From ea1bdcc9710bb730fcf765c55875a6f102089f34 Mon Sep 17 00:00:00 2001 From: Stefan Kangas Date: Tue, 27 Sep 2022 18:16:51 +0200 Subject: [PATCH] Make format-spec support functions * lisp/format-spec.el (format-spec): Allow using a format as the substitution for a character. * doc/lispref/strings.texi (Custom Format Strings): Document the above change. * test/lisp/format-spec-tests.el (format-spec/function): New test. Ref. https://lists.gnu.org/r/emacs-devel/2022-09/msg01875.html --- doc/lispref/strings.texi | 5 +++++ etc/NEWS | 6 ++++++ lisp/format-spec.el | 16 ++++++++++++++-- test/lisp/format-spec-tests.el | 11 +++++++++++ 4 files changed, 36 insertions(+), 2 deletions(-) diff --git a/doc/lispref/strings.texi b/doc/lispref/strings.texi index 374381e595..af368f5d01 100644 --- a/doc/lispref/strings.texi +++ b/doc/lispref/strings.texi @@ -1293,6 +1293,11 @@ Custom Format Strings the order of associations in @var{spec-alist}. @end itemize +REPLACEMENT can also be a function taking no arguments. It will only +be called when the corresponding LETTER is used in the TEMPLATE. This +is useful, for example, to avoid prompting for input unless it is +needed. + The optional argument @var{ignore-missing} indicates how to handle specification characters in @var{template} that are not found in @var{spec-alist}. If it is @code{nil} or omitted, the function diff --git a/etc/NEWS b/etc/NEWS index 99243481a0..97838442db 100644 --- a/etc/NEWS +++ b/etc/NEWS @@ -3910,6 +3910,12 @@ the same but works by modifying LIST destructively. --- ** 'string-split' is now an alias for 'split-string'. ++++ +** 'format-spec' now accepts functions in the replacement. +The function is called only when used in the format string. This is +useful to avoid side-effects such as prompting, when the value is not +actually being used for anything. + +++ ** The variable 'max-specpdl-size' has been made obsolete. Now 'max-lisp-eval-depth' alone is used for limiting Lisp recursion diff --git a/lisp/format-spec.el b/lisp/format-spec.el index 45c19aebc8..1c817ea7fa 100644 --- a/lisp/format-spec.el +++ b/lisp/format-spec.el @@ -59,6 +59,17 @@ format-spec leading zeros or truncating leading characters until it's ten characters wide\". +If the substitution for a specification character is a function, +the function will be called only if FORMAT uses that character. +For example: + + (format-spec \"%n\" + \\=`((?n . ,(lambda () + (read-number \"Number: \"))))) + +Note that it is best to make sure the function is not quoted, +like above, so that it is compiled by the byte-compiler. + Any text properties of FORMAT are copied to the result, with any text properties of a %-spec itself copied to its substitution. @@ -94,14 +105,15 @@ format-spec (width (match-string 2)) (trunc (match-string 3)) (char (string-to-char (match-string 4))) - (text (assq char specification))) + (text (let ((res (cdr (assq char specification)))) + (if (functionp res) (funcall res) res)))) (when (and split (not (= (1- beg) split-start))) (push (buffer-substring split-start (1- beg)) split-result)) (cond (text ;; Handle flags. (setq text (format-spec--do-flags - (format "%s" (cdr text)) + (format "%s" text) (format-spec--parse-flags flags) (and width (string-to-number width)) (and trunc (car (read-from-string trunc 1))))) diff --git a/test/lisp/format-spec-tests.el b/test/lisp/format-spec-tests.el index 4a3cc74c33..bd493ae1d7 100644 --- a/test/lisp/format-spec-tests.el +++ b/test/lisp/format-spec-tests.el @@ -148,6 +148,17 @@ format-spec (format-spec fmt '((?b . "asd") (?a . "fgh"))) #("fgh%asdasd" 0 3 (a b) 3 4 (c d) 7 10 (e f)))))) +(ert-deftest format-spec/function () + (let* (called + (spec `((?a . "foo") + (?f . ,(lambda () + (setq called t) + "bar"))))) + (should (equal (format-spec "%a" spec) "foo")) + (should-not called) + (should (equal (format-spec "%f" spec) "bar")) + (should called))) + (ert-deftest format-spec-unknown () (should-error (format-spec "foo %b %z zot" '((?b . "bar")))) (should-error (format-spec "foo %b %%%z zot" '((?b . "bar")))) -- 2.30.2