// checkExprOrType checks that x is an expression or a type
// (and not a raw type such as [...]T).
//
func (p *parser) checkExprOrType(x ast.Expr) ast.Expr {
switch t := unparen(x).(type) {
case *ast.ParenExpr:
panic("unreachable")
case *ast.UnaryExpr:
if t.Op == token.RANGE {
// the range operator is only allowed at the top of a for statement
p.errorExpected(x.Pos(), "expression")
x = &ast.BadExpr{x.Pos(), x.End()}
}
case *ast.ArrayType:
if len, isEllipsis := t.Len.(*ast.Ellipsis); isEllipsis {
p.error(len.Pos(), "expected array length, found '...'")
x = &ast.BadExpr{x.Pos(), x.End()}
}
}
// all other nodes are expressions or types
return x
}
// Sets multiLine to true if the expression spans multiple lines.
func (p *printer) expr1(expr ast.Expr, prec1, depth int, ctxt exprContext, multiLine *bool) {
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, multiLine)
case *ast.KeyValueExpr:
p.expr(x.Key, multiLine)
p.print(x.Colon, token.COLON, blank)
p.expr(x.Value, multiLine)
case *ast.StarExpr:
const prec = token.UnaryPrec
if prec < prec1 {
// parenthesis needed
p.print(token.LPAREN)
p.print(token.MUL)
p.expr(x.X, multiLine)
p.print(token.RPAREN)
} else {
// no parenthesis needed
p.print(token.MUL)
p.expr(x.X, multiLine)
}
case *ast.UnaryExpr:
const prec = token.UnaryPrec
if prec < prec1 {
// parenthesis needed
p.print(token.LPAREN)
p.expr(x, multiLine)
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, 0, multiLine)
}
case *ast.BasicLit:
p.print(x)
case *ast.FuncLit:
p.expr(x.Type, multiLine)
p.funcBody(x.Body, p.distance(x.Type.Pos(), p.pos), true, multiLine)
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, reduceDepth(depth), multiLine) // parentheses undo one level of depth
} else {
p.print(token.LPAREN)
p.expr0(x.X, reduceDepth(depth), multiLine) // parentheses undo one level of depth
p.print(x.Rparen, token.RPAREN)
}
case *ast.SelectorExpr:
parts := selectorExprList(expr)
p.exprList(token.NoPos, parts, depth, periodSep, multiLine, token.NoPos)
case *ast.TypeAssertExpr:
p.expr1(x.X, token.HighestPrec, depth, 0, multiLine)
p.print(token.PERIOD, token.LPAREN)
if x.Type != nil {
p.expr(x.Type, multiLine)
} else {
p.print(token.TYPE)
}
p.print(token.RPAREN)
case *ast.IndexExpr:
// TODO(gri): should treat[] like parentheses and undo one level of depth
p.expr1(x.X, token.HighestPrec, 1, 0, multiLine)
p.print(x.Lbrack, token.LBRACK)
p.expr0(x.Index, depth+1, multiLine)
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, 0, multiLine)
p.print(x.Lbrack, token.LBRACK)
if x.Low != nil {
p.expr0(x.Low, depth+1, multiLine)
}
// blanks around ":" if both sides exist and either side is a binary expression
if depth <= 1 && x.Low != nil && x.High != nil && (isBinary(x.Low) || isBinary(x.High)) {
p.print(blank, token.COLON, blank)
} else {
p.print(token.COLON)
}
if x.High != nil {
p.expr0(x.High, depth+1, multiLine)
}
p.print(x.Rbrack, token.RBRACK)
case *ast.CallExpr:
if len(x.Args) > 1 {
depth++
}
p.expr1(x.Fun, token.HighestPrec, depth, 0, multiLine)
p.print(x.Lparen, token.LPAREN)
p.exprList(x.Lparen, x.Args, depth, commaSep|commaTerm, multiLine, x.Rparen)
if x.Ellipsis.IsValid() {
p.print(x.Ellipsis, token.ELLIPSIS)
}
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, compositeLit, multiLine)
}
p.print(x.Lbrace, token.LBRACE)
p.exprList(x.Lbrace, x.Elts, 1, commaSep|commaTerm, multiLine, x.Rbrace)
// do not insert extra line breaks because of comments before
// the closing '}' as it might break the code if there is no
// trailing ','
p.print(noExtraLinebreak, x.Rbrace, token.RBRACE, noExtraLinebreak)
case *ast.Ellipsis:
p.print(token.ELLIPSIS)
if x.Elt != nil {
p.expr(x.Elt, multiLine)
}
case *ast.ArrayType:
p.print(token.LBRACK)
if x.Len != nil {
p.expr(x.Len, multiLine)
}
p.print(token.RBRACK)
p.expr(x.Elt, multiLine)
case *ast.StructType:
p.print(token.STRUCT)
p.fieldList(x.Fields, x.Incomplete, ctxt|structType)
case *ast.FuncType:
p.print(token.FUNC)
p.signature(x.Params, x.Results, multiLine)
case *ast.InterfaceType:
p.print(token.INTERFACE)
p.fieldList(x.Methods, x.Incomplete, ctxt)
case *ast.MapType:
p.print(token.MAP, token.LBRACK)
p.expr(x.Key, multiLine)
p.print(token.RBRACK)
p.expr(x.Value, multiLine)
case *ast.ChanType:
switch x.Dir {
case ast.SEND | ast.RECV:
p.print(token.CHAN)
case ast.RECV:
p.print(token.ARROW, token.CHAN)
case ast.SEND:
p.print(token.CHAN, token.ARROW)
}
p.print(blank)
p.expr(x.Value, multiLine)
default:
panic("unreachable")
}
return
}
// checkExpr checks that x is an expression (and not a type).
func (p *parser) checkExpr(x ast.Expr) ast.Expr {
switch t := unparen(x).(type) {
case *ast.BadExpr:
case *ast.Ident:
case *ast.BasicLit:
case *ast.FuncLit:
case *ast.CompositeLit:
case *ast.ParenExpr:
panic("unreachable")
case *ast.SelectorExpr:
case *ast.IndexExpr:
case *ast.SliceExpr:
case *ast.TypeAssertExpr:
if t.Type == nil {
// the form X.(type) is only allowed in type switch expressions
p.errorExpected(x.Pos(), "expression")
x = &ast.BadExpr{x.Pos(), x.End()}
}
case *ast.CallExpr:
case *ast.StarExpr:
case *ast.UnaryExpr:
if t.Op == token.RANGE {
// the range operator is only allowed at the top of a for statement
p.errorExpected(x.Pos(), "expression")
x = &ast.BadExpr{x.Pos(), x.End()}
}
case *ast.BinaryExpr:
default:
// all other nodes are not proper expressions
p.errorExpected(x.Pos(), "expression")
x = &ast.BadExpr{x.Pos(), x.End()}
}
return x
}
func (p *parser) parseCommClause() *ast.CommClause {
if p.trace {
defer un(trace(p, "CommClause"))
}
// CommCase
pos := p.pos
var comm ast.Stmt
if p.tok == token.CASE {
p.next()
lhs := p.parseExprList()
if p.tok == token.ARROW {
// SendStmt
if len(lhs) > 1 {
p.errorExpected(lhs[0].Pos(), "1 expression")
// continue with first expression
}
arrow := p.pos
p.next()
rhs := p.parseExpr()
comm = &ast.SendStmt{lhs[0], arrow, rhs}
} else {
// RecvStmt
pos := p.pos
tok := p.tok
var rhs ast.Expr
if p.tok == token.ASSIGN || p.tok == token.DEFINE {
// RecvStmt with assignment
if len(lhs) > 2 {
p.errorExpected(lhs[0].Pos(), "1 or 2 expressions")
// continue with first two expressions
lhs = lhs[0:2]
}
p.next()
rhs = p.parseExpr()
} else {
// rhs must be single receive operation
if len(lhs) > 1 {
p.errorExpected(lhs[0].Pos(), "1 expression")
// continue with first expression
}
rhs = lhs[0]
lhs = nil // there is no lhs
}
if x, isUnary := rhs.(*ast.UnaryExpr); !isUnary || x.Op != token.ARROW {
p.errorExpected(rhs.Pos(), "send or receive operation")
rhs = &ast.BadExpr{rhs.Pos(), rhs.End()}
}
if lhs != nil {
comm = &ast.AssignStmt{lhs, pos, tok, []ast.Expr{rhs}}
} else {
comm = &ast.ExprStmt{rhs}
}
}
} else {
p.expect(token.DEFAULT)
}
colon := p.expect(token.COLON)
body := p.parseStmtList()
return &ast.CommClause{pos, comm, colon, body}
}