Mongodb v6.0.16 boost error when building from source with scons: run_it<FutureExecutorContinuationSharedState>' has no member named 'that'

I'm trying to build an older version of Mongod on Arch Linux. It's required by software called Deadline that I intend to use; Deadline's documentation says the following: "For maximum compatibility with Deadline, we recommend you use MongoDB version 5.0.0 through 6.0.16."

I followed Mongodb's build instructions (here) and tried to build v6.0.16 as well as v.6.0.15 and in both cases I have ended up with this specific error:

Compiling build/59f4f0dd/third_party/icu4c-57.1/source/common/unormcmp.o In file included from src/third_party/boost/libs/thread/src/pthread/thread.cpp:19: src/third_party/boost/boost/thread/future.hpp: In member function 'boost::detail::run_it<FutureExecutorContinuationSharedState>& boost::detail::run_it<FutureExecutorContinuationSharedState>:operator=(boost::detail::run_it<FutureExecutorContinuationSharedState>&&)': src/third_party/boost/boost/thread/future.hpp:4672:19: error: 'struct boost::detail::run_it<FutureExecutorContinuationSharedState>' has no member named 'that'; did you mean 'that_'? [-Wtemplate-body] 4672 | that_=x.that; | ^~~~ | that_

I have tried building it with gcc15, gcc12 and gcc8, with no success.

Here's my latest PKGBUILD that I use to do this. It demonstrates my exact steps:

pkgname=mongod
pkgver=6.0.15
pkgrel=1
pkgdesc="MongoDB Database Server (mongod) built from source"
arch=('x86_64')
url="https://www.mongodb.com"
license=('SSPL')
depends=()
makedepends=('python37' 'gcc' 'curl' 'xz')
source=("https://github.com/mongodb/mongo/archive/refs/tags/r${pkgver}.tar.gz"
        "fix-ctype-include.patch")
sha256sums=('2e5ed9326182b9c1cfa8e85e0e67f35f840fd6e2390e88198a185e822eb29275'
            'c994338420b3302c27af5ee59836cb66787c45f1ad72bf41dad32ab35c437165')  

prepare() {
    cd "$srcdir/mongo-r${pkgver}" 
    patch -p0 < "$srcdir/../fix-ctype-include.patch"
}

build() {
    cd "$srcdir/mongo-r${pkgver}"

    python3.7 -m venv venv
    source venv/bin/activate
    python3.7 -m pip install --upgrade pip setuptools wheel
    python3.7 -m pip install -r etc/pip/compile-requirements.txt
    
    local jobs=$(echo $MAKEFLAGS | grep -oP '(?<=-j)\d+' || echo $(( $(nproc) / 2 )))
    
    python3.7 buildscripts/scons.py install-mongod \
        --disable-warnings-as-errors \
        -j${jobs} \
        MONGO_VERSION=${pkgver} \
        LINKFLAGS="-static-libstdc++ -static-libgcc"
    deactivate
}

package() {
    cd "$srcdir/mongo-r${pkgver}"
    install -Dm755 build/install/bin/mongod "$pkgdir/usr/bin/mongod"
}

How can I get past this error?

Solution: there is a typo in a boost file, specifically here in src/third_party/boost/boost/thread/future.hpp line 4672:

that_=x.that; needs to be changed to that_=x.that_;