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[io] read checksum for zero-version foreign class #19507

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[io] read checksum for zero-version foreign class #19507

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67c85a0
[io] read checksum for zero-version foreign class
ferdymercury Aug 2, 2025
3ee5d77
[test] add test for foreign zero-version class
ferdymercury Aug 2, 2025
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11 changes: 7 additions & 4 deletions io/io/src/TBufferFile.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -2963,9 +2963,12 @@ Version_t TBufferFile::ReadVersion(UInt_t *startpos, UInt_t *bcnt, const TClass
if (version<=1) {
if (version <= 0) {
if (cl) {
if (cl->GetClassVersion() != 0
auto clversion = cl->GetClassVersion();
if ((clversion != 0
// If v.cnt < 6 then we have a class with a version that used to be zero and so there is no checksum.
&& (v.cnt && v.cnt >= 6)
&& (v.cnt && v.cnt >= 6)) ||
// ::WriteVersion for a foreign class (no ClassDef) but defining Class_Version() { return 0; } does write checksum.
(clversion == 0 && version == 0 && cl->IsForeign())
) {
UInt_t checksum = 0;
//*this >> checksum;
Expand All @@ -2975,11 +2978,11 @@ Version_t TBufferFile::ReadVersion(UInt_t *startpos, UInt_t *bcnt, const TClass
return vinfo->TStreamerInfo::GetClassVersion(); // Try to get inlining.
} else {
// There are some cases (for example when the buffer was stored outside of
// a ROOT file) where we do not have a TStreamerInfo. If the checksum is
// a ROOT file) where we do not have a TStreamerInfo. If the checksum is
// the one from the current class, we can still assume that we can read
// the data so let use it.
if (checksum==cl->GetCheckSum() || cl->MatchLegacyCheckSum(checksum)) {
version = cl->GetClassVersion();
version = clversion;
} else {
if (fParent) {
Error("ReadVersion", "Could not find the StreamerInfo with a checksum of 0x%x for the class \"%s\" in %s.",
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21 changes: 21 additions & 0 deletions io/io/test/TBufferFileTests.cxx
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Original file line number Diff line number Diff line change
@@ -1,7 +1,9 @@
#include "gtest/gtest.h"

#include "TBufferFile.h"
#include "TMemFile.h"
#include "TClass.h"
#include "TInterpreter.h"
#include <vector>
#include <iostream>

Expand All @@ -26,3 +28,22 @@ TEST(TBufferFile, ROOT_8367)
EXPECT_FLOAT_EQ(v2[6], 7.);
EXPECT_EQ(v2.size(), 7);
}

// https://github.com/root-project/root/issues/19371
#define MYSTRUCT0 struct MyS0 { static constexpr short Class_Version() { return 0; } };
#define MYSTRUCT1 struct MyS1 { static constexpr short Class_Version() { return 1; } };
MYSTRUCT0
MYSTRUCT1
#define TO_LITERAL(string) _QUOTE_(string)
TEST(TBufferFile, ForeignZeroVersionClass)
{
gInterpreter->Declare(TO_LITERAL(MYSTRUCT0));
gInterpreter->Declare(TO_LITERAL(MYSTRUCT1));
MyS0 s0;
MyS1 s1;
TMemFile f("mem19371.root", "RECREATE");
f.WriteObject(&s0, "s0");
f.WriteObject(&s1, "s1");
EXPECT_NE(f.Get<MyS0>("s0"), nullptr); // Before the fix, even if return was already not nullptr, this line was raising an Error thus test would fail with unexpected diagnostic
EXPECT_NE(f.Get<MyS1>("s1"), nullptr);
}
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