Introduce filter in Fixed/Variable sized Array types

runtime/interpreter/value.go

@@ -2443,6 +2443,28 @@
 				)
 			},
 		)
+
+	case sema.ArrayTypeFilterFunctionName:
+		return NewHostFunctionValue(
+			interpreter,
+			sema.ArrayFilterFunctionType(
+				v.SemaType(interpreter).ElementType(false),
+			),
+			func(invocation Invocation) Value {
+				interpreter := invocation.Interpreter
+
+				funcArgument, ok := invocation.Arguments[0].(FunctionValue)
+				if !ok {
+					panic(errors.NewUnreachableError())
+				}
+
+				return v.Filter(
+					interpreter,
+					invocation.LocationRange,
+					funcArgument,
+				)
+			},
+		)
 	}
 
 	return nil
@@ -2946,6 +2968,81 @@
 	)
 }
 
+func (v *ArrayValue) Filter(
+	interpreter *Interpreter,
+	locationRange LocationRange,
+	procedure FunctionValue,
+) Value {
+	filteredValues := make([]Value, 0)
+	filteredValuesCount := 0
+	i := 0
+
+	iterationInvocation := func(arrayElement Value) Invocation {
+		return NewInvocation(
+			interpreter,
+			nil,
+			nil,
+			[]Value{arrayElement},
+			[]sema.Type{sema.BoolType},
+			nil,
+			locationRange,
+		)
+	}
+
+	iterate := func() {
+		err := v.array.Iterate(
+			func(item atree.Value) (bool, error) {
+				arrayElement := MustConvertStoredValue(interpreter, item)
+
+				shouldInclude, ok := procedure.invoke(iterationInvocation(arrayElement)).(BoolValue)
+				if !ok {
+					panic(errors.NewUnreachableError())
+				}
+
+				if shouldInclude {
+					filteredValues = append(filteredValues, arrayElement)
+					filteredValuesCount++
+				}
+
+				i++
+				return true, nil
+			},
+		)
+
+		if err != nil {
+			panic(errors.NewExternalError(err))
+		}
+	}
+
+	iterate()
+
+	iterationIndex := 0
+	return NewArrayValueWithIterator(
+		interpreter,
+		NewVariableSizedStaticType(interpreter, v.Type.ElementType()),
+		common.ZeroAddress,
+		uint64(filteredValuesCount),
+		func() Value {
+
+			if iterationIndex == filteredValuesCount {
+				return nil
+			}
+
+			value := filteredValues[iterationIndex]
+			iterationIndex++
+
+			return value.Transfer(
+				interpreter,
+				locationRange,
+				atree.Address{},
+				false,
+				nil,
+				nil,
+			)
+		},
+	)
+}
+
 // NumberValue
 type NumberValue interface {
 	ComparableValue

runtime/sema/type.go

@@ -1795,6 +1795,13 @@ Returns a new array with contents in the reversed order.
 Available if the array element type is not resource-kinded.
 `
 
+const ArrayTypeFilterFunctionName = "filter"
+
+const arrayTypeFilterFunctionDocString = `
+Returns a new array whose elements are filtered by applying the filter function on each element of the original array.
+Available if the array element type is not resource-kinded.
+`
+
 func getArrayMembers(arrayType ArrayType) map[string]MemberResolver {
 
 	members := map[string]MemberResolver{
@@ -1913,6 +1920,31 @@ func getArrayMembers(arrayType ArrayType) map[string]MemberResolver {
 				)
 			},
 		},
+		ArrayTypeFilterFunctionName: {
+			Kind: common.DeclarationKindFunction,
+			Resolve: func(memoryGauge common.MemoryGauge, identifier string, targetRange ast.Range, report func(error)) *Member {
+
+				elementType := arrayType.ElementType(false)
+
+				if elementType.IsResourceType() {
+					report(
+						&InvalidResourceArrayMemberError{
+							Name:            identifier,
+							DeclarationKind: common.DeclarationKindFunction,
+							Range:           targetRange,
+						},
+					)
+				}
+
+				return NewPublicFunctionMember(
+					memoryGauge,
+					arrayType,
+					identifier,
+					ArrayFilterFunctionType(elementType),
+					arrayTypeFilterFunctionDocString,
+				)
+			},
+		},
 	}
 
 	// TODO: maybe still return members but report a helpful error?
@@ -2232,6 +2264,33 @@ func ArrayReverseFunctionType(arrayType ArrayType) *FunctionType {
 	}
 }
 
+func ArrayFilterFunctionType(elementType Type) *FunctionType {
+	// fun filter(_ function: ((T): Bool)): [T]
+	// funcType: elementType -> Bool
+	funcType := &FunctionType{
+		Parameters: []Parameter{
+			{
+				Identifier:     "element",
+				TypeAnnotation: NewTypeAnnotation(elementType),
+			},
+		},
+		ReturnTypeAnnotation: NewTypeAnnotation(BoolType),
+	}
+
+	return &FunctionType{
+		Parameters: []Parameter{
+			{
+				Label:          ArgumentLabelNotRequired,
+				Identifier:     "f",
+				TypeAnnotation: NewTypeAnnotation(funcType),
+			},
+		},
+		ReturnTypeAnnotation: NewTypeAnnotation(&VariableSizedType{
+			Type: elementType,
+		}),
+	}
+}
+
 // VariableSizedType is a variable sized array type
 type VariableSizedType struct {
 	Type                Type

runtime/tests/checker/arrays_dictionaries_test.go

@@ -1128,6 +1128,103 @@ func TestCheckResourceArrayReverseInvalid(t *testing.T) {
 	assert.IsType(t, &sema.InvalidResourceArrayMemberError{}, errs[0])
 }
 
+func TestCheckArrayFilter(t *testing.T) {
+
+	t.Parallel()
+
+	_, err := ParseAndCheck(t, `
+		fun test() {
+			let x = [1, 2, 3]
+			let onlyEven =
+				fun (_ x: Int): Bool {
+					return x % 2 == 0
+				}
+
+			let y = x.filter(onlyEven)
+		}
+
+		fun testFixedSize() {
+			let x : [Int; 5] = [1, 2, 3, 21, 30]
+			let onlyEvenInt =
+				fun (_ x: Int): Bool {
+					return x % 2 == 0
+				}
+
+			let y = x.filter(onlyEvenInt)
+		}
+    `)
+
+	require.NoError(t, err)
+}
+
+func TestCheckArrayFilterInvalidArgs(t *testing.T) {
+
+	t.Parallel()
+
+	testInvalidArgs := func(code string, expectedErrors []sema.SemanticError) {
+		_, err := ParseAndCheck(t, code)
+
+		errs := RequireCheckerErrors(t, err, len(expectedErrors))
+
+		for i, e := range expectedErrors {
+			assert.IsType(t, e, errs[i])
+		}
+	}
+
+	testInvalidArgs(`
+		fun test() {
+			let x = [1, 2, 3]
+			let y = x.filter(100)
+		}
+	`,
+		[]sema.SemanticError{
+			&sema.TypeMismatchError{},
+		},
+	)
+
+	testInvalidArgs(`
+		fun test() {
+			let x = [1, 2, 3]
+			let onlyEvenInt16 =
+				fun (_ x: Int16): Bool {
+					return x % 2 == 0
+				}
+
+			let y = x.filter(onlyEvenInt16)
+		}
+	`,
+		[]sema.SemanticError{
+			&sema.TypeMismatchError{},
+		},
+	)
+}
+
+func TestCheckResourceArrayFilterInvalid(t *testing.T) {
+
+	t.Parallel()
+
+	_, err := ParseAndCheck(t, `
+		resource X {}
+
+		fun test(): @[X] {
+			let xs <- [<-create X()]
+			let allResources =
+				fun (_ x: @X): Bool {
+					destroy x
+					return true
+				}
+
+			let filteredXs <-xs.filter(allResources)
+			destroy xs
+			return <- filteredXs
+		}
+    `)
+
+	errs := RequireCheckerErrors(t, err, 1)
+
+	assert.IsType(t, &sema.InvalidResourceArrayMemberError{}, errs[0])
+}
+
 func TestCheckArrayContains(t *testing.T) {
 
 	t.Parallel()