dev-db/mongodb: fix build issue w/ clang 20

upstream patch is applied, otherwise the build w/ clang 20 fails with:

> src/mongo/bson/util/bsoncolumnbuilder.h:285:49: error: call to deleted constructor of 'const mongo::TrackingAllocator<void> &'

However, the build still fails with:

> /usr/bin/x86_64-pc-linux-gnu-ld.bfd: build/gentoo/mongo/db/storage/wiredtiger/wiredtiger_record_store.o: in function `mongo::WiredTigerRecordStore::getEarliestOplogTimestamp(mongo::OperationContext*)':
> /usr/lib/gcc/x86_64-pc-linux-gnu/14/include/g++-v14/bits/atomic_base.h:1002:(.text+0x7da9): undefined reference to `__atomic_compare_exchange'
> clang++: error: linker command failed with exit code 1 (use -v to see invocation)

The reason is that Timestamp is a composite type, which requires -latomic
when building with clang++ and libstdc++. Mongodb's SConstruct only
checks for some basic types ('int64_t', 'uint64_t', 'int32_t', 'uint32_t'),
so this case is not detected.

Test case below:

$ cat a.cc
#include <atomic>
struct Timestamp { unsigned int t, i; };
template<typename T> struct AtomicWord {
    std::atomic<T> v;
    T compareAndSwap(T e, T n) {
        v.compare_exchange_strong(e,n); return e;
    }
};
int main() {
    AtomicWord<Timestamp> x;
    Timestamp a{0,0}, b{1,1};
    x.compareAndSwap(a,b);
    return 0;
}

$ clang++ -stdlib=libstdc++ a.cc
/usr/bin/x86_64-pc-linux-gnu-ld.bfd: /tmp/a-1e3f91.o: in function `std::atomic<Timestamp>::compare_exchange_strong(Timestamp&, Timestamp, std::memory_order, std::memory_order)':
a.cc:(.text._ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_[_ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_]+0x222): undefined reference to `__atomic_compare_exchange'
/usr/bin/x86_64-pc-linux-gnu-ld.bfd: a.cc:(.text._ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_[_ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_]+0x28d): undefined reference to `__atomic_compare_exchange'
/usr/bin/x86_64-pc-linux-gnu-ld.bfd: a.cc:(.text._ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_[_ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_]+0x2f8): undefined reference to `__atomic_compare_exchange'
/usr/bin/x86_64-pc-linux-gnu-ld.bfd: a.cc:(.text._ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_[_ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_]+0x3c1): undefined reference to `__atomic_compare_exchange'
/usr/bin/x86_64-pc-linux-gnu-ld.bfd: a.cc:(.text._ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_[_ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_]+0x42c): undefined reference to `__atomic_compare_exchange'
/usr/bin/x86_64-pc-linux-gnu-ld.bfd: /tmp/a-1e3f91.o:a.cc:(.text._ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_[_ZNSt6atomicI9TimestampE23compare_exchange_strongERS0_S0_St12memory_orderS3_]+0x497): more undefined references to `__atomic_compare_exchange' follow
clang++: error: linker command failed with exit code 1 (use -v to see invocation)

Signed-off-by: Z. Liu <zhixu.liu@gmail.com>
Part-of: https://github.com/gentoo/gentoo/pull/43808
Closes: https://github.com/gentoo/gentoo/pull/43808
Signed-off-by: Sam James <sam@gentoo.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/dev-db/mongodb/files/mongodb-8.0.8-fix-compile-error-due-to-deleted-constructor.patch b/dev-db/mongodb/files/mongodb-8.0.8-fix-compile-error-due-to-deleted-constructor.patch
new file mode 100644
index 000000000000..017aeee15ee1
--- /dev/null
+++ b/dev-db/mongodb/files/mongodb-8.0.8-fix-compile-error-due-to-deleted-constructor.patch
@@ -0,0 +1,28 @@
+https://jira.mongodb.org/browse/SERVER-97048
+
+From ce43ef7147fabfa5b7f14a3040a0fc19b9228d9f Mon Sep 17 00:00:00 2001
+From: James Bronsted <32047428+jpbronsted@users.noreply.github.com>
+Date: Wed, 27 Nov 2024 17:59:39 -0500
+Subject: [PATCH] SERVER-97048 fix compile error on Clang 19 due to
+ BSONColumnBuilder default constructor (#29231)
+
+GitOrigin-RevId: 82d5ad449944292fe4cfdb7a27886439725d58de
+
+diff --git a/src/mongo/bson/util/bsoncolumnbuilder.h b/src/mongo/bson/util/bsoncolumnbuilder.h
+index d9cd20e07b7..b7d36fa1b28 100644
+--- a/src/mongo/bson/util/bsoncolumnbuilder.h
++++ b/src/mongo/bson/util/bsoncolumnbuilder.h
+@@ -282,7 +282,9 @@ struct EncodingState {
+ template <class Allocator = std::allocator<void>>
+ class BSONColumnBuilder {
+ public:
+-    explicit BSONColumnBuilder(const Allocator& = {});
++    template <typename A = Allocator>
++    BSONColumnBuilder() : BSONColumnBuilder{A{}} {}
++    explicit BSONColumnBuilder(const Allocator&);
+     explicit BSONColumnBuilder(allocator_aware::BufBuilder<Allocator>, const Allocator& = {});
+ 
+     /**
+-- 
+2.49.1
+