Make some use of anonymous unions [libpq-oauth]

Make some use of anonymous unions, which are allowed as of C11, as examples and encouragement for future code, and to test compilers. This commit changes the json_field struct. Reviewed-by: Nathan Bossart <nathandbossart@gmail.com> Discussion: https://postgr.es/m/CAOYmi%2BnV25oC5uXFgWodydGrHkfWMDCLUcjbAreM3mNX%3DF2JWw%40mail.gmail.com

Author: jchampio

src/interfaces/libpq-oauth/oauth-curl.c

@@ -439,7 +439,7 @@ struct json_field
 {
 char **scalar;/* for all scalar types */
 struct curl_slist **array;/* for type == JSON_TOKEN_ARRAY_START */
-}target;
+};
 
 boolrequired;/* REQUIRED field, or just OPTIONAL? */
 };
@@ -561,8 +561,8 @@ oauth_json_object_field_start(void *state, char *name, bool isnull)
 {
 field = ctx->active;
 
-if ((field->type == JSON_TOKEN_ARRAY_START && *field->target.array)
-|| (field->type != JSON_TOKEN_ARRAY_START && *field->target.scalar))
+if ((field->type == JSON_TOKEN_ARRAY_START && *field->array)
+|| (field->type != JSON_TOKEN_ARRAY_START && *field->scalar))
 {
 oauth_parse_set_error(ctx, "field \"%s\" is duplicated",
  field->name);
@@ -706,7 +706,7 @@ oauth_json_scalar(void *state, char *token, JsonTokenType type)
 }
 
 /* ...and that a result has not already been set. */
-if (*field->target.scalar)
+if (*field->scalar)
 {
 Assert(false);
 oauth_parse_set_error(ctx,
@@ -715,8 +715,8 @@ oauth_json_scalar(void *state, char *token, JsonTokenType type)
 return JSON_SEM_ACTION_FAILED;
 }
 
-*field->target.scalar = strdup(token);
-if (!*field->target.scalar)
+*field->scalar = strdup(token);
+if (!*field->scalar)
 return JSON_OUT_OF_MEMORY;
 
 ctx->active = NULL;
@@ -738,11 +738,11 @@ oauth_json_scalar(void *state, char *token, JsonTokenType type)
 }
 
 /* Note that curl_slist_append() makes a copy of the token. */
-temp = curl_slist_append(*field->target.array, token);
+temp = curl_slist_append(*field->array, token);
 if (!temp)
 return JSON_OUT_OF_MEMORY;
 
-*field->target.array = temp;
+*field->array = temp;
 }
 }
 else
@@ -878,8 +878,8 @@ parse_oauth_json(struct async_ctx *actx, const struct json_field *fields)
 while (fields->name)
 {
 if (fields->required
-&& !*fields->target.scalar
-&& !*fields->target.array)
+&& !*fields->scalar
+&& !*fields->array)
 {
 actx_error(actx, "field \"%s\" is missing", fields->name);
 goto cleanup;