Ensure that RowExprs and whole-row Vars produce the expected column names.

At one time it wasn't terribly important what column names were associated
with the fields of a composite Datum, but since the introduction of
operations like row_to_json(), it's important that looking up the rowtype
ID embedded in the Datum returns the column names that users would expect.
That did not work terribly well before this patch: you could get the column
names of the underlying table, or column aliases from any level of the
query, depending on minor details of the plan tree.  You could even get
totally empty field names, which is disastrous for cases like row_to_json().

To fix this for whole-row Vars, look to the RTE referenced by the Var, and
make sure its column aliases are applied to the rowtype associated with
the result Datums.  This is a tad scary because we might have to return
a transient RECORD type even though the Var is declared as having some
named rowtype.  In principle it should be all right because the record
type will still be physically compatible with the named rowtype; but
I had to weaken one Assert in ExecEvalConvertRowtype, and there might be
third-party code containing similar assumptions.

Similarly, RowExprs have to be willing to override the column names coming
from a named composite result type and produce a RECORD when the column
aliases visible at the site of the RowExpr differ from the underlying
table's column names.

In passing, revert the decision made in commit 398f70ec07 to add
an alias-list argument to ExecTypeFromExprList: better to provide that
functionality in a separate function.  This also reverts most of the code
changes in d685814835, which we don't need because we're no longer
depending on the tupdesc found in the child plan node's result slot to be
blessed.

Back-patch to 9.4, but not earlier, since this solution changes the results
in some cases that users might not have realized were buggy.  We'll apply a
more restricted form of this patch in older branches.

src/test/regress/expected/rowtypes.out

@@ -474,3 +474,163 @@ select (row('Jim', 'Beam')).text;  -- error
 ERROR:  could not identify column "text" in record data type
 LINE 1: select (row('Jim', 'Beam')).text;
                 ^
+--
+-- Test that composite values are seen to have the correct column names
+-- (bug #11210 and other reports)
+--
+select row_to_json(i) from int8_tbl i;
+                  row_to_json                   
+------------------------------------------------
+ {"q1":123,"q2":456}
+ {"q1":123,"q2":4567890123456789}
+ {"q1":4567890123456789,"q2":123}
+ {"q1":4567890123456789,"q2":4567890123456789}
+ {"q1":4567890123456789,"q2":-4567890123456789}
+(5 rows)
+
+select row_to_json(i) from int8_tbl i(x,y);
+                 row_to_json                  
+----------------------------------------------
+ {"x":123,"y":456}
+ {"x":123,"y":4567890123456789}
+ {"x":4567890123456789,"y":123}
+ {"x":4567890123456789,"y":4567890123456789}
+ {"x":4567890123456789,"y":-4567890123456789}
+(5 rows)
+
+create temp view vv1 as select * from int8_tbl;
+select row_to_json(i) from vv1 i;
+                  row_to_json                   
+------------------------------------------------
+ {"q1":123,"q2":456}
+ {"q1":123,"q2":4567890123456789}
+ {"q1":4567890123456789,"q2":123}
+ {"q1":4567890123456789,"q2":4567890123456789}
+ {"q1":4567890123456789,"q2":-4567890123456789}
+(5 rows)
+
+select row_to_json(i) from vv1 i(x,y);
+                 row_to_json                  
+----------------------------------------------
+ {"x":123,"y":456}
+ {"x":123,"y":4567890123456789}
+ {"x":4567890123456789,"y":123}
+ {"x":4567890123456789,"y":4567890123456789}
+ {"x":4567890123456789,"y":-4567890123456789}
+(5 rows)
+
+select row_to_json(ss) from
+  (select q1, q2 from int8_tbl) as ss;
+                  row_to_json                   
+------------------------------------------------
+ {"q1":123,"q2":456}
+ {"q1":123,"q2":4567890123456789}
+ {"q1":4567890123456789,"q2":123}
+ {"q1":4567890123456789,"q2":4567890123456789}
+ {"q1":4567890123456789,"q2":-4567890123456789}
+(5 rows)
+
+select row_to_json(ss) from
+  (select q1, q2 from int8_tbl offset 0) as ss;
+                  row_to_json                   
+------------------------------------------------
+ {"q1":123,"q2":456}
+ {"q1":123,"q2":4567890123456789}
+ {"q1":4567890123456789,"q2":123}
+ {"q1":4567890123456789,"q2":4567890123456789}
+ {"q1":4567890123456789,"q2":-4567890123456789}
+(5 rows)
+
+select row_to_json(ss) from
+  (select q1 as a, q2 as b from int8_tbl) as ss;
+                 row_to_json                  
+----------------------------------------------
+ {"a":123,"b":456}
+ {"a":123,"b":4567890123456789}
+ {"a":4567890123456789,"b":123}
+ {"a":4567890123456789,"b":4567890123456789}
+ {"a":4567890123456789,"b":-4567890123456789}
+(5 rows)
+
+select row_to_json(ss) from
+  (select q1 as a, q2 as b from int8_tbl offset 0) as ss;
+                 row_to_json                  
+----------------------------------------------
+ {"a":123,"b":456}
+ {"a":123,"b":4567890123456789}
+ {"a":4567890123456789,"b":123}
+ {"a":4567890123456789,"b":4567890123456789}
+ {"a":4567890123456789,"b":-4567890123456789}
+(5 rows)
+
+select row_to_json(ss) from
+  (select q1 as a, q2 as b from int8_tbl) as ss(x,y);
+                 row_to_json                  
+----------------------------------------------
+ {"x":123,"y":456}
+ {"x":123,"y":4567890123456789}
+ {"x":4567890123456789,"y":123}
+ {"x":4567890123456789,"y":4567890123456789}
+ {"x":4567890123456789,"y":-4567890123456789}
+(5 rows)
+
+select row_to_json(ss) from
+  (select q1 as a, q2 as b from int8_tbl offset 0) as ss(x,y);
+                 row_to_json                  
+----------------------------------------------
+ {"x":123,"y":456}
+ {"x":123,"y":4567890123456789}
+ {"x":4567890123456789,"y":123}
+ {"x":4567890123456789,"y":4567890123456789}
+ {"x":4567890123456789,"y":-4567890123456789}
+(5 rows)
+
+explain (costs off)
+select row_to_json(q) from
+  (select thousand, tenthous from tenk1
+   where thousand = 42 and tenthous < 2000 offset 0) q;
+                         QUERY PLAN                          
+-------------------------------------------------------------
+ Subquery Scan on q
+   ->  Index Only Scan using tenk1_thous_tenthous on tenk1
+         Index Cond: ((thousand = 42) AND (tenthous < 2000))
+(3 rows)
+
+select row_to_json(q) from
+  (select thousand, tenthous from tenk1
+   where thousand = 42 and tenthous < 2000 offset 0) q;
+           row_to_json           
+---------------------------------
+ {"thousand":42,"tenthous":42}
+ {"thousand":42,"tenthous":1042}
+(2 rows)
+
+select row_to_json(q) from
+  (select thousand as x, tenthous as y from tenk1
+   where thousand = 42 and tenthous < 2000 offset 0) q;
+    row_to_json    
+-------------------
+ {"x":42,"y":42}
+ {"x":42,"y":1042}
+(2 rows)
+
+select row_to_json(q) from
+  (select thousand as x, tenthous as y from tenk1
+   where thousand = 42 and tenthous < 2000 offset 0) q(a,b);
+    row_to_json    
+-------------------
+ {"a":42,"b":42}
+ {"a":42,"b":1042}
+(2 rows)
+
+create temp table tt1 as select * from int8_tbl limit 2;
+create temp table tt2 () inherits(tt1);
+insert into tt2 values(0,0);
+select row_to_json(r) from (select q2,q1 from tt1 offset 0) r;
+           row_to_json            
+----------------------------------
+ {"q2":456,"q1":123}
+ {"q2":4567890123456789,"q1":123}
+ {"q2":0,"q1":0}
+(3 rows)
+

src/test/regress/sql/rowtypes.sql

@@ -227,3 +227,47 @@ select cast (row('Jim', 'Beam') as text);
 select (row('Jim', 'Beam'))::text;
 select text(row('Jim', 'Beam'));  -- error
 select (row('Jim', 'Beam')).text;  -- error
+
+--
+-- Test that composite values are seen to have the correct column names
+-- (bug #11210 and other reports)
+--
+
+select row_to_json(i) from int8_tbl i;
+select row_to_json(i) from int8_tbl i(x,y);
+
+create temp view vv1 as select * from int8_tbl;
+select row_to_json(i) from vv1 i;
+select row_to_json(i) from vv1 i(x,y);
+
+select row_to_json(ss) from
+  (select q1, q2 from int8_tbl) as ss;
+select row_to_json(ss) from
+  (select q1, q2 from int8_tbl offset 0) as ss;
+select row_to_json(ss) from
+  (select q1 as a, q2 as b from int8_tbl) as ss;
+select row_to_json(ss) from
+  (select q1 as a, q2 as b from int8_tbl offset 0) as ss;
+select row_to_json(ss) from
+  (select q1 as a, q2 as b from int8_tbl) as ss(x,y);
+select row_to_json(ss) from
+  (select q1 as a, q2 as b from int8_tbl offset 0) as ss(x,y);
+
+explain (costs off)
+select row_to_json(q) from
+  (select thousand, tenthous from tenk1
+   where thousand = 42 and tenthous < 2000 offset 0) q;
+select row_to_json(q) from
+  (select thousand, tenthous from tenk1
+   where thousand = 42 and tenthous < 2000 offset 0) q;
+select row_to_json(q) from
+  (select thousand as x, tenthous as y from tenk1
+   where thousand = 42 and tenthous < 2000 offset 0) q;
+select row_to_json(q) from
+  (select thousand as x, tenthous as y from tenk1
+   where thousand = 42 and tenthous < 2000 offset 0) q(a,b);
+
+create temp table tt1 as select * from int8_tbl limit 2;
+create temp table tt2 () inherits(tt1);
+insert into tt2 values(0,0);
+select row_to_json(r) from (select q2,q1 from tt1 offset 0) r;