go-jsonnet/parser.go

package jsonnet

import (
	"fmt"
)

type precedence int

const (
	applyPrecedence      precedence = 2  // Function calls and indexing.
	unaryPrecedence      precedence = 4  // Logical and bitwise negation, unary + -
	beforeElsePrecedence precedence = 15 // True branch of an if.
	maxPrecedence        precedence = 16 // Local, If, Import, Function, Error
)

// ---------------------------------------------------------------------------

func makeUnexpectedError(t token, while string) error {
	return makeStaticError(
		fmt.Sprintf("Unexpected: %v while %v", t, while), t.loc)
}

func locFromTokens(begin, end *token) LocationRange {
	return makeLocationRange(begin.loc.FileName, begin.loc.Begin, end.loc.End)
}

func locFromTokenAST(begin *token, end astNode) LocationRange {
	return makeLocationRange(begin.loc.FileName, begin.loc.Begin, end.Loc().End)
}

// ---------------------------------------------------------------------------

type parser struct {
	t     tokens
	currT int
}

func makeParser(t tokens) *parser {
	return &parser{
		t: t,
	}
}

func (p *parser) pop() *token {
	t := &p.t[p.currT]
	p.currT++
	return t
}

func (p *parser) popExpect(tk tokenKind) (*token, error) {
	t := p.pop()
	if t.kind != tk {
		return nil, makeStaticError(
			fmt.Sprintf("Expected token %v but got %v", tk, t), t.loc)
	}
	return t, nil
}

func (p *parser) popExpectOp(op string) (*token, error) {
	t := p.pop()
	if t.kind != tokenOperator || t.data != op {
		return nil, makeStaticError(
			fmt.Sprintf("Expected operator %v but got %v", op, t), t.loc)
	}
	return t, nil
}

func (p *parser) peek() *token {
	return &p.t[p.currT]
}

func (p *parser) parseIdentifierList(elementKind string) (identifiers, bool, error) {
	_, exprs, got_comma, err := p.parseCommaList(tokenParenR, elementKind)
	if err != nil {
		return identifiers{}, false, err
	}
	var ids identifiers
	for _, n := range exprs {
		v, ok := n.(*astVar)
		if !ok {
			return identifiers{}, false, makeStaticError(fmt.Sprintf("Not an identifier: %v", n), *n.Loc())
		}
		ids = append(ids, v.id)
	}
	return ids, got_comma, nil
}

func (p *parser) parseCommaList(end tokenKind, elementKind string) (*token, astNodes, bool, error) {
	var exprs astNodes
	got_comma := false
	first := true
	for {
		next := p.peek();
		if !first && !got_comma {
			if next.kind == tokenComma {
				p.pop()
				next = p.peek()
				got_comma = true
			}
		}
		if next.kind == end {
			// got_comma can be true or false here.
			return p.pop(), exprs, got_comma, nil
		}
		if !first && !got_comma {
			return nil, nil, false, makeStaticError(fmt.Sprintf("Expected a comma before next %s.", elementKind), next.loc)
		}

		expr, err := p.parse(maxPrecedence)
		if err != nil {
			return nil, nil, false, err
		}
		exprs = append(exprs, expr)
		got_comma = false
		first = false
	}
}

func (p *parser) parse(prec precedence) (astNode, error) {
	begin := p.peek()

	switch begin.kind {
	// These cases have effectively maxPrecedence as the first
	// call to parse will parse them.
	case tokenAssert:
		p.pop()
		cond, err := p.parse(maxPrecedence)
		if err != nil {
			return nil, err
		}
		var msg astNode
		if p.peek().kind == tokenColon {
			p.pop()
			msg, err = p.parse(maxPrecedence)
			if err != nil {
				return nil, err
			}
		}
		_, err = p.popExpect(tokenSemicolon)
		if err != nil {
			return nil, err
		}
		rest, err := p.parse(maxPrecedence)
		if err != nil {
			return nil, err
		}
		return &astAssert{
			astNodeBase: astNodeBase{locFromTokenAST(begin, rest)},
			cond:        cond,
			message:     msg,
			rest:        rest,
		}, nil

	case tokenError:
		p.pop()
		expr, err := p.parse(maxPrecedence)
		if err != nil {
			return nil, err
		}
		return &astError{
			astNodeBase: astNodeBase{locFromTokenAST(begin, expr)},
			expr:        expr,
		}, nil

	case tokenIf:
		p.pop()
		cond, err := p.parse(maxPrecedence)
		if err != nil {
			return nil, err
		}
		_, err = p.popExpect(tokenThen)
		if err != nil {
			return nil, err
		}
		branchTrue, err := p.parse(maxPrecedence)
		if err != nil {
			return nil, err
		}
		var branchFalse astNode
		lr := locFromTokenAST(begin, branchTrue)
		if p.peek().kind == tokenElse {
			p.pop()
			branchFalse, err = p.parse(maxPrecedence)
			if err != nil {
				return nil, err
			}
			lr = locFromTokenAST(begin, branchFalse)
		}
		return &astConditional{
			astNodeBase: astNodeBase{lr},
			cond:        cond,
			branchTrue:  branchTrue,
			branchFalse: branchFalse,
		}, nil
	case tokenFunction:
		p.pop()
		next := p.pop()
		if next.kind == tokenParenL {
			params, got_comma, err := p.parseIdentifierList("function parameter")
			if err != nil {
				return nil, err
			}
			body, err := p.parse(maxPrecedence)
			if err != nil {
				return nil, err
			}
			return &astFunction{
				astNodeBase: astNodeBase{locFromTokenAST(begin, body)},
				parameters:  params,
				trailingComma: got_comma,
				body: body,
			}, nil
		} else {
			return nil, makeStaticError(fmt.Sprintf("Expected ( but got %v", next), next.loc)
		}
	}

	return nil, nil
}

// ---------------------------------------------------------------------------

func parse(t tokens) (astNode, error) {
	p := makeParser(t)
	expr, err := p.parse(maxPrecedence)
	if err != nil {
		return nil, err
	}

	if p.peek().kind != tokenEndOfFile {
		return nil, makeStaticError(fmt.Sprintf("Did not expect: %v", p.peek()), p.peek().loc)
	}

	return expr, nil
}