ARROW-12619: [Python] pyarrow sdist should not require git

There is a fallback_version configuration option for setuptools_scm which we don't use: https://github.com/pypa/setuptools_scm#configuration-parameters

Although this setting seems to have issues according to pypa/setuptools_scm#549
We already have a workaround in setup.py for the functionality of the fallback_version option, but it is disabled for the case of sdist: https://github.com/apache/arrow/blob/master/python/setup.py#L529

Closes #10342 from kszucs/ARROW-12619

Authored-by: Krisztián Szűcs <szucs.krisztian@gmail.com>
Signed-off-by: Krisztián Szűcs <szucs.krisztian@gmail.com>

ci/scripts/python_sdist_test.sh

@@ -42,10 +42,16 @@ export PYARROW_WITH_DATASET=${ARROW_DATASET:-OFF}
 # unset ARROW_HOME
 # apt purge -y pkg-config
 
+# ARROW-12619
+if command -v git &> /dev/null; then
+  echo "Git exists, remove it from PATH before executing this script."
+  exit 1
+fi
+
 if [ -n "${PYARROW_VERSION:-}" ]; then
   sdist="${arrow_dir}/python/dist/pyarrow-${PYARROW_VERSION}.tar.gz"
 else
-  sdist=$(ls "${arrow_dir}/python/dist/pyarrow-*.tar.gz" | sort -r | head -n1)
+  sdist=$(ls ${arrow_dir}/python/dist/pyarrow-*.tar.gz | sort -r | head -n1)
 fi
 ${PYTHON:-python} -m pip install ${sdist}
 

docker-compose.yml

@@ -712,6 +712,7 @@ services:
     volumes: *ubuntu-volumes
     command: >
       /bin/bash -c "
+        apt remove -y git &&
         /arrow/ci/scripts/cpp_build.sh /arrow /build &&
         /arrow/ci/scripts/python_sdist_test.sh /arrow"
 

python/setup.py

@@ -522,12 +522,8 @@ def _move_shared_libs_unix(build_prefix, build_lib, lib_name):
 default_version = '4.0.0'
 if (not os.path.exists('../.git') and
         not os.environ.get('SETUPTOOLS_SCM_PRETEND_VERSION')):
-    if os.path.exists('PKG-INFO'):
-        # We're probably in a Python sdist, setuptools_scm will handle fine
-        pass
-    else:
-        os.environ['SETUPTOOLS_SCM_PRETEND_VERSION'] = \
-            default_version.replace('-SNAPSHOT', 'a0')
+    os.environ['SETUPTOOLS_SCM_PRETEND_VERSION'] = \
+        default_version.replace('-SNAPSHOT', 'a0')
 
 
 # See https://github.com/pypa/setuptools_scm#configuration-parameters