bash completion: fixed invalid identifier (spack#4079)

* bash completion: fixed `_spack_create-db-tarball': not a valid identifier

* bash completion: dashes are translated to underscores

This also fixes the name of the subfunction to be called, as apparently
it was not updated after moving the command `create-db-tarball`.

share/spack/spack-completion.bash

@@ -53,6 +53,9 @@ function _bash_completion_spack {
     # For example, `spack -d install []` will call _spack_install
     # and `spack compiler add []` will call _spack_compiler_add
     local subfunction=$(IFS='_'; echo "_${COMP_WORDS_NO_FLAGS[*]}")
+    # Translate dashes to underscores, as dashes are not permitted in
+    # compatibility mode. See https://github.com/LLNL/spack/pull/4079
+    subfunction=${subfunction//-/_}
 
     # However, the word containing the current cursor position needs to be
     # added regardless of whether or not it is a flag. This allows us to
@@ -288,7 +291,7 @@ function _spack_debug {
     fi
 }
 
-function _spack_create-db-tarball {
+function _spack_debug_create_db_tarball {
     compgen -W "-h --help" -- "$cur"
 }