bug#34294: 27.0.50; flymake-start-on-save-buffer has no effect

[Juri Linkov <juri@linkov.net>]

João, if you are not very busy atm, could you please look at this patch.

> Everything is done in the following patch that doesn't break old versions:
>
> diff --git a/etc/TODO b/etc/TODO
> index ccb82cd296..dc594a007e 100644
> --- a/etc/TODO
> +++ b/etc/TODO
> @@ -143,15 +143,6 @@ See the 'test' directory for examples.
>  
>  * Small but important fixes needed in existing features:
>  
> -** Flymake's customization mechanism needs to be both simpler (fewer
> -levels of indirection) and better documented, so it is easier to
> -understand.  I find it quite hard to figure out what compilation
> -command it will use.
> -
> -I suggest totally rewriting that part of Flymake, using the simplest
> -mechanism that suffices for the specific needs.  That will be easy
> -for users to customize.
> -
>  ** Distribute a bar cursor of width > 1 evenly between the two glyphs
>     on each side of the bar (what to do at the edges?).
>  
> diff --git a/lisp/progmodes/flymake.el b/lisp/progmodes/flymake.el
> index 261e50a613..ddf12328da 100644
> --- a/lisp/progmodes/flymake.el
> +++ b/lisp/progmodes/flymake.el
> @@ -4,7 +4,7 @@
>  
>  ;; Author:  Pavel Kobyakov <pk_at_work@yahoo.com>
>  ;; Maintainer: João Távora <joaotavora@gmail.com>
> -;; Version: 1.0.5
> +;; Version: 1.0.6
>  ;; Package-Requires: ((emacs "26.1"))
>  ;; Keywords: c languages tools
>  
> @@ -38,10 +38,9 @@
>  ;; The main interactive entry point is the `flymake-mode' minor mode,
>  ;; which periodically and automatically initiates checks as the user
>  ;; is editing the buffer.  The variables `flymake-no-changes-timeout',
> -;; `flymake-start-syntax-check-on-newline' and
> -;; `flymake-start-on-flymake-mode' give finer control over the events
> -;; triggering a check, as does the interactive command
> -;; `flymake-start', which immediately starts a check.
> +;; `flymake-start-on-newline' and `flymake-start-on-flymake-mode'
> +;; give finer control over the events triggering a check, as does the
> +;; interactive command `flymake-start', which immediately starts a check.
>  ;;
>  ;; Shortly after each check, a summary of collected diagnostics should
>  ;; appear in the mode-line.  If it doesn't, there might not be a
> @@ -178,14 +177,19 @@ flymake-fringe-indicator-position
>  		 (const right-fringe)
>  		 (const :tag "No fringe indicators" nil)))
>  
> -(defcustom flymake-start-syntax-check-on-newline t
> +(define-obsolete-variable-alias 'flymake-start-syntax-check-on-newline
> +  'flymake-start-on-newline "27.1")
> +
> +(defcustom flymake-start-on-newline t
>    "Start syntax check if newline char was added/removed from the buffer."
>    :type 'boolean)
>  
>  (defcustom flymake-no-changes-timeout 0.5
>    "Time to wait after last change before automatically checking buffer.
> -If nil, never start checking buffer automatically like this."
> -  :type 'number)
> +If nil, never start checking buffer automatically like this.
> +You may also want to disable `flymake-start-on-newline'."
> +  :type '(choice (number :tag "Timeout in seconds")
> +                 (const :tag "No check on timeout" nil)))
>  
>  (defcustom flymake-gui-warnings-enabled t
>    "Enables/disables GUI warnings."
> @@ -203,7 +207,7 @@ flymake-start-on-flymake-mode
>    :type 'boolean)
>  
>  (defcustom flymake-start-on-save-buffer t
> -  "If non-nil start syntax check when a buffer is saved.
> +  "If non-nil, start syntax check when a buffer is saved.
>  Specifically, start it when the saved buffer is actually displayed."
>    :version "27.1"
>    :type 'boolean)
> @@ -939,12 +943,11 @@ flymake-mode
>  called backends, and visually annotates the buffer with the
>  results.
>  
> -Flymake performs these checks while the user is editing.  The
> -customization variables `flymake-start-on-flymake-mode',
> -`flymake-no-changes-timeout' and
> -`flymake-start-syntax-check-on-newline' determine the exact
> -circumstances whereupon Flymake decides to initiate a check of
> -the buffer.
> +Flymake performs these checks while the user is editing.
> +The customization variables `flymake-start-on-flymake-mode',
> +`flymake-no-changes-timeout' and `flymake-start-on-newline'
> +determine the exact circumstances whereupon Flymake decides
> +to initiate a check of the buffer.
>  
>  The commands `flymake-goto-next-error' and
>  `flymake-goto-prev-error' can be used to navigate among Flymake
> @@ -1036,7 +1039,7 @@ flymake-after-change-function
>  START and STOP and LEN are as in `after-change-functions'."
>    (let((new-text (buffer-substring start stop)))
>      (push (list start stop new-text) flymake--recent-changes)
> -    (when (and flymake-start-syntax-check-on-newline (equal new-text "\n"))
> +    (when (and flymake-start-on-newline (equal new-text "\n"))
>        (flymake-log :debug "starting syntax check as new-line has been seen")
>        (flymake-start t))
>      (flymake--schedule-timer-maybe)))