route/vendor/github.com/hashicorp/hil/eval.go

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2017-12-02 23:34:35 +00:00
package hil
import (
"bytes"
"errors"
"fmt"
"sync"
"github.com/hashicorp/hil/ast"
)
// EvalConfig is the configuration for evaluating.
type EvalConfig struct {
// GlobalScope is the global scope of execution for evaluation.
GlobalScope *ast.BasicScope
// SemanticChecks is a list of additional semantic checks that will be run
// on the tree prior to evaluating it. The type checker, identifier checker,
// etc. will be run before these automatically.
SemanticChecks []SemanticChecker
}
// SemanticChecker is the type that must be implemented to do a
// semantic check on an AST tree. This will be called with the root node.
type SemanticChecker func(ast.Node) error
// EvaluationResult is a struct returned from the hil.Eval function,
// representing the result of an interpolation. Results are returned in their
// "natural" Go structure rather than in terms of the HIL AST. For the types
// currently implemented, this means that the Value field can be interpreted as
// the following Go types:
// TypeInvalid: undefined
// TypeString: string
// TypeList: []interface{}
// TypeMap: map[string]interface{}
// TypBool: bool
type EvaluationResult struct {
Type EvalType
Value interface{}
}
// InvalidResult is a structure representing the result of a HIL interpolation
// which has invalid syntax, missing variables, or some other type of error.
// The error is described out of band in the accompanying error return value.
var InvalidResult = EvaluationResult{Type: TypeInvalid, Value: nil}
// errExitUnknown is an internal error that when returned means the result
// is an unknown value. We use this for early exit.
var errExitUnknown = errors.New("unknown value")
func Eval(root ast.Node, config *EvalConfig) (EvaluationResult, error) {
output, outputType, err := internalEval(root, config)
if err != nil {
return InvalidResult, err
}
// If the result contains any nested unknowns then the result as a whole
// is unknown, so that callers only have to deal with "entirely known"
// or "entirely unknown" as outcomes.
if ast.IsUnknown(ast.Variable{Type: outputType, Value: output}) {
outputType = ast.TypeUnknown
output = UnknownValue
}
switch outputType {
case ast.TypeList:
val, err := VariableToInterface(ast.Variable{
Type: ast.TypeList,
Value: output,
})
return EvaluationResult{
Type: TypeList,
Value: val,
}, err
case ast.TypeMap:
val, err := VariableToInterface(ast.Variable{
Type: ast.TypeMap,
Value: output,
})
return EvaluationResult{
Type: TypeMap,
Value: val,
}, err
case ast.TypeString:
return EvaluationResult{
Type: TypeString,
Value: output,
}, nil
case ast.TypeBool:
return EvaluationResult{
Type: TypeBool,
Value: output,
}, nil
case ast.TypeUnknown:
return EvaluationResult{
Type: TypeUnknown,
Value: UnknownValue,
}, nil
default:
return InvalidResult, fmt.Errorf("unknown type %s as interpolation output", outputType)
}
}
// Eval evaluates the given AST tree and returns its output value, the type
// of the output, and any error that occurred.
func internalEval(root ast.Node, config *EvalConfig) (interface{}, ast.Type, error) {
// Copy the scope so we can add our builtins
if config == nil {
config = new(EvalConfig)
}
scope := registerBuiltins(config.GlobalScope)
implicitMap := map[ast.Type]map[ast.Type]string{
ast.TypeFloat: {
ast.TypeInt: "__builtin_FloatToInt",
ast.TypeString: "__builtin_FloatToString",
},
ast.TypeInt: {
ast.TypeFloat: "__builtin_IntToFloat",
ast.TypeString: "__builtin_IntToString",
},
ast.TypeString: {
ast.TypeInt: "__builtin_StringToInt",
ast.TypeFloat: "__builtin_StringToFloat",
ast.TypeBool: "__builtin_StringToBool",
},
ast.TypeBool: {
ast.TypeString: "__builtin_BoolToString",
},
}
// Build our own semantic checks that we always run
tv := &TypeCheck{Scope: scope, Implicit: implicitMap}
ic := &IdentifierCheck{Scope: scope}
// Build up the semantic checks for execution
checks := make(
[]SemanticChecker,
len(config.SemanticChecks),
len(config.SemanticChecks)+2)
copy(checks, config.SemanticChecks)
checks = append(checks, ic.Visit)
checks = append(checks, tv.Visit)
// Run the semantic checks
for _, check := range checks {
if err := check(root); err != nil {
return nil, ast.TypeInvalid, err
}
}
// Execute
v := &evalVisitor{Scope: scope}
return v.Visit(root)
}
// EvalNode is the interface that must be implemented by any ast.Node
// to support evaluation. This will be called in visitor pattern order.
// The result of each call to Eval is automatically pushed onto the
// stack as a LiteralNode. Pop elements off the stack to get child
// values.
type EvalNode interface {
Eval(ast.Scope, *ast.Stack) (interface{}, ast.Type, error)
}
type evalVisitor struct {
Scope ast.Scope
Stack ast.Stack
err error
lock sync.Mutex
}
func (v *evalVisitor) Visit(root ast.Node) (interface{}, ast.Type, error) {
// Run the actual visitor pattern
root.Accept(v.visit)
// Get our result and clear out everything else
var result *ast.LiteralNode
if v.Stack.Len() > 0 {
result = v.Stack.Pop().(*ast.LiteralNode)
} else {
result = new(ast.LiteralNode)
}
resultErr := v.err
if resultErr == errExitUnknown {
// This means the return value is unknown and we used the error
// as an early exit mechanism. Reset since the value on the stack
// should be the unknown value.
resultErr = nil
}
// Clear everything else so we aren't just dangling
v.Stack.Reset()
v.err = nil
t, err := result.Type(v.Scope)
if err != nil {
return nil, ast.TypeInvalid, err
}
return result.Value, t, resultErr
}
func (v *evalVisitor) visit(raw ast.Node) ast.Node {
if v.err != nil {
return raw
}
en, err := evalNode(raw)
if err != nil {
v.err = err
return raw
}
out, outType, err := en.Eval(v.Scope, &v.Stack)
if err != nil {
v.err = err
return raw
}
v.Stack.Push(&ast.LiteralNode{
Value: out,
Typex: outType,
})
if outType == ast.TypeUnknown {
// Halt immediately
v.err = errExitUnknown
return raw
}
return raw
}
// evalNode is a private function that returns an EvalNode for built-in
// types as well as any other EvalNode implementations.
func evalNode(raw ast.Node) (EvalNode, error) {
switch n := raw.(type) {
case *ast.Index:
return &evalIndex{n}, nil
case *ast.Call:
return &evalCall{n}, nil
case *ast.Conditional:
return &evalConditional{n}, nil
case *ast.Output:
return &evalOutput{n}, nil
case *ast.LiteralNode:
return &evalLiteralNode{n}, nil
case *ast.VariableAccess:
return &evalVariableAccess{n}, nil
default:
en, ok := n.(EvalNode)
if !ok {
return nil, fmt.Errorf("node doesn't support evaluation: %#v", raw)
}
return en, nil
}
}
type evalCall struct{ *ast.Call }
func (v *evalCall) Eval(s ast.Scope, stack *ast.Stack) (interface{}, ast.Type, error) {
// Look up the function in the map
function, ok := s.LookupFunc(v.Func)
if !ok {
return nil, ast.TypeInvalid, fmt.Errorf(
"unknown function called: %s", v.Func)
}
// The arguments are on the stack in reverse order, so pop them off.
args := make([]interface{}, len(v.Args))
for i, _ := range v.Args {
node := stack.Pop().(*ast.LiteralNode)
if node.IsUnknown() {
// If any arguments are unknown then the result is automatically unknown
return UnknownValue, ast.TypeUnknown, nil
}
args[len(v.Args)-1-i] = node.Value
}
// Call the function
result, err := function.Callback(args)
if err != nil {
return nil, ast.TypeInvalid, fmt.Errorf("%s: %s", v.Func, err)
}
return result, function.ReturnType, nil
}
type evalConditional struct{ *ast.Conditional }
func (v *evalConditional) Eval(s ast.Scope, stack *ast.Stack) (interface{}, ast.Type, error) {
// On the stack we have literal nodes representing the resulting values
// of the condition, true and false expressions, but they are in reverse
// order.
falseLit := stack.Pop().(*ast.LiteralNode)
trueLit := stack.Pop().(*ast.LiteralNode)
condLit := stack.Pop().(*ast.LiteralNode)
if condLit.IsUnknown() {
// If our conditional is unknown then our result is also unknown
return UnknownValue, ast.TypeUnknown, nil
}
if condLit.Value.(bool) {
return trueLit.Value, trueLit.Typex, nil
} else {
return falseLit.Value, trueLit.Typex, nil
}
}
type evalIndex struct{ *ast.Index }
func (v *evalIndex) Eval(scope ast.Scope, stack *ast.Stack) (interface{}, ast.Type, error) {
key := stack.Pop().(*ast.LiteralNode)
target := stack.Pop().(*ast.LiteralNode)
variableName := v.Index.Target.(*ast.VariableAccess).Name
if key.IsUnknown() {
// If our key is unknown then our result is also unknown
return UnknownValue, ast.TypeUnknown, nil
}
// For target, we'll accept collections containing unknown values but
// we still need to catch when the collection itself is unknown, shallowly.
if target.Typex == ast.TypeUnknown {
return UnknownValue, ast.TypeUnknown, nil
}
switch target.Typex {
case ast.TypeList:
return v.evalListIndex(variableName, target.Value, key.Value)
case ast.TypeMap:
return v.evalMapIndex(variableName, target.Value, key.Value)
default:
return nil, ast.TypeInvalid, fmt.Errorf(
"target %q for indexing must be ast.TypeList or ast.TypeMap, is %s",
variableName, target.Typex)
}
}
func (v *evalIndex) evalListIndex(variableName string, target interface{}, key interface{}) (interface{}, ast.Type, error) {
// We assume type checking was already done and we can assume that target
// is a list and key is an int
list, ok := target.([]ast.Variable)
if !ok {
return nil, ast.TypeInvalid, fmt.Errorf(
"cannot cast target to []Variable, is: %T", target)
}
keyInt, ok := key.(int)
if !ok {
return nil, ast.TypeInvalid, fmt.Errorf(
"cannot cast key to int, is: %T", key)
}
if len(list) == 0 {
return nil, ast.TypeInvalid, fmt.Errorf("list is empty")
}
if keyInt < 0 || len(list) < keyInt+1 {
return nil, ast.TypeInvalid, fmt.Errorf(
"index %d out of range for list %s (max %d)",
keyInt, variableName, len(list))
}
returnVal := list[keyInt].Value
returnType := list[keyInt].Type
return returnVal, returnType, nil
}
func (v *evalIndex) evalMapIndex(variableName string, target interface{}, key interface{}) (interface{}, ast.Type, error) {
// We assume type checking was already done and we can assume that target
// is a map and key is a string
vmap, ok := target.(map[string]ast.Variable)
if !ok {
return nil, ast.TypeInvalid, fmt.Errorf(
"cannot cast target to map[string]Variable, is: %T", target)
}
keyString, ok := key.(string)
if !ok {
return nil, ast.TypeInvalid, fmt.Errorf(
"cannot cast key to string, is: %T", key)
}
if len(vmap) == 0 {
return nil, ast.TypeInvalid, fmt.Errorf("map is empty")
}
value, ok := vmap[keyString]
if !ok {
return nil, ast.TypeInvalid, fmt.Errorf(
"key %q does not exist in map %s", keyString, variableName)
}
return value.Value, value.Type, nil
}
type evalOutput struct{ *ast.Output }
func (v *evalOutput) Eval(s ast.Scope, stack *ast.Stack) (interface{}, ast.Type, error) {
// The expressions should all be on the stack in reverse
// order. So pop them off, reverse their order, and concatenate.
nodes := make([]*ast.LiteralNode, 0, len(v.Exprs))
haveUnknown := false
for range v.Exprs {
n := stack.Pop().(*ast.LiteralNode)
nodes = append(nodes, n)
// If we have any unknowns then the whole result is unknown
// (we must deal with this first, because the type checker can
// skip type conversions in the presence of unknowns, and thus
// any of our other nodes may be incorrectly typed.)
if n.IsUnknown() {
haveUnknown = true
}
}
if haveUnknown {
return UnknownValue, ast.TypeUnknown, nil
}
// Special case the single list and map
if len(nodes) == 1 {
switch t := nodes[0].Typex; t {
case ast.TypeList:
fallthrough
case ast.TypeMap:
fallthrough
case ast.TypeUnknown:
return nodes[0].Value, t, nil
}
}
// Otherwise concatenate the strings
var buf bytes.Buffer
for i := len(nodes) - 1; i >= 0; i-- {
if nodes[i].Typex != ast.TypeString {
return nil, ast.TypeInvalid, fmt.Errorf(
"invalid output with %s value at index %d: %#v",
nodes[i].Typex,
i,
nodes[i].Value,
)
}
buf.WriteString(nodes[i].Value.(string))
}
return buf.String(), ast.TypeString, nil
}
type evalLiteralNode struct{ *ast.LiteralNode }
func (v *evalLiteralNode) Eval(ast.Scope, *ast.Stack) (interface{}, ast.Type, error) {
return v.Value, v.Typex, nil
}
type evalVariableAccess struct{ *ast.VariableAccess }
func (v *evalVariableAccess) Eval(scope ast.Scope, _ *ast.Stack) (interface{}, ast.Type, error) {
// Look up the variable in the map
variable, ok := scope.LookupVar(v.Name)
if !ok {
return nil, ast.TypeInvalid, fmt.Errorf(
"unknown variable accessed: %s", v.Name)
}
return variable.Value, variable.Type, nil
}