// 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
}
// 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}
}