sql: fix pg_proc virtual oid index

Previously, the pg_proc virtual oid index was broken for user-defined
functions.

Release note: None (no release with this bug)

pkg/sql/logictest/testdata/logic_test/udf

@@ -174,6 +174,13 @@ FROM pg_catalog.pg_proc WHERE proname IN ('proc_f', 'proc_f_2');
 100119  proc_f    105  1546506610  14  true   true   false  i  2  25  25 20  {i,i}  {"",b}  SELECT 'hello';
 100121  proc_f_2  120  1546506610  14  false  false  false  v  1  25  25     {i}    NULL    SELECT 'hello';
 
+# Ensure that the pg_proc virtual index works properly.
+
+query TT
+SELECT oid, proname FROM pg_proc WHERE oid = 'sc.proc_f_2'::regproc
+----
+100121  proc_f_2
+
 statement ok
 USE defaultdb;
 

pkg/sql/pg_catalog.go

@@ -2568,21 +2568,16 @@ https://www.postgresql.org/docs/9.5/catalog-pg-proc.html`,
 				coid := tree.MustBeDOid(unwrappedConstraint)
 				ooid := coid.Oid
 
-				name, overload, err := p.ResolveFunctionByOID(ctx, ooid)
-				if err != nil {
-					if errors.Is(err, tree.ErrFunctionUndefined) {
-						return false, nil //nolint:returnerrcheck
-					}
-					return false, err
-				}
-
 				if funcdesc.IsOIDUserDefinedFunc(ooid) {
-					fnDesc, err := p.Descriptors().ByID(p.Txn()).WithoutNonPublic().Get().Function(ctx, descpb.ID(overload.Oid))
+					fnDesc, err := p.Descriptors().ByID(p.Txn()).WithoutNonPublic().Get().Function(ctx, funcdesc.UserDefinedFunctionOIDToID(ooid))
 					if err != nil {
+						if errors.Is(err, tree.ErrFunctionUndefined) {
+							return false, nil //nolint:returnerrcheck
+						}
 						return false, err
 					}
 
-					scDesc, err := p.Descriptors().ByIDWithLeased(p.Txn()).WithoutNonPublic().Get().Schema(ctx, descpb.ID(ooid))
+					scDesc, err := p.Descriptors().ByIDWithLeased(p.Txn()).WithoutNonPublic().Get().Schema(ctx, fnDesc.GetParentSchemaID())
 					if err != nil {
 						return false, err
 					}
@@ -2597,7 +2592,15 @@ https://www.postgresql.org/docs/9.5/catalog-pg-proc.html`,
 					return true, nil
 
 				} else {
-					err := addPgProcBuiltinRow(tree.NewDOid(catconstants.PgCatalogID), name, addRow)
+					name, _, err := p.ResolveFunctionByOID(ctx, ooid)
+					if err != nil {
+						if errors.Is(err, tree.ErrFunctionUndefined) {
+							return false, nil //nolint:returnerrcheck
+						}
+						return false, err
+					}
+
+					err = addPgProcBuiltinRow(tree.NewDOid(catconstants.PgCatalogID), name, addRow)
 					if err != nil {
 						return false, err
 					}