Cache autotools configurations.

autocache

#!/bin/bash
if [ "$#" -lt 1 ]; then
  echo "Usage: $0 <mode> [configure-args...]"
  exit 1
fi
SCRIPT="$0"
case "$SCRIPT" in
  /*) DIR=$(dirname "$SCRIPT") ;;
  *) DIR=$(cd "$(dirname "$SCRIPT")" && pwd) ;;
esac
MODE="$1"
shift
CFG_HASH=$(md5sum ${DIR}/configure | cut -d' ' -f1)
RESTORE_SCRIPT="${DIR}/configure.${MODE}"
BEFORE=$(mktemp)
AFTER=$(mktemp)
CHANGED=$(mktemp)
find ${DIR}/ -type f -printf '%P\t%T@\n' | sort > "$BEFORE"
${DIR}/configure "$@"
find ${DIR}/ -type f -printf '%P\t%T@\n' | sort > "$AFTER"
comm -13 "$BEFORE" "$AFTER" | cut -f1 > "$CHANGED"
sort -u "$CHANGED" -o "$CHANGED"
if [ ! -s "$CHANGED" ]; then
  echo "No files changed by ./configure"
  rm -f "$BEFORE" "$AFTER" "$CHANGED"
  exit 0
fi
[ -f "$RESTORE_SCRIPT" ] && rm -f "$RESTORE_SCRIPT"
{
  echo '#!/bin/sh'
  echo "CFG_HASH='${CFG_HASH}'"
  cat <<'EOF'
SCRIPT="$0"
case "$SCRIPT" in
  /*) DIR=$(dirname "$SCRIPT") ;;
  *) DIR=$(cd "$(dirname "$SCRIPT")" && pwd) ;;
esac
HASH=$(md5sum "$DIR/configure" | cut -d' ' -f1)
if [ "$HASH" != "$CFG_HASH" ]; then
  echo "Warning: configure script has changed, aborting restore."
  exit 1
fi
EOF
} > "$RESTORE_SCRIPT"
shar -VQx $(cat "$CHANGED") >> "$RESTORE_SCRIPT" 2>/dev/null
TMPSED=$(mktemp)
sed 's/then ${echo} "x - removed lock directory ${lock_dir}."/then :/g' "$RESTORE_SCRIPT" > "$TMPSED"
mv "$TMPSED" "$RESTORE_SCRIPT"
chmod +x "$RESTORE_SCRIPT"
rm "$BEFORE" "$AFTER" "$CHANGED"

Usage instructions:

Instead of:

% # Slow (7s):
% ./configure "CXX=clang" "CXXFLAGS=-mavx -Ofast -fno-rtti -flto -fvisibility=hidden" \
            "CC=clang" "CFLAGS=-mavx -Ofast -fno-rtti -flto -fvisibility=hidden"

consider doing

% # Slow (8s):
% ./autocache release-linux "CXX=clang" "CXXFLAGS=-mavx -Ofast -fno-rtti -flto -fvisibility=hidden" \
            "CC=clang" "CFLAGS=-mavx -Ofast -fno-rtti -flto -fvisibility=hidden"
% # Fast (0.5s):
% ./configure.release-linux