Fix bugs in polymorphic-argument resolution for multiranges.

We failed to deal with an UNKNOWN-type input for
anycompatiblemultirange; that should throw an error indicating
that we don't know how to resolve the multirange type.

We also failed to infer the type of an anycompatiblerange output
from an anycompatiblemultirange input or vice versa.

Per bug #17066 from Alexander Lakhin.  Back-patch to v14
where multiranges were added.

Discussion: https://postgr.es/m/17066-16a37f6223a8470b@postgresql.org

src/test/regress/expected/polymorphism.out

@@ -179,6 +179,72 @@ LINE 2:   from polyf(11, array[1, 2.2], 42, 34.5);
 HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
 drop function polyf(a anyelement, b anyarray,
                     c anycompatible, d anycompatible);
+create function polyf(anyrange) returns anymultirange
+as 'select multirange($1);' language sql;
+select polyf(int4range(1,10));
+  polyf   
+----------
+ {[1,10)}
+(1 row)
+
+select polyf(null);
+ERROR:  could not determine polymorphic type because input has type unknown
+drop function polyf(anyrange);
+create function polyf(anymultirange) returns anyelement
+as 'select lower($1);' language sql;
+select polyf(int4multirange(int4range(1,10), int4range(20,30)));
+ polyf 
+-------
+     1
+(1 row)
+
+select polyf(null);
+ERROR:  could not determine polymorphic type because input has type unknown
+drop function polyf(anymultirange);
+create function polyf(anycompatiblerange) returns anycompatiblemultirange
+as 'select multirange($1);' language sql;
+select polyf(int4range(1,10));
+  polyf   
+----------
+ {[1,10)}
+(1 row)
+
+select polyf(null);
+ERROR:  could not determine polymorphic type anycompatiblerange because input has type unknown
+drop function polyf(anycompatiblerange);
+create function polyf(anymultirange) returns anyrange
+as 'select range_merge($1);' language sql;
+select polyf(int4multirange(int4range(1,10), int4range(20,30)));
+ polyf  
+--------
+ [1,30)
+(1 row)
+
+select polyf(null);
+ERROR:  could not determine polymorphic type because input has type unknown
+drop function polyf(anymultirange);
+create function polyf(anycompatiblemultirange) returns anycompatiblerange
+as 'select range_merge($1);' language sql;
+select polyf(int4multirange(int4range(1,10), int4range(20,30)));
+ polyf  
+--------
+ [1,30)
+(1 row)
+
+select polyf(null);
+ERROR:  could not determine polymorphic type anycompatiblerange because input has type unknown
+drop function polyf(anycompatiblemultirange);
+create function polyf(anycompatiblemultirange) returns anycompatible
+as 'select lower($1);' language sql;
+select polyf(int4multirange(int4range(1,10), int4range(20,30)));
+ polyf 
+-------
+     1
+(1 row)
+
+select polyf(null);
+ERROR:  could not determine polymorphic type anycompatiblemultirange because input has type unknown
+drop function polyf(anycompatiblemultirange);
 --
 -- Polymorphic aggregate tests
 --
@@ -1914,7 +1980,7 @@ LINE 1: select x, pg_typeof(x) from anyctest(11.2, multirange(int4ra...
                                     ^
 HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
 select x, pg_typeof(x) from anyctest(11.2, '{[4,7)}') x;  -- fail
-ERROR:  could not identify anycompatiblemultirange type
+ERROR:  could not determine polymorphic type anycompatiblemultirange because input has type unknown
 drop function anyctest(anycompatible, anycompatiblemultirange);
 create function anyctest(anycompatiblemultirange, anycompatiblemultirange)
 returns anycompatible as $$

src/test/regress/expected/rangefuncs.out

@@ -1609,7 +1609,7 @@ DROP FUNCTION dup(f1 anycompatiblerange);
 CREATE FUNCTION bad (f1 anyarray, out f2 anycompatible, out f3 anycompatiblearray)
 AS 'select $1, array[$1,$1]' LANGUAGE sql;
 ERROR:  cannot determine result data type
-DETAIL:  A result of type anycompatible requires at least one input of type anycompatible, anycompatiblearray, anycompatiblenonarray, or anycompatiblerange.
+DETAIL:  A result of type anycompatible requires at least one input of type anycompatible, anycompatiblearray, anycompatiblenonarray, anycompatiblerange, or anycompatiblemultirange.
 --
 -- table functions
 --

src/test/regress/sql/polymorphism.sql

@@ -126,6 +126,54 @@ select x, pg_typeof(x), y, pg_typeof(y)
 drop function polyf(a anyelement, b anyarray,
                     c anycompatible, d anycompatible);
 
+create function polyf(anyrange) returns anymultirange
+as 'select multirange($1);' language sql;
+
+select polyf(int4range(1,10));
+select polyf(null);
+
+drop function polyf(anyrange);
+
+create function polyf(anymultirange) returns anyelement
+as 'select lower($1);' language sql;
+
+select polyf(int4multirange(int4range(1,10), int4range(20,30)));
+select polyf(null);
+
+drop function polyf(anymultirange);
+
+create function polyf(anycompatiblerange) returns anycompatiblemultirange
+as 'select multirange($1);' language sql;
+
+select polyf(int4range(1,10));
+select polyf(null);
+
+drop function polyf(anycompatiblerange);
+
+create function polyf(anymultirange) returns anyrange
+as 'select range_merge($1);' language sql;
+
+select polyf(int4multirange(int4range(1,10), int4range(20,30)));
+select polyf(null);
+
+drop function polyf(anymultirange);
+
+create function polyf(anycompatiblemultirange) returns anycompatiblerange
+as 'select range_merge($1);' language sql;
+
+select polyf(int4multirange(int4range(1,10), int4range(20,30)));
+select polyf(null);
+
+drop function polyf(anycompatiblemultirange);
+
+create function polyf(anycompatiblemultirange) returns anycompatible
+as 'select lower($1);' language sql;
+
+select polyf(int4multirange(int4range(1,10), int4range(20,30)));
+select polyf(null);
+
+drop function polyf(anycompatiblemultirange);
+
 
 --
 -- Polymorphic aggregate tests