error on invalid primary key definition

fixes #6

Author: Jeff Wendling

syntax/parse_field_ref.go

@@ -74,6 +74,10 @@ func parseRelativeFieldRefs(node *tupleNode) (*ast.RelativeFieldRefs, error) {
 			return nil, err
 		}
 		if ref_token == nil {
+			if len(refs.Refs) == 0 {
+				return nil, errutil.New(node.getPos(),
+					"must specify some field references")
+			}
 			return refs, nil
 		}
 		refs.Refs = append(refs.Refs, relativeFieldRefFromToken(ref_token))

syntax/parse_model.go

@@ -14,7 +14,9 @@
 
 package syntax
 
-import "gopkg.in/spacemonkeygo/dbx.v1/ast"
+import (
+	"gopkg.in/spacemonkeygo/dbx.v1/ast"
+)
 
 func parseModel(node *tupleNode) (*ast.Model, error) {
 	model := new(ast.Model)

testdata/build/bad_key.dbx

@@ -0,0 +1,6 @@
+//test:fail_gen must specify some field references
+
+model foo (
+    key
+    field pk serial64
+)