Maintaining pg4n

Backend

Implementing semantic analysis modules

Most of the semantic analysis modules have been implemented by parsing the SQL with sqlglot. Only few of the Checker classes use the query evaluation plan (QEP).

Thoughts on syntax error analysis

PsqlWrapper has a hook_syntax_f function parameter (of type str -> str), which is called with PsqlParser.parse_syntax_error-produced string, ideally “ERROR: … ^”, which, to our understanding, will always include the whole result, and also the SQL query itself (as caret will point to it), so it does not have to be parsed separately. A syntax error analysis component should then return a message string, and it will be displayed in exactly the same way as semantic error strings.

Changing error messages

One can change error messages by changing the check member function of the class in each of the _checker.py files. check() returns either the error message or None. One can also change the ErrorFormatter class to influence the output format for the error message.

Frontend

Fixing parsing/interception bugs

If improper parsing is suspected, turn PsqlParser.debug to True, that way all ParserException.explains are saved into psqlparser.log. These exceptions are verbose, and will require fair amount of sifting. If improper interception by PsqlWrapper is suspected, turn PsqlWrapper.debug to True, to have current pyte display contents copied to pyte.screen on every update, and pexpect terminal control stream appended into psqlwrapper.log. Any wrapper issues are expected to be quite obtuse to fix, as they likely are pexpect or pyte library issues.

pyparsing documentation is available on Welcome to PyParsing’s documentation!

Extending parsers

To our knowledge, there are no interdependencies with the parser functions, so they should be able to be extended as needed, and new ones added.

Known limitations

pexpect does not seem to handle all terminal traffic. pyte and user terminal occasionally disagree on contents when user uses ctrl-R to fetch past queries, which prevents screenscraping SQL query properly. pyte also disagrees on display contents when exiting a separate query results screen, but this has no impact on pg4n performance.
Semantic error modules are expected to produce false negatives.