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check_types.go
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/
check_types.go
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package lang
import (
"fmt"
"sync"
"github.com/hashicorp/terraform/config/lang/ast"
)
// TypeCheck implements ast.Visitor for type checking an AST tree.
// It requires some configuration to look up the type of nodes.
//
// It also optionally will not type error and will insert an implicit
// type conversions for specific types if specified by the Implicit
// field. Note that this is kind of organizationally weird to put into
// this structure but we'd rather do that than duplicate the type checking
// logic multiple times.
type TypeCheck struct {
Scope ast.Scope
// Implicit is a map of implicit type conversions that we can do,
// and that shouldn't error. The key of the first map is the from type,
// the key of the second map is the to type, and the final string
// value is the function to call (which must be registered in the Scope).
Implicit map[ast.Type]map[ast.Type]string
// Stack of types. This shouldn't be used directly except by implementations
// of TypeCheckNode.
Stack []ast.Type
err error
lock sync.Mutex
}
// TypeCheckNode is the interface that must be implemented by any
// ast.Node that wants to support type-checking. If the type checker
// encounters a node that doesn't implement this, it will error.
type TypeCheckNode interface {
TypeCheck(*TypeCheck) (ast.Node, error)
}
func (v *TypeCheck) Visit(root ast.Node) error {
v.lock.Lock()
defer v.lock.Unlock()
defer v.reset()
root.Accept(v.visit)
return v.err
}
func (v *TypeCheck) visit(raw ast.Node) ast.Node {
if v.err != nil {
return raw
}
var result ast.Node
var err error
switch n := raw.(type) {
case *ast.Arithmetic:
tc := &typeCheckArithmetic{n}
result, err = tc.TypeCheck(v)
case *ast.Call:
tc := &typeCheckCall{n}
result, err = tc.TypeCheck(v)
case *ast.Concat:
tc := &typeCheckConcat{n}
result, err = tc.TypeCheck(v)
case *ast.LiteralNode:
tc := &typeCheckLiteral{n}
result, err = tc.TypeCheck(v)
case *ast.VariableAccess:
tc := &typeCheckVariableAccess{n}
result, err = tc.TypeCheck(v)
default:
tc, ok := raw.(TypeCheckNode)
if !ok {
err = fmt.Errorf("unknown node for type check: %#v", raw)
break
}
result, err = tc.TypeCheck(v)
}
if err != nil {
pos := raw.Pos()
v.err = fmt.Errorf("At column %d, line %d: %s",
pos.Column, pos.Line, err)
}
return result
}
type typeCheckArithmetic struct {
n *ast.Arithmetic
}
func (tc *typeCheckArithmetic) TypeCheck(v *TypeCheck) (ast.Node, error) {
// The arguments are on the stack in reverse order, so pop them off.
exprs := make([]ast.Type, len(tc.n.Exprs))
for i, _ := range tc.n.Exprs {
exprs[len(tc.n.Exprs)-1-i] = v.StackPop()
}
// Determine the resulting type we want. We do this by going over
// every expression until we find one with a type we recognize.
// We do this because the first expr might be a string ("var.foo")
// and we need to know what to implicit to.
mathFunc := "__builtin_IntMath"
mathType := ast.TypeInt
for _, v := range exprs {
exit := true
switch v {
case ast.TypeInt:
mathFunc = "__builtin_IntMath"
mathType = v
case ast.TypeFloat:
mathFunc = "__builtin_FloatMath"
mathType = v
default:
exit = false
}
// We found the type, so leave
if exit {
break
}
}
// Verify the args
for i, arg := range exprs {
if arg != mathType {
cn := v.ImplicitConversion(exprs[i], mathType, tc.n.Exprs[i])
if cn != nil {
tc.n.Exprs[i] = cn
continue
}
return nil, fmt.Errorf(
"operand %d should be %s, got %s",
i+1, mathType, arg)
}
}
// Modulo doesn't work for floats
if mathType == ast.TypeFloat && tc.n.Op == ast.ArithmeticOpMod {
return nil, fmt.Errorf("modulo cannot be used with floats")
}
// Return type
v.StackPush(mathType)
// Replace our node with a call to the proper function. This isn't
// type checked but we already verified types.
args := make([]ast.Node, len(tc.n.Exprs)+1)
args[0] = &ast.LiteralNode{
Value: tc.n.Op,
Typex: ast.TypeInt,
Posx: tc.n.Pos(),
}
copy(args[1:], tc.n.Exprs)
return &ast.Call{
Func: mathFunc,
Args: args,
Posx: tc.n.Pos(),
}, nil
}
type typeCheckCall struct {
n *ast.Call
}
func (tc *typeCheckCall) TypeCheck(v *TypeCheck) (ast.Node, error) {
// Look up the function in the map
function, ok := v.Scope.LookupFunc(tc.n.Func)
if !ok {
return nil, fmt.Errorf("unknown function called: %s", tc.n.Func)
}
// The arguments are on the stack in reverse order, so pop them off.
args := make([]ast.Type, len(tc.n.Args))
for i, _ := range tc.n.Args {
args[len(tc.n.Args)-1-i] = v.StackPop()
}
// Verify the args
for i, expected := range function.ArgTypes {
if expected == ast.TypeAny {
continue
}
if args[i] != expected {
cn := v.ImplicitConversion(args[i], expected, tc.n.Args[i])
if cn != nil {
tc.n.Args[i] = cn
continue
}
return nil, fmt.Errorf(
"%s: argument %d should be %s, got %s",
tc.n.Func, i+1, expected, args[i])
}
}
// If we're variadic, then verify the types there
if function.Variadic && function.VariadicType != ast.TypeAny {
args = args[len(function.ArgTypes):]
for i, t := range args {
if t != function.VariadicType {
realI := i + len(function.ArgTypes)
cn := v.ImplicitConversion(
t, function.VariadicType, tc.n.Args[realI])
if cn != nil {
tc.n.Args[realI] = cn
continue
}
return nil, fmt.Errorf(
"%s: argument %d should be %s, got %s",
tc.n.Func, realI,
function.VariadicType, t)
}
}
}
// Return type
v.StackPush(function.ReturnType)
return tc.n, nil
}
type typeCheckConcat struct {
n *ast.Concat
}
func (tc *typeCheckConcat) TypeCheck(v *TypeCheck) (ast.Node, error) {
n := tc.n
types := make([]ast.Type, len(n.Exprs))
for i, _ := range n.Exprs {
types[len(n.Exprs)-1-i] = v.StackPop()
}
// All concat args must be strings, so validate that
for i, t := range types {
if t != ast.TypeString {
cn := v.ImplicitConversion(t, ast.TypeString, n.Exprs[i])
if cn != nil {
n.Exprs[i] = cn
continue
}
return nil, fmt.Errorf(
"argument %d must be a string", i+1)
}
}
// This always results in type string
v.StackPush(ast.TypeString)
return n, nil
}
type typeCheckLiteral struct {
n *ast.LiteralNode
}
func (tc *typeCheckLiteral) TypeCheck(v *TypeCheck) (ast.Node, error) {
v.StackPush(tc.n.Typex)
return tc.n, nil
}
type typeCheckVariableAccess struct {
n *ast.VariableAccess
}
func (tc *typeCheckVariableAccess) TypeCheck(v *TypeCheck) (ast.Node, error) {
// Look up the variable in the map
variable, ok := v.Scope.LookupVar(tc.n.Name)
if !ok {
return nil, fmt.Errorf(
"unknown variable accessed: %s", tc.n.Name)
}
// Add the type to the stack
v.StackPush(variable.Type)
return tc.n, nil
}
func (v *TypeCheck) ImplicitConversion(
actual ast.Type, expected ast.Type, n ast.Node) ast.Node {
if v.Implicit == nil {
return nil
}
fromMap, ok := v.Implicit[actual]
if !ok {
return nil
}
toFunc, ok := fromMap[expected]
if !ok {
return nil
}
return &ast.Call{
Func: toFunc,
Args: []ast.Node{n},
Posx: n.Pos(),
}
}
func (v *TypeCheck) reset() {
v.Stack = nil
v.err = nil
}
func (v *TypeCheck) StackPush(t ast.Type) {
v.Stack = append(v.Stack, t)
}
func (v *TypeCheck) StackPop() ast.Type {
var x ast.Type
x, v.Stack = v.Stack[len(v.Stack)-1], v.Stack[:len(v.Stack)-1]
return x
}