cancelvars := make(map[*types.Var]ast.Node)

	// TODO(adonovan): opt: refactor to make a single pass
	// over the AST using inspect.WithStack and node types
	// {FuncDecl,FuncLit,CallExpr,SelectorExpr}.

	// Find the set of cancel vars to analyze.
	stack := make([]ast.Node, 0, 32)
	ast.Inspect(node, func(n ast.Node) bool {
		switch n.(type) {
		case *ast.FuncLit:
			if len(stack) > 0 {

// a go or defer statement; that is, whether it's a regular function
// call without arguments or results.
func validGoDeferCall(call ir.Node) bool {
	if call, ok := call.(*ir.CallExpr); ok && call.Op() == ir.OCALLFUNC && len(call.KeepAlive) == 0 {
		sig := call.Fun.Type()
		return sig.NumParams()+sig.NumResults() == 0
	}
	return false
}

// walkGoDefer walks an OGO or ODEFER node.

func TestErrorCalls(t *testing.T) {
	files, err := pkgFiles(".")
	if err != nil {
		t.Fatal(err)
	}

	for _, file := range files {
		syntax.Inspect(file, func(n syntax.Node) bool {
			call, _ := n.(*syntax.CallExpr)
			if call == nil {
				return true
			}
			selx, _ := call.Fun.(*syntax.SelectorExpr)
			if selx == nil {
				return true
			}
			if !(isName(selx.X, "check") && isName(selx.Sel, "errorf")) {

			m = n.X
		case *TypeSwitchGuard:
			if n.Lhs != nil {
				m = n.Lhs
				continue
			}
			m = n.X
		case *Operation:
			if n.Y != nil {
				m = n.X
				continue
			}
			return n.Pos()
		case *CallExpr:
			m = n.Fun
		case *ListExpr:
			if len(n.ElemList) > 0 {
				m = n.ElemList[0]
				continue
			}
			return n.Pos()
		// types
		// case *ArrayType:
		// case *SliceType:
		// case *DotsType:

}

// AppendElemRType asserts that n is an "append" operation, and
// returns an expression that yields the *runtime._type value
// representing the result slice type's element type.
func AppendElemRType(pos src.XPos, n *ir.CallExpr) ir.Node {
	assertOp(n, ir.OAPPEND)
	if hasRType(n, n.RType, "RType") {
		return n.RType
	}
	return sliceElemRType(pos, n.Type())
}

// CompareRType asserts that n is a comparison (== or !=) operation

			start = n
			end = n
		} else {
			end.then = n
			end = n
		}
	}
	for _, stmt := range body {
		switch stmt := stmt.(type) {
		case *ast.ExprStmt:
			if x, _ := stmt.X.(*ast.CallExpr); x != nil {
				funstr := exprToString(x.Fun)
				if funstr == "putattr" {
					form, _ := x.Args[3].(*ast.Ident)
					if form == nil {
						t.Fatalf("%s invalid use of putattr", fset.Position(x.Pos()))
					}

// do not return, so the builder can remove infeasible graph edges
// following such calls.  The builder calls mayReturn only for a
// CallExpr beneath an ExprStmt.
func New(body *ast.BlockStmt, mayReturn func(*ast.CallExpr) bool) *CFG {
	b := builder{
		mayReturn: mayReturn,
		cfg:       new(CFG),
	}
	b.current = b.newBlock(KindBody, body)
	b.stmt(body)

		return 1 << nBasicLit
	case *ast.BinaryExpr:
		return 1 << nBinaryExpr
	case *ast.BlockStmt:
		return 1 << nBlockStmt
	case *ast.BranchStmt:
		return 1 << nBranchStmt
	case *ast.CallExpr:
		return 1 << nCallExpr
	case *ast.CaseClause:
		return 1 << nCaseClause
	case *ast.ChanType:
		return 1 << nChanType
	case *ast.CommClause:
		return 1 << nCommClause
	case *ast.Comment:
		return 1 << nComment

		return check.isTerminating(s.Stmt, s.Label.Value)

	case *syntax.ExprStmt:
		// calling the predeclared (possibly parenthesized) panic() function is terminating
		if call, ok := syntax.Unparen(s.X).(*syntax.CallExpr); ok && check.isPanic[call] {
			return true
		}

	case *syntax.ReturnStmt:
		return true

	case *syntax.BranchStmt:
		if s.Tok == syntax.Goto || s.Tok == syntax.Fallthrough {
			return true
		}

	case *ast.LabeledStmt:
		return check.isTerminating(s.Stmt, s.Label.Name)

	case *ast.ExprStmt:
		// calling the predeclared (possibly parenthesized) panic() function is terminating
		if call, ok := ast.Unparen(s.X).(*ast.CallExpr); ok && check.isPanic[call] {
			return true
		}

	case *ast.ReturnStmt:
		return true

	case *ast.BranchStmt:
		if s.Tok == token.GOTO || s.Tok == token.FALLTHROUGH {
			return true
		}