sql: handle implicit record return types better

This PR validates the UDF return type at build time if it is a
user-defined type. If the return type is no longer compatible with what
the UDF body returns, we return an error instead. This is more in line
with postgres behavior.

Fixes: 95558
Epic: CRDB-19496
Release note (sql change): UDFs with implicit record return types will
return an error when called if the return type has been altered and is
no longer compatible with the body of the UDF.

pkg/sql/logictest/testdata/logic_test/udf

@@ -3044,3 +3044,50 @@ query I
 SELECT count(descriptor) FROM system.descriptor WHERE id = $dropped_fn_id;
 ----
 0
+
+subtest udt_alter
+
+statement ok
+CREATE TABLE t_alter (
+  a INT PRIMARY KEY,
+  b INT
+)
+
+statement ok
+CREATE FUNCTION f_rtbl() RETURNS t_alter LANGUAGE SQL AS 'SELECT 1, 2;'
+
+query T
+SELECT f_rtbl();
+----
+(1,2)
+
+statement ok
+ALTER TABLE t_alter DROP COLUMN b;
+
+statement error pq: return type mismatch in function declared to return t_alter
+SELECT f_rtbl();
+
+statement ok
+ALTER TABLE t_alter ADD COLUMN b INT;
+
+query T
+SELECT f_rtbl();
+----
+(1,2)
+
+statement ok
+SET enable_experimental_alter_column_type_general=true
+
+statement ok
+ALTER TABLE t_alter ALTER b TYPE FLOAT;
+
+statement error pq: return type mismatch in function declared to return t_alter
+SELECT f_rtbl();
+
+statement ok
+ALTER TABLE t_alter ALTER b TYPE INT;
+
+query T
+SELECT f_rtbl();
+----
+(1,2)

pkg/sql/logictest/testdata/logic_test/udf_star

@@ -173,16 +173,20 @@ SELECT f_allcolsel_alias()
 ----
 (1,2)
 
+# Return an error after adding a column when the table is used as the return
+# type. Note that this behavior is ok for late binding.
 statement ok
 ALTER TABLE t_twocol ADD COLUMN c INT DEFAULT 5;
 
-# TODO(#95558): With early binding, postgres returns an error after adding a
-# column when the table is used as the return type. Note that this behavior is
-# ok for late binding.
-query T
+statement error pq: return type mismatch in function declared to return t_twocol
+SELECT f_unqualified_twocol()
+
+# Dropping the new column renders the function usable again.
+statement ok
+ALTER TABLE t_twocol DROP COLUMN c;
+
+statement ok
 SELECT f_unqualified_twocol()
-----
-(1,2)
 
 # Altering a column type is not allowed in postgres or CRDB.
 statement error pq: cannot alter type of column "b" because function "f_unqualified_twocol" depends on it

pkg/sql/opt/optbuilder/scalar.go

@@ -688,6 +688,22 @@ func (b *Builder) buildUDF(
 			// ConvertUDFToSubquery.
 			physProps.Ordering = props.OrderingChoice{}
 
+			// Validate that user defined return types match the original return types
+			// defined in the function.
+			rtyp := f.ResolvedType()
+			if rtyp.UserDefined() {
+				funcReturnType, err := tree.ResolveType(b.ctx,
+					&tree.OIDTypeReference{OID: rtyp.Oid()}, b.semaCtx.TypeResolver)
+				if err != nil {
+					panic(err)
+				}
+				if !funcReturnType.Equivalent(rtyp) {
+					panic(pgerror.Newf(
+						pgcode.InvalidFunctionDefinition,
+						"return type mismatch in function declared to return %s", rtyp.Name()))
+				}
+			}
+
 			// If there are multiple output columns, we must combine them into a
 			// tuple - only a single column can be returned from a UDF.
 			if cols := physProps.Presentation; len(cols) > 1 {