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GODRIVER-3574 Align BSON interface slice decoding with json package. #2075

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Merged
merged 6 commits into from
Jun 4, 2025
Merged

GODRIVER-3574 Align BSON interface slice decoding with json package. #2075

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3551518
Align BSON interface slice decoding with json package.
qingyang-hu May 29, 2025
b57049b
Merge branch 'master' into godriver3574
qingyang-hu Jun 3, 2025
841cd96
add tests
qingyang-hu Jun 3, 2025
779d6b0
fix tests
qingyang-hu Jun 3, 2025
0bb71be
update comments
qingyang-hu Jun 4, 2025
033957f
fix typo
qingyang-hu Jun 4, 2025
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3 changes: 3 additions & 0 deletions bson/bsoncodec.go
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,9 @@ func (vde ValueDecoderError) Error() string {
if vde.Received.IsValid() {
received = vde.Received.Type().String()
}
if !vde.Received.CanSet() {
received = "unsettable " + received
}
return fmt.Sprintf("%s can only decode valid and settable %s, but got %s", vde.Name, strings.Join(typeKinds, ", "), received)
}

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23 changes: 23 additions & 0 deletions bson/decoder_test.go
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Expand Up @@ -172,6 +172,29 @@ func TestDecodingInterfaces(t *testing.T) {
assert.Equal(t, testStruct{[3]interface{}{&str, &i, nil}}, receiver)
}

return data, &receiver, check
},
},
{
name: "struct with interface slice containing concrete values",
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@prestonvasquez prestonvasquez Jun 4, 2025

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Could we rename this to "overwriting prepopulated slice?"

stub: func() ([]byte, interface{}, func(*testing.T)) {
type testStruct struct {
Values []interface{}
}

data := docToBytes(struct {
Values []interface{}
}{
Values: []interface{}{1, 2, 3},
})

receiver := testStruct{[]interface{}{7, 8}}

check := func(t *testing.T) {
t.Helper()
assert.Equal(t, testStruct{[]interface{}{1, 2, int32(3)}}, receiver)
}

return data, &receiver, check
},
},
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11 changes: 10 additions & 1 deletion bson/default_value_decoders.go
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Expand Up @@ -1351,14 +1351,17 @@ func decodeDefault(dc DecodeContext, vr ValueReader, val reflect.Value) ([]refle
}

var elem reflect.Value
if vDecoder == nil {
if vDecoder == nil && idx < val.Len() {
elem = val.Index(idx).Elem()
switch {
case elem.Kind() != reflect.Ptr || elem.IsNil():
valueDecoder, err := dc.LookupDecoder(elem.Type())
if err != nil {
return nil, err
}
if !elem.CanSet() {
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@prestonvasquez prestonvasquez Jun 4, 2025

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This change is really nuanced. Can we add a comment here noting why we do this? "If an element is unsettable and allocated, it must be overwritten."

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@prestonvasquez prestonvasquez Jun 4, 2025

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I also suggest making the following changes to make this more readable:

isInterfaceSlice := eType.Kind() == reflect.Interface && val.Len() > 0

// If this is not an interface slice with pre-populated elements, we can look
// up the decoder for eType once.
var vDecoder ValueDecoder
if !isInterfaceSlice {
	vDecoder, err = dc.LookupDecoder(eType)
	if err != nil {
		return nil, err
	}
}

for {
	// ...
	if isInterfaceSlice && idx < val.Len() {
		// Decode into an existing interface{} slot.
		
		// ...
	} else {
		// For non-interface slices, or if we've exhuasted the pre-populated
		// slots, we create a fresh value.
		if vDecoder == nil {
			// ...
		}

		//...
	}
}

elem = reflect.New(elem.Type()).Elem()
}
err = valueDecoder.DecodeValue(dc, vr, elem)
if err != nil {
return nil, newDecodeError(strconv.Itoa(idx), err)
Expand All @@ -1380,6 +1383,12 @@ func decodeDefault(dc DecodeContext, vr ValueReader, val reflect.Value) ([]refle
}
}
} else {
if vDecoder == nil {
vDecoder, err = dc.LookupDecoder(eType)
if err != nil {
return nil, err
}
}
elem, err = decodeTypeOrValueWithInfo(vDecoder, dc, vr, eType)
if err != nil {
return nil, newDecodeError(strconv.Itoa(idx), err)
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