// Insert inserts the given declaration into the current scope.
func (s *Scope) Insert(decl ast.Decl) error {
// Early return for first-time declarations.
ident := decl.Name()
if ident == nil {
// Anonymous function parameter declaration.
return nil
}
name := ident.String()
prev, ok := s.Decls[name]
if !ok {
s.Decls[name] = decl
return nil
}
prevIdent := prev.Name()
if prevIdent.NamePos == ident.NamePos {
// Identifier already added to scope.
return nil
}
// Previously declared.
if !types.Equal(prev.Type(), decl.Type()) {
return errors.Newf(ident.Start(), "redefinition of %q with type %q instead of %q", name, decl.Type(), prev.Type())
}
// The last tentative definition becomes the definition, unless defined
// explicitly (e.g. having an initializer or function body).
if !s.IsDef(prev) {
s.Decls[name] = decl
return nil
}
// Definition already present in scope.
if s.IsDef(decl) {
// TODO: Consider adding support for multiple errors (and potentially
// warnings and notifications).
//
// If support for notifications are added, add a note of the previous declaration.
// errors.Notef(prevIdent.Start(), "previous definition of %q", name)
return errors.Newf(ident.Start(), "redefinition of %q", name)
}
// Declaration of previously declared identifier.
return nil
}
// checkNestedFunctions reports an error if the given function contains any
// nested function definitions.
func checkNestedFunctions(fn *ast.FuncDecl) error {
if !astutil.IsDef(fn) {
return nil
}
check := func(n ast.Node) error {
if n, ok := n.(*ast.FuncDecl); ok {
return errors.Newf(n.FuncName.Start(), "nested functions not allowed")
}
return nil
}
nop := func(ast.Node) error { return nil }
if err := astutil.WalkBeforeAfter(fn.Body, check, nop); err != nil {
return errutil.Err(err)
}
return nil
}
// check type-checks the given file.
func check(file *ast.File, exprTypes map[ast.Expr]types.Type) error {
// funcs is a stack of function declarations, where the top-most entry
// represents the currently active function.
var funcs []*types.Func
// check type-checks the given node.
check := func(n ast.Node) error {
switch n := n.(type) {
case *ast.BlockStmt:
// Verify that array declarations have an explicit size or an
// initializer.
for _, item := range n.Items {
switch item := item.(type) {
case *ast.VarDecl:
typ := item.Type()
if typ, ok := typ.(*types.Array); ok {
if typ.Len == 0 && item.Val == nil {
return errors.Newf(item.VarName.NamePos, "array size or initializer missing for %q", item.VarName)
}
}
}
}
case *ast.VarDecl:
typ := n.Type()
// TODO: Evaluate if the type-checking of identifiers could be made
// more generic. Consider if a new variable declaration type was added
// alongside of ast.VarDecl, e.g. ast.Field. Then the type-checking
// code would have to be duplicated to ast.Field. A more generic
// approach that may be worth exploring is to do the type-checking
// directly on *ast.Ident. A naive implementation has been attempted
// using *ast.Ident, which failed since "void" refers to itself as a
// VarDecl, whos types is "void".
if n.VarName != nil && types.IsVoid(typ) {
return errors.Newf(n.VarName.NamePos, `%q has invalid type "void"`, n.VarName)
}
if typ, ok := typ.(*types.Array); ok {
if types.IsVoid(typ.Elem) {
return errors.Newf(n.VarName.NamePos, `invalid element type "void" of array %q`, n.VarName)
}
}
case *ast.FuncDecl:
if astutil.IsDef(n) {
// push function declaration.
funcs = append(funcs, n.Type().(*types.Func))
// Verify that parameter names are not obmitted in function
// definitions.
for _, param := range n.FuncType.Params {
if !types.IsVoid(param.Type()) && param.VarName == nil {
return errors.Newf(param.VarType.Start(), "parameter name obmitted")
}
}
// Verify that non-void functions end with return statement.
if !types.IsVoid(n.Type().(*types.Func).Result) {
// endsWithReturn reports whether the given block item ends with
// a return statement. The following two terminating statements
// are supported, recursively.
//
// return;
//
// if (cond) {
// return;
// } else {
// return;
// }
var endsWithReturn func(ast.Node) bool
endsWithReturn = func(node ast.Node) bool {
last := node
if block, ok := node.(*ast.BlockStmt); ok {
items := block.Items
if len(items) == 0 {
// node ends without a return statement.
return false
}
last = items[len(items)-1]
}
switch last := last.(type) {
case *ast.ReturnStmt:
// node ends with a return statement.
return true
case *ast.IfStmt:
if last.Else == nil {
// node may ends without a return statement if the else-
// branch is invoked.
return false
}
return endsWithReturn(last.Body) && endsWithReturn(last.Else)
default:
// node may end without return statement.
return false
}
}
missing := !endsWithReturn(n.Body)
// Missing return statements are valid from the main function.
//
// NOTE: "reaching the } that terminates the main function
// returns a value of 0." (see §5.1.2.2.3 in the C11 spec)
if missing && n.FuncName.String() != "main" {
return errors.Newf(n.Body.Rbrace, "missing return at end of non-void function %q", n.FuncName)
}
}
}
case *ast.ReturnStmt:
// Verify result type.
curFunc := funcs[len(funcs)-1]
var resultType types.Type
resultType = &types.Basic{Kind: types.Void}
if n.Result != nil {
resultType = exprTypes[n.Result]
}
if !isCompatible(resultType, curFunc.Result) {
resultPos := n.Start()
if n.Result != nil {
resultPos = n.Result.Start()
}
return errors.Newf(resultPos, "returning %q from a function with incompatible result type %q", resultType, curFunc.Result)
}
case *ast.CallExpr:
funcType, ok := n.Name.Decl.Type().(*types.Func)
if !ok {
return errors.Newf(n.Lparen, "cannot call non-function %q of type %q", n.Name, funcType)
}
// TODO: Implement support for functions with variable arguments (i.e.
// ellipsis).
// Verify call without arguments.
if len(n.Args) == 0 && len(funcType.Params) == 1 && types.IsVoid(funcType.Params[0].Type) {
return nil
}
// Check number of arguments.
if len(n.Args) < len(funcType.Params) {
return errors.Newf(n.Lparen, "calling %q with too few arguments; expected %d, got %d", n.Name, len(funcType.Params), len(n.Args))
}
if len(n.Args) > len(funcType.Params) {
return errors.Newf(n.Lparen, "calling %q with too many arguments; expected %d, got %d", n.Name, len(funcType.Params), len(n.Args))
}
// Check that call argument types match the function parameter types.
for i, param := range funcType.Params {
arg := n.Args[i]
argType := exprTypes[arg]
paramType := param.Type
if !isCompatibleArg(argType, paramType) {
return errors.Newf(arg.Start(), "calling %q with incompatible argument type %q to parameter of type %q", n.Name, argType, paramType)
}
}
case *ast.FuncType:
for _, param := range n.Params {
paramType := param.Type()
if len(n.Params) > 1 && types.IsVoid(paramType) {
return errors.Newf(n.Lparen, `"void" must be the only parameter`)
}
}
case *ast.IndexExpr:
indexType, ok := exprTypes[n.Index]
if !ok {
panic(fmt.Sprintf("unable to locate type of expression %v", n.Index))
}
if !types.IsInteger(indexType) {
return errors.Newf(n.Index.Start(), "invalid array index; expected integer, got %q", indexType)
}
default:
// TODO: Implement type-checking for remaining node types.
//log.Printf("not type-checked: %T\n", n)
}
return nil
}
// after reverts to the outer function after traversing function definitions.
after := func(n ast.Node) error {
switch n := n.(type) {
case *ast.FuncDecl:
if astutil.IsDef(n) {
// pop function declaration.
funcs = funcs[:len(funcs)-1]
}
}
return nil
}
// Walk the AST of the given file to perform type-checking.
if err := astutil.WalkBeforeAfter(file, check, after); err != nil {
return errutil.Err(err)
}
return nil
}
// resolve performs identifier resolution, mapping identifiers to corresponding
// declarations.
func resolve(file *ast.File, scopes map[ast.Node]*Scope) error {
// TODO: Verify that type keywords cannot be redeclared.
// Pre-pass, add keyword types and universe scope.
universe := NewScope(nil)
charIdent := &ast.Ident{NamePos: universePos, Name: "char"}
charDecl := &ast.TypeDef{DeclType: charIdent, TypeName: charIdent, Val: &types.Basic{Kind: types.Char}}
charIdent.Decl = charDecl
intIdent := &ast.Ident{NamePos: universePos, Name: "int"}
intDecl := &ast.TypeDef{DeclType: intIdent, TypeName: intIdent, Val: &types.Basic{Kind: types.Int}}
intIdent.Decl = intDecl
voidIdent := &ast.Ident{NamePos: universePos, Name: "void"}
voidDecl := &ast.TypeDef{DeclType: voidIdent, TypeName: voidIdent, Val: &types.Basic{Kind: types.Void}}
voidIdent.Decl = voidDecl
universeDecls := []*ast.TypeDef{
charDecl,
intDecl,
voidDecl,
}
for _, decl := range universeDecls {
if err := universe.Insert(decl); err != nil {
return errutil.Err(err)
}
}
// First pass, add global declarations to file scope.
fileScope := NewScope(universe)
scopes[file] = fileScope
fileScope.IsDef = func(decl ast.Decl) bool {
// Consider variable declarations as tentative definitions; i.e. return
// false, unless variable definition.
return decl.Value() != nil
}
for _, decl := range file.Decls {
if err := fileScope.Insert(decl); err != nil {
return errutil.Err(err)
}
}
// skip specifies that the block statement body of a function declaration
// should skip creating a nested scope, as it has already been created by its
// function declaration, so that function parameters are placed within the
// correct scope.
skip := false
// scope specifies the current lexical scope.
scope := fileScope
// resolve performs identifier resolution, mapping identifiers to the
// corresponding declarations of the closest lexical scope.
resolve := func(n ast.Node) error {
switch n := n.(type) {
case ast.Decl:
// Insert declaration into the scope if not already added by the
// file scope pre-pass.
if scope != fileScope {
if err := scope.Insert(n); err != nil {
return errutil.Err(err)
}
}
// Create nested scope for function definitions.
if fn, ok := n.(*ast.FuncDecl); ok {
if astutil.IsDef(fn) {
skip = true
}
scope = NewScope(scope)
scopes[fn] = scope
}
case *ast.BlockStmt:
if !skip {
scope = NewScope(scope)
scopes[n] = scope
}
skip = false
case *ast.Ident:
decl, ok := scope.Lookup(n.Name)
if !ok {
return errors.Newf(n.Start(), "undeclared identifier %q", n)
}
n.Decl = decl
}
return nil
}
// after reverts to the outer scope after traversing block statements.
after := func(n ast.Node) error {
if _, ok := n.(*ast.BlockStmt); ok {
scope = scope.Outer
} else if fn, ok := n.(*ast.FuncDecl); ok && !astutil.IsDef(fn) {
scope = scope.Outer
}
return nil
}
// Walk the AST of the given file to resolve identifiers.
if err := astutil.WalkBeforeAfter(file, resolve, after); err != nil {
return errutil.Err(err)
}
return nil
}
// typeOf returns the type of the given expression.
func typeOf(n ast.Expr) (types.Type, error) {
switch n := n.(type) {
case *ast.BasicLit:
// "The type of an integer constant is the first of the corresponding
// list in which its value can be represented." [C99 draft 6.4.4.1.5]
switch n.Kind {
case token.CharLit:
// "An integer character constant has type int." [C99 draft 6.4.4.4.10]
return &types.Basic{Kind: types.Int}, nil
case token.IntLit:
return &types.Basic{Kind: types.Int}, nil
default:
panic(fmt.Sprintf("support for basic literal type %v not yet implemented", n.Kind))
}
case *ast.BinaryExpr:
// See [C99 draft 6.3.1.8 Usual arithmetic conversions]
xType, err := typeOf(n.X)
if err != nil {
return nil, errutil.Err(err)
}
yType, err := typeOf(n.Y)
if err != nil {
return nil, errutil.Err(err)
}
if n.Op == token.Assign {
if !isAssignable(n.X) {
return nil, errors.Newf(n.OpPos, "cannot assign to %q of type %q", n.X, xType)
}
if !isCompatible(xType, yType) {
return nil, errors.Newf(n.OpPos, "cannot assign to %q (type mismatch between %q and %q)", n.X, xType, yType)
}
// TODO: !types.Equal(higherPrecision(xType, yType), xType) could be
// used for loss of percision warning.
return xType, nil
}
if types.IsVoid(xType) || types.IsVoid(yType) {
return nil, errors.Newf(n.OpPos, "invalid operands to binary expression: %v (%q and %q)", n, xType, yType)
}
if !isCompatible(xType, yType) {
return nil, errors.Newf(n.OpPos, "invalid operation: %v (type mismatch between %q and %q)", n, xType, yType)
}
// TODO: Implement better implicit conversion. Future: Make sure to
// promote types early when implementing signed/unsigned types and
// types need to be promoted anyway later. Be careful of bug:
// https://youtu.be/Ux0YnVEaI6A?t=279
// Implement according to [C99 draft 6.3.1.8 Usual arithmetic conversions]
return higherPrecision(xType, yType), nil
case *ast.CallExpr:
typ := n.Name.Decl.Type()
if typ, ok := typ.(*types.Func); ok {
return typ.Result, nil
}
return nil, errors.Newf(n.Lparen, "cannot call non-function %q of type %q", n.Name, typ)
case *ast.Ident:
return n.Decl.Type(), nil
case *ast.IndexExpr:
typ := n.Name.Decl.Type()
if typ, ok := typ.(*types.Array); ok {
return typ.Elem, nil
}
return nil, errors.Newf(n.Lbracket, "invalid operation: %v (type %q does not support indexing)", n, typ)
case *ast.ParenExpr:
return typeOf(n.X)
case *ast.UnaryExpr:
// TODO: Add support for pointers.
return typeOf(n.X)
default:
panic(fmt.Sprintf("support for type %T not yet implemented.", n))
}
}