neo-go/pkg/compiler/func_scope.go

package compiler

import (
	"go/ast"
	"go/token"
	"go/types"
)

// A funcScope represents the scope within the function context.
// It holds al the local variables along with the initialized struct positions.
type funcScope struct {
	// Identifier of the function.
	name string

	// Selector of the function if there is any. Only functions imported
	// from other packages should have a selector.
	selector *ast.Ident

	// The declaration of the function in the AST. Nil if this scope is not a function.
	decl *ast.FuncDecl

	// Package where the function is defined.
	pkg *types.Package

	// Program label of the scope
	label uint16

	// Range of opcodes corresponding to the function.
	rng DebugRange
	// Variables together with it's type in neo-vm.
	variables []string

	// deferStack is a stack containing encountered `defer` statements.
	deferStack []deferInfo
	// finallyProcessed is a index of static slot with boolean flag determining
	// if `defer` statement was already processed.
	finallyProcessedIndex int

	// Local variables
	vars varScope

	// voidCalls are basically functions that return their value
	// into nothing. The stack has their return value but there
	// is nothing that consumes it. We need to keep track of
	// these functions so we can cleanup (drop) the returned
	// value from the stack. We also need to add every voidCall
	// return value to the stack size.
	voidCalls map[*ast.CallExpr]bool

	// Local variable counter.
	i int
}

type deferInfo struct {
	catchLabel   uint16
	finallyLabel uint16
	expr         *ast.CallExpr
}

func (c *codegen) newFuncScope(decl *ast.FuncDecl, label uint16) *funcScope {
	var name string
	if decl.Name != nil {
		name = decl.Name.Name
	}
	return &funcScope{
		name:      name,
		decl:      decl,
		label:     label,
		pkg:       c.currPkg,
		vars:      newVarScope(),
		voidCalls: map[*ast.CallExpr]bool{},
		variables: []string{},
		i:         -1,
	}
}

func (c *codegen) getFuncNameFromDecl(pkgPath string, decl *ast.FuncDecl) string {
	name := decl.Name.Name
	if decl.Recv != nil {
		name = decl.Recv.List[0].Type.(*ast.Ident).Name + "." + name
	}
	return c.getIdentName(pkgPath, name)
}

// analyzeVoidCalls checks for functions that are not assigned
// and therefore we need to cleanup the return value from the stack.
func (c *funcScope) analyzeVoidCalls(node ast.Node) bool {
	switch n := node.(type) {
	case *ast.AssignStmt:
		for i := 0; i < len(n.Rhs); i++ {
			switch n.Rhs[i].(type) {
			case *ast.CallExpr:
				return false
			}
		}
	case *ast.ReturnStmt:
		if len(n.Results) > 0 {
			switch n.Results[0].(type) {
			case *ast.CallExpr:
				return false
			}
		}
	case *ast.BinaryExpr:
		return false
	case *ast.IfStmt:
		// we can't just return `false`, because we still need to process body
		ce, ok := n.Cond.(*ast.CallExpr)
		if ok {
			c.voidCalls[ce] = false
		}
	case *ast.SwitchStmt:
		ce, ok := n.Tag.(*ast.CallExpr)
		if ok {
			c.voidCalls[ce] = false
		}
	case *ast.CaseClause:
		for _, e := range n.List {
			ce, ok := e.(*ast.CallExpr)
			if ok {
				c.voidCalls[ce] = false
			}
		}
	case *ast.CallExpr:
		_, ok := c.voidCalls[n]
		if !ok {
			c.voidCalls[n] = true
		}
		return false
	}
	return true
}

func (c *funcScope) countLocals() int {
	size := 0
	hasDefer := false
	ast.Inspect(c.decl, func(n ast.Node) bool {
		switch n := n.(type) {
		case *ast.FuncType:
			num := n.Results.NumFields()
			if num != 0 && len(n.Results.List[0].Names) != 0 {
				size += num
			}
		case *ast.AssignStmt:
			if n.Tok == token.DEFINE {
				size += len(n.Lhs)
			}
		case *ast.DeferStmt:
			hasDefer = true
			return false
		case *ast.ReturnStmt, *ast.IfStmt:
			size++
		// This handles the inline GenDecl like "var x = 2"
		case *ast.ValueSpec:
			size += len(n.Names)
		case *ast.RangeStmt:
			if n.Tok == token.DEFINE {
				if n.Key != nil {
					size++
				}
				if n.Value != nil {
					size++
				}
			}
		}
		return true
	})
	if hasDefer {
		c.finallyProcessedIndex = size
		size++
	}
	return size
}

func (c *funcScope) countArgs() int {
	n := c.decl.Type.Params.NumFields()
	if c.decl.Recv != nil {
		n += c.decl.Recv.NumFields()
	}
	return n
}

func (c *funcScope) stackSize() int64 {
	size := c.countLocals()
	numArgs := c.countArgs()
	return int64(size + numArgs)
}

// newVariable creates a new local variable or argument in the scope of the function.
func (c *funcScope) newVariable(t varType, name string) int {
	return c.vars.newVariable(t, name)
}

// newLocal creates a new local variable into the scope of the function.
func (c *funcScope) newLocal(name string) int {
	return c.newVariable(varLocal, name)
}