engine: resources, lang: Set resource fields more accurately

There were some bugs about setting resource fields that were structs
with various fields. This makes things more strict and correct. Now we
check for duplicate field names earlier (duplicates due to identical
aliases) and we also don't try and set private fields, or incorrectly
set partial structs.

Most interestingly, this also cleans up all of the resources and ensures
that each one has nicer docs and a clear struct tag for fields that we
want to use in mcl. These are mandatory now, and if you're missing the
tag, then we will ignore the field.

engine/util/util.go

@@ -252,87 +252,29 @@ func LangFieldNameToStructFieldName(kind string) (map[string]string, error) {
 	return mapping, nil // lang field name -> field name
 }
 
-// StructKindToFieldNameTypeMap returns a map from field name to expected type
-// in the lang type system.
-func StructKindToFieldNameTypeMap(kind string) (map[string]*types.Type, error) {
+// LangFieldNameToStructType returns the mapping from lang (AST) field names,
+// and the expected type in our type system for each.
+func LangFieldNameToStructType(kind string) (map[string]*types.Type, error) {
 	res, err := engine.NewResource(kind)
 	if err != nil {
 		return nil, err
 	}
 
-	sv := reflect.ValueOf(res).Elem() // pointer to struct, then struct
-	if k := sv.Kind(); k != reflect.Struct {
-		return nil, fmt.Errorf("expected struct, got: %s", k)
-	}
-
-	result := make(map[string]*types.Type)
-
-	st := reflect.TypeOf(res).Elem() // pointer to struct, then struct
-	for i := 0; i < st.NumField(); i++ {
-		field := st.Field(i)
-		name := field.Name
-		// TODO: in future, skip over fields that don't have a `lang` tag
-		//if name == "Base" { // TODO: hack!!!
-		//	continue
-		//}
-
-		// Skip unexported fields. These should never be mapped golang<->mcl.
-		//if field.PkgPath != "" { // pre-golang 1.17
-		if !field.IsExported() {
-			continue
-		}
-
-		typ, err := types.TypeOf(field.Type)
-		// some types (eg complex64) aren't convertible, so skip for now...
-		if err != nil {
-			continue
-			//return nil, errwrap.Wrapf(err, "could not identify type of field `%s`", name)
-		}
-		result[name] = typ
-	}
-
-	return result, nil
-}
-
-// LangFieldNameToStructType returns the mapping from lang (AST) field names,
-// and the expected type in our type system for each.
-func LangFieldNameToStructType(kind string) (map[string]*types.Type, error) {
-	// returns a mapping between fieldName and expected *types.Type
-	fieldNameTypMap, err := StructKindToFieldNameTypeMap(kind)
-	if err != nil {
-		return nil, errwrap.Wrapf(err, "could not determine types for `%s` resource", kind)
-	}
-
-	mapping, err := LangFieldNameToStructFieldName(kind)
+	gtyp := reflect.TypeOf(res)
+	st, err := types.ResTypeOf(gtyp)
 	if err != nil {
 		return nil, err
 	}
-
-	// transform from field name to tag name
-	typMap := make(map[string]*types.Type)
-	for name, typ := range fieldNameTypMap {
-		if strings.Title(name) != name {
-			continue // skip private fields
-		}
-
-		found := false
-		for k, v := range mapping {
-			if v != name {
-				continue
-			}
-			// found
-			if found { // previously found!
-				return nil, fmt.Errorf("duplicate mapping for: %s", name)
-			}
-			typMap[k] = typ
-			found = true // :)
-		}
-		if !found {
-			return nil, fmt.Errorf("could not find mapping for: %s", name)
-		}
+	if st == nil {
+		return nil, fmt.Errorf("got empty type")
 	}
+	if st.Kind != types.KindStruct {
+		return nil, fmt.Errorf("not a struct kind")
+	}
+	// unpack the top-level struct, it should have the field names matching
+	// the parameters of the struct.
 
-	return typMap, nil
+	return st.Map, nil
 }
 
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