Snapshot of make-requirements-if-needed.sh

make-requirements-if-needed.sh

#!/usr/bin/env bash
# Run `make requirements` if virtualenv or requirements dir has changed since
# last run.

set -eu -o pipefail

if [[ -z "${VIRTUAL_ENV:-}" ]]; then
    echo >&2 "Not in a virtualenv"
    exit 1
fi

if [[ ! -d "requirements" ]]; then
    echo >&2 "./requirements/ missing from current dir"
    exit 1
fi

# Bare filename to write at root of virtualenv.
hashfile_name="deps-venv.chk"
# Actual path
hashfile_path="$VIRTUAL_ENV/$hashfile_name"

function fingerprint_data_venv() {
    # The virtualenv is large, so do a fingerprint that is fast. And
    # it isn't directly affected by git checkouts, so we don't have to
    # worry about spurious file modification time changes. Therefore,
    # use file metadata rather than contents.
    #
    # For fingerprinting of these we include paths (sorted) with full
    # metadata.
    find "$VIRTUAL_ENV" -printf '%P %t %s %i %m %U %G\n' \
        | grep -vP "^\\Q${hashfile_name}\\E " \
        | sort
}

function fingerprint_data_reqs() {
    # The requirements files are small, so we can use contents-based
    # fingerprinting. These files also have their metadata changed by
    # git branch switching, and we don't want the fingerprint to
    # change just because we've switched branches and then switched
    # back again. That's a reason to avoid using the metadata, even
    # though it might be a little faster.
    #
    # All we need for fingerprinting are the file paths (in order)
    # along with a hash of each file's contents.
    find "./requirements/" -type f | sort | xargs -r sha256sum 2>/dev/null
}

function compute_fingerprint() {
    # Combine the two fingerprint data sources and hash it all together
    (fingerprint_data_venv && fingerprint_data_reqs) \
        | sha256sum | head -c64
}

do_run=yes
if [[ -f "${hashfile_path}" ]]; then
    prev_hash="$(cat -- "${hashfile_path}")"
    cur_hash="$(compute_fingerprint)"
    if [[ "$prev_hash" == "$cur_hash" ]]; then
        echo >&2 "Dependency hashes match, skipping 'make requirements'"
        do_run=no
    else
        echo >&2 "Dependency hashes do not match; running 'make requirements'"
        echo >&2 "(prev=$prev_hash, cur=$cur_hash)"
    fi
else
    echo >&2 "Dependency hash file not found"
fi

if [[ "$do_run" == 'yes' ]]; then
    make requirements
fi

compute_fingerprint > "${hashfile_path}"