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Disallowed 0 byte structs.

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This is because they are incompatible with C++ and possibly other
languages that make them minimum size 1 (to make sure multiple
such objects don't reside at the same address). Forcing them to size
1 was also not practical, as that is requires updating the logic
of a lot of implementations and thus possibly backwards incompatible.

More here: https://github.com/google/flatbuffers/issues/4122

Change-Id: I2bfdc8597b7cfd2235bb4074bb2ae06f81f8e57d
This commit is contained in:
Wouter van Oortmerssen
2018-10-29 17:40:19 -07:00
parent 705577de51
commit 160e8f2fdc
8 changed files with 19 additions and 14 deletions
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25
src/idl_parser.cpp
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@@ -1778,21 +1778,24 @@ CheckedError Parser::ParseDecl() {
EXPECT('{');
while (token_ != '}') ECHECK(ParseField(*struct_def));
auto force_align = struct_def->attributes.Lookup("force_align");
if (fixed && force_align) {
auto align = static_cast<size_t>(atoi(force_align->constant.c_str()));
if (force_align->type.base_type != BASE_TYPE_INT ||
align < struct_def->minalign || align > FLATBUFFERS_MAX_ALIGNMENT ||
align & (align - 1))
return Error(
"force_align must be a power of two integer ranging from the"
"struct\'s natural alignment to " +
NumToString(FLATBUFFERS_MAX_ALIGNMENT));
struct_def->minalign = align;
if (fixed) {
if (force_align) {
auto align = static_cast<size_t>(atoi(force_align->constant.c_str()));
if (force_align->type.base_type != BASE_TYPE_INT ||
align < struct_def->minalign || align > FLATBUFFERS_MAX_ALIGNMENT ||
align & (align - 1))
return Error(
"force_align must be a power of two integer ranging from the"
"struct\'s natural alignment to " +
NumToString(FLATBUFFERS_MAX_ALIGNMENT));
struct_def->minalign = align;
}
if (!struct_def->bytesize) return Error("size 0 structs not allowed");
}
struct_def->PadLastField(struct_def->minalign);
// Check if this is a table that has manual id assignments
auto &fields = struct_def->fields.vec;
if (!struct_def->fixed && fields.size()) {
if (!fixed && fields.size()) {
size_t num_id_fields = 0;
for (auto it = fields.begin(); it != fields.end(); ++it) {
if ((*it)->attributes.Lookup("id")) num_id_fields++;