        context = context.parent;
      }
    }

    // search current file
    var elementsLookup = this.program.elementsLookup;
    if (element = elementsLookup.get(identifier.range.source.internalPath + PATH_DELIMITER + name)) {
      this.currentThisExpression = null;
      this.currentElementExpression = null;
      return element; // GLOBAL, FUNCTION_PROTOTYPE, CLASS_PROTOTYPE
    }

    // search global scope
    if (element = elementsLookup.get(name)) {
      this.currentThisExpression = null;
      this.currentElementExpression = null;
      return element; // GLOBAL, FUNCTION_PROTOTYPE, CLASS_PROTOTYPE
    }

    if (reportMode == ReportMode.REPORT) {
      this.error(
        DiagnosticCode.Cannot_find_name_0,
        identifier.range, name
      );
    }
    return null;
  }

  /** Resolves a lazily compiled global, i.e. a static class field. */
  ensureResolvedLazyGlobal(global: Global, reportMode: ReportMode = ReportMode.REPORT): bool {
    if (global.is(CommonFlags.RESOLVED)) return true;
    var resolveType = assert(global.declaration).type;
    if (!resolveType) return false;
    var resolvedType = this.resolveType(resolveType, null, reportMode);
    if (!resolvedType) return false;
    global.type = resolvedType;
    global.set(CommonFlags.RESOLVED);
    return true;
  }

  /** Resolves a property access to the element it refers to. */
  resolvePropertyAccess(
    propertyAccess: PropertyAccessExpression,
    contextualFunction: Function,
    contextualType: Type,
    reportMode: ReportMode = ReportMode.REPORT
  ): Element | null {
    // start by resolving the lhs target (expression before the last dot)
    var targetExpression = propertyAccess.expression;
    var target = this.resolveExpression(targetExpression, contextualFunction, contextualType, reportMode); // reports
    if (!target) return null;

    // at this point we know exactly what the target is, so look up the element within
    var propertyName = propertyAccess.property.text;

    // Resolve variable-likes to the class type they reference first
    switch (target.kind) {
      case ElementKind.GLOBAL: if (!this.ensureResolvedLazyGlobal(<Global>target, reportMode)) return null;
      case ElementKind.LOCAL:
      case ElementKind.FIELD: {
        let type = (<VariableLikeElement>target).type;
        assert(type != Type.void);
        let classReference = type.classReference;
        if (!classReference) {
          let basicClasses = this.program.basicClasses;
          if (!type.is(TypeFlags.REFERENCE) && basicClasses.has(type.kind)) {
            classReference = assert(basicClasses.get(type.kind));
          } else {
            this.error(
              DiagnosticCode.Property_0_does_not_exist_on_type_1,
              propertyAccess.property.range, propertyName, (<VariableLikeElement>target).type.toString()
            );
            return null;
          }
        }
        target = classReference;
        break;
      }
      case ElementKind.PROPERTY: {
        let getter = this.resolveFunction(
          assert((<Property>target).getterPrototype),
          null,
          makeMap<string,Type>(),
          reportMode
        );
        if (!getter) return null;
        let classReference = getter.signature.returnType.classReference;
        if (!classReference) {
          this.error(
            DiagnosticCode.Property_0_does_not_exist_on_type_1,
            propertyAccess.property.range, propertyName, getter.signature.returnType.toString()
          );
          return null;
        }
        target = classReference;
        break;
      }
      case ElementKind.CLASS: {
        let elementExpression = this.currentElementExpression;
        if (elementExpression) {
          let indexedGet = (<Class>target).lookupOverload(OperatorKind.INDEXED_GET);
          if (!indexedGet) {
            this.error(
              DiagnosticCode.Index_signature_is_missing_in_type_0,
              elementExpression.range, (<Class>target).internalName
            );
            return null;
          }
          let returnType = indexedGet.signature.returnType;
          if (!(target = returnType.classReference)) {
            this.error(
              DiagnosticCode.Property_0_does_not_exist_on_type_1,
              propertyAccess.property.range, propertyName, returnType.toString()
            );
            return null;
          }
        }
        break;
      }
    }

    // Look up the member within
    switch (target.kind) {
      case ElementKind.CLASS_PROTOTYPE:
      case ElementKind.CLASS: {
        do {
          let members = target.members;
          let member: Element | null;
          if (members && (member = members.get(propertyName))) {
            this.currentThisExpression = targetExpression;
            this.currentElementExpression = null;
            return member; // instance FIELD, static GLOBAL, FUNCTION_PROTOTYPE...
          }
          // traverse inherited static members on the base prototype if target is a class prototype
          if (target.kind == ElementKind.CLASS_PROTOTYPE) {
            if ((<ClassPrototype>target).basePrototype) {
              target = <ClassPrototype>(<ClassPrototype>target).basePrototype;
            } else {
              break;
            }
          // traverse inherited instance members on the base class if target is a class instance
          } else if (target.kind == ElementKind.CLASS) {
            if ((<Class>target).base) {
              target = <Class>(<Class>target).base;
            } else {
              break;
            }
          } else {
            break;
          }
        } while (true);
        break;
      }
      default: { // enums or other namespace-like elements
        let members = target.members;
        if (members) {
          let member = members.get(propertyName);
          if (member) {
            this.currentThisExpression = targetExpression;
            this.currentElementExpression = null;
            return member; // static ENUMVALUE, static GLOBAL, static FUNCTION_PROTOTYPE...
          }
        }
        break;
      }
    }
    this.error(
      DiagnosticCode.Property_0_does_not_exist_on_type_1,
      propertyAccess.property.range, propertyName, target.internalName
    );
    return null;
  }

  resolveElementAccess(
    elementAccess: ElementAccessExpression,
    contextualFunction: Function,
    contextualType: Type,
    reportMode: ReportMode = ReportMode.REPORT
  ): Element | null {
    var targetExpression = elementAccess.expression;
    var target = this.resolveExpression(targetExpression, contextualFunction, contextualType, reportMode);
    if (!target) return null;
    switch (target.kind) {
      case ElementKind.GLOBAL: if (!this.ensureResolvedLazyGlobal(<Global>target, reportMode)) return null;
      case ElementKind.LOCAL:
      case ElementKind.FIELD: {
        let type = (<VariableLikeElement>target).type;
        if (target = type.classReference) {
          this.currentThisExpression = targetExpression;
          this.currentElementExpression = elementAccess.elementExpression;
          return target;
        }
        break;
      }
      case ElementKind.CLASS: {
        let indexedGet = (<Class>target).lookupOverload(OperatorKind.INDEXED_GET);
        if (!indexedGet) {
          if (reportMode == ReportMode.REPORT) {
            this.error(
              DiagnosticCode.Index_signature_is_missing_in_type_0,
              elementAccess.range, (<Class>target).internalName
            );
          }
          return null;
        }
        if (targetExpression.kind == NodeKind.ELEMENTACCESS) { // nested element access
          let returnType = indexedGet.signature.returnType;
          if (target = returnType.classReference) {
            this.currentThisExpression = targetExpression;
            this.currentElementExpression = elementAccess.elementExpression;
            return target;
          }
          return null;
        }
        this.currentThisExpression = targetExpression;
        this.currentElementExpression = elementAccess.elementExpression;
        return target;
      }
    }
    if (reportMode == ReportMode.REPORT) {
      this.error(
        DiagnosticCode.Operation_not_supported,
        targetExpression.range
      );
    }
    return null;
  }

  determineIntegerLiteralType(
    intValue: I64,
    contextualType: Type
  ): Type {

    if (!contextualType.is(TypeFlags.REFERENCE)) {
      // compile to contextualType if matching
      switch (contextualType.kind) {
        case TypeKind.I8: {
          if (i64_is_i8(intValue)) return Type.i8;
          break;
        }
        case TypeKind.U8: {
          if (i64_is_u8(intValue)) return Type.u8;
          break;
        }
        case TypeKind.I16: {
          if (i64_is_i16(intValue)) return Type.i16;
          break;
        }
        case TypeKind.U16: {
          if (i64_is_u16(intValue)) return Type.u16;
          break;
        }
        case TypeKind.I32: {
          if (i64_is_i32(intValue)) return Type.i32;
          break;
        }
        case TypeKind.U32: {
          if (i64_is_u32(intValue)) return Type.u32;
          break;
        }
        case TypeKind.BOOL: {
          if (i64_is_bool(intValue)) return Type.bool;
          break;
        }
        case TypeKind.ISIZE: {
          if (!this.program.options.isWasm64) {
            if (i64_is_i32(intValue)) return Type.isize32;
            break;
          }
          return Type.isize64;
        }
        case TypeKind.USIZE: {
          if (!this.program.options.isWasm64) {
            if (i64_is_u32(intValue)) return Type.usize32;
            break;
          }
          return Type.usize64;
        }
        case TypeKind.I64: return Type.i64;
        case TypeKind.U64: return Type.u64;
        case TypeKind.F32: return Type.f32;
        case TypeKind.F64: return Type.f64;
        case TypeKind.VOID: break; // best fitting below
        default: assert(false);
      }
    }

    // otherwise compile to best fitting native type
    if (i64_is_i32(intValue)) return Type.i32;
    if (i64_is_u32(intValue)) return Type.u32;
    return Type.i64;
  }

  resolveExpression(
    expression: Expression,
    contextualFunction: Function,
    contextualType: Type = Type.void,
    reportMode: ReportMode = ReportMode.REPORT
  ): Element | null {
    while (expression.kind == NodeKind.PARENTHESIZED) {
      expression = (<ParenthesizedExpression>expression).expression;
    }
    switch (expression.kind) {
      case NodeKind.ASSERTION: {
        if ((<AssertionExpression>expression).assertionKind == AssertionKind.NONNULL) {
          return this.resolveExpression(
            (<AssertionExpression>expression).expression,
            contextualFunction,
            contextualType,
            reportMode
          );
        }
        let type = this.resolveType(
          assert((<AssertionExpression>expression).toType),
          contextualFunction.flow.contextualTypeArguments,
          reportMode
        );
        if (!type) return null;
        let element: Element | null = type.classReference;
        if (!element) {
          let signature = type.signatureReference;
          if (!signature) return null;
          element = signature.asFunctionTarget(this.program);
        }
        this.currentThisExpression = null;
        this.currentElementExpression = null;
        return element;
      }
      case NodeKind.UNARYPREFIX: {
        // TODO: overloads
        switch ((<UnaryPrefixExpression>expression).operator) {
          case Token.MINUS: {
            let operand = (<UnaryPrefixExpression>expression).operand;
            // implicitly negate if an integer literal to distinguish between i32/u32/i64
            if (operand.kind == NodeKind.LITERAL && (<LiteralExpression>operand).literalKind == LiteralKind.INTEGER) {
              let type = this.determineIntegerLiteralType(
                i64_sub(i64_zero, (<IntegerLiteralExpression>operand).value),
                contextualType
              );
              return assert(this.program.basicClasses.get(type.kind));
            }
            return this.resolveExpression(
              operand,
              contextualFunction,
              contextualType,
              reportMode
            );
          }
          case Token.PLUS:
          case Token.PLUS_PLUS:
          case Token.MINUS_MINUS: {
            return this.resolveExpression(
              (<UnaryPrefixExpression>expression).operand,
              contextualFunction,
              contextualType,
              reportMode
            );
          }
          case Token.EXCLAMATION: {
            return assert(this.program.basicClasses.get(TypeKind.BOOL));
          }
          case Token.TILDE: {
            let resolvedOperand = this.resolveExpression(
              (<UnaryPrefixExpression>expression).operand,
              contextualFunction,
              contextualType,
              reportMode
            );
            if (!resolvedOperand) return null;
            throw new Error("not implemented"); // TODO: should all elements have a corresponding type right away?
          }
          default: assert(false);
        }
        return null;
      }
      case NodeKind.UNARYPOSTFIX: {
        // TODO: overloads
        switch ((<UnaryPostfixExpression>expression).operator) {
          case Token.PLUS_PLUS:
          case Token.MINUS_MINUS: {
            return this.resolveExpression(
              (<UnaryPostfixExpression>expression).operand,
              contextualFunction,
              contextualType,
              reportMode
            );
          }
          default: assert(false);
        }
        return null;
      }
      case NodeKind.BINARY: {
        // TODO: all sorts of unary and binary expressions, which means looking up overloads and
        // evaluating their return types, knowing the semantics of different operators etc.
        // should probably share that code with the compiler somehow, as it also does exactly this.
        throw new Error("not implemented");
      }
      case NodeKind.THIS: { // -> Class / ClassPrototype
        if (contextualFunction.flow.is(FlowFlags.INLINE_CONTEXT)) {
          let explicitLocal = contextualFunction.flow.getScopedLocal("this");
          if (explicitLocal) {
            this.currentThisExpression = null;
            this.currentElementExpression = null;
            return explicitLocal;
          }
        }
        let parent = contextualFunction.parent;
        if (parent) {
          this.currentThisExpression = null;
          this.currentElementExpression = null;
          return parent;
        }
        if (reportMode == ReportMode.REPORT) {
          this.error(
            DiagnosticCode._this_cannot_be_referenced_in_current_location,
            expression.range
          );
        }
        return null;
      }
      case NodeKind.SUPER: { // -> Class
        if (contextualFunction.flow.is(FlowFlags.INLINE_CONTEXT)) {
          let explicitLocal = contextualFunction.flow.getScopedLocal("super");
          if (explicitLocal) {
            this.currentThisExpression = null;
            this.currentElementExpression = null;
            return explicitLocal;
          }
        }
        let parent = contextualFunction.parent;
        if (parent && parent.kind == ElementKind.CLASS && (parent = (<Class>parent).base)) {
          this.currentThisExpression = null;
          this.currentElementExpression = null;
          return parent;
        }
        if (reportMode == ReportMode.REPORT) {
          this.error(
            DiagnosticCode._super_can_only_be_referenced_in_a_derived_class,
            expression.range
          );
        }
        return null;
      }
      case NodeKind.IDENTIFIER: {
        return this.resolveIdentifier(<IdentifierExpression>expression, contextualFunction, reportMode);
      }
      case NodeKind.LITERAL: {
        switch ((<LiteralExpression>expression).literalKind) {
          case LiteralKind.INTEGER: {
            return assert(
              this.program.basicClasses.get(
                this.determineIntegerLiteralType(
                  (<IntegerLiteralExpression>expression).value,
                  contextualType
                ).kind
              )
            );
          }
          case LiteralKind.FLOAT: {
            this.currentThisExpression = expression;
            this.currentElementExpression = null;
            return assert(
              this.program.basicClasses.get(
                contextualType == Type.f32
                  ? TypeKind.F32
                  : TypeKind.F64
              )
            );
          }
          case LiteralKind.STRING: {
            this.currentThisExpression = expression;
            this.currentElementExpression = null;
            return this.program.stringInstance;
          }
          // case LiteralKind.ARRAY: // TODO
        }
        break;
      }
      case NodeKind.PROPERTYACCESS: {
        return this.resolvePropertyAccess(
          <PropertyAccessExpression>expression,
          contextualFunction,
          contextualType,
          reportMode
        );
      }
      case NodeKind.ELEMENTACCESS: {
        return this.resolveElementAccess(
          <ElementAccessExpression>expression,
          contextualFunction,
          contextualType,
          reportMode
        );
      }
      case NodeKind.CALL: {
        let targetExpression = (<CallExpression>expression).expression;
        let target = this.resolveExpression(targetExpression, contextualFunction, contextualType, reportMode);
        if (!target) return null;
        if (target.kind == ElementKind.FUNCTION_PROTOTYPE) {
          let instance = this.resolveFunctionInclTypeArguments(
            <FunctionPrototype>target,
            (<CallExpression>expression).typeArguments,
            makeMap<string,Type>(contextualFunction.flow.contextualTypeArguments),
            expression,
            reportMode
          );
          if (!instance) return null;
          let returnType = instance.signature.returnType;
          let classType = returnType.classReference;
          if (classType) {
            // reuse resolvedThisExpression (might be property access)
            // reuse resolvedElementExpression (might be element access)
            return classType;
          } else {
            let signature = returnType.signatureReference;
            if (signature) {
              let functionTarget = signature.asFunctionTarget(this.program);
              // reuse resolvedThisExpression (might be property access)
              // reuse resolvedElementExpression (might be element access)
              return functionTarget;
            }
          }
          if (reportMode == ReportMode.REPORT) {
            this.error(
              DiagnosticCode.Cannot_invoke_an_expression_whose_type_lacks_a_call_signature_Type_0_has_no_compatible_call_signatures,
              targetExpression.range, target.internalName
            );
          }
          return null;
        }
        break;
      }
    }
    if (reportMode == ReportMode.REPORT) {
      this.error(
        DiagnosticCode.Operation_not_supported,
        expression.range
      );
    }
    return null;
  }

  /** Resolves a function prototype to an instance using the specified concrete type arguments. */
  resolveFunction(
    prototype: FunctionPrototype,
    typeArguments: Type[] | null,
    contextualTypeArguments: Map<string,Type> = makeMap<string,Type>(),
    reportMode: ReportMode = ReportMode.REPORT
  ): Function | null {
    var classTypeArguments = prototype.classTypeArguments; // set only if partially resolved
    var classInstanceKey = classTypeArguments ? typesToString(classTypeArguments) : "";
    var instanceKey = typeArguments ? typesToString(typeArguments) : "";
    var classInstances = prototype.instances.get(classInstanceKey);
    if (classInstances) {
      let instance = classInstances.get(instanceKey);
      if (instance) return instance;
    }

    var declaration = prototype.declaration;
    var isInstance = prototype.is(CommonFlags.INSTANCE);
    var classPrototype = prototype.classPrototype;

    // apply class type arguments if a partially resolved instance method
    if (classTypeArguments) prototype.applyClassTypeArguments(contextualTypeArguments);

    // override with function specific type arguments
    var signatureNode = declaration.signature;
    var functionTypeParameters = declaration.typeParameters;
    var numFunctionTypeArguments: i32;
    if (typeArguments && (numFunctionTypeArguments = typeArguments.length)) {
      assert(functionTypeParameters && numFunctionTypeArguments == functionTypeParameters.length);
      for (let i = 0; i < numFunctionTypeArguments; ++i) {
        contextualTypeArguments.set(
          (<TypeParameterNode[]>functionTypeParameters)[i].name.text,
          typeArguments[i]
        );
      }
    } else {
      assert(!functionTypeParameters || functionTypeParameters.length == 0);
    }

    // resolve class if an instance method
    var classInstance: Class | null = null;
    var thisType: Type | null = null;
    if (isInstance) {
      classInstance = this.resolveClass(
        assert(classPrototype),
        classTypeArguments,
        contextualTypeArguments,
        reportMode
      );
      if (!classInstance) return null;
      let explicitThisType = signatureNode.explicitThisType;
      if (explicitThisType) {
        thisType = this.resolveType(explicitThisType, contextualTypeArguments, reportMode);
        if (!thisType) return null;
      } else {
        thisType = classInstance.type;
      }
      contextualTypeArguments.set("this", thisType);
    } else {
      if (signatureNode.explicitThisType) {
        this.error(
          DiagnosticCode._this_cannot_be_referenced_in_current_location,
          signatureNode.explicitThisType.range
        ); // recoverable
      }
    }

    // resolve signature node
    var signatureParameters = signatureNode.parameters;
    var signatureParameterCount = signatureParameters.length;
    var parameterTypes = new Array<Type>(signatureParameterCount);
    var parameterNames = new Array<string>(signatureParameterCount);
    var requiredParameters = 0;
    for (let i = 0; i < signatureParameterCount; ++i) {