diff --git a/bash_completion b/bash_completion
index 12172ab3a29..9d745ba8d10 100644
--- a/bash_completion
+++ b/bash_completion
@@ -439,6 +439,7 @@ _comp_split()
 # @var[in] $?
 # @var[in] _var
 # @var[in] _append
+# @var[in] _upvars
 # @return original $?
 _comp_compgen__error_fallback()
 {
@@ -449,6 +450,10 @@ _comp_compgen__error_fallback()
     else
         eval -- "$_var=()"
     fi
+    if ((${#_upvars[@]})); then
+        _comp_unlocal "${_upvars[@]}"
+        _upvars=()
+    fi
     return "$_status"
 }
 
@@ -478,6 +483,13 @@ _comp_compgen__error_fallback()
 #           is ${cur-}.
 #   -R      The same as -c ''.  Use raw outputs without filtering.
 #   -C dir  Evaluate compgen/generator in the specified directory.
+#   -P pref Prepend the prefix to the generated completions.  Unlike `compgen
+#           -P prefix`, this prefix is subject to filtering by `cur`.  When a
+#           non-empty prefix is specified, first `cur` is tested whether it is
+#           consistent with the prefix.  Then, `cur` is reduced for the part
+#           excluding the prefix, and the normal completion generation is
+#           performed.  Finally, the prefix is prepended to generated
+#           completions.
 # @var[in,opt] cur  Used as the default value of a prefix to filter the
 #   completions.
 #
@@ -562,6 +574,7 @@ _comp_compgen()
     local _var=
     local _cur=${_comp_compgen__cur-${cur-}}
     local _dir=""
+    local _prefix=""
     local _ifs=$' \t\n' _has_ifs=""
     local _icmd="" _xcmd=""
     local -a _upvars=()
@@ -572,7 +585,7 @@ _comp_compgen()
         shopt -u nocasematch
     fi
     local OPTIND=1 OPTARG="" OPTERR=0 _opt
-    while getopts ':av:U:Rc:C:lF:i:x:' _opt "$@"; do
+    while getopts ':av:U:Rc:C:P:lF:i:x:' _opt "$@"; do
         case $_opt in
             a) _append=set ;;
             v)
@@ -601,6 +614,7 @@ _comp_compgen()
                 fi
                 _dir=$OPTARG
                 ;;
+            P) _prefix=$OPTARG ;;
             l) _has_ifs=set _ifs=$'\n' ;;
             F) _has_ifs=set _ifs=$OPTARG ;;
             [ix])
@@ -636,6 +650,19 @@ _comp_compgen()
         [[ $_append ]] || _append=${_comp_compgen__append-}
     fi
 
+    local _prefix_fail=""
+    if [[ $_prefix ]]; then
+        if [[ $_cur == "$_prefix"* ]]; then
+            _cur=${_cur#"$_prefix"}
+        elif [[ $_prefix == "$_cur"* ]]; then
+            _cur=""
+        else
+            # No completions are generated because the current word does not match
+            # the prefix.
+            _prefix_fail=set
+        fi
+    fi
+
     if [[ $1 != -* ]]; then
         # usage: _comp_compgen [options] NAME args
         if [[ $_has_ifs ]]; then
@@ -657,6 +684,11 @@ _comp_compgen()
         fi
         shift
 
+        if [[ $_prefix_fail ]]; then
+            _comp_compgen__error_fallback
+            return 1
+        fi
+
         _comp_compgen__call_generator "$@"
     else
         # usage: _comp_compgen [options] -- [compgen_options]
@@ -680,6 +712,11 @@ _comp_compgen()
             return 2
         fi
 
+        if [[ $_prefix_fail ]]; then
+            _comp_compgen__error_fallback
+            return 1
+        fi
+
         _comp_compgen__call_builtin "$@"
     fi
 }
@@ -694,8 +731,6 @@ _comp_compgen()
 # @var[in] _var
 _comp_compgen__call_generator()
 {
-    ((${#_upvars[@]})) && _comp_unlocal "${_upvars[@]}"
-
     if [[ $_dir ]]; then
         local _original_pwd=$PWD
         local PWD=${PWD-} OLDPWD=${OLDPWD-}
@@ -708,14 +743,28 @@ _comp_compgen__call_generator()
             }
     fi
 
+    ((${#_upvars[@]})) && _comp_unlocal "${_upvars[@]}"
+
     local _comp_compgen__append=$_append
     local _comp_compgen__var=$_var
     local _comp_compgen__cur=$_cur cur=$_cur
+    if [[ $_prefix ]]; then
+        local -a tmp=()
+        local _comp_compgen__var=tmp
+        local _comp_compgen__append=""
+    fi
     # Note: we use $1 as a part of a function name, and we use $2... as
     # arguments to the function if any.
     # shellcheck disable=SC2145
     "${_generator[@]}" "$@"
     local _status=$?
+    if [[ $_prefix ]]; then
+        local _i
+        for _i in "${!tmp[@]}"; do
+            tmp[_i]=$_prefix${tmp[_i]}
+        done
+        _comp_compgen -RU tmp ${_append:+-a} -v "$_var" -- -W '"${tmp[@]}"'
+    fi
 
     # Go back to the original directory.
     # Note: Failure of this line results in the change of the current
@@ -770,6 +819,13 @@ if ((BASH_VERSINFO[0] > 5 || BASH_VERSINFO[0] == 5 && BASH_VERSINFO[1] >= 3)); t
 
         ((${#_upvars[@]})) && _comp_unlocal "${_upvars[@]}"
         ((${#_result[@]})) || return
+
+        if [[ $_prefix ]]; then
+            local _i
+            for _i in "${!_result[@]}"; do
+                _result[_i]=$_prefix${_result[_i]}
+            done
+        fi
         if [[ $_append ]]; then
             eval -- "$_var+=(\"\${_result[@]}\")"
         else
@@ -794,7 +850,13 @@ else
         }
 
         ((${#_upvars[@]})) && _comp_unlocal "${_upvars[@]}"
-        _comp_split -l ${_append:+-a} "$_var" "$_result"
+
+        if [[ $_prefix ]]; then
+            _comp_split -l ${_append:+-a} "$_var" \
+                "$(IFS=$'\n' compgen -W '$_result' -P "$_prefix")"
+        else
+            _comp_split -l ${_append:+-a} "$_var" "$_result"
+        fi
     }
 fi
 
@@ -1852,7 +1914,7 @@ _comp_compgen_tilde()
 {
     if [[ ${cur-} == \~* && $cur != */* ]]; then
         # Try generate ~username completions
-        if _comp_compgen -c "${cur#\~}" -- -P '~' -u; then
+        if _comp_compgen -P '~' -- -u; then
             # 2>/dev/null for direct invocation, e.g. in the
             # _comp_compgen_tilde unit test
             compopt -o filenames 2>/dev/null
diff --git a/completions/7z b/completions/7z
index 027f84be652..7333ba605e7 100644
--- a/completions/7z
+++ b/completions/7z
@@ -15,20 +15,17 @@ _comp_cmd_7z()
 
     case $cur in
         -ao*)
-            _comp_compgen -c "${cur:3}" -- -P"${cur:0:3}" -W 'a s t u'
+            _comp_compgen -P "-ao" -- -W 'a s t u'
             return
             ;;
         -?(a)[ix]*)
-            local opt
-            if [[ $cur == -a[ix]* ]]; then
-                opt=${cur:0:3} cur=${cur:3}
-            else
-                opt=${cur:0:2} cur=${cur:2}
-            fi
             if [[ $cur != *[@\!]* ]]; then
-                _comp_compgen -- -P"$opt" -W '@ ! r@ r-@ r0@ r! r-! r0!'
-            elif [[ $cur == ?(r@(-|0|))@* ]]; then
-                _comp_compgen -c "${cur#*@}" -- -P"${opt}${cur%%@*}@" -f
+                [[ $cur =~ ^-a?[ix] ]]
+                local prefix=${BASH_REMATCH-}
+                _comp_compgen -P "$prefix" -- -W '@ ! r@ r-@ r0@ r! r-! r0!'
+            elif [[ $cur =~ ^-a?[ix](r|r-|r0)?@ ]]; then
+                local prefix=${BASH_REMATCH-}
+                _comp_compgen -P "$prefix" -- -f
                 compopt -o filenames
             fi
             return
@@ -43,31 +40,30 @@ _comp_cmd_7z()
             ;;
         -o* | -w?*)
             compopt -o filenames
-            _comp_compgen -c "${cur:2}" -- -d -P"${cur:0:2}" -S/
+            _comp_compgen -P "${cur:0:2}" -- -d -S/
             compopt -o nospace
             return
             ;;
         -r?*)
-            _comp_compgen -c "${cur:2}" -- -P"${cur:0:2}" -W '- 0'
+            _comp_compgen -P "-r" -- -W '- 0'
             return
             ;;
         -scs*)
-            _comp_compgen -c "${cur:4}" -- -P"${cur:0:4}" -W 'UTF-8 WIN DOS'
+            _comp_compgen -P "-scs" -- -W 'UTF-8 WIN DOS'
             return
             ;;
         -ssc?*)
-            _comp_compgen -c "${cur:4}" -- -P"${cur:0:4}" -W '-'
+            _comp_compgen -P "-ssc" -- -W '-'
             return
             ;;
         -t*)
             if [[ $mode == w ]]; then
-                _comp_compgen -c "${cur:2}" -- -P"${cur:0:2}" -W '7z bzip2 gzip
-                    swfc tar wim xz zip'
+                _comp_compgen -P "-t" -- -W '7z bzip2 gzip swfc tar wim xz zip'
             else
-                _comp_compgen -c "${cur:2}" -- -P"${cur:0:2}" -W '7z apm arj
-                    bzip2 cab chm cpio cramfs deb dmg elf fat flv gzip hfs iso
-                    lzh lzma lzma86 macho mbr mslz mub nsis ntfs pe ppmd rar
-                    rpm squashfs swf swfc tar udf vhd wim xar xz z zip'
+                _comp_compgen -P "-t" -- -W '7z apm arj bzip2 cab chm cpio
+                    cramfs deb dmg elf fat flv gzip hfs iso lzh lzma lzma86
+                    macho mbr mslz mub nsis ntfs pe ppmd rar rpm squashfs swf
+                    swfc tar udf vhd wim xar xz z zip'
             fi
             return
             ;;
diff --git a/completions/_mount b/completions/_mount
index ab385f11288..23ef20515b1 100644
--- a/completions/_mount
+++ b/completions/_mount
@@ -44,7 +44,7 @@ _comp_cmd_mount()
         host=${cur#//}
         host=${host%%/*}
         if [[ $host ]]; then
-            _comp_compgen -c "${cur#//"$host"}" split -P "//$host" -- "$(
+            _comp_compgen -P "//$host" split -- "$(
                 smbclient -d 0 -NL "$host" 2>/dev/null |
                     command sed -ne '/^[[:blank:]]*Sharename/,/^$/p' |
                     command sed -ne '3,$s|^[^A-Za-z]*\([^[:blank:]]*\).*$|/\1|p'
diff --git a/completions/_mount.linux b/completions/_mount.linux
index 3d4c30794b4..4ad2ae23401 100644
--- a/completions/_mount.linux
+++ b/completions/_mount.linux
@@ -8,24 +8,18 @@ _comp_cmd_mount()
     local cur prev words cword comp_args
     _comp_initialize -n =: -- "$@" || return
 
-    local split=""
     case "$prev" in
         -t | --types)
             # find /lib/modules/$(uname -r)/ -type f -path '*/fs/*.ko' -printf '%f\n' | cut -d. -f1
             # FIXME: no<fstype>
-            if [[ $cur == ?*,* ]]; then
-                prev="${cur%,*}"
-                cur="${cur##*,}"
-                split=set
-            fi
-            _comp_compgen -- -W 'auto adfs affs autofs btrfs cifs coda cramfs
-                davfs debugfs devpts efs ext2 ext3 ext4 fuse hfs hfsplus hpfs
-                iso9660 jffs2 jfs minix msdos ncpfs nfs nfs4 ntfs ntfs-3g proc
-                qnx4 ramfs reiserfs romfs squashfs smbfs sysv tmpfs ubifs udf
-                ufs umsdos usbfs vfat xfs'
-            _comp_compgen -a fstypes
-            [[ $split ]] && ((${#COMPREPLY[@]})) &&
-                _comp_compgen -Rv COMPREPLY -- -P "$prev," -W '"${COMPREPLY[@]}"'
+            [[ $cur =~ ^.+, ]]
+            local prefix=${BASH_REMATCH-}
+            _comp_compgen -P "$prefix" -- -W 'auto adfs affs autofs btrfs cifs
+                coda cramfs davfs debugfs devpts efs ext2 ext3 ext4 fuse hfs
+                hfsplus hpfs iso9660 jffs2 jfs minix msdos ncpfs nfs nfs4 ntfs
+                ntfs-3g proc qnx4 ramfs reiserfs romfs squashfs smbfs sysv
+                tmpfs ubifs udf ufs umsdos usbfs vfat xfs'
+            _comp_compgen -aP "$prefix" fstypes
             return
             ;;
         --bind | -B | --rbind | -R)
@@ -66,61 +60,58 @@ _comp_cmd_mount()
             # no<fstype> is not a real fstype, reset to "auto"
             [[ $fstype == no?* ]] && fstype=auto
             # split options list
-            if [[ $cur == ?*,* ]]; then
-                prev="${cur%,*}"
-                cur="${cur##*,}"
-                split=set
-            fi
+            [[ $cur =~ ^.+, ]]
+            local prefix=${BASH_REMATCH-}
             # no completion if $cur is opt=smth
-            [[ $cur == *=* ]] && return
+            [[ ${cur##*,} == *=* ]] && return
             # mount options
-            _comp_compgen -- -W 'loop {,a}sync {,no}atime {,no}auto
-                {,fs,def,root}context= defaults {,no}dev {,no}diratime dirsync
-                {,no}exec group {,no}iversion {,no}mand _netdev nofail
-                {,no}relatime {,no}strictatime {,no}suid owner remount ro rw
-                {,no}user users'
+            _comp_compgen -P "$prefix" -- -W 'loop {,a}sync {,no}atime
+                {,no}auto {,fs,def,root}context= defaults {,no}dev
+                {,no}diratime dirsync {,no}exec group {,no}iversion {,no}mand
+                _netdev nofail {,no}relatime {,no}strictatime {,no}suid owner
+                remount ro rw {,no}user users'
             case "$fstype" in
                 adfs | auto)
-                    _comp_compgen -a -- -W '{u,g}id= {own,oth}mask='
+                    _comp_compgen -aP "$prefix" -- -W '{u,g}id= {own,oth}mask='
                     ;;&
                 affs | auto)
-                    _comp_compgen -a -- -W '{u,g}id= set{u,g}id= mode= protect
-                        usemp verbose prefix= volume= reserved= root= bs=
-                        {,no,usr,grp}quota'
+                    _comp_compgen -aP "$prefix" -- -W '{u,g}id= set{u,g}id=
+                        mode= protect usemp verbose prefix= volume= reserved=
+                        root= bs= {,no,usr,grp}quota'
                     ;;&
                 btrfs | auto)
-                    _comp_compgen -a -- -W 'degraded subvol= subvolid= device=
-                        nodatasum nodatacow nobarrier max_inline= alloc_start=
-                        thread_pool= compress= compress-force= ssd noacl
-                        notreelog flushoncommit metadata_ratio=
-                        {,no}space_cache clear_cache user_subvol_rm_allowed
-                        autodefrag inode_cache'
+                    _comp_compgen -aP "$prefix" -- -W 'degraded subvol=
+                        subvolid= device= nodatasum nodatacow nobarrier
+                        max_inline= alloc_start= thread_pool= compress=
+                        compress-force= ssd noacl notreelog flushoncommit
+                        metadata_ratio= {,no}space_cache clear_cache
+                        user_subvol_rm_allowed autodefrag inode_cache'
                     ;;&
                 cifs | auto)
-                    _comp_compgen -a -- -W 'user= password= credentials=
-                        {u,g}id= force{u,g}id port= servern= netbiosname=
-                        {file,dir}_mode= ip= domain= guest iocharset
-                        {,no}setuids {,no,dyn}perm directio {,no}mapchars
-                        {,no}intr hard soft noacl nocase sec= nobrl sfu
-                        {,no}serverino nounix nouser_xattr {r,w}size=
+                    _comp_compgen -aP "$prefix" -- -W 'user= password=
+                        credentials= {u,g}id= force{u,g}id port= servern=
+                        netbiosname= {file,dir}_mode= ip= domain= guest
+                        iocharset {,no}setuids {,no,dyn}perm directio
+                        {,no}mapchars {,no}intr hard soft noacl nocase sec=
+                        nobrl sfu {,no}serverino nounix nouser_xattr {r,w}size=
                         rwpidforward backup{u,g}id cache='
                     ;;&
                 davfs | auto)
-                    _comp_compgen -a -- -W 'conf= {file,dir}_mode= {u,g}id=
-                        username='
+                    _comp_compgen -aP "$prefix" -- -W 'conf= {file,dir}_mode=
+                        {u,g}id= username='
                     ;;&
                 ext[2-4] | auto)
-                    _comp_compgen -a -- -W '{,no}acl bsddf minixdf check= debug
-                        errors= {,no}grpid {bsd,sysv}groups {,no,usr,grp}quota
-                        nobh nouid32 oldalloc orlov res{u,g}id= sb=
-                        {,no}user_xattr'
+                    _comp_compgen -aP "$prefix" -- -W '{,no}acl bsddf minixdf
+                        check= debug errors= {,no}grpid {bsd,sysv}groups
+                        {,no,usr,grp}quota nobh nouid32 oldalloc orlov
+                        res{u,g}id= sb= {,no}user_xattr'
                     ;;&
                 ext[34] | auto)
-                    _comp_compgen -a -- -W 'journal= journal_dev= norecovery
-                        noload data= barrier= commit='
+                    _comp_compgen -aP "$prefix" -- -W 'journal= journal_dev=
+                        norecovery noload data= barrier= commit='
                     ;;&
                 ext4 | auto)
-                    _comp_compgen -a -- -W 'journal_checksum
+                    _comp_compgen -aP "$prefix" -- -W 'journal_checksum
                         journal_async_commit nobarrier inode_readahead= stripe=
                         {,no}delalloc abort {max,min}_batch_time=
                         journal_ioprio= {,no}auto_da_alloc {,no}discard nouid32
@@ -128,83 +119,87 @@ _comp_cmd_mount()
                         max_dir_size_kb= i_version'
                     ;;&
                 msdos | umsdos | vfat | auto)
-                    _comp_compgen -a -- -W 'blocksize= {u,g}id= {u,d,f}mask=
-                        allow_utime= check= codepage= conv= cvf_format=
-                        cvf_option= debug fat= iocharset= tz= quiet showexec
-                        sys_immutable flush usefree {,no}dots dotsOK='
+                    _comp_compgen -aP "$prefix" -- -W 'blocksize= {u,g}id=
+                        {u,d,f}mask= allow_utime= check= codepage= conv=
+                        cvf_format= cvf_option= debug fat= iocharset= tz= quiet
+                        showexec sys_immutable flush usefree {,no}dots dotsOK='
                     ;;&
                 vfat | auto)
-                    _comp_compgen -a -- -W 'uni_xlate posix nonumtail utf8
-                        shortname='
+                    _comp_compgen -aP "$prefix" -- -W 'uni_xlate posix
+                        nonumtail utf8 shortname='
                     ;;&
                 iso9660 | auto)
-                    _comp_compgen -a -- -W 'norock nojoliet check= {u,g}id=
-                        map= mode= unhide block= conv= cruft session= sbsector=
-                        iocharset= utf8'
+                    _comp_compgen -aP "$prefix" -- -W 'norock nojoliet check=
+                        {u,g}id= map= mode= unhide block= conv= cruft session=
+                        sbsector= iocharset= utf8'
                     ;;&
                 jffs2 | auto)
-                    _comp_compgen -a -- -W 'compr= rp_size='
+                    _comp_compgen -aP "$prefix" -- -W 'compr= rp_size='
                     ;;&
                 jfs | auto)
-                    _comp_compgen -a -- -W 'iocharset= resize= {,no}integrity
-                        errors= {,no,usr,grp}quota'
+                    _comp_compgen -aP "$prefix" -- -W 'iocharset= resize=
+                        {,no}integrity errors= {,no,usr,grp}quota'
                     ;;&
                 nfs | nfs4 | auto)
-                    _comp_compgen -a -- -W 'soft hard timeo= retrans= {r,w}size=
-                        {,no}ac acreg{min,max}= acdir{min,max}= actimeo= bg fg
-                        retry= sec= {,no}sharecache {,no}resvport lookupcache=
-                        proto= port= {,no}intr {,no}cto {,nfs}vers='
+                    _comp_compgen -aP "$prefix" -- -W 'soft hard timeo=
+                        retrans= {r,w}size= {,no}ac acreg{min,max}=
+                        acdir{min,max}= actimeo= bg fg retry= sec=
+                        {,no}sharecache {,no}resvport lookupcache= proto= port=
+                        {,no}intr {,no}cto {,nfs}vers='
                     ;;&
                 nfs | auto)
-                    _comp_compgen -a -- -W 'udp tcp rdma mount{port,proto,host}=
-                        mountvers= namlen={,no}lock {,no}acl {,no}rdirplus
-                        {,no}fsc'
+                    _comp_compgen -aP "$prefix" -- -W 'udp tcp rdma
+                        mount{port,proto,host}= mountvers= namlen={,no}lock
+                        {,no}acl {,no}rdirplus {,no}fsc'
                     ;;&
                 nfs4 | auto)
-                    _comp_compgen -a -- -W 'clientaddr= {,no}migration'
+                    _comp_compgen -aP "$prefix" -- -W 'clientaddr=
+                        {,no}migration'
                     ;;&
                 ntfs-3g)
-                    _comp_compgen -a -- -W '{u,g}id= {u,f,d}mask= usermapping=
-                        permissions inherit locale= force {,no}recover
-                        ignore_case remove_hiberfile show_sys_files
-                        hide_{hid,dot}_files windows_names allow_other
-                        max_read= silent no_def_opts streams_interface=
-                        user_xattr efs_raw {,no}compression debug no_detach'
+                    _comp_compgen -aP "$prefix" -- -W '{u,g}id= {u,f,d}mask=
+                        usermapping= permissions inherit locale= force
+                        {,no}recover ignore_case remove_hiberfile
+                        show_sys_files hide_{hid,dot}_files windows_names
+                        allow_other max_read= silent no_def_opts
+                        streams_interface= user_xattr efs_raw {,no}compression
+                        debug no_detach'
                     ;;&
                 proc | auto)
-                    _comp_compgen -a -- -W '{u,g}id='
+                    _comp_compgen -aP "$prefix" -- -W '{u,g}id='
                     ;;&
                 reiserfs | auto)
-                    _comp_compgen -a -- -W 'conv hash=
+                    _comp_compgen -aP "$prefix" -- -W 'conv hash=
                         {,no_un}hashed_relocation noborder nolog notail
                         replayonly resize= user_xattr acl barrier='
                     ;;&
                 tmpfs | auto)
-                    _comp_compgen -a -- -W 'size= nr_blocks= nr_inodes= mode=
-                      {u,g}id= mpol='
+                    _comp_compgen -aP "$prefix" -- -W 'size= nr_blocks=
+                        nr_inodes= mode= {u,g}id= mpol='
                     ;;&
                 udf | auto)
-                    _comp_compgen -a -- -W '{u,g}id= umask= unhide undelete
-                        nostrict iocharset bs= novrs session= anchor= volume=
-                        partition= lastblock= fileset= rootdir='
+                    _comp_compgen -aP "$prefix" -- -W '{u,g}id= umask= unhide
+                        undelete nostrict iocharset bs= novrs session= anchor=
+                        volume= partition= lastblock= fileset= rootdir='
                     ;;&
                 usbfs | auto)
-                    _comp_compgen -a -- -W 'dev{u,g}id= devmode= bus{u,g}id=
-                        busmode= list{u,g}id= listmode='
+                    _comp_compgen -aP "$prefix" -- -W 'dev{u,g}id= devmode=
+                        bus{u,g}id= busmode= list{u,g}id= listmode='
                     ;;&
                 xfs | auto)
-                    _comp_compgen -a -- -W 'allocsize= {,no}attr2 barrier dmapi
-                        {,no}grpid {bsd,sysv}groups ihashsize= {,no}ikeep
-                        inode{32,64} {,no}largeio logbufs= logbsize= logdev=
-                        rtdev= mtpt= noalign norecovery nouuid osyncisosync
-                        {u,g,p}qnoenforce {,u,usr,g,grp,p,prj}quota sunit=
-                        swidth= swalloc'
+                    _comp_compgen -aP "$prefix" -- -W 'allocsize= {,no}attr2
+                        barrier dmapi {,no}grpid {bsd,sysv}groups ihashsize=
+                        {,no}ikeep inode{32,64} {,no}largeio logbufs= logbsize=
+                        logdev= rtdev= mtpt= noalign norecovery nouuid
+                        osyncisosync {u,g,p}qnoenforce
+                        {,u,usr,g,grp,p,prj}quota sunit= swidth= swalloc'
                     ;;&
             esac
             # COMP_WORDBREAKS is a real pain in the ass
-            prev="${prev##*["$COMP_WORDBREAKS"]}"
-            [[ $split ]] && ((${COMPREPLY[@]})) &&
-                _comp_compgen -Rv COMPREPLY -- -P "$prev," -W '"${COMPREPLY[@]}"'
+            if ((${#COMPREPLY[@]})) && [[ $prefix == *["$COMP_WORDBREAKS"]* ]]; then
+                local tmp=${prefix%["$COMP_WORDBREAKS"]*}
+                COMPREPLY=("${COMPREPLY[@]#"$tmp"?}")
+            fi
             [[ ${COMPREPLY-} == *= ]] && compopt -o nospace
             return
             ;;
@@ -236,7 +231,7 @@ _comp_cmd_mount()
         host=${cur#//}
         host=${host%%/*}
         if [[ $host ]]; then
-            _comp_compgen -c "${cur#//"$host"}" split -P "//$host" -- "$(
+            _comp_compgen -P "//$host" split -- "$(
                 smbclient -d 0 -NL "$host" 2>/dev/null |
                     command sed -ne '/^[[:blank:]]*Sharename/,/^$/p' |
                     command sed -ne '3,$s|^[^A-Za-z]*\([^[:blank:]]*\).*$|/\1|p'
diff --git a/completions/_umount.linux b/completions/_umount.linux
index 5540e8eac65..d5692f46af1 100644
--- a/completions/_umount.linux
+++ b/completions/_umount.linux
@@ -98,20 +98,14 @@ _comp_cmd_umount()
     case "$prev" in
         -t)
             # FIXME: no<fstype>
-            local split=""
-            if [[ $cur == ?*,* ]]; then
-                prev="${cur%,*}"
-                cur="${cur##*,}"
-                split=set
-            fi
-            _comp_compgen -- -W 'adfs affs autofs btrfs cifs coda cramfs
-                debugfs devpts efs ext2 ext3 ext4 fuse hfs hfsplus hpfs iso9660
-                jfs minix msdos ncpfs nfs nfs4 ntfs ntfs-3g proc qnx4 ramfs
-                reiserfs romfs squashfs smbfs sysv tmpfs ubifs udf ufs umsdos
-                usbfs vfat xfs'
-            _comp_compgen -a fstypes
-            [[ $split ]] && ((${#COMPREPLY[@]})) &&
-                _comp_compgen -Rv COMPREPLY -- -P "$prev," -W '"${COMPREPLY[@]}"'
+            [[ $cur =~ ^.+, ]]
+            local prefix=${BASH_REMATCH-}
+            _comp_compgen -P "$prefix" -- -W 'adfs affs autofs btrfs cifs coda
+                cramfs debugfs devpts efs ext2 ext3 ext4 fuse hfs hfsplus hpfs
+                iso9660 jfs minix msdos ncpfs nfs nfs4 ntfs ntfs-3g proc qnx4
+                ramfs reiserfs romfs squashfs smbfs sysv tmpfs ubifs udf ufs
+                umsdos usbfs vfat xfs'
+            _comp_compgen -aP "$prefix" fstypes
             return
             ;;
         -O)
diff --git a/completions/curl b/completions/curl
index 96e4b221edd..dc61bc4ccf6 100644
--- a/completions/curl
+++ b/completions/curl
@@ -53,13 +53,12 @@ _comp_cmd_curl()
         --data | --data-ascii | --data-binary | --data-urlencode | --json | \
             --header | --proxy-header | --write-out | -${noargopts}[dHw])
             if [[ $cur == \@* ]]; then
-                _comp_compgen -c "${cur:1}" filedir
-                _comp_compgen -a -c "${cur:1}" -- -W '-'
-                if [[ ${#COMPREPLY[@]} -eq 1 && -d ${COMPREPLY[0]} ]]; then
+                _comp_compgen -P @ filedir
+                _comp_compgen -aP @ -- -W '-'
+                if [[ ${#COMPREPLY[@]} -eq 1 && -d ${COMPREPLY[0]#@} ]]; then
                     COMPREPLY[0]+=/
                     compopt -o nospace
                 fi
-                COMPREPLY=("${COMPREPLY[@]/#/@}")
             fi
             return
             ;;
diff --git a/completions/dot b/completions/dot
index dcb84369b28..8f1a56366a8 100644
--- a/completions/dot
+++ b/completions/dot
@@ -13,21 +13,20 @@ _comp_cmd_dot()
             ;;
         -T*)
             # generate langs
-            _comp_compgen -c "${cur#-T}" split -P "-T" -- "$(
+            _comp_compgen -P "-T" split -- "$(
                 "$1" -TNON_EXISTENT 2>&1 | command sed -ne 's/.*one of://p'
             )"
             return
             ;;
         -K*)
             # generate layouts
-            _comp_compgen -c "${cur#-K}" split -P "-K" -- "$(
+            _comp_compgen -P "-K" split -- "$(
                 "$1" -KNON_EXISTENT 2>&1 | command sed -ne 's/.*one of://p'
             )"
             return
             ;;
         -o*)
-            _comp_compgen -c "${cur#-o}" filedir &&
-                COMPREPLY=("${COMPREPLY[@]/#/-o}")
+            _comp_compgen -P "-o" filedir
             return
             ;;
     esac
diff --git a/completions/gprof b/completions/gprof
index cb186330c95..798df5a3358 100644
--- a/completions/gprof
+++ b/completions/gprof
@@ -10,12 +10,11 @@ _comp_cmd_gprof()
             return
             ;;
         -S*)
-            _comp_compgen -c "${cur:2}" filedir
-            ((${#COMPREPLY[@]})) && COMPREPLY=("${COMPREPLY[@]/#/-S}")
+            _comp_compgen -P "-S" filedir
             return
             ;;
         -O*)
-            _comp_compgen -c "${cur:2}" -- -P -O -W 'auto bsd 4.4bsd magic
+            _comp_compgen -P "-O" -- -W 'auto bsd 4.4bsd magic
                 prof'
             return
             ;;
diff --git a/completions/kcov b/completions/kcov
index 20a62f22c5e..573a48aa86a 100644
--- a/completions/kcov
+++ b/completions/kcov
@@ -28,17 +28,23 @@ _comp_cmd_kcov()
             return
             ;;
         --limits | -l)
-            if [[ $cur == ?*,* ]]; then
-                prev="${cur%,*}"
-                cur="${cur##*,}"
-                _comp_compgen -- -W "{0..100}"
-                ((${#COMPREPLY[@]} == 1)) &&
-                    _comp_compgen -Rv COMPREPLY -- -P "$prev," -W '"$COMPREPLY"'
+            # Complete the option argument of the form "--limits low,high".
+            local prefix
+            if [[ $cur =~ ^.+, ]]; then
+                prefix=$BASH_REMATCH
             else
-                _comp_compgen -- -W "{0..100}"
-                ((${#COMPREPLY[@]} == 1)) && COMPREPLY=("${COMPREPLY/%/,}")
+                prefix=""
                 compopt -o nospace
             fi
+            _comp_compgen -P "$prefix" -- -W "{0..100}" &&
+                if ((${#COMPREPLY[@]} == 1)); then
+                    # When we complete the "low" part, we suffix a comma.
+                    [[ $prefix ]] || COMPREPLY=("${COMPREPLY[@]/%/,}")
+                else
+                    # When the result is not unique, we do not show the prefix
+                    # part on the list.
+                    COMPREPLY=("${COMPREPLY[@]##*,}")
+                fi
             return
             ;;
         --title | -t | --include-pattern | --exclude-pattern | --path-strip-level)
diff --git a/completions/lintian b/completions/lintian
index 51402b2a86f..ac3fb7af316 100644
--- a/completions/lintian
+++ b/completions/lintian
@@ -12,10 +12,9 @@ _comp_cmd_lintian__tags()
             tags=$(command sed -e "s/\<$item\>//g" <<<"$tags")
         done
         _comp_compgen -aR -- -W "$tags"
-    elif [[ $cur == *,* ]]; then
-        _comp_compgen -ac "${cur##*,}" -- -P "${cur%,*}," -W "$tags"
     else
-        _comp_compgen -a -- -W "$tags"
+        [[ $cur == ^.*, ]]
+        _comp_compgen -aP "${BASH_REMATCH-}" -- -W "$tags"
     fi
 }
 
@@ -37,10 +36,9 @@ _comp_cmd_lintian__checks()
             done
         done
         _comp_compgen -aR -- -W "$checks"
-    elif [[ $cur == *,* ]]; then
-        _comp_compgen -ac "${cur##*,}" -- -P "${cur%,*}," -W "$checks"
     else
-        _comp_compgen -a -- -W "$checks"
+        [[ $cur == ^.*, ]]
+        _comp_compgen -aP "${BASH_REMATCH-}" -- -W "$checks"
     fi
 }
 
@@ -57,10 +55,9 @@ _comp_cmd_lintian__infos()
             infos=$(command sed -e "s/\<$item\>//g" <<<"$infos")
         done
         _comp_compgen -aR -- -W "$infos"
-    elif [[ $cur == *,* ]]; then
-        _comp_compgen -ac "${cur##*,}" -- -P "${cur%,*}," -W "$infos"
     else
-        _comp_compgen -a -- -W "$infos"
+        [[ $cur == ^.*, ]]
+        _comp_compgen -aP "${BASH_REAMTCH-}" -- -W "$infos"
     fi
 }
 
diff --git a/completions/protoc b/completions/protoc
index ac93e1cab74..9f8c1b54d9f 100644
--- a/completions/protoc
+++ b/completions/protoc
@@ -31,13 +31,11 @@ _comp_cmd_protoc()
 
     case $cur in
         -o*)
-            _comp_compgen -c "${cur:2}" filedir
-            ((${#COMPREPLY[@]})) && COMPREPLY=("${COMPREPLY[@]/#/-o}")
+            _comp_compgen -P "-o" filedir
             return
             ;;
         -I*)
-            _comp_compgen -c "${cur:2}" filedir -d
-            ((${#COMPREPLY[@]})) && COMPREPLY=("${COMPREPLY[@]/#/-I}")
+            _comp_compgen -P "-I" filedir -d
             return
             ;;
         -*)
diff --git a/completions/ssh b/completions/ssh
index db30ba340f7..90ea9c403a8 100644
--- a/completions/ssh
+++ b/completions/ssh
@@ -371,9 +371,7 @@ _comp_cmd_ssh()
     esac
 
     if [[ $cur == -F* ]]; then
-        _comp_compgen -c "${cur#-F}" filedir
-        # Prefix completions with '-F'
-        COMPREPLY=("${COMPREPLY[@]/#/-F}")
+        _comp_compgen -P "-F" filedir
     elif [[ $cur == -* ]]; then
         _comp_compgen_usage
     else
@@ -447,9 +445,7 @@ _comp_cmd_sftp()
     esac
 
     if [[ $cur == -F* ]]; then
-        _comp_compgen -c "${cur#-F}" filedir
-        # Prefix completions with '-F'
-        COMPREPLY=("${COMPREPLY[@]/#/-F}")
+        _comp_compgen -P "-F" filedir
     elif [[ $cur == -* ]]; then
         _comp_compgen_usage
     else
diff --git a/completions/strings b/completions/strings
index 52464a80d62..228da782d38 100644
--- a/completions/strings
+++ b/completions/strings
@@ -37,13 +37,10 @@ _comp_cmd_strings()
                 command sed -e "s/\[-number\]//")"
         [[ ${COMPREPLY-} == *= ]] && compopt -o nospace
         return
-    elif [[ $cur == @* ]]; then
-        _comp_compgen -c "${cur:1}" filedir &&
-            COMPREPLY=("${COMPREPLY[@]/#/@}")
-        return
     fi
 
-    _comp_compgen_filedir
+    [[ $cur =~ ^@ ]]
+    _comp_compgen -P "${BASH_REMATCH-}" filedir
 } &&
     complete -F _comp_cmd_strings strings
 
diff --git a/completions/tshark b/completions/tshark
index b7e2f6a398c..9da06391b78 100644
--- a/completions/tshark
+++ b/completions/tshark
@@ -26,8 +26,7 @@ _comp_cmd_tshark()
                     _comp_cmd_tshark__prefs="$("$1" -G defaultprefs 2>/dev/null | command sed -ne 's/^#\{0,1\}\([a-z0-9_.-]\{1,\}:\).*/\1/p' |
                         tr '\n' ' ')"
                 : ${prefix:=}
-                _comp_compgen -c "${cur:${#prefix}}" -- -P "$prefix" \
-                    -W "$_comp_cmd_tshark__prefs"
+                _comp_compgen -P "$prefix" -- -W "$_comp_cmd_tshark__prefs"
                 [[ ${COMPREPLY-} == *: ]] && compopt -o nospace
             fi
             return
@@ -101,8 +100,7 @@ _comp_cmd_tshark()
             if [[ ${cur:${#prefix}} == lua_script:* ]]; then
                 _comp_compgen -c "${cur#*:}" filedir lua
             else
-                _comp_compgen -c "${cur:${#prefix}}" -- -P "$prefix" \
-                    -W 'lua_script:'
+                _comp_compgen -P "$prefix" -- -W 'lua_script:'
                 [[ ${COMPREPLY-} == *: ]] && compopt -o nospace
             fi
             return
diff --git a/completions/upgradepkg b/completions/upgradepkg
index 0012f6282c3..30f6fb9e232 100644
--- a/completions/upgradepkg
+++ b/completions/upgradepkg
@@ -10,13 +10,11 @@ _comp_cmd_upgradepkg()
         return
     fi
 
-    if [[ $cur == ?*%* ]]; then
-        prev="${cur%%?(\\)%*}"
-        cur="${cur#*%}"
-        local nofiles=""
+    if [[ $cur =~ ^[^%]+% ]]; then
+        local prefix=$BASH_REMATCH nofiles=""
         compopt -o filenames
-        _comp_compgen -- -P "$prev%" -f -X "!*.t[bgxl]z" || nofiles=set
-        _comp_compgen -a -- -P "$prev%" -S '/' -d
+        _comp_compgen -P "$prefix" -- -f -X "!*.t[bgxl]z" || nofiles=set
+        _comp_compgen -aP "$prefix" -- -S '/' -d
         [[ $nofiles ]] && compopt -o nospace
         return
     fi
diff --git a/completions/xgamma b/completions/xgamma
index 2a0c40973f5..a265cd5ae79 100644
--- a/completions/xgamma
+++ b/completions/xgamma
@@ -32,8 +32,8 @@ _comp_cmd_xgamma()
                 # local screen numbers
                 local t screens=$(xrandr --query 2>/dev/null | command sed -ne \
                     '/^Screen /s|^Screen \{1,\}\(.*\):.*$|\1|p' 2>/dev/null)
-                t="${cur#:}"
-                _comp_compgen -c "${cur##*.}" -- -P "${t%.*}." -W '$screens'
+                cur="${cur#:}"
+                _comp_compgen -P "${cur%.*}." -- -W '$screens'
             elif [[ $cur != *:* ]]; then
                 # complete hostnames
                 _comp_compgen_known_hosts -c -- "$cur"
diff --git a/doc/api-and-naming.md b/doc/api-and-naming.md
index 824e351e154..c82179365ce 100644
--- a/doc/api-and-naming.md
+++ b/doc/api-and-naming.md
@@ -143,12 +143,12 @@ concept is later extended to also mean "eXported".
 
 The generator functions, which have names of the form `_comp_compgen_NAME`, are
 used to generate completion candidates.  A generator function is supposed to be
-called by `_comp_compgen [OPTS] NAME ARGS` where `OPTS = -aRl|-v var|-c cur|-C
-dir|-F sep` are the options to modify the behavior (see the code comment of
-`_comp_compgen` for details).  When there are no `opts`, the generator function
-is supposed to be directly called as `_comp_compgen_NAME ARGS`.  The result is
-stored in the target variable (which is `COMPREPLY` by default but can be
-specified by `-v var` in `OPTS`).
+called by `_comp_compgen [OPTS] NAME ARGS` where `OPTS = -aR|-v var|-c cur|-C
+dir|-U var|-P pref` are the options to modify the behavior (see the code
+comment of `_comp_compgen` for details).  When there are no `opts`, the
+generator function is supposed to be directly called as `_comp_compgen_NAME
+ARGS`.  The result is stored in the target variable (which is `COMPREPLY` by
+default but can be specified by `-v var` in `OPTS`).
 
 ### Implementing a generator function
 
diff --git a/test/t/unit/test_unit_compgen.py b/test/t/unit/test_unit_compgen.py
index fb04d7472af..310609dc6e0 100644
--- a/test/t/unit/test_unit_compgen.py
+++ b/test/t/unit/test_unit_compgen.py
@@ -172,3 +172,49 @@ def test_9_inherit_a(self, bash, functions):
             bash, "_comp__test_compgen gen9", want_output=True
         )
         assert output.strip() == "<11><11>"
+
+    def test_10_option_P_unmatching_prefix(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "_comp__test_compgen -c 'x' -P 'prefix,' -- -W 'alpha apple beta lemon'",
+            want_output=True,
+        )
+        assert output.strip() == ""
+
+    def test_10_option_P_incomplete_prefix(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "_comp__test_compgen -c 'pre' -P 'prefix,' -- -W 'alpha apple beta lemon'",
+            want_output=True,
+        )
+        assert (
+            output.strip()
+            == "<prefix,alpha><prefix,apple><prefix,beta><prefix,lemon>"
+        )
+
+    def test_10_option_P_exact_prefix(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "_comp__test_compgen -c 'prefix,' -P 'prefix,' -- -W 'alpha apple beta lemon'",
+            want_output=True,
+        )
+        assert (
+            output.strip()
+            == "<prefix,alpha><prefix,apple><prefix,beta><prefix,lemon>"
+        )
+
+    def test_10_option_P_starts_with_prefix(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "_comp__test_compgen -c 'prefix,a' -P 'prefix,' -- -W 'alpha apple beta lemon'",
+            want_output=True,
+        )
+        assert output.strip() == "<prefix,alpha><prefix,apple>"
+
+    def test_10_option_P_no_match(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "_comp__test_compgen -c 'prefix,x' -P 'prefix,' -- -W 'alpha apple beta lemon'",
+            want_output=True,
+        )
+        assert output.strip() == ""