Custom CCACHE_DIR environment has no effect when running sandbox.sh

[Goodwu]

Let's have a look at add_ccache_mount() function in ${HOME}/.opam/opam-init/hooks/sandbox.sh

add_ccache_mount() {
  if command -v ccache > /dev/null; then
      CCACHE_DIR=$HOME/.ccache
      ccache_dir_regex='cache_dir = (.*)$'
      local IFS=$'\n'
      for f in $(ccache --print-config 2>/dev/null); do
        if [[ $f =~ $ccache_dir_regex ]]; then
          CCACHE_DIR=${BASH_REMATCH[1]}
        fi
      done
      add_mounts rw $CCACHE_DIR
  fi
}

$CCACHE_DIR is used by ccache to customize ccache directory, and it's overwritten here by

      CCACHE_DIR=$HOME/.ccache

and

          CCACHE_DIR=${BASH_REMATCH[1]}

So the environment variable I set before has no effect here.
The shell variable CCACHE_DIR should be renamed to avoid confliction.

[dra27]

The first setting looks like a "complete" bug - the ccache manual has clear details on how it finds ccache.conf and setting it here skips steps 1-3 of its algorithm.

The second setting should be guarded with local to stop any change to the variable leaking to the exec call.

While we're there, the dance with a for loop can be much more simply converted to:

  local CCACHE_DIR="$(ccache --print-config 2>/dev/null | sed -n -e 's/cache_dir = //p')"
  test -z "$CCACHE_DIR" || add_mounts rw "$CCACHE_DIR"

that should then have the desired effect that cache_dir is read-write in the sandbox!