parse.go

/*
Copyright 2016-2017 by Milo Christiansen

This software is provided 'as-is', without any express or implied warranty. In
no event will the authors be held liable for any damages arising from the use of
this software.

Permission is granted to anyone to use this software for any purpose, including
commercial applications, and to alter it and redistribute it freely, subject to
the following restrictions:

1. The origin of this software must not be misrepresented; you must not claim
that you wrote the original software. If you use this software in a product, an
acknowledgment in the product documentation would be appreciated but is not
required.

2. Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.

3. This notice may not be removed or altered from any source distribution.
*/

package ast

import "fmt"
import "github.com/milochristiansen/lua/luautil"

//import "runtime"

type parser struct {
	l *lexer
}

// Parse reads Lua source into an AST using the types in this package.
func Parse(source string, line int) (block []Stmt, err error) {
	p := &parser{
		l: newLexer(source, line),
	}

	defer func() {
		if x := recover(); x != nil {
			//fmt.Println("Stack Trace:")
			//buf := make([]byte, 4096)
			//buf = buf[:runtime.Stack(buf, true)]
			//fmt.Printf("%s\n", buf)

			switch e := x.(type) {
			case luautil.Error:
				e.Msg = fmt.Sprintf("%v On Line: %v", e.Msg, p.l.tokenline)
				err = e
			case error:
				err = &luautil.Error{Err: e, Type: luautil.ErrTypWrapped}
			default:
				err = &luautil.Error{Msg: fmt.Sprint(x), Type: luautil.ErrTypEvil}
			}
		}
	}()

	for !p.l.checkLook(tknINVALID) {
		block = append(block, p.statement())
	}
	return block, nil
}

func (p *parser) funcDeclStat(local bool) Stmt {
	p.l.getCurrent(tknFunction)

	// Function declarations are exploded into an explicit assignment statement.
	node := stmtLine(&Assign{
		LocalFunc: local,
		Targets:   []Expr{nil},
		Values:    []Expr{nil},
	}, p.l.current.Line)

	// Read Name
	var ident Expr
	hasSelf := false
	if local {
		p.l.getCurrent(tknName)
		ident = exprLine(&ConstIdent{
			Value: p.l.current.Lexeme,
		}, p.l.current.Line)
	} else {
		ident = p.ident()
		if p.l.checkLook(tknColon) {
			hasSelf = true
			p.l.getCurrent(tknColon)
			line := p.l.current.Line
			p.l.getCurrent(tknName)
			ident = exprLine(&TableAccessor{
				Obj: ident,
				Key: exprLine(&ConstString{
					Value: p.l.current.Lexeme,
				}, p.l.current.Line),
			}, line)
		}
	}
	node.(*Assign).Targets[0] = ident

	// Read Parameters and Block
	node.(*Assign).Values[0] = p.funcDeclBody(hasSelf)
	return node
}

// The block opener must have already been read
func (p *parser) block(enders ...int) []Stmt {
	rtn := []Stmt{}
	for !p.l.checkLook(append(enders, tknINVALID)...) {
		rtn = append(rtn, p.statement())
	}
	p.l.getCurrent(enders...)
	return rtn
}

func (p *parser) statement() Stmt {
	switch p.l.look.Type {
	case tknUnnecessary: // ;
		p.l.getCurrent(tknUnnecessary)
		return stmtLine(&DoBlock{Block: nil}, p.l.current.Line) // FIXME!
	case tknIf:
		p.l.getCurrent(tknIf)
		line := p.l.current.Line
		node := stmtLine(&If{
			Cond: p.expression(),
		}, line)
		rnode := node
		p.l.getCurrent(tknThen)
		node.(*If).Then = p.block(tknElse, tknElseif, tknEnd)
	loop:
		for {
			switch p.l.current.Type {
			case tknElse:
				node.(*If).Else = p.block(tknEnd)
				break loop
			case tknElseif:
				line := p.l.current.Line
				pnode := node
				node = stmtLine(&If{
					Cond: p.expression(),
				}, line)

				p.l.getCurrent(tknThen)

				node.(*If).Then = p.block(tknElse, tknElseif, tknEnd)

				pnode.(*If).Else = []Stmt{node}
			case tknEnd:
				break loop
			default:
				panic("IMPOSSIBLE")
			}
		}
		return rnode
	case tknWhile:
		p.l.getCurrent(tknWhile)
		line := p.l.current.Line
		cond := p.expression()
		p.l.getCurrent(tknDo)
		return stmtLine(&WhileLoop{
			Cond:  cond,
			Block: p.block(tknEnd),
		}, line)
	case tknDo:
		p.l.getCurrent(tknDo)
		line := p.l.current.Line
		rtn := p.block(tknEnd)
		return stmtLine(&DoBlock{Block: rtn}, line)
	case tknFor:
		p.l.getCurrent(tknFor)
		line := p.l.current.Line

		// Numeric: var = a, b, c
		counter := ""
		var i, l, s Expr

		// Generic: <vars...> in <expr | expr, expr, expr>
		locals := []string{}
		init := []Expr{}

		p.l.getCurrent(tknName)
		numeric := p.l.checkLook(tknSet)

		if numeric {
			counter = p.l.current.Lexeme
			p.l.getCurrent(tknSet)
			i = p.expression()
			p.l.getCurrent(tknSeperator)
			l = p.expression()
			if p.l.checkLook(tknSeperator) {
				p.l.getCurrent(tknSeperator)
				s = p.expression()
			} else {
				s = exprLine(&ConstInt{Value: "1"}, p.l.current.Line)
			}
		} else {
			for {
				locals = append(locals, p.l.current.Lexeme)
				if !p.l.checkLook(tknSeperator) {
					break
				}
				p.l.getCurrent(tknSeperator)
				p.l.getCurrent(tknName)
			}
			p.l.getCurrent(tknIn)
			for {
				init = append(init, p.expression())
				if !p.l.checkLook(tknSeperator) {
					break
				}
				p.l.getCurrent(tknSeperator)
			}
		}
		p.l.getCurrent(tknDo)
		if numeric {
			return stmtLine(&ForLoopNumeric{
				Counter: counter,
				Init:    i,
				Limit:   l,
				Step:    s,
				Block:   p.block(tknEnd),
			}, line)
		}
		return stmtLine(&ForLoopGeneric{
			Locals: locals,
			Init:   init,
			Block:  p.block(tknEnd),
		}, line)
	case tknRepeat:
		p.l.getCurrent(tknRepeat)
		line := p.l.current.Line
		blk := p.block(tknUntil)
		return stmtLine(&RepeatUntilLoop{
			Cond:  p.expression(),
			Block: blk,
		}, line)
	case tknFunction:
		return p.funcDeclStat(false)
	case tknLocal:
		p.l.getCurrent(tknLocal)
		line := p.l.current.Line
		if p.l.checkLook(tknFunction) {
			// This is incorrect, "local function f" should translate to "local f; f = function" not "local f = function".
			// The compiler has some special case code to correct this.
			return p.funcDeclStat(true)
		}
		targets := []Expr{}
		c := 0
		for !p.l.checkLook(tknSet) {
			c++
			p.l.getCurrent(tknName)
			targets = append(targets, exprLine(&ConstIdent{
				Value: p.l.current.Lexeme,
			}, p.l.current.Line))
			if !p.l.checkLook(tknSeperator) {
				break
			}
			p.l.getCurrent(tknSeperator)
		}

		vals := []Expr{}
		if p.l.checkLook(tknSet) {
			p.l.getCurrent(tknSet)
			vals = append(vals, p.expression())
			for p.l.checkLook(tknSeperator) {
				p.l.getCurrent(tknSeperator)
				vals = append(vals, p.expression())
			}
		}
		return stmtLine(&Assign{
			LocalDecl: true,
			Targets:   targets,
			Values:    vals,
		}, line)
	case tknDblColon:
		p.l.getCurrent(tknDblColon)
		line := p.l.current.Line
		p.l.getCurrent(tknName)
		lbl := p.l.current.Lexeme
		p.l.getCurrent(tknDblColon)
		return stmtLine(&Label{Label: lbl}, line)
	case tknReturn:
		p.l.getCurrent(tknReturn)
		line := p.l.current.Line
		items := []Expr{}
		for !p.l.checkLook(tknEnd, tknElse, tknElseif, tknUntil, tknUnnecessary, tknINVALID) {
			items = append(items, p.expression())
			if !p.l.checkLook(tknSeperator) {
				break
			}
			p.l.getCurrent(tknSeperator)
		}
		return stmtLine(&Return{Items: items}, line)
	case tknBreak:
		p.l.getCurrent(tknBreak)
		return stmtLine(&Goto{Label: "break", IsBreak: true}, p.l.current.Line)
	case tknContinue:
		// The lexer will never generate this unless you uncomment the definition for the "continue" keyword.
		p.l.getCurrent(tknContinue)
		return stmtLine(&Goto{Label: "continue", IsBreak: true}, p.l.current.Line)
	case tknGoto:
		p.l.getCurrent(tknGoto)
		line := p.l.current.Line
		p.l.getCurrent(tknName)
		return stmtLine(&Goto{Label: p.l.current.Lexeme}, line)
	default:
		ident := p.suffixedValue()
		line := p.l.current.Line
		if v, ok := ident.(*FuncCall); ok {
			return Stmt(v)
		}

		targets := []Expr{ident}
		for p.l.checkLook(tknSeperator) {
			p.l.getCurrent(tknSeperator)
			targets = append(targets, p.suffixedValue())
		}
		p.l.getCurrent(tknSet)
		vals := []Expr{p.expression()}
		for p.l.checkLook(tknSeperator) {
			p.l.getCurrent(tknSeperator)
			vals = append(vals, p.expression())
		}
		return stmtLine(&Assign{
			Targets: targets,
			Values:  vals,
		}, line)
	}
	panic("UNREACHABLE")
}