Emacs: fido-mode for Name Completion

By Xah Lee. Date: 2023-08-23. Last updated: 2023-09-26.

This page is for Emacs 28 (Released 2022-04) or later.

What is fido-mode • fido-vertical-mode

fido-mode is a feature that does name completion in minibuffer. fido-mode emulates ido mode behavior. (fido is a nickname for “fake-ido”) fido-mode is new in Emacs 27 (Released 2020-08)
fido-vertical-mode is like fido-mode, but show choices vertically. fido-vertical-mode is new in Emacs 28 (Released 2022-04)

fido-mode and fido-vertical-mode are part of icomplete-mode. They first turn on icomplete-mode. [see Emacs: icomplete, Name Completion]

Difference between fido-mode and icomplete-mode

There are two aspects of difference, submission and match method.

Submit Choice Difference

icomplete-mode requires you to complete first, then submit your answer. Two distinct steps.
fido-mode always just select the closest match and submit it.

The disadvantage of icomplete-mode way is that it's one more keystroke.
The disadvantage of fido-mode way is that if you are creating a new file (new name), it always submits a existing file name. You have to specifically press some key to tell it you don't want any existing choices. Or answer a prompt that ask you if you want to overwrite. (RISKY)

Matching Method Difference

icomplete-mode does not use flex match by default. You have to type the starting letter of a name in order to complete.
fido-mode use flex match (it matches any substring or subset of chars in order.). Usually saves a lot keystrokes.

fido-mode

Activates icomplete-mode, but use flex match. That is, you can type any char that are contained in the name.
No need to press Tab.
Press Enter selects the first matched item and exit.

fido-vertical-mode

Activates fido-mode, but show choices vertically.

Warning: copy/rename file in dired overwrites

⚠ Warning: with fido mode on, when creating a file, or copying a file, etc in dired , be sure to press Ctrl+d to select current dir. Otherwise, if you press Enter, it selects current file choice and prompt to override file.

fido-vertical-mode keys

Ctrl+d: do not use any suggestion, but use the current typed. This is important, when you want to create a new file, dir, or dired for copy file, rename file. (corresponding command is badly named icomplete-fido-delete-char)
Enter: Select current choice

Alt+j: icomplete-fido-exit “Attempt to exit minibuffer immediately with current input.”
Alt+t: icomplete-force-complete “Complete the icomplete minibuffer.”
Ctrl+j: icomplete-force-complete-and-exit “Complete the minibuffer with the longest possible match and exit. Use the first of the matches if there are any displayed, and use the default otherwise.”

→: next choice
←: Prev choice

↓: next choice
↑: Prev choice

Ctrl+s: next choice
Ctrl+r: Prev choice

Ctrl+.: next choice
Ctrl+,: Prev choice

Ctrl+n: next choice
Ctrl+p: Prev choice

Alt+<: icomplete-vertical-goto-first
Alt+>: icomplete-vertical-goto-last