php2go/hoistpass.go

package main

import (
	"fmt"

	"github.com/z7zmey/php-parser/node"
	"github.com/z7zmey/php-parser/node/expr"
	"github.com/z7zmey/php-parser/node/expr/binary"
	"github.com/z7zmey/php-parser/node/scalar"
	"github.com/z7zmey/php-parser/node/stmt"

	"php2go/parseutil"
)

type hoistPass struct {
	mw        *parseutil.MutatingWalker
	nextHoist func(stmts ...node.Node) error
}

func (this *hoistPass) Enter(n_ *node.Node) error {
	n := *n_ // not a copy

	switch n := n.(type) {
	case *stmt.StmtList:
		return this.enterStmtList(&n.Stmts) // We can inject extra entries here

	case *stmt.Function:
		// We can inject extra entries here
		// Note that we are NOT walking the other parts of this AST node
		//  (e.g. function parameters, function name, ...) since presumably they
		//  can't contain any hoistable statements
		return this.enterStmtList(&n.Stmts)

	case *node.Root:
		return this.enterStmtList(&n.Stmts)

	case *binary.BooleanAnd:
		return this.enterShortCircuitingBinOp(&n.Left, &n.Right)

	case *binary.BooleanOr:
		return this.enterShortCircuitingBinOp(&n.Left, &n.Right)

	case *binary.LogicalAnd:
		return this.enterShortCircuitingBinOp(&n.Left, &n.Right)

	case *binary.LogicalOr:
		return this.enterShortCircuitingBinOp(&n.Left, &n.Right)

	case *expr.PreInc:
		// Hoist the whole increment expression up to statement context
		// We also have to convert it to a post-increment
		err := this.nextHoist(stmt.NewExpression(expr.NewPostInc(n.Variable)))
		if err != nil {
			return parseErr{n, err}
		}

		// FIXME detect interior function calls since we may be dangerously doubling up on that
		// For a more complex expression it is probably OK to use a temporary variable

		// We also need to replace our own node with just the value itself
		*n_ = n.Variable

	case *expr.PostInc:
		// Hoist the whole increment expression up to statement context
		err := this.nextHoist(stmt.NewExpression(n))
		if err != nil {
			return parseErr{n, err}
		}

		// We also need to replace our own node. The resulting value would normally
		// be one less than the current value
		// PHP only supports lvalues for pre/postinc expressions so it should
		// be fine in all Go contexts too to reuse the variable expression
		// FIXME except for $foo[rand()]++

		*n_ = binary.NewPlus(n.Variable, scalar.NewLnumber(`1`))

	}

	return nil // TODO
}

func (this *hoistPass) enterShortCircuitingBinOp(left, right *node.Node) error {
	// These wreck our ability to hoist, since we can't neccessarily just move
	// the right-hand side operand out
	// Although it's still safe to walk the left-hand side
	err := this.mw.Walk(left)
	if err != nil {
		return err
	}

	lastHoist := this.nextHoist
	this.nextHoist = func(stmts ...node.Node) error {
		return parseErr{*right, fmt.Errorf("Can't determine how to hoist expression on right-hand side of && expression")}
	}
	err = this.mw.Walk(right)
	if err != nil {
		return err
	}

	this.nextHoist = lastHoist

	return parseutil.ErrDoNotWalkDeeper // since we already did it
}

func (this *hoistPass) enterStmtList(stmtList *[]node.Node) error {

	// We can inject extra entries here
	// In order to do so, we need to perform the interior Walk ourselves
	// so that we know exactly where to put the extra entries

	// Take stmtList by pointer so we can replace the slice outright

	anyMutations := false
	lastHoist := this.nextHoist

	ret := make([]node.Node, 0, len(*stmtList))

	this.nextHoist = func(stmts ...node.Node) error {
		anyMutations = true
		ret = append(ret, stmts...)
		return nil
	}

	for i, _ := range *stmtList {
		err := this.mw.Walk(&(*stmtList)[i])
		if err != nil {
			return err
		}
		ret = append(ret, (*stmtList)[i]) // *after* the hoisted statements
	}

	this.nextHoist = lastHoist

	if anyMutations {
		*stmtList = ret // our modified copy
	}

	return parseutil.ErrDoNotWalkDeeper // since we already did it
}

func runHoistPass(root *node.Node) error {
	hp := hoistPass{}

	hp.mw = &parseutil.MutatingWalker{
		EnterNode: hp.Enter,
		LeaveNode: parseutil.MutatingWalkerNoop,
	}
	hp.nextHoist = func(stmts ...node.Node) error {
		return fmt.Errorf("nowhere available to hoist %d statements", len(stmts))
	}

	return hp.mw.Walk(root)
}