perf(bash-v2): standard completion optimizations (#1683)

Refactor to remove two loops over the entire list of candidates.

Format descriptions only for completions that are actually going to be
displayed, instead of for all candidates.

Format descriptions inline in completions array, removing need for a
command substitution/subshell and a printf escape per displayed
completion.

bash_completionsV2.go

@@ -177,40 +177,28 @@ __%[1]s_handle_standard_completion_case() {
     local tab=$'\t' comp
 
     local longest=0
+    local compline
     # Look for the longest completion so that we can format things nicely
-    while IFS='' read -r comp; do
+    while IFS='' read -r compline; do
         # Strip any description before checking the length
-        comp=${comp%%%%$tab*}
+        comp=${compline%%%%$tab*}
         # Only consider the completions that match
         comp=$(compgen -W "$comp" -- "$cur")
+        [[ -z $comp ]] && continue
+        COMPREPLY+=("$compline")
         if ((${#comp}>longest)); then
             longest=${#comp}
         fi
     done < <(printf "%%s\n" "${out}")
 
-    local completions=()
-    while IFS='' read -r comp; do
-        if [ -z "$comp" ]; then
-            continue
-        fi
-
-        __%[1]s_debug "Original comp: $comp"
-        comp="$(__%[1]s_format_comp_descriptions "$comp" "$longest")"
-        __%[1]s_debug "Final comp: $comp"
-        completions+=("$comp")
-    done < <(printf "%%s\n" "${out}")
-
-    while IFS='' read -r comp; do
-        COMPREPLY+=("$comp")
-    done < <(compgen -W "${completions[*]}" -- "$cur")
-
     # If there is a single completion left, remove the description text
     if [ ${#COMPREPLY[*]} -eq 1 ]; then
         __%[1]s_debug "COMPREPLY[0]: ${COMPREPLY[0]}"
-        comp="${COMPREPLY[0]%%%% *}"
+        comp="${COMPREPLY[0]%%%%$tab*}"
         __%[1]s_debug "Removed description from single completion, which is now: ${comp}"
-        COMPREPLY=()
-        COMPREPLY+=("$comp")
+        COMPREPLY[0]=$comp
+    else # Format the descriptions
+        __%[1]s_format_comp_descriptions $longest
     fi
 }
 
@@ -230,11 +218,15 @@ __%[1]s_handle_special_char()
 __%[1]s_format_comp_descriptions()
 {
     local tab=$'\t'
-    local comp="$1"
-    local longest=$2
+    local comp desc maxdesclength
+    local longest=$1
 
+    local i ci
+    for ci in ${!COMPREPLY[*]}; do
+        comp=${COMPREPLY[ci]}
         # Properly format the description string which follows a tab character if there is one
         if [[ "$comp" == *$tab* ]]; then
+            __%[1]s_debug "Original comp: $comp"
             desc=${comp#*$tab}
             comp=${comp%%%%$tab*}
 
@@ -263,10 +255,10 @@ __%[1]s_format_comp_descriptions()
                 fi
                 comp+="  ($desc)"
             fi
+            COMPREPLY[ci]=$comp
+            __%[1]s_debug "Final comp: $comp"
         fi
-
-    # Must use printf to escape all special characters
-    printf "%%q" "${comp}"
+    done
 }
 
 __start_%[1]s()