forked from hashicorp/terraform
/
eval.go
222 lines (184 loc) · 5.58 KB
/
eval.go
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package lang
import (
"bytes"
"fmt"
"sync"
"github.com/hashicorp/terraform/config/lang/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
// Eval evaluates the given AST tree and returns its output value, the type
// of the output, and any error that occurred.
func Eval(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",
},
}
// 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
// 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,
})
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.Call:
return &evalCall{n}, nil
case *ast.Concat:
return &evalConcat{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)
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 evalConcat struct{ *ast.Concat }
func (v *evalConcat) 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))
for range v.Exprs {
nodes = append(nodes, stack.Pop().(*ast.LiteralNode))
}
var buf bytes.Buffer
for i := len(nodes) - 1; i >= 0; i-- {
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
}