4c804fbdfb
Commit 989be0810dffd08b added a flex/bison lexer/parser to interpret synchronous_standby_names. It was done in a pretty crufty way, though, making assorted end-use sites responsible for calling the parser at the right times. That was not only vulnerable to errors of omission, but made it possible that lexer/parser errors occur at very undesirable times, and created memory leakages even if there was no error. Instead, perform the parsing once during check_synchronous_standby_names and let guc.c manage the resulting data. To do that, we have to flatten the parsed representation into a single hunk of malloc'd memory, but that is not very hard. While at it, work a little harder on making useful error reports for parsing problems; the previous code felt that "synchronous_standby_names parser returned 1" was an appropriate user-facing error message. (To be fair, it did also log a syntax error message, but separately from the GUC problem report, which is at best confusing.) It had some outright bugs in the face of invalid input, too. I (tgl) also concluded that we need to restrict unquoted names in synchronous_standby_names to be just SQL identifiers. The previous coding would accept darn near anything, which (1) makes the quoting convention both nearly-unnecessary and formally ambiguous, (2) makes it very hard to understand what is a syntax error and what is a creative interpretation of the input as a standby name, and (3) makes it impossible to further extend the syntax in future without a compatibility break. I presume that we're intending future extensions of the syntax, else this parsing infrastructure is massive overkill, so (3) is an important objection. Since we've taken a compatibility hit for non-identifier names with this change anyway, we might as well lock things down now and insist that users use double quotes for standby names that aren't identifiers. Kyotaro Horiguchi and Tom Lane
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