Re: [HACKERS] plpgsql - additional extra checks

From: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
To: Stephen Frost <sfrost(at)snowman(dot)net>
Cc: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Daniel Gustafsson <daniel(at)yesql(dot)se>, Marko Tiikkaja <marko(at)joh(dot)to>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, David Steele <david(at)pgmasters(dot)net>
Subject: Re: [HACKERS] plpgsql - additional extra checks
Date: 2018-01-07 08:31:40
Message-ID: CAFj8pRAhxkLA7cS=x+uT8ZUrpXUWjdJuvjoGqkGJSm9xYb_7qw@mail.gmail.com
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Hi

2018-01-07 0:59 GMT+01:00 Stephen Frost <sfrost(at)snowman(dot)net>:

> Greetings Pavel,
>
> * Pavel Stehule (pavel(dot)stehule(at)gmail(dot)com) wrote:
> > 2017-11-30 3:44 GMT+01:00 Michael Paquier <michael(dot)paquier(at)gmail(dot)com>:
> > > At least documentation needs patching, or this is going to generate
> > > warnings on HEAD at compilation. I am moving this to next CF for lack
> > > of reviews, and the status is waiting on author as this needs at least
> > > a couple of doc fixes.
> >
> > fixed doc attached
>
> Looks like this patch should have been in "Needs Review" state, not
> "Waiting for author", since it does apply, build and pass make
> check-world, but as I'm signed up to review it, I'll do so here:
>
> diff --git a/doc/src/sgml/plpgsql.sgml b/doc/src/sgml/plpgsql.sgml
> index 7d23ed437e..efa48bc13c 100644
> --- a/doc/src/sgml/plpgsql.sgml
> +++ b/doc/src/sgml/plpgsql.sgml
> @@ -4963,6 +4963,11 @@ a_output := a_output || $$ if v_$$ ||
> referrer_keys.kind || $$ like '$$
> so you are advised to test in a separate development environment.
> </para>
>
> + <para>
> + The setting <varname>plpgsql.extra_warnings</varname> to
> <literal>all</literal> is a
> + good idea in developer or test environments.
> + </para>
>
> Better language for this would be:
>
> Setting <varname>plpgsql.extra_warnings</varname>, or
> <varname>plpgsql.extra_errors</varname>, as appropriate, to
> <literal>all</literal> is encouraged in development and/or testing
> environments.
>
> @@ -4979,6 +4984,30 @@ a_output := a_output || $$ if v_$$ ||
> referrer_keys.kind || $$ like '$$
> </para>
> </listitem>
> </varlistentry>
> +
> + <varlistentry>
> + <term><varname>strict_multi_assignment</varname></term>
> + <listitem>
> + <para>
> + Some <application>PL/PgSQL</application> commands allows to assign
> a values to
> + more than one variable. The number of target variables should not be
> + equal to number of source values. Missing values are replaced by
> NULL
> + value, spare values are ignored. More times this situation signalize
> + some error.
> + </para>
> + </listitem>
> + </varlistentry>
>
> Better language:
>
> Some <application>PL/PgSQL</application> commands allow assigning values
> to more than one variable at a time, such as SELECT INTO. Typically,
> the number of target variables and the number of source variables should
> match, though <application>PL/PgSQL</application> will use NULL for
> missing values and extra variables are ignored. Enabling this check
> will cause <application>PL/PgSQL</application> to throw a WARNING or
> ERROR whenever the number of target variables and the number of source
> variables are different.
>
> + <varlistentry>
> + <term><varname>too_many_rows</varname></term>
> + <listitem>
> + <para>
> + When result is assigned to a variable by <literal>INTO</literal>
> clause,
> + checks if query returns more than one row. In this case the
> assignment
> + is not deterministic usually - and it can be signal some issues in
> design.
> + </para>
> + </listitem>
> + </varlistentry>
> </variablelist>
>
> Better language:
>
> Enabling this check will cause <application>PL/PgSQL</application> to
> check if a given query returns more than one row when an
> <literal>INTO</literal> clause is used. As an INTO statement will only
> ever use one row, having a query return multiple rows is generally
> either inefficient and/or nondeterministic and therefore is likely an
> error.
>
> @@ -4997,6 +5026,34 @@ WARNING: variable "f1" shadows a previously
> defined variable
> LINE 3: f1 int;
> ^
> CREATE FUNCTION
> +</programlisting>
> +
> + The another example shows the effect of <varname>plpgsql.extra_
> warnings</varname>
> + set to <varname>strict_multi_assignment</varname>:
> +<programlisting>
>
> Better language:
>
> The below example shows the effects of setting
> <varname>plpgsql.extra_warnings</varname> to
> <varname>strict_multi_assignment</varname>:
>
> diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
> index ec480cb0ba..0879e84cd2 100644
> --- a/src/pl/plpgsql/src/pl_exec.c
> +++ b/src/pl/plpgsql/src/pl_exec.c
> @@ -3629,6 +3629,24 @@ exec_stmt_execsql(PLpgSQL_execstate *estate,
> long tcount;
> int rc;
> PLpgSQL_expr *expr = stmt->sqlstmt;
> + bool too_many_rows_check;
> + int too_many_rows_level;
> +
> + if (plpgsql_extra_errors & PLPGSQL_XCHECK_TOOMANYROWS)
> + {
> + too_many_rows_check = true;
> + too_many_rows_level = ERROR;
> + }
> + else if (plpgsql_extra_warnings & PLPGSQL_XCHECK_TOOMANYROWS)
> + {
> + too_many_rows_check = true;
> + too_many_rows_level = WARNING;
> + }
> + else
> + {
> + too_many_rows_check = false;
> + too_many_rows_level = NOTICE;
> + }
>
>
> I'm not sure why we need two variables here- couldn't we simply look at
> too_many_rows_level? eg: too_many_rows_level >= WARNING ? ...
>
> Not as big a deal, but I would change it to be 'check_too_many_rows' as
> a variable name too.
>
> @@ -3678,7 +3696,7 @@ exec_stmt_execsql(PLpgSQL_execstate *estate,
> */
> if (stmt->into)
> {
> - if (stmt->strict || stmt->mod_stmt)
> + if (stmt->strict || stmt->mod_stmt || too_many_rows_check)
> tcount = 2;
> else
> tcount = 1;
>
> The comment above this block needs updating for this change and, in
> general, there's probably other pieces of code that this patch
> changes where the comments should either be improved or ones added.
>
>
> @@ -6033,12 +6051,48 @@ exec_move_row(PLpgSQL_execstate *estate,
> int t_natts;
> int fnum;
> int anum;
> + bool strict_multiassignment_check;
> + int strict_multiassignment_level;
> +
> + if (plpgsql_extra_errors & PLPGSQL_XCHECK_
> STRICTMULTIASSIGNMENT)
> + {
> + strict_multiassignment_check = true;
> + strict_multiassignment_level = ERROR;
> + }
> + else if (plpgsql_extra_warnings & PLPGSQL_XCHECK_
> STRICTMULTIASSIGNMENT)
> + {
> + strict_multiassignment_check = true;
> + strict_multiassignment_level = WARNING;
> + }
> + else
> + {
> + strict_multiassignment_check = false;
> + strict_multiassignment_level = NOTICE;
> + }
>
> Same comments for this, more-or-less, as the above sections.
>
> if (HeapTupleIsValid(tup))
> t_natts = HeapTupleHeaderGetNatts(tup->t_data);
> else
> t_natts = 0;
>
> + if (strict_multiassignment_check)
> + {
> + int i;
> +
> + anum = 0;
> + for (i = 0; i < td_natts; i++)
> + if (!TupleDescAttr(tupdesc,
> i)->attisdropped)
> + anum++;
> +
> + if (anum != row->nfields)
> + {
> + ereport(strict_multiassignment_level,
> + (errcode(ERRCODE_DATATYPE_
> MISMATCH),
> + errmsg("Number of
> evaluated attributies (%d) does not match expected attributies (%d)",
> +
> anum, row->nfields)));
> + }
> + }
>
> I would have thought you'd incorporate this into the loop below instead
> of adding a whole new section..? At the least, this should include
> better comments, and isn't there an issue here where you aren't
> accounting for dropped columns in row structs? See the comments in the
> loop below this.
>
> I'd suggest you try to construct a case which (incorrectly) throws a
> warning for a row struct with a dropped column with your current patch
> and then add that to the regression tests too, since it appears to have
> been missed.
>
> There, now it's in the correct Waiting for Author state. :)
>

thank you for comments. All should be fixed in attached patch

Regards

Pavel

> Thanks!
>
> Stephen
>

Attachment Content-Type Size
plpgsql-extra-check-180107.patch text/x-patch 15.5 KB

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