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astmapper.go
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astmapper.go
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package astmapper
import (
"github.com/pkg/errors"
"github.com/prometheus/prometheus/promql/parser"
)
// ASTMapper is the exported interface for mapping between multiple AST representations
type ASTMapper interface {
Map(node parser.Node) (parser.Node, error)
}
// MapperFunc is a function adapter for ASTMapper
type MapperFunc func(node parser.Node) (parser.Node, error)
// Map applies a mapperfunc as an ASTMapper
func (fn MapperFunc) Map(node parser.Node) (parser.Node, error) {
return fn(node)
}
// MultiMapper can compose multiple ASTMappers
type MultiMapper struct {
mappers []ASTMapper
}
// Map implements ASTMapper
func (m *MultiMapper) Map(node parser.Node) (parser.Node, error) {
var result parser.Node = node
var err error
if len(m.mappers) == 0 {
return nil, errors.New("MultiMapper: No mappers registered")
}
for _, x := range m.mappers {
result, err = x.Map(result)
if err != nil {
return nil, err
}
}
return result, nil
}
// Register adds ASTMappers into a multimapper.
// Since registered functions are applied in the order they're registered, it's advised to register them
// in decreasing priority and only operate on nodes that each function cares about, defaulting to CloneNode.
func (m *MultiMapper) Register(xs ...ASTMapper) {
m.mappers = append(m.mappers, xs...)
}
// NewMultiMapper instaniates an ASTMapper from multiple ASTMappers
func NewMultiMapper(xs ...ASTMapper) *MultiMapper {
m := &MultiMapper{}
m.Register(xs...)
return m
}
// CloneNode is a helper function to clone a node.
func CloneNode(node parser.Node) (parser.Node, error) {
return parser.ParseExpr(node.String())
}
// NodeMapper either maps a single AST node or returns the unaltered node.
// It also returns a bool to signal that no further recursion is necessary.
// This is helpful because it allows mappers to only implement logic for node types they want to change.
// It makes some mappers trivially easy to implement
type NodeMapper interface {
MapNode(node parser.Node) (mapped parser.Node, finished bool, err error)
}
// NodeMapperFunc is an adapter for NodeMapper
type NodeMapperFunc func(node parser.Node) (parser.Node, bool, error)
// MapNode applies a NodeMapperFunc as a NodeMapper
func (f NodeMapperFunc) MapNode(node parser.Node) (parser.Node, bool, error) {
return f(node)
}
// NewASTNodeMapper creates an ASTMapper from a NodeMapper
func NewASTNodeMapper(mapper NodeMapper) ASTNodeMapper {
return ASTNodeMapper{mapper}
}
// ASTNodeMapper is an ASTMapper adapter which uses a NodeMapper internally.
type ASTNodeMapper struct {
NodeMapper
}
// Map implements ASTMapper from a NodeMapper
func (nm ASTNodeMapper) Map(node parser.Node) (parser.Node, error) {
node, fin, err := nm.MapNode(node)
if err != nil {
return nil, err
}
if fin {
return node, nil
}
switch n := node.(type) {
case nil:
// nil handles cases where we check optional fields that are not set
return nil, nil
case parser.Expressions:
for i, e := range n {
mapped, err := nm.Map(e)
if err != nil {
return nil, err
}
n[i] = mapped.(parser.Expr)
}
return n, nil
case *parser.AggregateExpr:
expr, err := nm.Map(n.Expr)
if err != nil {
return nil, err
}
n.Expr = expr.(parser.Expr)
return n, nil
case *parser.BinaryExpr:
lhs, err := nm.Map(n.LHS)
if err != nil {
return nil, err
}
n.LHS = lhs.(parser.Expr)
rhs, err := nm.Map(n.RHS)
if err != nil {
return nil, err
}
n.RHS = rhs.(parser.Expr)
return n, nil
case *parser.Call:
for i, e := range n.Args {
mapped, err := nm.Map(e)
if err != nil {
return nil, err
}
n.Args[i] = mapped.(parser.Expr)
}
return n, nil
case *parser.SubqueryExpr:
mapped, err := nm.Map(n.Expr)
if err != nil {
return nil, err
}
n.Expr = mapped.(parser.Expr)
return n, nil
case *parser.ParenExpr:
mapped, err := nm.Map(n.Expr)
if err != nil {
return nil, err
}
n.Expr = mapped.(parser.Expr)
return n, nil
case *parser.UnaryExpr:
mapped, err := nm.Map(n.Expr)
if err != nil {
return nil, err
}
n.Expr = mapped.(parser.Expr)
return n, nil
case *parser.EvalStmt:
mapped, err := nm.Map(n.Expr)
if err != nil {
return nil, err
}
n.Expr = mapped.(parser.Expr)
return n, nil
case *parser.NumberLiteral, *parser.StringLiteral, *parser.VectorSelector, *parser.MatrixSelector:
return n, nil
default:
panic(errors.Errorf("nodeMapper: unhandled node type %T", node))
}
}