• Tom Lane's avatar
    Fix list-munging bug that broke SQL function result coercions. · c8ab9701
    Tom Lane authored
    Since commit 913bbd88, check_sql_fn_retval() can either insert type
    coercion steps in-line in the Query that produces the SQL function's
    results, or generate a new top-level Query to perform the coercions,
    if modifying the Query's output in-place wouldn't be safe.  However,
    it appears that the latter case has never actually worked, because
    the code tried to inject the new Query back into the query list it was
    passed ... which is not the list that will be used for later processing
    when we execute the SQL function "normally" (without inlining it).
    So we ended up with no coercion happening at run-time, leading to
    wrong results or crashes depending on the datatypes involved.
    
    While the regression tests look like they cover this area well enough,
    through a huge bit of bad luck all the test cases that exercise the
    separate-Query path were checking either inline-able cases (which
    accidentally didn't have the bug) or cases that are no-ops at runtime
    (e.g., varchar to text), so that the failure to perform the coercion
    wasn't obvious.  The fact that the cases that don't work weren't
    allowed at all before v13 probably contributed to not noticing the
    problem sooner, too.
    
    To fix, get rid of the separate "flat" list of Query nodes and instead
    pass the real two-level list that is going to be used later.  I chose
    to make the same change in check_sql_fn_statements(), although that has
    no actual bug, just so that we don't need that data structure at all.
    
    This is an API change, as evidenced by the adjustments needed to
    callers outside functions.c.  That's a bit scary to be doing in a
    released branch, but so far as I can tell from a quick search,
    there are no outside callers of these functions (and they are
    sufficiently specific to our semantics for SQL-language functions that
    it's not apparent why any extension would need to call them).  In any
    case, v13 already changed the API of check_sql_fn_retval() compared to
    prior branches.
    
    Per report from pinker.  Back-patch to v13 where this code came in.
    
    Discussion: https://postgr.es/m/1603050466566-0.post@n3.nabble.com
    c8ab9701
functions.c 61.1 KB