Add bash completion sourcing, with cache

Recommendations came from this blog post:
    https://blog.gitbutler.com/how-git-core-devs-configure-git/

Let's see how this works out lol

Test

bash/.bashrc

@@ -133,6 +133,59 @@ if [ -f "$HOME/.private_functions" ] && [ -r "$HOME/.private_functions" ]; then
   . "$HOME/.private_functions"
 fi
 
+source_completions() {
+  # Source completions if they are available
+  completion_dirs=(
+    "/usr/share/bash-completion/completions"
+    "/etc/bash_completion.d"
+  )
+  cache_dir="${XDG_CACHE_HOME}/bash-completion-sourcing"
+
+  if [ "${BUILD_CACHE}" ]; then
+    mkdir -p "${cache_dir}"
+  fi
+
+  # Base completion sourcing, later completions will fail without this
+  if [ -r "/usr/share/bash-completion/bash_completion" ]; then
+    . "/usr/share/bash-completion/bash_completion"
+  elif [ -r "/etc/bash_completion" ]; then
+    . "/etc/bash_completion"
+  fi
+
+  # Completions from packages
+  export TIMEFORMAT="%R"
+  for completion_dir in "${completion_dirs[@]}"; do
+    if [ -d "${completion_dir}" ] && [ -r "${completion_dir}" ]; then
+      for completion_file in "${completion_dir}"/*; do
+        if [ "$BUILD_CACHE" ]; then
+          echo "Sourcing ${completion_file}"
+          . "${completion_file}"
+          timeavg=$(time (. "${completion_file}") 2>&1 1>/dev/null)
+          timeavg=$(echo $timeavg | cut -d '.' -f 2)
+          if [ "${timeavg}" -gt 100 ]; then
+            echo "This ones slow, adding to cache"
+            echo "${timeavg}" > "${cache_dir}/$(basename ${completion_file})"
+          elif [ "${timeavg}" -gt 10 ]; then
+            echo "This ones a little slow"
+            echo "${timeavg}"
+          fi
+        else
+          if ! [ -e "${cache_dir}/$(basename ${completion_file})" ]; then
+            . "${completion_file}"
+          else
+            :
+          fi
+        fi
+      done
+    fi
+  done
+  unset TIMEFORMAT
+}
+
+if [ "$BASH_COMPLETION_ENABLED" ]; then
+  source_completions
+fi
+
 # Preserve the usefulness of set -x by attempting to hide everything that
 # happens in prompt_command
 preserve_xtrace() {

install.sh

@@ -6,6 +6,7 @@ set -ex
 echo "PWD: $PWD"
 # Coder dotfiles (and most other ways of doing this) will not do a recursive clone, so do that in install script.
 git submodule init && git submodule update
+
 # Match case insensitively to make things easier for this part
 shopt -s nocasematch