sql: enable support for udfs calling other udfs

Previously, we blocked the ability of one UDF to call another UDF due to
a lack of dependency tracking. This patch removes this limitation by
allowing user-defined functions to reference other user-defined functions
in their bodies.

Informs: cockroachdb#88198
Release note: None

pkg/sql/logictest/testdata/logic_test/procedure

@@ -118,7 +118,7 @@ CREATE OR REPLACE PROCEDURE p2() LANGUAGE SQL AS $$
   CALL p();
 $$
 
-statement error pgcode 42883 unknown function: p\(\)
+statement error pgcode 42809 p\(\) is a procedure
 CREATE FUNCTION err(i INT) RETURNS VOID LANGUAGE SQL AS 'SELECT p()'
 
 statement error pgcode 0A000 unimplemented: CALL usage inside a function definition

pkg/sql/logictest/testdata/logic_test/udf_oid_ref

@@ -97,17 +97,16 @@ CREATE FUNCTION f_in_udf() RETURNS INT LANGUAGE SQL AS $$ SELECT 1 $$;
 let $fn_oid
 SELECT oid FROM pg_catalog.pg_proc WHERE proname = 'f_in_udf'
 
-# TODO(chengxiong,mgartner): Fix this test when we enable support of calling UDFs from UDFs.
-statement error pgcode 42883 pq: function \d+ not found
+statement ok
 CREATE FUNCTION f_using_udf() RETURNS INT LANGUAGE SQL AS $$ SELECT [FUNCTION $fn_oid]() $$;
 
 # 814 is the OID of builtin function "length" with signature, and it's ok to
 # call it from a UDF.
 statement ok
-CREATE FUNCTION f_using_udf() RETURNS INT LANGUAGE SQL AS $$ SELECT [FUNCTION 814]('abc') $$;
+CREATE FUNCTION f_using_udf_2() RETURNS INT LANGUAGE SQL AS $$ SELECT [FUNCTION 814]('abc') $$;
 
 query I
-SELECT f_using_udf();
+SELECT f_using_udf_2();
 ----
 3
 

pkg/sql/logictest/testdata/logic_test/udf_unsupported

@@ -41,11 +41,11 @@ subtest disallow_udf_in_views_and_udf
 statement ok
 CREATE FUNCTION test_vf_f() RETURNS STRING LANGUAGE SQL AS $$ SELECT lower('hello') $$;
 
-statement error pgcode 42883 pq: unknown function: test_vf_f\(\)\nHINT:.*intention was to use a user-defined function in the function body, which is currently not supported.
+statement ok
 CREATE FUNCTION test_vf_g() RETURNS STRING LANGUAGE SQL AS $$ SELECT test_vf_f() $$;
 
 statement ok
-CREATE FUNCTION test_vf_g() RETURNS STRING LANGUAGE SQL AS $$ SELECT lower('hello') $$;
+CREATE FUNCTION test_vf_g_2() RETURNS STRING LANGUAGE SQL AS $$ SELECT lower('hello') $$;
 
 statement error pgcode 42883 pq: unknown function: test_vf_f\(\)\nHINT:.*intention was to use a user-defined function in the view query, which is currently not supported.
 CREATE VIEW v AS SELECT test_vf_f();
@@ -139,7 +139,7 @@ CREATE FUNCTION rec(i INT) RETURNS INT LANGUAGE SQL AS 'SELECT CASE i WHEN 0 THE
 statement ok
 CREATE FUNCTION other_udf() RETURNS INT LANGUAGE SQL AS 'SELECT 1'
 
-statement error pgcode 42883 unknown function: other_udf()
+statement ok
 CREATE FUNCTION err() RETURNS INT LANGUAGE SQL AS 'SELECT other_udf()'
 
 subtest end

pkg/sql/opt/optbuilder/create_function.go

@@ -50,11 +50,6 @@ func (b *Builder) buildCreateFunction(cf *tree.CreateRoutine, inScope *scope) (o
 	schID := b.factory.Metadata().AddSchema(sch)
 	cf.Name.ObjectNamePrefix = resName
 
-	// TODO(#88198): this is a hack to disallow UDF usage in UDF and we will
-	// need to lift this hack when we plan to allow it.
-	preFuncResolver := b.semaCtx.FunctionResolver
-	b.semaCtx.FunctionResolver = nil
-
 	b.insideFuncDef = true
 	b.trackSchemaDeps = true
 	// Make sure datasource names are qualified.
@@ -70,7 +65,6 @@ func (b *Builder) buildCreateFunction(cf *tree.CreateRoutine, inScope *scope) (o
 		b.evalCtx.Annotations = oldEvalCtxAnn
 		b.semaCtx.Annotations = oldSemaCtxAnn
 
-		b.semaCtx.FunctionResolver = preFuncResolver
 		switch recErr := recover().(type) {
 		case nil:
 			// No error.