Exemplo n.º 1
0
// 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
}
Exemplo n.º 2
0
// 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
}
Exemplo n.º 3
0
// 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
}
Exemplo n.º 4
0
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}
}