fix(bash): Fix bash completion for suggestions that contain special characters.

Special characters include whitepace, so this is more general than
 #1743. This should also fix #1740.

I added some test cases to cobra-completion-testing. This PR makes them
pass. It also doesn't trip any of the performance regression tests. I'm
happy to submit those tests as a PR as well.
  - https://github.com/JeffFaer/cobra-completion-testing/tree/special_characters
  - 52254c1a25

Signed-off-by: Jeffrey Faer <jeffrey.faer@gmail.com>

bash_completionsV2.go

@@ -59,7 +59,10 @@ __%[1]s_get_completion_results() {
     # Prepare the command to request completions for the program.
     # Calling ${words[0]} instead of directly %[1]s allows handling aliases
     args=("${words[@]:1}")
-    requestComp="${words[0]} %[2]s ${args[*]}"
+    requestComp="${words[0]} %[2]s"
+    if [[ "${#args[@]}" -gt 0 ]]; then
+        requestComp+="$(printf " %%q" "${args[@]}")"
+    fi
 
     lastParam=${words[$((${#words[@]}-1))]}
     lastChar=${lastParam:$((${#lastParam}-1)):1}
@@ -224,15 +227,24 @@ __%[1]s_handle_completion_types() {
         # completions at once on the command-line we must remove the descriptions.
         # https://github.com/spf13/cobra/issues/1508
         local tab=$'\t' comp
-        while IFS='' read -r comp; do
+        local matches=()
+        for comp in "${completions[@]}"; do
             [[ -z $comp ]] && continue
             # Strip any description
             comp=${comp%%%%$tab*}
             # Only consider the completions that match
             if [[ $comp == "$cur"* ]]; then
-                COMPREPLY+=("$comp")
-            fi
-        done < <(printf "%%s\n" "${completions[@]}")
+                # Strictly speaking we could append directly to COMPREPLY here.
+                # But there's a pretty big performance hit involved with
+                # creating one subshell to printf %%q for each completion that
+                # matches. Instead, batch all the matches up so we can quote
+                # them all at once in a single printf call.
+                matches+=( "$comp" )
+           fi
+        done
+        while IFS='' read -r comp; do
+            COMPREPLY+=( "$comp" )
+        done < <(printf "%%q\n" "${matches[@]}")
         ;;
 
     *)
@@ -247,7 +259,12 @@ __%[1]s_handle_standard_completion_case() {
 
     # Short circuit to optimize if we don't have descriptions
     if [[ "${completions[*]}" != *$tab* ]]; then
-        IFS=$'\n' read -ra COMPREPLY -d '' < <(compgen -W "${completions[*]}" -- "$cur")
+        # compgen's -W option respects shell quoting, so we need to escape.
+        local compgen_words="$(printf "%%q\n" "${completions[@]}")"
+        # compgen appears to respect shell quoting _after_ checking whether
+        # they have the right prefix, so we also need to quote cur.
+        local compgen_cur="$(printf "%%q" "${cur}")"
+        IFS=$'\n' read -ra COMPREPLY -d '' < <(IFS=$'\n'; compgen -W "${compgen_words}" -- "${compgen_cur}")
         return 0
     fi
 
@@ -271,7 +288,7 @@ __%[1]s_handle_standard_completion_case() {
         __%[1]s_debug "COMPREPLY[0]: ${COMPREPLY[0]}"
         comp="${COMPREPLY[0]%%%%$tab*}"
         __%[1]s_debug "Removed description from single completion, which is now: ${comp}"
-        COMPREPLY[0]=$comp
+        COMPREPLY[0]="$(printf "%%q" "${comp}")"
     else # Format the descriptions
         __%[1]s_format_comp_descriptions $longest
     fi