Try to resolve all elements in an expression to a known const

This is used in the subprocess launching test but will be added to
others as applicable.

This also closes #28

core/resolve.go

@@ -0,0 +1,79 @@
+// (c) Copyright 2016 Hewlett Packard Enterprise Development LP
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package core
+
+import "go/ast"
+
+func resolveIdent(n *ast.Ident, c *Context) bool {
+	if n.Obj == nil || n.Obj.Kind != ast.Var {
+		return true
+	}
+	if node, ok := n.Obj.Decl.(ast.Node); ok {
+		return TryResolve(node, c)
+	}
+	return false
+}
+
+func resolveAssign(n *ast.AssignStmt, c *Context) bool {
+	for _, arg := range n.Rhs {
+		if !TryResolve(arg, c) {
+			return false
+		}
+	}
+	return true
+}
+
+func resolveCompLit(n *ast.CompositeLit, c *Context) bool {
+	for _, arg := range n.Elts {
+		if !TryResolve(arg, c) {
+			return false
+		}
+	}
+	return true
+}
+
+func resolveBinExpr(n *ast.BinaryExpr, c *Context) bool {
+	return (TryResolve(n.X, c) && TryResolve(n.Y, c))
+}
+
+func resolveCallExpr(n *ast.CallExpr, c *Context) bool {
+	// TODO(tkelsey): next step, full function resolution
+	return false
+}
+
+func TryResolve(n ast.Node, c *Context) bool {
+	switch node := n.(type) {
+	case *ast.BasicLit:
+		return true
+
+	case *ast.CompositeLit:
+		return resolveCompLit(node, c)
+
+	case *ast.Ident:
+		return resolveIdent(node, c)
+
+	case *ast.AssignStmt:
+		return resolveAssign(node, c)
+
+	case *ast.CallExpr:
+		return resolveCallExpr(node, c)
+
+	case *ast.BinaryExpr:
+		return resolveBinExpr(node, c)
+	}
+
+	ast.Print(c.FileSet, n)
+	return false
+}