psql: Add leakproof indicator to \df+, \do+, \dAo+, and \dC+ output.

This allows users to determine whether particular functions are
leakproof, and whether the underlying functions used by operators and
casts are leakproof. This is useful to determine whether indexes can
be used in queries on security barrier views or tables with row-level
security policies.

Yugo Nagata, reviewed by Erik Wienhold and Dean Rasheed.

Discussion: https://postgr.es/m/20240701220817.483f9b645b95611f8b1f65da%40sranhm.sraoss.co.jp

doc/src/sgml/planstats.sgml

@@ -729,6 +729,9 @@ EXPLAIN (ANALYZE, TIMING OFF, BUFFERS OFF) SELECT * FROM t WHERE a <= 49 AND
    accurately, the function that the operator is based on).  If not, then the
    selectivity estimator will behave as if no statistics are available, and
    the planner will proceed with default or fall-back assumptions.
+   The <xref linkend="app-psql"/> program's
+   <command><link linkend="app-psql-meta-command-do-lc">\do+</link></command>
+   meta-command is useful to determine which operators are marked as leakproof.
   </para>
 
   <para>

doc/src/sgml/ref/psql-ref.sgml

@@ -1420,7 +1420,8 @@ SELECT $1 \parse stmt1
         is specified, only members of operator families whose names match that
         pattern are listed.
         If <literal>+</literal> is appended to the command name, each operator
-        is listed with its sort operator family (if it is an ordering operator).
+        is listed with its sort operator family (if it is an ordering operator),
+        and whether its underlying function is leakproof.
         </para>
         </listitem>
       </varlistentry>
@@ -1509,8 +1510,9 @@ SELECT $1 \parse stmt1
         If <replaceable class="parameter">pattern</replaceable>
         is specified, only casts whose source or target types match the
         pattern are listed.
-        If <literal>+</literal> is appended to the command name, each object
-        is listed with its associated description.
+        If <literal>+</literal> is appended to the command name, additional
+        information about each cast is shown, including whether its underlying
+        function is leakproof, and the cast's description.
         </para>
         </listitem>
       </varlistentry>
@@ -1711,9 +1713,9 @@ SELECT $1 \parse stmt1
         modifier to include system objects.
         If the form <literal>\df+</literal> is used, additional information
         about each function is shown, including volatility,
-        parallel safety, owner, security classification, access privileges,
-        language, internal name (for C and internal functions only),
-        and description.
+        parallel safety, owner, security classification, whether it is
+        leakproof, access privileges, language, internal name (for C and
+        internal functions only), and description.
         Source code for a specific function can be seen
         using <literal>\sf</literal>.
         </para>
@@ -1862,8 +1864,8 @@ SELECT $1 \parse stmt1
         pattern or the <literal>S</literal> modifier to include system
         objects.
         If <literal>+</literal> is appended to the command name,
-        additional information about each operator is shown, currently just
-        the name of the underlying function.
+        additional information about each operator is shown, including
+        the name of the underlying function, and whether it is leakproof.
         </para>
         </listitem>
       </varlistentry>

doc/src/sgml/rules.sgml

@@ -2167,6 +2167,17 @@ CREATE VIEW phone_number WITH (security_barrier) AS
     view's row filters.
 </para>
 
+<para>
+    For example, an index scan cannot be selected for queries on security
+    barrier views (or tables with row-level security policies) if an
+    operator used in the <literal>WHERE</literal> clause is associated with the
+    operator family of the index, but its underlying function is not marked
+    <literal>LEAKPROOF</literal>. The <xref linkend="app-psql"/> program's
+    <command><link linkend="app-psql-meta-command-dao">\dAo+</link></command>
+    meta-command is useful to list operator families and determine which of
+    their operators are marked as leakproof.
+</para>
+
 <para>
     It is important to understand that even a view created with the
     <literal>security_barrier</literal> option is intended to be secure only