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Fancy completion all over Emacs, not just for buffers and files.
Emacs Lisp Shell
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ChangeLog Version 3.5 Fix typo in README
ido-completing-read+.el Version 3.6
ido-ubiquitous.el Version 3.6 Improve


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Gimme some ido... everywhere! This pacakge replaces stock emacs completion with ido completion wherever it is possible to do so without breaking things.

Get it from MELPA:

Version 3.0 changes

ido-ubiquitous version 3.0 is a major update, including a split into two packages, and some of the configuration options have changed in non-backwards-compatible ways. If you have customized ido-ubiquitous, be sure to check out M-x customize-group ido-ubiquitous and M-x customize-group ido-completing-read+ after updating to 3.0 and make sure the new settings are to your liking.

How to enable ido in as many places as possible

If you are using this package, you probably want to enable ido everywhere that it is possible to do so. Here are all the places to enable ido that I'm aware of. (Note that most of these variables can also be set via M-x customize-variable if you prefer that.)

Ido itself

First, enable ido-mode and ido-everywhere.

(ido-mode 1)
(ido-everywhere 1)

ido-ubiquitous (this package)

Install this package and then turn on ido-ubiquitous-mode:

(require 'ido-ubiquitous)
(ido-ubiquitous-mode 1)


Smex allows you to use ido for completion of commands in M-x, with enhancements like putting your most-used commands at the front of the list. First install the smex package, then follow the directions to set up key-bindings for it.


If you want to use ido for yes-or-no questions, even though it's massive overkill, install the ido-yes-or-no package (soon to be available from MELPA):

ido for describe-face and certain other commands

Some commands, such as describe-face, use completing-read-multiple instead of completing-read. You can get ido completion for these commands with crm-custom-mode, which replaces completing-read-multiple with repeated calls to completing-read, which would then use ido thanks to ido-ubiquitous-mode. First, install the crm-custom package from MELPA:

Then enable the mode:

(crm-custom-mode 1)

Rememebr that when using this mode, completion for affected commands will continue to read additional items until you use C-j to enter an empty input, which terminates the completion. (Due to this quirk, I do not find this mode to be very useful in conjunction with ido, but it does work.)

Packages with built-in ido support

Finally, some packages implement their own completion customizations, and ido-ubiquitous specifically avoids interfering with these, so you need to enable them separately.

  • Org Mode: (setq org-completion-use-ido t)
  • Magit: (setq magit-completing-read-function 'magit-ido-completing-read)
  • Gnus: (setq gnus-completing-read-function 'gnus-ido-completing-read)

(You can also use M-x customize-variable to set all of these options.)

"But some commands still aren't using ido! What gives?"

There are some features of completing-read that ido cannot handle, and by default ido-ubiquitous tries to get out of the way whenever it detects that these features might be used. But the detection is not perfect and errs on the side of caution, so ido may be disabled for commands where it is actually perfectly safe. If you find a command that you think should be using ido but isn't, you can try customizing ido-ubiquitous-command-overrides to tell ido-ubiquitous that certain commands are safe for ido completion, or you can customize ido-ubiquitous-allow-on-functional-collection and ido-ubiquitous-max-items to turn off the saveguards and always force ido in ambiguous cases. Be aware, this could cause certain commands not to work correctly or at all.

How ido-ubiquitous decides when to replace completing-read

Emacs' completing-read is a complex function with many advanced features and some quirks that are only maintained for backwards compatibility. Not all of these features are supported by ido, so it is impossible to always replace completing-read with ido completion. Furthermore, it's not always possible to detect based on the arguments to completing-read whether such ido-incompatible features are being used or not. ido-ubiquitous uses a series of heuristics to determine whether unsupported features might be used, and also supports an override feature to correct it when the heuristics get things wrong.

Each time completing-read is invoked, ido-ubiquitous selects one of 3 modes:

  • enable: use ido completion;
  • enable-old: use ido completion, but with a compatibility fix for old-style default selection; and
  • disable: no ido completion.

The following describes how ido-ubiquitous selects the appropriate mode, and what to do when you think it is making the wrong choice.

When the collection is a function

One feature of completing-read is that the collection argument can be a function. This function could simply return a list of all possible completions, in which case it would be safe to use ido, or it could implement a completely new completion system, in which case using ido would interfere with this new completion system (for an example of this, see the tmm command). But ido-ubiquitous cannot tell by looking at the function which kind it is, so it errs on the side of caution and disables itself whenever the collection is a function, unless an override exists telling it that the command is safe for ido completion. You can turn off this safeguard by customizing ido-ubiquitous-allow-on-functional-collection. Be aware that enabling this will likely break completion entirely in any command that uses this feature to implement non-standard completion.

If you run across a command that unexpectedly uses normal Emacs completion instead of ido completion, it's likely that either this or the following option is to blame.

When the collection is very large

Ido can get slow on very large collections, so by default ido-ubiquitous disables itself for collections with more than 30,000 items in them. You can change this threshold by customizing ido-cr+-max-items.

Old-style default selection

The enable-old mode of operation is required because the old way for completing-read to indicate that the user simply pressed RET and selected the default option was to return an empty string. When this old-style mode is used, completing-read doesn't even know what the default is supposed to be -- the calling code handles all of that. But in ido, simply pressing RET will return the first item of the list, not an empty string. The way to enter an empty string in ido is C-j. The enable-old mode enables ido completion, but swaps the meaning of C-j and RET if you haven't entered any text or cycled the options yet (once you do either of those, C-j and RET regain their standard meanings). This allows you to select the default by pressing RET as soon as the completion prompt appears, as intended (C-j would select the first item).

Unfortuantely, there is no way for ido-ubiquitous to detect when a command is using this old-style default selection, so instead it uses a built-in set of overrides telling it about commands that are known to use old-style defaults. If you discover a command where pressing RET or C-j at an empty prompt is not doing what you expect it to, there's a good chance that you need to add an enable-old override for that command. Luckily, since this is an obsolete usage pattern, it is unlikely that any Elisp functions written since 1990 or so will need to be added to this list.

"A command is not working the way I expect it to! What should I do?"

First, invoke the ido-ubiquitous-debug-mode and ido-cr+-debug-mode commands (ido-cr+ is a lower-level package underlying ido-ubiquitous and implementing generic improvements to ido-completing-read). Then, with these two modes active, run the offending command. Then examine the Messages buffer, where ido-ubiquitous will explain which mode of operation it selected and why. Based on this, you can add an override to ido-ubiquitous-command-overrides. If you are not familiar with the structure of this variable, I recommend using M-x customize-variable to edit it, which will help you get it right. If ido completion was skipped ido completion because the collection was too large, try giving ico-cr+-max-items a larger value, or set it to nil if your computer is fast enough to handle any size of collection.

New versions often include new overrides, but Emacs will not edit your override variables if you have already customized them. So, if you have recently upgraded ido-ubiquitous, remember to invoke ido-ubiquitous-restore-default-overrides to add in any new overrides.

If you do add any overrides yourself, please also report them at so I can add them to the default set for future versions.

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