bash_completion: small optimization

Right now we always call "hg help $cmd" to get the canonical name of $cmd
(i.e. to go from "co" to "update").

This patch optimistically assumes that $cmd is already the canonical form
and tries to generate completions for it.  If that fails, it falls back
to canonicalizing $cmd and trying again.

This means that:

- if a command or alias is explicitly handled by the
  _hg_command_specific function, things get somewhat faster

- as long as the canonical $cmd is handled by _hg_command_specific, all
  its aliases and abbreviations are also handled.

contrib/bash_completion

@@ -1,160 +1,189 b''
 shopt -s extglob
 
 _hg_commands()
 {
     local commands
     commands="$("$hg" debugcomplete "$cur" 2>/dev/null)" || commands=""
     COMPREPLY=(${COMPREPLY[@]:-} $(compgen -W '$commands' -- "$cur"))
 }
 
 _hg_paths()
 {
     local paths="$("$hg" paths 2>/dev/null | sed -e 's/ = .*$//')"
     COMPREPLY=(${COMPREPLY[@]:-} $(compgen -W '$paths' -- "$cur"))
 }
 
 _hg_repos()
 {
     local i
     for i in $(compgen -d -- "$cur"); do
 	test ! -d "$i"/.hg || COMPREPLY=(${COMPREPLY[@]:-} "$i")
     done
 }
 
 _hg_status()
 {
     local files="$("$hg" status -n$1 . 2>/dev/null)"
     COMPREPLY=(${COMPREPLY[@]:-} $(compgen -W '$files' -- "$cur"))
 }
 
 _hg_tags()
 {
     local tags="$("$hg" tags -q 2>/dev/null)"
     local IFS=$'\n'
     COMPREPLY=(${COMPREPLY[@]:-} $(compgen -W '$tags' -- "$cur"))
 }
 
 # this is "kind of" ugly...
 _hg_count_non_option()
 {
     local i count=0
     local filters="$1"
 
     for ((i=1; $i<=$COMP_CWORD; i++)); do
 	if [[ "${COMP_WORDS[i]}" != -* ]]; then
 	    if [[ ${COMP_WORDS[i-1]} == @($filters|$global_args) ]]; then
 		continue
 	    fi
 	    count=$(($count + 1))
 	fi
     done
 
     echo $(($count - 1))
 }
 
 _hg()
 {
     local cur prev cmd opts i
     # global options that receive an argument
     local global_args='--cwd|-R|--repository'
     local hg="$1"
 
     COMPREPLY=()
     cur="$2"
     prev="$3"
 
     # searching for the command
     # (first non-option argument that doesn't follow a global option that
     #  receives an argument)
     for ((i=1; $i<=$COMP_CWORD; i++)); do
 	if [[ ${COMP_WORDS[i]} != -* ]]; then
 	    if [[ ${COMP_WORDS[i-1]} != @($global_args) ]]; then
 		cmd="${COMP_WORDS[i]}"
 		break
 	    fi
 	fi
     done
 
     if [[ "$cur" == -* ]]; then
 	opts=$("$hg" debugcomplete --options "$cmd" 2>/dev/null)
 
 	COMPREPLY=(${COMPREPLY[@]:-} $(compgen -W '$opts' -- "$cur"))
 	return
     fi
 
     # global options
     case "$prev" in
 	-R|--repository)
 	    _hg_repos
 	    return
 	;;
 	--cwd)
 	    # Stick with default bash completion
 	    return
 	;;
     esac
 
     if [ -z "$cmd" ] || [ $COMP_CWORD -eq $i ]; then
 	_hg_commands
 	return
     fi
 
-    # canonicalize command name
-    cmd=$("$hg" -q help "$cmd" 2>/dev/null | sed -e 's/^hg //; s/ .*//; 1q')
+    # try to generate completion candidates for whatever command the user typed
+    local help
+    local canonical=0
+    if _hg_command_specific; then
+	return
+    fi
 
-    if [ "$cmd" != status ] && [ "$prev" = -r ] || [ "$prev" = --rev ]; then
-	_hg_tags
+    # canonicalize the command name and try again
+    help=$("$hg" help "$cmd" 2>/dev/null)
+    if [ $? -ne 0 ]; then
+	# Probably either the command doesn't exist or it's ambiguous
 	return
     fi
+    cmd=${help#hg }
+    cmd=${cmd%%[$' \n']*}
+    canonical=1
+    _hg_command_specific
+}
+
+_hg_command_specific()
+{
+    if [ "$cmd" != status ] && [ "$prev" = -r ] || [ "$prev" == --rev ]; then
+	if [ $canonical = 1 ]; then
+	    _hg_tags
+	    return 0
+	elif [[ status != "$cmd"* ]]; then
+	    _hg_tags
+	    return 0
+	else
+	    return 1
+	fi
+    fi
 
     case "$cmd" in
 	help)
 	    _hg_commands
 	;;
 	export|manifest|update)
 	    _hg_tags
 	;;
 	pull|push|outgoing|incoming)
 	    _hg_paths
 	    _hg_repos
 	;;
 	paths)
 	    _hg_paths
 	;;
 	add)
 	    _hg_status "u"
 	;;
 	commit)
 	    _hg_status "mar"
 	;;
 	remove)
 	    _hg_status "d"
 	;;
 	forget)
 	    _hg_status "a"
 	;;
 	diff)
 	    _hg_status "mar"
 	;;
 	revert)
 	    _hg_status "mard"
 	;;
 	clone)
 	    local count=$(_hg_count_non_option)
 	    if [ $count = 1 ]; then
 		_hg_paths
 	    fi
 	    _hg_repos
 	;;
 	debugindex|debugindexdot)
 	    COMPREPLY=(${COMPREPLY[@]:-} $(compgen -f -X "!*.i" -- "$cur"))
 	;;
 	debugdata)
 	    COMPREPLY=(${COMPREPLY[@]:-} $(compgen -f -X "!*.d" -- "$cur"))
 	;;
+	*)
+	    return 1
+	;;
     esac
 
+    return 0
 }
 
 complete -o bashdefault -o default -F _hg hg 2>/dev/null \
     || complete -o default -F _hg hg