Exemplo n.º 1
0
func (check *Checker) constDecl(obj *Const, typ, init ast.Expr) {
	assert(obj.typ == nil)

	if obj.visited {
		obj.typ = Typ[Invalid]
		return
	}
	obj.visited = true

	// use the correct value of iota
	assert(check.iota == nil)
	check.iota = obj.val
	defer func() { check.iota = nil }()

	// provide valid constant value under all circumstances
	obj.val = constant.MakeUnknown()

	// determine type, if any
	if typ != nil {
		t := check.typ(typ)
		if !isConstType(t) {
			check.errorf(typ.Pos(), "invalid constant type %s", t)
			obj.typ = Typ[Invalid]
			return
		}
		obj.typ = t
	}

	// check initialization
	var x operand
	if init != nil {
		check.expr(&x, init)
	}
	check.initConst(obj, &x)
}
Exemplo n.º 2
0
func (check *Checker) recordCommaOkTypes(x ast.Expr, a [2]Type) {
	assert(x != nil)
	if a[0] == nil || a[1] == nil {
		return
	}
	assert(isTyped(a[0]) && isTyped(a[1]) && isBoolean(a[1]))
	if m := check.Types; m != nil {
		for {
			tv := m[x]
			assert(tv.Type != nil) // should have been recorded already
			pos := x.Pos()
			tv.Type = NewTuple(
				NewVar(pos, check.pkg, "", a[0]),
				NewVar(pos, check.pkg, "", a[1]),
			)
			m[x] = tv
			// if x is a parenthesized expression (p.X), update p.X
			p, _ := x.(*ast.ParenExpr)
			if p == nil {
				break
			}
			x = p.X
		}
	}
}
Exemplo n.º 3
0
// typExpr type-checks the type expression e and returns its type, or Typ[Invalid].
// If def != nil, e is the type specification for the named type def, declared
// in a type declaration, and def.underlying will be set to the type of e before
// any components of e are type-checked. Path contains the path of named types
// referring to this type.
//
func (check *Checker) typExpr(e ast.Expr, def *Named, path []*TypeName) (T Type) {
	if trace {
		check.trace(e.Pos(), "%s", e)
		check.indent++
		defer func() {
			check.indent--
			check.trace(e.Pos(), "=> %s", T)
		}()
	}

	T = check.typExprInternal(e, def, path)
	assert(isTyped(T))
	check.recordTypeAndValue(e, typexpr, T, nil)

	return
}
Exemplo n.º 4
0
// rawExpr typechecks expression e and initializes x with the expression
// value or type. If an error occurred, x.mode is set to invalid.
// If hint != nil, it is the type of a composite literal element.
//
func (check *Checker) rawExpr(x *operand, e ast.Expr, hint Type) exprKind {
	if trace {
		check.trace(e.Pos(), "%s", e)
		check.indent++
		defer func() {
			check.indent--
			check.trace(e.Pos(), "=> %s", x)
		}()
	}

	kind := check.exprInternal(x, e, hint)

	// convert x into a user-friendly set of values
	// TODO(gri) this code can be simplified
	var typ Type
	var val constant.Value
	switch x.mode {
	case invalid:
		typ = Typ[Invalid]
	case novalue:
		typ = (*Tuple)(nil)
	case constant_:
		typ = x.typ
		val = x.val
	default:
		typ = x.typ
	}
	assert(x.expr != nil && typ != nil)

	if isUntyped(typ) {
		// delay type and value recording until we know the type
		// or until the end of type checking
		check.rememberUntyped(x.expr, false, x.mode, typ.(*Basic), val)
	} else {
		check.recordTypeAndValue(e, x.mode, typ, val)
	}

	return kind
}
Exemplo n.º 5
0
// exprInternal contains the core of type checking of expressions.
// Must only be called by rawExpr.
//
func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
	// make sure x has a valid state in case of bailout
	// (was issue 5770)
	x.mode = invalid
	x.typ = Typ[Invalid]

	switch e := e.(type) {
	case *ast.BadExpr:
		goto Error // error was reported before

	case *ast.Ident:
		check.ident(x, e, nil, nil)

	case *ast.Ellipsis:
		// ellipses are handled explicitly where they are legal
		// (array composite literals and parameter lists)
		check.error(e.Pos(), "invalid use of '...'")
		goto Error

	case *ast.BasicLit:
		x.setConst(e.Kind, e.Value)
		if x.mode == invalid {
			check.invalidAST(e.Pos(), "invalid literal %v", e.Value)
			goto Error
		}

	case *ast.FuncLit:
		if sig, ok := check.typ(e.Type).(*Signature); ok {
			// Anonymous functions are considered part of the
			// init expression/func declaration which contains
			// them: use existing package-level declaration info.
			check.funcBody(check.decl, "", sig, e.Body)
			x.mode = value
			x.typ = sig
		} else {
			check.invalidAST(e.Pos(), "invalid function literal %s", e)
			goto Error
		}

	case *ast.CompositeLit:
		typ := hint
		openArray := false
		if e.Type != nil {
			// [...]T array types may only appear with composite literals.
			// Check for them here so we don't have to handle ... in general.
			typ = nil
			if atyp, _ := e.Type.(*ast.ArrayType); atyp != nil && atyp.Len != nil {
				if ellip, _ := atyp.Len.(*ast.Ellipsis); ellip != nil && ellip.Elt == nil {
					// We have an "open" [...]T array type.
					// Create a new ArrayType with unknown length (-1)
					// and finish setting it up after analyzing the literal.
					typ = &Array{len: -1, elem: check.typ(atyp.Elt)}
					openArray = true
				}
			}
			if typ == nil {
				typ = check.typ(e.Type)
			}
		}
		if typ == nil {
			// TODO(gri) provide better error messages depending on context
			check.error(e.Pos(), "missing type in composite literal")
			goto Error
		}

		switch typ, _ := deref(typ); utyp := typ.Underlying().(type) {
		case *Struct:
			if len(e.Elts) == 0 {
				break
			}
			fields := utyp.fields
			if _, ok := e.Elts[0].(*ast.KeyValueExpr); ok {
				// all elements must have keys
				visited := make([]bool, len(fields))
				for _, e := range e.Elts {
					kv, _ := e.(*ast.KeyValueExpr)
					if kv == nil {
						check.error(e.Pos(), "mixture of field:value and value elements in struct literal")
						continue
					}
					key, _ := kv.Key.(*ast.Ident)
					if key == nil {
						check.errorf(kv.Pos(), "invalid field name %s in struct literal", kv.Key)
						continue
					}
					i := fieldIndex(utyp.fields, check.pkg, key.Name)
					if i < 0 {
						check.errorf(kv.Pos(), "unknown field %s in struct literal", key.Name)
						continue
					}
					fld := fields[i]
					check.recordUse(key, fld)
					// 0 <= i < len(fields)
					if visited[i] {
						check.errorf(kv.Pos(), "duplicate field name %s in struct literal", key.Name)
						continue
					}
					visited[i] = true
					check.expr(x, kv.Value)
					etyp := fld.typ
					if !check.assignment(x, etyp) {
						if x.mode != invalid {
							check.errorf(x.pos(), "cannot use %s as %s value in struct literal", x, etyp)
						}
						continue
					}
				}
			} else {
				// no element must have a key
				for i, e := range e.Elts {
					if kv, _ := e.(*ast.KeyValueExpr); kv != nil {
						check.error(kv.Pos(), "mixture of field:value and value elements in struct literal")
						continue
					}
					check.expr(x, e)
					if i >= len(fields) {
						check.error(x.pos(), "too many values in struct literal")
						break // cannot continue
					}
					// i < len(fields)
					fld := fields[i]
					if !fld.Exported() && fld.pkg != check.pkg {
						check.errorf(x.pos(), "implicit assignment to unexported field %s in %s literal", fld.name, typ)
						continue
					}
					etyp := fld.typ
					if !check.assignment(x, etyp) {
						if x.mode != invalid {
							check.errorf(x.pos(), "cannot use %s as %s value in struct literal", x, etyp)
						}
						continue
					}
				}
				if len(e.Elts) < len(fields) {
					check.error(e.Rbrace, "too few values in struct literal")
					// ok to continue
				}
			}

		case *Array:
			n := check.indexedElts(e.Elts, utyp.elem, utyp.len)
			// if we have an "open" [...]T array, set the length now that we know it
			if openArray {
				utyp.len = n
			}

		case *Slice:
			check.indexedElts(e.Elts, utyp.elem, -1)

		case *Map:
			visited := make(map[interface{}][]Type, len(e.Elts))
			for _, e := range e.Elts {
				kv, _ := e.(*ast.KeyValueExpr)
				if kv == nil {
					check.error(e.Pos(), "missing key in map literal")
					continue
				}
				check.exprWithHint(x, kv.Key, utyp.key)
				if !check.assignment(x, utyp.key) {
					if x.mode != invalid {
						check.errorf(x.pos(), "cannot use %s as %s key in map literal", x, utyp.key)
					}
					continue
				}
				if x.mode == constant_ {
					duplicate := false
					// if the key is of interface type, the type is also significant when checking for duplicates
					if _, ok := utyp.key.Underlying().(*Interface); ok {
						for _, vtyp := range visited[x.val] {
							if Identical(vtyp, x.typ) {
								duplicate = true
								break
							}
						}
						visited[x.val] = append(visited[x.val], x.typ)
					} else {
						_, duplicate = visited[x.val]
						visited[x.val] = nil
					}
					if duplicate {
						check.errorf(x.pos(), "duplicate key %s in map literal", x.val)
						continue
					}
				}
				check.exprWithHint(x, kv.Value, utyp.elem)
				if !check.assignment(x, utyp.elem) {
					if x.mode != invalid {
						check.errorf(x.pos(), "cannot use %s as %s value in map literal", x, utyp.elem)
					}
					continue
				}
			}

		default:
			// if utyp is invalid, an error was reported before
			if utyp != Typ[Invalid] {
				check.errorf(e.Pos(), "invalid composite literal type %s", typ)
				goto Error
			}
		}

		x.mode = value
		x.typ = typ

	case *ast.ParenExpr:
		kind := check.rawExpr(x, e.X, nil)
		x.expr = e
		return kind

	case *ast.SelectorExpr:
		check.selector(x, e)

	case *ast.IndexExpr:
		check.expr(x, e.X)
		if x.mode == invalid {
			goto Error
		}

		valid := false
		length := int64(-1) // valid if >= 0
		switch typ := x.typ.Underlying().(type) {
		case *Basic:
			if isString(typ) {
				valid = true
				if x.mode == constant_ {
					length = int64(len(constant.StringVal(x.val)))
				}
				// an indexed string always yields a byte value
				// (not a constant) even if the string and the
				// index are constant
				x.mode = value
				x.typ = universeByte // use 'byte' name
			}

		case *Array:
			valid = true
			length = typ.len
			if x.mode != variable {
				x.mode = value
			}
			x.typ = typ.elem

		case *Pointer:
			if typ, _ := typ.base.Underlying().(*Array); typ != nil {
				valid = true
				length = typ.len
				x.mode = variable
				x.typ = typ.elem
			}

		case *Slice:
			valid = true
			x.mode = variable
			x.typ = typ.elem

		case *Map:
			var key operand
			check.expr(&key, e.Index)
			if !check.assignment(&key, typ.key) {
				if key.mode != invalid {
					check.invalidOp(key.pos(), "cannot use %s as map index of type %s", &key, typ.key)
				}
				goto Error
			}
			x.mode = mapindex
			x.typ = typ.elem
			x.expr = e
			return expression
		}

		if !valid {
			check.invalidOp(x.pos(), "cannot index %s", x)
			goto Error
		}

		if e.Index == nil {
			check.invalidAST(e.Pos(), "missing index for %s", x)
			goto Error
		}

		check.index(e.Index, length)
		// ok to continue

	case *ast.SliceExpr:
		check.expr(x, e.X)
		if x.mode == invalid {
			goto Error
		}

		valid := false
		length := int64(-1) // valid if >= 0
		switch typ := x.typ.Underlying().(type) {
		case *Basic:
			if isString(typ) {
				if slice3(e) {
					check.invalidOp(x.pos(), "3-index slice of string")
					goto Error
				}
				valid = true
				if x.mode == constant_ {
					length = int64(len(constant.StringVal(x.val)))
				}
				// spec: "For untyped string operands the result
				// is a non-constant value of type string."
				if typ.kind == UntypedString {
					x.typ = Typ[String]
				}
			}

		case *Array:
			valid = true
			length = typ.len
			if x.mode != variable {
				check.invalidOp(x.pos(), "cannot slice %s (value not addressable)", x)
				goto Error
			}
			x.typ = &Slice{elem: typ.elem}

		case *Pointer:
			if typ, _ := typ.base.Underlying().(*Array); typ != nil {
				valid = true
				length = typ.len
				x.typ = &Slice{elem: typ.elem}
			}

		case *Slice:
			valid = true
			// x.typ doesn't change
		}

		if !valid {
			check.invalidOp(x.pos(), "cannot slice %s", x)
			goto Error
		}

		x.mode = value

		// spec: "Only the first index may be omitted; it defaults to 0."
		if slice3(e) && (e.High == nil || sliceMax(e) == nil) {
			check.error(e.Rbrack, "2nd and 3rd index required in 3-index slice")
			goto Error
		}

		// check indices
		var ind [3]int64
		for i, expr := range []ast.Expr{e.Low, e.High, sliceMax(e)} {
			x := int64(-1)
			switch {
			case expr != nil:
				// The "capacity" is only known statically for strings, arrays,
				// and pointers to arrays, and it is the same as the length for
				// those types.
				max := int64(-1)
				if length >= 0 {
					max = length + 1
				}
				if t, ok := check.index(expr, max); ok && t >= 0 {
					x = t
				}
			case i == 0:
				// default is 0 for the first index
				x = 0
			case length >= 0:
				// default is length (== capacity) otherwise
				x = length
			}
			ind[i] = x
		}

		// constant indices must be in range
		// (check.index already checks that existing indices >= 0)
	L:
		for i, x := range ind[:len(ind)-1] {
			if x > 0 {
				for _, y := range ind[i+1:] {
					if y >= 0 && x > y {
						check.errorf(e.Rbrack, "invalid slice indices: %d > %d", x, y)
						break L // only report one error, ok to continue
					}
				}
			}
		}

	case *ast.TypeAssertExpr:
		check.expr(x, e.X)
		if x.mode == invalid {
			goto Error
		}
		xtyp, _ := x.typ.Underlying().(*Interface)
		if xtyp == nil {
			check.invalidOp(x.pos(), "%s is not an interface", x)
			goto Error
		}
		// x.(type) expressions are handled explicitly in type switches
		if e.Type == nil {
			check.invalidAST(e.Pos(), "use of .(type) outside type switch")
			goto Error
		}
		T := check.typ(e.Type)
		if T == Typ[Invalid] {
			goto Error
		}
		check.typeAssertion(x.pos(), x, xtyp, T)
		x.mode = commaok
		x.typ = T

	case *ast.CallExpr:
		return check.call(x, e)

	case *ast.StarExpr:
		check.exprOrType(x, e.X)
		switch x.mode {
		case invalid:
			goto Error
		case typexpr:
			x.typ = &Pointer{base: x.typ}
		default:
			if typ, ok := x.typ.Underlying().(*Pointer); ok {
				x.mode = variable
				x.typ = typ.base
			} else {
				check.invalidOp(x.pos(), "cannot indirect %s", x)
				goto Error
			}
		}

	case *ast.UnaryExpr:
		check.expr(x, e.X)
		if x.mode == invalid {
			goto Error
		}
		check.unary(x, e, e.Op)
		if x.mode == invalid {
			goto Error
		}
		if e.Op == token.ARROW {
			x.expr = e
			return statement // receive operations may appear in statement context
		}

	case *ast.BinaryExpr:
		check.binary(x, e, e.X, e.Y, e.Op)
		if x.mode == invalid {
			goto Error
		}

	case *ast.KeyValueExpr:
		// key:value expressions are handled in composite literals
		check.invalidAST(e.Pos(), "no key:value expected")
		goto Error

	case *ast.ArrayType, *ast.StructType, *ast.FuncType,
		*ast.InterfaceType, *ast.MapType, *ast.ChanType:
		x.mode = typexpr
		x.typ = check.typ(e)
		// Note: rawExpr (caller of exprInternal) will call check.recordTypeAndValue
		// even though check.typ has already called it. This is fine as both
		// times the same expression and type are recorded. It is also not a
		// performance issue because we only reach here for composite literal
		// types, which are comparatively rare.

	default:
		panic(fmt.Sprintf("%s: unknown expression type %T", check.fset.Position(e.Pos()), e))
	}

	// everything went well
	x.expr = e
	return expression

Error:
	x.mode = invalid
	x.expr = e
	return statement // avoid follow-up errors
}
Exemplo n.º 6
0
// updateExprType updates the type of x to typ and invokes itself
// recursively for the operands of x, depending on expression kind.
// If typ is still an untyped and not the final type, updateExprType
// only updates the recorded untyped type for x and possibly its
// operands. Otherwise (i.e., typ is not an untyped type anymore,
// or it is the final type for x), the type and value are recorded.
// Also, if x is a constant, it must be representable as a value of typ,
// and if x is the (formerly untyped) lhs operand of a non-constant
// shift, it must be an integer value.
//
func (check *Checker) updateExprType(x ast.Expr, typ Type, final bool) {
	old, found := check.untyped[x]
	if !found {
		return // nothing to do
	}

	// update operands of x if necessary
	switch x := x.(type) {
	case *ast.BadExpr,
		*ast.FuncLit,
		*ast.CompositeLit,
		*ast.IndexExpr,
		*ast.SliceExpr,
		*ast.TypeAssertExpr,
		*ast.StarExpr,
		*ast.KeyValueExpr,
		*ast.ArrayType,
		*ast.StructType,
		*ast.FuncType,
		*ast.InterfaceType,
		*ast.MapType,
		*ast.ChanType:
		// These expression are never untyped - nothing to do.
		// The respective sub-expressions got their final types
		// upon assignment or use.
		if debug {
			check.dump("%s: found old type(%s): %s (new: %s)", x.Pos(), x, old.typ, typ)
			unreachable()
		}
		return

	case *ast.CallExpr:
		// Resulting in an untyped constant (e.g., built-in complex).
		// The respective calls take care of calling updateExprType
		// for the arguments if necessary.

	case *ast.Ident, *ast.BasicLit, *ast.SelectorExpr:
		// An identifier denoting a constant, a constant literal,
		// or a qualified identifier (imported untyped constant).
		// No operands to take care of.

	case *ast.ParenExpr:
		check.updateExprType(x.X, typ, final)

	case *ast.UnaryExpr:
		// If x is a constant, the operands were constants.
		// They don't need to be updated since they never
		// get "materialized" into a typed value; and they
		// will be processed at the end of the type check.
		if old.val != nil {
			break
		}
		check.updateExprType(x.X, typ, final)

	case *ast.BinaryExpr:
		if old.val != nil {
			break // see comment for unary expressions
		}
		if isComparison(x.Op) {
			// The result type is independent of operand types
			// and the operand types must have final types.
		} else if isShift(x.Op) {
			// The result type depends only on lhs operand.
			// The rhs type was updated when checking the shift.
			check.updateExprType(x.X, typ, final)
		} else {
			// The operand types match the result type.
			check.updateExprType(x.X, typ, final)
			check.updateExprType(x.Y, typ, final)
		}

	default:
		unreachable()
	}

	// If the new type is not final and still untyped, just
	// update the recorded type.
	if !final && isUntyped(typ) {
		old.typ = typ.Underlying().(*Basic)
		check.untyped[x] = old
		return
	}

	// Otherwise we have the final (typed or untyped type).
	// Remove it from the map of yet untyped expressions.
	delete(check.untyped, x)

	// If x is the lhs of a shift, its final type must be integer.
	// We already know from the shift check that it is representable
	// as an integer if it is a constant.
	if old.isLhs && !isInteger(typ) {
		check.invalidOp(x.Pos(), "shifted operand %s (type %s) must be integer", x, typ)
		return
	}

	// Everything's fine, record final type and value for x.
	check.recordTypeAndValue(x, old.mode, typ, old.val)
}
Exemplo n.º 7
0
// typExprInternal drives type checking of types.
// Must only be called by typExpr.
//
func (check *Checker) typExprInternal(e ast.Expr, def *Named, path []*TypeName) Type {
	switch e := e.(type) {
	case *ast.BadExpr:
		// ignore - error reported before

	case *ast.Ident:
		var x operand
		check.ident(&x, e, def, path)

		switch x.mode {
		case typexpr:
			typ := x.typ
			def.setUnderlying(typ)
			return typ
		case invalid:
			// ignore - error reported before
		case novalue:
			check.errorf(x.pos(), "%s used as type", &x)
		default:
			check.errorf(x.pos(), "%s is not a type", &x)
		}

	case *ast.SelectorExpr:
		var x operand
		check.selector(&x, e)

		switch x.mode {
		case typexpr:
			typ := x.typ
			def.setUnderlying(typ)
			return typ
		case invalid:
			// ignore - error reported before
		case novalue:
			check.errorf(x.pos(), "%s used as type", &x)
		default:
			check.errorf(x.pos(), "%s is not a type", &x)
		}

	case *ast.ParenExpr:
		return check.typExpr(e.X, def, path)

	case *ast.ArrayType:
		if e.Len != nil {
			typ := new(Array)
			def.setUnderlying(typ)
			typ.len = check.arrayLength(e.Len)
			typ.elem = check.typExpr(e.Elt, nil, path)
			return typ

		} else {
			typ := new(Slice)
			def.setUnderlying(typ)
			typ.elem = check.typ(e.Elt)
			return typ
		}

	case *ast.StructType:
		typ := new(Struct)
		def.setUnderlying(typ)
		check.structType(typ, e, path)
		return typ

	case *ast.StarExpr:
		typ := new(Pointer)
		def.setUnderlying(typ)
		typ.base = check.typ(e.X)
		return typ

	case *ast.FuncType:
		typ := new(Signature)
		def.setUnderlying(typ)
		check.funcType(typ, nil, e)
		return typ

	case *ast.InterfaceType:
		typ := new(Interface)
		def.setUnderlying(typ)
		check.interfaceType(typ, e, def, path)
		return typ

	case *ast.MapType:
		typ := new(Map)
		def.setUnderlying(typ)

		typ.key = check.typ(e.Key)
		typ.elem = check.typ(e.Value)

		// spec: "The comparison operators == and != must be fully defined
		// for operands of the key type; thus the key type must not be a
		// function, map, or slice."
		//
		// Delay this check because it requires fully setup types;
		// it is safe to continue in any case (was issue 6667).
		check.delay(func() {
			if !Comparable(typ.key) {
				check.errorf(e.Key.Pos(), "invalid map key type %s", typ.key)
			}
		})

		return typ

	case *ast.ChanType:
		typ := new(Chan)
		def.setUnderlying(typ)

		dir := SendRecv
		switch e.Dir {
		case ast.SEND | ast.RECV:
			// nothing to do
		case ast.SEND:
			dir = SendOnly
		case ast.RECV:
			dir = RecvOnly
		default:
			check.invalidAST(e.Pos(), "unknown channel direction %d", e.Dir)
			// ok to continue
		}

		typ.dir = dir
		typ.elem = check.typ(e.Value)
		return typ

	default:
		check.errorf(e.Pos(), "%s is not a type", e)
	}

	typ := Typ[Invalid]
	def.setUnderlying(typ)
	return typ
}
Exemplo n.º 8
0
func (p *printer) expr1(expr ast.Expr, prec1, depth int) {
	p.print(expr.Pos())

	switch x := expr.(type) {
	case *ast.BadExpr:
		p.print("BadExpr")

	case *ast.Ident:
		p.print(x)

	case *ast.BinaryExpr:
		if depth < 1 {
			p.internalError("depth < 1:", depth)
			depth = 1
		}
		p.binaryExpr(x, prec1, cutoff(x, depth), depth)

	case *ast.KeyValueExpr:
		p.expr(x.Key)
		p.print(x.Colon, token.COLON, blank)
		p.expr(x.Value)

	case *ast.StarExpr:
		const prec = token.UnaryPrec
		if prec < prec1 {
			// parenthesis needed
			p.print(token.LPAREN)
			p.print(token.MUL)
			p.expr(x.X)
			p.print(token.RPAREN)
		} else {
			// no parenthesis needed
			p.print(token.MUL)
			p.expr(x.X)
		}

	case *ast.UnaryExpr:
		const prec = token.UnaryPrec
		if prec < prec1 {
			// parenthesis needed
			p.print(token.LPAREN)
			p.expr(x)
			p.print(token.RPAREN)
		} else {
			// no parenthesis needed
			p.print(x.Op)
			if x.Op == token.RANGE {
				// TODO(gri) Remove this code if it cannot be reached.
				p.print(blank)
			}
			p.expr1(x.X, prec, depth)
		}

	case *ast.BasicLit:
		p.print(x)

	case *ast.FuncLit:
		p.expr(x.Type)
		p.adjBlock(p.distanceFrom(x.Type.Pos()), blank, x.Body)

	case *ast.ParenExpr:
		if _, hasParens := x.X.(*ast.ParenExpr); hasParens {
			// don't print parentheses around an already parenthesized expression
			// TODO(gri) consider making this more general and incorporate precedence levels
			p.expr0(x.X, depth)
		} else {
			p.print(token.LPAREN)
			p.expr0(x.X, reduceDepth(depth)) // parentheses undo one level of depth
			p.print(x.Rparen, token.RPAREN)
		}

	case *ast.SelectorExpr:
		p.expr1(x.X, token.HighestPrec, depth)
		p.print(token.PERIOD)
		if line := p.lineFor(x.Sel.Pos()); p.pos.IsValid() && p.pos.Line < line {
			p.print(indent, newline, x.Sel.Pos(), x.Sel, unindent)
		} else {
			p.print(x.Sel.Pos(), x.Sel)
		}

	case *ast.TypeAssertExpr:
		p.expr1(x.X, token.HighestPrec, depth)
		p.print(token.PERIOD, x.Lparen, token.LPAREN)
		if x.Type != nil {
			p.expr(x.Type)
		} else {
			p.print(token.TYPE)
		}
		p.print(x.Rparen, token.RPAREN)

	case *ast.IndexExpr:
		// TODO(gri): should treat[] like parentheses and undo one level of depth
		p.expr1(x.X, token.HighestPrec, 1)
		p.print(x.Lbrack, token.LBRACK)
		p.expr0(x.Index, depth+1)
		p.print(x.Rbrack, token.RBRACK)

	case *ast.SliceExpr:
		// TODO(gri): should treat[] like parentheses and undo one level of depth
		p.expr1(x.X, token.HighestPrec, 1)
		p.print(x.Lbrack, token.LBRACK)
		indices := []ast.Expr{x.Low, x.High}
		if x.Max != nil {
			indices = append(indices, x.Max)
		}
		for i, y := range indices {
			if i > 0 {
				// blanks around ":" if both sides exist and either side is a binary expression
				// TODO(gri) once we have committed a variant of a[i:j:k] we may want to fine-
				//           tune the formatting here
				x := indices[i-1]
				if depth <= 1 && x != nil && y != nil && (isBinary(x) || isBinary(y)) {
					p.print(blank, token.COLON, blank)
				} else {
					p.print(token.COLON)
				}
			}
			if y != nil {
				p.expr0(y, depth+1)
			}
		}
		p.print(x.Rbrack, token.RBRACK)

	case *ast.CallExpr:
		if len(x.Args) > 1 {
			depth++
		}
		if _, ok := x.Fun.(*ast.FuncType); ok {
			// conversions to literal function types require parentheses around the type
			p.print(token.LPAREN)
			p.expr1(x.Fun, token.HighestPrec, depth)
			p.print(token.RPAREN)
		} else {
			p.expr1(x.Fun, token.HighestPrec, depth)
		}
		p.print(x.Lparen, token.LPAREN)
		if x.Ellipsis.IsValid() {
			p.exprList(x.Lparen, x.Args, depth, 0, x.Ellipsis)
			p.print(x.Ellipsis, token.ELLIPSIS)
			if x.Rparen.IsValid() && p.lineFor(x.Ellipsis) < p.lineFor(x.Rparen) {
				p.print(token.COMMA, formfeed)
			}
		} else {
			p.exprList(x.Lparen, x.Args, depth, commaTerm, x.Rparen)
		}
		p.print(x.Rparen, token.RPAREN)

	case *ast.CompositeLit:
		// composite literal elements that are composite literals themselves may have the type omitted
		if x.Type != nil {
			p.expr1(x.Type, token.HighestPrec, depth)
		}
		p.print(x.Lbrace, token.LBRACE)
		p.exprList(x.Lbrace, x.Elts, 1, commaTerm, x.Rbrace)
		// do not insert extra line break following a /*-style comment
		// before the closing '}' as it might break the code if there
		// is no trailing ','
		mode := noExtraLinebreak
		// do not insert extra blank following a /*-style comment
		// before the closing '}' unless the literal is empty
		if len(x.Elts) > 0 {
			mode |= noExtraBlank
		}
		p.print(mode, x.Rbrace, token.RBRACE, mode)

	case *ast.Ellipsis:
		p.print(token.ELLIPSIS)
		if x.Elt != nil {
			p.expr(x.Elt)
		}

	case *ast.ArrayType:
		p.print(token.LBRACK)
		if x.Len != nil {
			p.expr(x.Len)
		}
		p.print(token.RBRACK)
		p.expr(x.Elt)

	case *ast.StructType:
		p.print(token.STRUCT)
		p.fieldList(x.Fields, true, x.Incomplete)

	case *ast.FuncType:
		p.print(token.FUNC)
		p.signature(x.Params, x.Results)

	case *ast.InterfaceType:
		p.print(token.INTERFACE)
		p.fieldList(x.Methods, false, x.Incomplete)

	case *ast.MapType:
		p.print(token.MAP, token.LBRACK)
		p.expr(x.Key)
		p.print(token.RBRACK)
		p.expr(x.Value)

	case *ast.ChanType:
		switch x.Dir {
		case ast.SEND | ast.RECV:
			p.print(token.CHAN)
		case ast.RECV:
			p.print(token.ARROW, token.CHAN) // x.Arrow and x.Pos() are the same
		case ast.SEND:
			p.print(token.CHAN, x.Arrow, token.ARROW)
		}
		p.print(blank)
		p.expr(x.Value)

	default:
		panic("unreachable")
	}

	return
}