Add comments

ci/scripts/java_build.sh

@@ -75,6 +75,10 @@ fi
 # Use `2 * ncores` threads
 mvn="${mvn} -T 2C"
 
+# https://github.com/apache/arrow/issues/41429
+# TODO: We want to out-of-source build. This is a workaround. We copy
+# all needed files to the build directory from the source directory
+# and build in the build directory.
 mkdir -p ${build_dir}
 rm -rf ${build_dir}/format
 cp -aL ${arrow_dir}/format ${build_dir}/

ci/scripts/js_build.sh

@@ -25,6 +25,10 @@ build_dir=${2}
 
 : ${BUILD_DOCS_JS:=OFF}
 
+# https://github.com/apache/arrow/issues/41429
+# TODO: We want to out-of-source build. This is a workaround. We copy
+# all needed files to the build directory from the source directory
+# and build in the build directory.
 rm -rf ${build_dir}/js
 mkdir -p ${build_dir}
 cp -aL ${arrow_dir}/LICENSE.txt ${build_dir}/

ci/scripts/python_build.sh

@@ -78,6 +78,10 @@ export PYARROW_PARALLEL=${n_jobs}
 export CMAKE_PREFIX_PATH
 export LD_LIBRARY_PATH=${ARROW_HOME}/lib:${LD_LIBRARY_PATH}
 
+# https://github.com/apache/arrow/issues/41429
+# TODO: We want to out-of-source build. This is a workaround. We copy
+# all needed files to the build directory from the source directory
+# and build in the build directory.
 rm -rf ${python_build_dir}
 cp -aL ${source_dir} ${python_build_dir}
 pushd ${python_build_dir}
@@ -89,6 +93,9 @@ ${PYTHON:-python} -m pip install --no-deps --no-build-isolation -vv .
 popd
 
 if [ "${BUILD_DOCS_PYTHON}" == "ON" ]; then
+  # https://github.com/apache/arrow/issues/41429
+  # TODO: We want to out-of-source build. This is a workaround.
+  #
   # Copy docs/source because the "autosummary_generate = True"
   # configuration generates files to docs/source/python/generated/.
   rm -rf ${python_build_dir}/docs/source

ci/scripts/r_build.sh

@@ -24,6 +24,10 @@ build_dir=${2}
 
 : ${BUILD_DOCS_R:=OFF}
 
+# https://github.com/apache/arrow/issues/41429
+# TODO: We want to out-of-source build. This is a workaround. We copy
+# all needed files to the build directory from the source directory
+# and build in the build directory.
 rm -rf ${build_dir}/r
 cp -aL ${source_dir} ${build_dir}/r
 pushd ${build_dir}/r

docker-compose.yml

@@ -1779,6 +1779,8 @@ services:
         maven: ${MAVEN}
         node: ${NODE}
         base: ${REPO}:${ARCH}-debian-${DEBIAN}-python-3
+    # This is for Chromium used by Mermaid. Chromium uses namespace
+    # isolation for security by default.
     cap_add:
       - SYS_ADMIN
     environment: