Why are auto completion's candidates different with dabbrev-completion?

[IceAsteroid]

I know in order for dabbrew-completion to work properly, I need to set up lsp-mode #369 for it. But why does auto completion popup work by default? It provides not only candidates that are already in the buffer, but also more than that like in an IDE.

Is it expected? Why does auto completion work by default for additional candidates without additional configurations or packages?

Here's the screenshot of auto completion

dabbrew-completion:

If so, how can I make the two consistent with each other?

Here's my config:

  ;; Install & Configure corfu.el,
  ;;-An in buffer popup for text/code completion
  (use-package corfu
    (setq
    :ensure t
    :custom
    ;; (corfu-cycle t)                ;; Enable cycling for `corfu-next/previous'
    ;; (corfu-preselect 'prompt)         ;; Always preselect the prompt
    ;; (corfu-auto t)                 ;; Enable auto completion
    (corfu-cycle t)           ;; Enable for Tab to scroll
    (corfu-preselect 'prompt) ;; Enable for Tab to scroll
    (corfu-echo-documentation 0.25)
    (setq-local corfu-auto        t
	    corfu-auto-delay  0 ;; TOO SMALL - NOT RECOMMENDED
	    corfu-auto-prefix 1 ;; TOO SMALL - NOT RECOMMENDED
	    completion-styles '(basic))
    (corfu-auto t
		corfu-quit-no-match 'separator) ;; Enable auto completion
    ;; (corfu-separator ?\s)          ;; Orderless field separator
    ;; (corfu-quit-at-boundary nil)   ;; Never quit at completion boundary
    ;; (corfu-quit-no-match nil)      ;; Never quit, even if there is no match
    ;; (corfu-preview-current nil)    ;; Disable current candidate preview
    ;; (corfu-preselect 'prompt)      ;; Preselect the prompt
    ;; (corfu-on-exact-match nil)     ;; Configure handling of exact matches
    ;; (corfu-scroll-margin 5)        ;; Use scroll margin

    ;; Enable Corfu only for certain modes.
    ;; :hook ((prog-mode . corfu-mode)
    ;;        (shell-mode . corfu-mode)
    ;;        (eshell-mode . corfu-mode))

    ;; Recommended: Enbale Corfu globally.  This is recommended since Dabbrev can
    ;; be used globally (M-/).  See also the customization variable
    ;; `global-corfu-modes' to exclude certain modes.
    :bind
    ;; Use TAB for cycling, default is `corfu-complete'.
    (:map corfu-map
	  ("TAB" . corfu-next)
	  ([tab] . corfu-next)
	  ("S-TAB" . corfu-previous)
	  ([backtab] . corfu-previous))
    :init
    (global-corfu-mode 1)
    (corfu-history-mode 1)
    (corfu-popupinfo-mode 1)
    :config
    )

;; Tweak built-in completion Dabbrev.el to be used with corfu
  ;; Use Dabbrev with Corfu
  (use-package dabbrev
	  :elpaca nil  ;;Turn off elpaca, since dabbrev is built-in
	  :bind
	  ;; Swap M-/ and C-M-/
	  (
	   ;;("C-<tab>" . dabbrev-completion)
	   ("M-<tab>" . dabbrev-completion)
	   ;;("M-/" . dabbrev-expand)
	   )
	  :custom
	  (dabbrev-ignored-buffer-regexps '("\\.\\(?:pdf\\|jpe?g\\|png\\)\\'")))

[IceAsteroid]

I see, by default, the auto completion of corfu, only works for elisp source files without further configuration.

I figured it out, I have to bind "completion-at-point" to a key instead of binding "dabbrew-completion", the latter only shows in buffer candidates.

Now the results of auto completion and a keybinding with "completion-at-point" are identical by default in an elisp source file.

[IceAsteroid]

dabbrev is for word completion, not for programming completion.

[hmelman]

dabbrev is for word completion, not for programming completion.

I don't think this true, I regularly use it to expand symbols in code.