config/lang: implement type lookup

config/lang/ast/ast.go

@@ -18,7 +18,7 @@ type Pos struct {
 	Column, Line int // Column/Line number, starting at 1
 }
 
-func (p *Pos) String() string {
+func (p Pos) String() string {
 	return fmt.Sprintf("%d:%d", p.Line, p.Column)
 }
 

config/lang/engine.go

@@ -11,10 +11,8 @@ import (
 // Engine is the execution engine for this language. It should be configured
 // prior to running Execute.
 type Engine struct {
-	// VarMap and FuncMap are the mappings of identifiers to functions
-	// and variable values.
-	VarMap  map[string]Variable
-	FuncMap map[string]Function
+	// GlobalScope is the global scope of execution for this engine.
+	GlobalScope *Scope
 
 	// SemanticChecks is a list of additional semantic checks that will be run
 	// on the tree prior to executing it. The type checker, identifier checker,
@@ -26,26 +24,10 @@ type Engine struct {
 // semantic check on an AST tree. This will be called with the root node.
 type SemanticChecker func(ast.Node) error
 
-// Variable is a variable value for execution given as input to the engine.
-// It records the value of a variables along with their type.
-type Variable struct {
-	Value interface{}
-	Type  ast.Type
-}
-
-// Function defines a function that can be executed by the engine.
-// The type checker will validate that the proper types will be called
-// to the callback.
-type Function struct {
-	ArgTypes   []ast.Type
-	ReturnType ast.Type
-	Callback   func([]interface{}) (interface{}, error)
-}
-
 // Execute executes the given ast.Node and returns its final value, its
 // type, and an error if one exists.
 func (e *Engine) Execute(root ast.Node) (interface{}, ast.Type, error) {
-	v := &executeVisitor{Engine: e}
+	v := &executeVisitor{Scope: e.GlobalScope}
 	return v.Visit(root)
 }
 
@@ -53,7 +35,7 @@ func (e *Engine) Execute(root ast.Node) (interface{}, ast.Type, error) {
 // a program. Note at this point it is assumed that the types check out
 // and the identifiers exist.
 type executeVisitor struct {
-	Engine *Engine
+	Scope *Scope
 
 	stack []*ast.LiteralNode
 	err   error
@@ -104,7 +86,7 @@ func (v *executeVisitor) visit(raw ast.Node) {
 
 func (v *executeVisitor) visitCall(n *ast.Call) {
 	// Look up the function in the map
-	function, ok := v.Engine.FuncMap[n.Func]
+	function, ok := v.Scope.FuncMap[n.Func]
 	if !ok {
 		v.err = fmt.Errorf("unknown function called: %s", n.Func)
 		return
@@ -156,7 +138,7 @@ func (v *executeVisitor) visitLiteral(n *ast.LiteralNode) {
 
 func (v *executeVisitor) visitVariableAccess(n *ast.VariableAccess) {
 	// Look up the variable in the map
-	variable, ok := v.Engine.VarMap[n.Name]
+	variable, ok := v.Scope.VarMap[n.Name]
 	if !ok {
 		v.err = fmt.Errorf("unknown variable accessed: %s", n.Name)
 		return
@@ -177,3 +159,38 @@ func (v *executeVisitor) stackPop() *ast.LiteralNode {
 	x, v.stack = v.stack[len(v.stack)-1], v.stack[:len(v.stack)-1]
 	return x
 }
+
+// Scope represents a lookup scope for execution.
+type Scope struct {
+	// VarMap and FuncMap are the mappings of identifiers to functions
+	// and variable values.
+	VarMap  map[string]Variable
+	FuncMap map[string]Function
+}
+
+// Variable is a variable value for execution given as input to the engine.
+// It records the value of a variables along with their type.
+type Variable struct {
+	Value interface{}
+	Type  ast.Type
+}
+
+// Function defines a function that can be executed by the engine.
+// The type checker will validate that the proper types will be called
+// to the callback.
+type Function struct {
+	ArgTypes   []ast.Type
+	ReturnType ast.Type
+	Callback   func([]interface{}) (interface{}, error)
+}
+
+// LookupVar will look up a variable by name.
+// TODO test
+func (s *Scope) LookupVar(n string) (Variable, bool) {
+	if s == nil {
+		return Variable{}, false
+	}
+
+	v, ok := s.VarMap[n]
+	return v, ok
+}

config/lang/engine_test.go

@@ -10,14 +10,14 @@ import (
 func TestEngineExecute(t *testing.T) {
 	cases := []struct {
 		Input      string
-		Engine     *Engine
+		Scope      *Scope
 		Error      bool
 		Result     interface{}
 		ResultType ast.Type
 	}{
 		{
 			"foo",
-			&Engine{},
+			nil,
 			false,
 			"foo",
 			ast.TypeString,
@@ -25,7 +25,7 @@ func TestEngineExecute(t *testing.T) {
 
 		{
 			"foo ${bar}",
-			&Engine{
+			&Scope{
 				VarMap: map[string]Variable{
 					"bar": Variable{
 						Value: "baz",
@@ -40,7 +40,7 @@ func TestEngineExecute(t *testing.T) {
 
 		{
 			"foo ${rand()}",
-			&Engine{
+			&Scope{
 				FuncMap: map[string]Function{
 					"rand": Function{
 						ReturnType: ast.TypeString,
@@ -62,7 +62,8 @@ func TestEngineExecute(t *testing.T) {
 			t.Fatalf("Error: %s\n\nInput: %s", err, tc.Input)
 		}
 
-		out, outType, err := tc.Engine.Execute(node)
+		engine := &Engine{GlobalScope: tc.Scope}
+		out, outType, err := engine.Execute(node)
 		if (err != nil) != tc.Error {
 			t.Fatalf("Error: %s\n\nInput: %s", err, tc.Input)
 		}

config/lang/transform_implicit_types_test.go

@@ -0,0 +1,74 @@
+package lang
+
+import (
+	"testing"
+
+	"github.com/hashicorp/terraform/config/lang/ast"
+)
+
+func TestLookupType(t *testing.T) {
+	cases := []struct {
+		Input  ast.Node
+		Scope  *Scope
+		Output ast.Type
+		Error  bool
+	}{
+		{
+			&customUntyped{},
+			nil,
+			ast.TypeInvalid,
+			true,
+		},
+
+		{
+			&customTyped{},
+			nil,
+			ast.TypeString,
+			false,
+		},
+
+		{
+			&ast.LiteralNode{
+				Value: 42,
+				Type:  ast.TypeInt,
+			},
+			nil,
+			ast.TypeInt,
+			false,
+		},
+
+		{
+			&ast.VariableAccess{
+				Name: "foo",
+			},
+			&Scope{
+				VarMap: map[string]Variable{
+					"foo": Variable{Type: ast.TypeInt},
+				},
+			},
+			ast.TypeInt,
+			false,
+		},
+	}
+
+	for _, tc := range cases {
+		actual, err := LookupType(tc.Input, tc.Scope)
+		if (err != nil) != tc.Error {
+			t.Fatalf("bad: %s\n\nInput: %#v", err, tc.Input)
+		}
+		if actual != tc.Output {
+			t.Fatalf("bad: %s\n\nInput: %#v", actual, tc.Input)
+		}
+	}
+}
+
+type customUntyped struct{}
+
+func (n customUntyped) Accept(ast.Visitor) {}
+func (n customUntyped) Pos() (v ast.Pos)   { return }
+
+type customTyped struct{}
+
+func (n customTyped) Accept(ast.Visitor)            {}
+func (n customTyped) Pos() (v ast.Pos)              { return }
+func (n customTyped) Type(*Scope) (ast.Type, error) { return ast.TypeString, nil }

config/lang/types.go

@@ -0,0 +1,58 @@
+package lang
+
+import (
+	"fmt"
+
+	"github.com/hashicorp/terraform/config/lang/ast"
+)
+
+// LookupType looks up the type of the given node with the given scope.
+func LookupType(raw ast.Node, scope *Scope) (ast.Type, error) {
+	switch n := raw.(type) {
+	case *ast.LiteralNode:
+		return typedLiteralNode{n}.Type(scope)
+	case *ast.VariableAccess:
+		return typedVariableAccess{n}.Type(scope)
+	default:
+		if t, ok := raw.(TypedNode); ok {
+			return t.Type(scope)
+		}
+
+		return ast.TypeInvalid, fmt.Errorf(
+			"unknown node to get type of: %T", raw)
+	}
+}
+
+// TypedNode is an interface that custom AST nodes should implement
+// if they want to work with LookupType. All the builtin AST nodes have
+// implementations of this.
+type TypedNode interface {
+	Type(*Scope) (ast.Type, error)
+}
+
+type typedLiteralNode struct {
+	n *ast.LiteralNode
+}
+
+func (n typedLiteralNode) Type(s *Scope) (ast.Type, error) {
+	return n.n.Type, nil
+}
+
+type typedVariableAccess struct {
+	n *ast.VariableAccess
+}
+
+func (n typedVariableAccess) Type(s *Scope) (ast.Type, error) {
+	v, ok := s.LookupVar(n.n.Name)
+	if !ok {
+		return ast.TypeInvalid, fmt.Errorf(
+			"%s: couldn't find variable %s", n.n.Pos(), n.n.Name)
+	}
+
+	return v.Type, nil
+}
+
+var supportedTransforms = map[ast.Type]ast.Type{
+	ast.TypeString: ast.TypeInt,
+	ast.TypeInt:    ast.TypeString,
+}