sql: avoid internal error when type-checking routine in edge case

We just saw a sentry issue where `tree.Overload.Types` was `nil`. This
is unexpected, and it resulted in a interface conversion panic during
type-checking because we assumed that this field is castable to
`tree.ParamTypes`. This usage was introduced in 92240f8
and is now fixed in this commit.

I've audited the code and couldn't find a way for us to produce such
a routine, so there is no reproduction test case added. I did add
a defensive mechanism to ensure that all builtin overloads (i.e.
non-user-defined) have non-nil `Types` set. This commit also removes an
unused (but somewhat related) method from the catalog.

Release note: None

Author: yuzefovich

pkg/sql/catalog/funcdesc/func_desc.go

@@ -608,11 +608,6 @@ func (desc *Mutable) SetDeclarativeSchemaChangerState(state *scpb.DescriptorStat
 	desc.DeclarativeSchemaChangerState = state
 }
 
-// AddParams adds function parameters to the parameter list.
-func (desc *Mutable) AddParams(params ...descpb.FunctionDescriptor_Parameter) {
-	desc.Params = append(desc.Params, params...)
-}
-
 // SetVolatility sets the volatility attribute.
 func (desc *Mutable) SetVolatility(v catpb.Function_Volatility) {
 	desc.Volatility = v

pkg/sql/sem/builtins/builtinsregistry/builtins_registry.go

@@ -26,6 +26,11 @@ func Register(name string, props *tree.FunctionProperties, overloads []tree.Over
 	if _, exists := registry[name]; exists {
 		panic("duplicate builtin: " + name)
 	}
+	for _, overload := range overloads {
+		if overload.Types == nil || overload.Types == tree.TypeList(nil) {
+			panic("nil Types field for builtin: " + name)
+		}
+	}
 	registry[name] = definition{
 		props:     props,
 		overloads: overloads,

pkg/sql/sem/tree/overload.go

@@ -17,6 +17,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/volatility"
 	"github.com/cockroachdb/cockroach/pkg/sql/types"
+	"github.com/cockroachdb/cockroach/pkg/util/buildutil"
 	"github.com/cockroachdb/cockroach/pkg/util/intsets"
 	"github.com/cockroachdb/errors"
 	"github.com/cockroachdb/redact"
@@ -1108,7 +1109,19 @@ func (s *overloadTypeChecker) typeCheckOverloadedExprs(
 			// Don't filter builtin routines.
 			return true
 		}
-		params := ol.Types.(ParamTypes)
+		params, ok := ol.Types.(ParamTypes)
+		if !ok {
+			if buildutil.CrdbTestBuild {
+				// All user-defined routines are expected to have non-nil
+				// ParamTypes set.
+				panic(errors.AssertionFailedf(
+					"found user-defined routine with non-ParamTypes Types field, %v", ol,
+				))
+			}
+			// Don't filter overloads that have nil ParamTypes or have variadic
+			// or homogeneous types.
+			return true
+		}
 		var outParams ParamTypes
 		if ol.Type == ProcedureRoutine && foundOutParams {
 			outParams = ol.OutParamTypes.(ParamTypes)