feat: add support for nil in function calls (fixes #277)

lexer.go

@@ -18,6 +18,7 @@ const (
 	TokenString
 	TokenNumber
 	TokenSymbol
+	TokenNil
 )
 
 var (
@@ -96,6 +97,8 @@ func (t *Token) String() string {
 		typ = "String"
 	case TokenSymbol:
 		typ = "Symbol"
+	case TokenNil:
+		typ = "Nil"
 	default:
 		typ = "Unknown"
 	}
@@ -371,6 +374,10 @@ func (l *lexer) stateIdentifier() lexerStateFn {
 			l.emit(TokenKeyword)
 			return l.stateCode
 		}
+		if kw == "nil" {
+			l.emit(TokenNil)
+			return l.stateCode
+		}
 	}
 	l.emit(TokenIdentifier)
 	return l.stateCode

pongo2_template_test.go

@@ -188,6 +188,17 @@ Yep!`,
 			}
 			return pongo2.AsValue(s)
 		},
+		"func_ensure_nil": func(x any) bool {
+			return x == nil
+		},
+		"func_ensure_nil_variadic": func(args ...any) bool {
+			for _, i := range args {
+				if i != nil {
+					return false
+				}
+			}
+			return true
+		},
 	},
 	"complex": map[string]any{
 		"is_admin": isAdmin,
@@ -316,6 +327,17 @@ func TestTemplate_Functions(t *testing.T) {
 			errorMessage: "[Error (where: execution) in <string> | Line 1 Col 4 near 'testFunc'] the second return value is not an error",
 			wantErr:      true,
 		},
+		{
+			name:     "NilToNonNilParameter",
+			template: "{{ testFunc(nil) }}",
+			context: pongo2.Context{
+				"testFunc": func(i int) int {
+					return 1
+				},
+			},
+			errorMessage: "[Error (where: execution) in <string> | Line 1 Col 4 near 'testFunc'] function input argument 0 of 'testFunc' must be of type int or *pongo2.Value (not <nil>)",
+			wantErr:      true,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

pongo2_test.go

@@ -10,9 +10,7 @@ import (
 // Hook up gocheck into the "go test" runner.
 func Test(t *testing.T) { TestingT(t) }
 
-type TestSuite struct {
-	tpl *pongo2.Template
-}
+type TestSuite struct{}
 
 var (
 	_          = Suite(&TestSuite{})

template_tests/function_calls_wrapper.tpl

@@ -8,4 +8,9 @@
 {{ simple.func_variadic_sum_int(1, 19, 185) }}
 {{ simple.func_variadic_sum_int2() }}
 {{ simple.func_variadic_sum_int2(2) }}
-{{ simple.func_variadic_sum_int2(1, 7, 100) }}
+{{ simple.func_variadic_sum_int2(1, 7, 100) }}
+eqnil: {{ simple.func_ensure_nil(nil) }}
+neqnil: {{ simple.func_ensure_nil(1) }}
+v1: {{ simple.func_ensure_nil_variadic(nil) }}
+v2: {{ simple.func_ensure_nil_variadic() }}
+v3: {{ simple.func_ensure_nil_variadic(nil, 1, nil, "test") }}

template_tests/function_calls_wrapper.tpl.out

@@ -8,4 +8,9 @@ hello, john doe
 205
 0
 2
-108
+108
+eqnil: True
+neqnil: False
+v1: True
+v2: True
+v3: False

variable.go

@@ -11,6 +11,7 @@ const (
 	varTypeInt = iota
 	varTypeIdent
 	varTypeSubscript
+	varTypeNil
 )
 
 var (
@@ -23,6 +24,7 @@ type variablePart struct {
 	s         string
 	i         int
 	subscript IEvaluator
+	isNil     bool
 
 	isFunctionCall bool
 	callingArgs    []functionCallArgument // needed for a function call, represents all argument nodes (INode supports nested function calls)
@@ -419,14 +421,18 @@ func (vr *variableResolver) resolve(ctx *ExecutionContext) (*Value, error) {
 							return nil, fmt.Errorf("function input argument %d of '%s' must be of type %s or *pongo2.Value (not %T)",
 								idx, vr.String(), fnArg.String(), pv.Interface())
 						}
-						// Function's argument has another type, using the interface-value
-						parameters = append(parameters, reflect.ValueOf(pv.Interface()))
 					} else {
 						if fnArg != reflect.TypeOf(pv.Interface()) && fnArg.Kind() != reflect.Interface {
 							return nil, fmt.Errorf("function variadic input argument of '%s' must be of type %s or *pongo2.Value (not %T)",
 								vr.String(), fnArg.String(), pv.Interface())
 						}
-						// Function's argument has another type, using the interface-value
+					}
+
+					if pv.IsNil() {
+						// Workaround to present an interface nil as reflect.Value
+						var empty any = nil
+						parameters = append(parameters, reflect.ValueOf(&empty).Elem())
+					} else {
 						parameters = append(parameters, reflect.ValueOf(pv.Interface()))
 					}
 				} else {
@@ -623,6 +629,13 @@ variableLoop:
 					})
 					p.Consume() // consume: NUMBER
 					continue variableLoop
+				case TokenNil:
+					resolver.parts = append(resolver.parts, &variablePart{
+						typ:   varTypeNil,
+						isNil: true,
+					})
+					p.Consume() // consume: NIL
+					continue variableLoop
 				default:
 					return nil, p.Error("This token is not allowed within a variable name.", t2)
 				}