Don't try to render attributes with no data type

Also improve documentation for --stop/-s

Closes #83

puccini-tosca/README.md

@@ -53,10 +53,10 @@ If you need more diagnostics for TOSCA parsing use the `parse` command. It works
 `compile` but does not emit Clout. Instead, it provides you various flages for examining the
 internal workings of Puccini's TOSCA parser.
 
-Use `--stop/-s` to specify a [phase](../tosca/parser/) (1-5) at which you wish the parser to stop.
-This could be useful if you're getting too many problems in your report and wish to minimize them
-to a more manageable list. Note that `-s 0` will skip the TOSCA parser entirely and just check that
-the YAML input is readable.
+By default Puccini will attempt all [5 parser phases](../tosca/parser/). This is in order to give
+users as complete a problem report as possible. However, if you're getting too many problems it
+may be useful to specify `--stop/-s` with a phase number (1-5) at which you wish the to stop. Note
+that `-s 0` will skip the TOSCA parser entirely and just check that the YAML input is readable.
 
 `--dump/-d` is used to dump the internal data of phases. You may specify multiple phases to dump
 using ",", e.g. `-d 2,3,4`. Per phase you will see:

tosca/grammars/tosca_v2_0/attribute-definition.go

@@ -94,7 +94,7 @@ func (self *AttributeDefinition) Render() {
 
 	self.render()
 
-	if self.Default != nil {
+	if (self.Default != nil) && (self.DataType != nil) {
 		// The "default" value must be a valid value of the type
 		self.Default.RenderAttribute(self.DataType, self, false, false)
 	}

tosca/grammars/tosca_v2_0/constraint-clause.go

@@ -130,13 +130,16 @@ func (self *ConstraintClause) IsNativeArgument(index uint) bool {
 type ConstraintClauses []*ConstraintClause
 
 func (self ConstraintClauses) Append(constraints ConstraintClauses) ConstraintClauses {
-	var r ConstraintClauses
 	length := len(self)
 	if length > 0 {
-		r = make(ConstraintClauses, length)
+		r := make(ConstraintClauses, length)
 		copy(r, self)
+		return append(r, constraints...)
+	} else {
+		r := make(ConstraintClauses, len(constraints))
+		copy(r, constraints)
+		return r
 	}
-	return append(r, constraints...)
 }
 
 func (self ConstraintClauses) Render(dataType *DataType) {

tosca/read.go

@@ -197,15 +197,20 @@ func NewReadField(fieldName string, tag string, context *Context, entity reflect
 }
 
 func (self *ReadField) Read() {
+	field := self.Entity.FieldByName(self.FieldName)
+	fieldType := field.Type()
+
 	childData, ok := self.Context.Data.(ard.Map)[self.Key]
 	if !ok {
+		if reflection.IsSliceOfPtrToStruct(fieldType) {
+			// If we have no items, at least have an empty slice
+			// so that "require" will not see a nil here
+			field.Set(reflect.MakeSlice(fieldType, 0, 0))
+		}
 		return
 	}
 
-	field := self.Entity.FieldByName(self.FieldName)
-
 	if self.Reader != nil {
-		fieldType := field.Type()
 		if reflection.IsSliceOfPtrToStruct(fieldType) {
 			// Field is compatible with []*interface{}
 			slice := field
@@ -234,7 +239,7 @@ func (self *ReadField) Read() {
 			if slice.IsNil() {
 				// If we have no items, at least have an empty slice
 				// so that "require" will not see a nil here
-				slice = reflect.MakeSlice(slice.Type(), 0, 0)
+				slice = reflect.MakeSlice(fieldType, 0, 0)
 			}
 			field.Set(slice)
 		} else if reflection.IsMapOfStringToPtrToStruct(fieldType) {