code.delx.au - gnu-emacs/blob - lisp/emacs-lisp/macroexp.el

   1 ;;; macroexp.el --- Additional macro-expansion support -*- lexical-binding: t; coding: utf-8 -*-
   2 ;;
   3 ;; Copyright (C) 2004-2012 Free Software Foundation, Inc.
   4 ;;
   5 ;; Author: Miles Bader <miles@gnu.org>
   6 ;; Keywords: lisp, compiler, macros
   7
   8 ;; This file is part of GNU Emacs.
   9
  10 ;; GNU Emacs is free software: you can redistribute it and/or modify
  11 ;; it under the terms of the GNU General Public License as published by
  12 ;; the Free Software Foundation, either version 3 of the License, or
  13 ;; (at your option) any later version.
  14
  15 ;; GNU Emacs is distributed in the hope that it will be useful,
  16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 ;; GNU General Public License for more details.
  19
  20 ;; You should have received a copy of the GNU General Public License
  21 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  22
  23 ;;; Commentary:
  24 ;;
  25 ;; This file contains macro-expansions functions that are not defined in
  26 ;; the Lisp core, namely `macroexpand-all', which expands all macros in
  27 ;; a form, not just a top-level one.
  28 ;;
  29
  30 ;;; Code:
  31
  32 ;; Bound by the top-level `macroexpand-all', and modified to include any
  33 ;; macros defined by `defmacro'.
  34 (defvar macroexpand-all-environment nil)
  35
  36 (defun macroexp--cons (car cdr original-cons)
  37   "Return (CAR . CDR), using ORIGINAL-CONS if possible."
  38   (if (and (eq car (car original-cons)) (eq cdr (cdr original-cons)))
  39       original-cons
  40     (cons car cdr)))
  41
  42 ;; We use this special macro to iteratively process forms and share list
  43 ;; structure of the result with the input.  Doing so recursively using
  44 ;; `macroexp--cons' results in excessively deep recursion for very long
  45 ;; input forms.
  46 (defmacro macroexp--accumulate (var+list &rest body)
  47   "Return a list of the results of evaluating BODY for each element of LIST.
  48 Evaluate BODY with VAR bound to each `car' from LIST, in turn.
  49 Return a list of the values of the final form in BODY.
  50 The list structure of the result will share as much with LIST as
  51 possible (for instance, when BODY just returns VAR unchanged, the
  52 result will be eq to LIST).
  53
  54 \(fn (VAR LIST) BODY...)"
  55   (declare (indent 1))
  56   (let ((var (car var+list))
  57         (list (cadr var+list))
  58         (shared (make-symbol "shared"))
  59         (unshared (make-symbol "unshared"))
  60         (tail (make-symbol "tail"))
  61         (new-el (make-symbol "new-el")))
  62     `(let* ((,shared ,list)
  63             (,unshared nil)
  64             (,tail ,shared)
  65             ,var ,new-el)
  66        (while (consp ,tail)
  67          (setq ,var (car ,tail)
  68                ,new-el (progn ,@body))
  69          (unless (eq ,var ,new-el)
  70            (while (not (eq ,shared ,tail))
  71              (push (pop ,shared) ,unshared))
  72            (setq ,shared (cdr ,shared))
  73            (push ,new-el ,unshared))
  74          (setq ,tail (cdr ,tail)))
  75        (nconc (nreverse ,unshared) ,shared))))
  76
  77 (defun macroexp--all-forms (forms &optional skip)
  78   "Return FORMS with macros expanded.  FORMS is a list of forms.
  79 If SKIP is non-nil, then don't expand that many elements at the start of
  80 FORMS."
  81   (macroexp--accumulate (form forms)
  82     (if (or (null skip) (zerop skip))
  83         (macroexp--expand-all form)
  84       (setq skip (1- skip))
  85       form)))
  86
  87 (defun macroexp--all-clauses (clauses &optional skip)
  88   "Return CLAUSES with macros expanded.
  89 CLAUSES is a list of lists of forms; any clause that's not a list is ignored.
  90 If SKIP is non-nil, then don't expand that many elements at the start of
  91 each clause."
  92   (macroexp--accumulate (clause clauses)
  93     (if (listp clause)
  94         (macroexp--all-forms clause skip)
  95       clause)))
  96
  97 (defun macroexp--compiler-macro (handler form)
  98   (condition-case err
  99       (apply handler form (cdr form))
 100     (error (message "Compiler-macro error for %S: %S" (car form) err)
 101            form)))
 102
 103 (defun macroexp--eval-if-compile (&rest _forms)
 104   "Pseudo function used internally by macroexp to delay warnings.
 105 The purpose is to delay warnings to bytecomp.el, so they can use things
 106 like `byte-compile-log-warning' to get better file-and-line-number data
 107 and also to avoid outputting the warning during normal execution."
 108   nil)
 109 (put 'macroexp--eval-if-compile 'byte-compile
 110      (lambda (form)
 111        (mapc (lambda (x) (funcall (eval x))) (cdr form))
 112        (byte-compile-constant nil)))
 113
 114 (autoload 'byte-compile-warn-obsolete "bytecomp")
 115 (autoload 'byte-compile-log-warning "bytecomp")
 116
 117 (defun macroexp--expand-all (form)
 118   "Expand all macros in FORM.
 119 This is an internal version of `macroexpand-all'.
 120 Assumes the caller has bound `macroexpand-all-environment'."
 121   (if (and (listp form) (eq (car form) 'backquote-list*))
 122       ;; Special-case `backquote-list*', as it is normally a macro that
 123       ;; generates exceedingly deep expansions from relatively shallow input
 124       ;; forms.  We just process it `in reverse' -- first we expand all the
 125       ;; arguments, _then_ we expand the top-level definition.
 126       (macroexpand (macroexp--all-forms form 1)
 127                    macroexpand-all-environment)
 128     ;; Normal form; get its expansion, and then expand arguments.
 129     (let ((new-form
 130            (macroexpand form macroexpand-all-environment)))
 131       (setq form
 132             (if (and (not (eq form new-form)) ;It was a macro call.
 133                      (car-safe form)
 134                      (symbolp (car form))
 135                      (get (car form) 'byte-obsolete-info))
 136                 `(progn (macroexp--eval-if-compile
 137                          (lambda () (byte-compile-warn-obsolete ',(car form))))
 138                         ,new-form)
 139               new-form)))
 140     (pcase form
 141       (`(cond . ,clauses)
 142        (macroexp--cons 'cond (macroexp--all-clauses clauses) form))
 143       (`(condition-case . ,(or `(,err ,body . ,handlers) dontcare))
 144        (macroexp--cons
 145         'condition-case
 146         (macroexp--cons err
 147                     (macroexp--cons (macroexp--expand-all body)
 148                                 (macroexp--all-clauses handlers 1)
 149                                 (cddr form))
 150                     (cdr form))
 151         form))
 152       (`(,(or `defvar `defconst) . ,_) (macroexp--all-forms form 2))
 153       (`(function ,(and f `(lambda . ,_)))
 154        (macroexp--cons 'function
 155                    (macroexp--cons (macroexp--all-forms f 2)
 156                                nil
 157                                (cdr form))
 158                    form))
 159       (`(,(or `function `quote) . ,_) form)
 160       (`(,(and fun (or `let `let*)) . ,(or `(,bindings . ,body) dontcare))
 161        (macroexp--cons fun
 162                    (macroexp--cons (macroexp--all-clauses bindings 1)
 163                                (macroexp--all-forms body)
 164                                (cdr form))
 165                    form))
 166       (`(,(and fun `(lambda . ,_)) . ,args)
 167        ;; Embedded lambda in function position.
 168        (macroexp--cons (macroexp--all-forms fun 2)
 169                    (macroexp--all-forms args)
 170                    form))
 171       ;; The following few cases are for normal function calls that
 172       ;; are known to funcall one of their arguments.  The byte
 173       ;; compiler has traditionally handled these functions specially
 174       ;; by treating a lambda expression quoted by `quote' as if it
 175       ;; were quoted by `function'.  We make the same transformation
 176       ;; here, so that any code that cares about the difference will
 177       ;; see the same transformation.
 178       ;; First arg is a function:
 179       (`(,(and fun (or `funcall `apply `mapcar `mapatoms `mapconcat `mapc))
 180          ',(and f `(lambda . ,_)) . ,args)
 181        (byte-compile-log-warning
 182         (format "%s quoted with ' rather than with #'"
 183                 (list 'lambda (nth 1 f) '...))
 184         t)
 185        ;; We don't use `macroexp--cons' since there's clearly a change.
 186        (cons fun
 187              (cons (macroexp--expand-all (list 'function f))
 188                    (macroexp--all-forms args))))
 189       ;; Second arg is a function:
 190       (`(,(and fun (or `sort)) ,arg1 ',(and f `(lambda . ,_)) . ,args)
 191        (byte-compile-log-warning
 192         (format "%s quoted with ' rather than with #'"
 193                 (list 'lambda (nth 1 f) '...))
 194         t)
 195        ;; We don't use `macroexp--cons' since there's clearly a change.
 196        (cons fun
 197              (cons (macroexp--expand-all arg1)
 198                    (cons (macroexp--expand-all
 199                           (list 'function f))
 200                          (macroexp--all-forms args)))))
 201       (`(,func . ,_)
 202        ;; Macro expand compiler macros.  This cannot be delayed to
 203        ;; byte-optimize-form because the output of the compiler-macro can
 204        ;; use macros.
 205        (let ((handler (function-get func 'compiler-macro)))
 206          (if (null handler)
 207              ;; No compiler macro.  We just expand each argument (for
 208              ;; setq/setq-default this works alright because the variable names
 209              ;; are symbols).
 210              (macroexp--all-forms form 1)
 211            ;; If the handler is not loaded yet, try (auto)loading the
 212            ;; function itself, which may in turn load the handler.
 213            (unless (functionp handler)
 214              (ignore-errors
 215                (autoload-do-load (indirect-function func) func)))
 216            (let ((newform (macroexp--compiler-macro handler form)))
 217              (if (eq form newform)
 218                  ;; The compiler macro did not find anything to do.
 219                  (if (equal form (setq newform (macroexp--all-forms form 1)))
 220                      form
 221                    ;; Maybe after processing the args, some new opportunities
 222                    ;; appeared, so let's try the compiler macro again.
 223                    (setq form (macroexp--compiler-macro handler newform))
 224                    (if (eq newform form)
 225                        newform
 226                      (macroexp--expand-all newform)))
 227                (macroexp--expand-all newform))))))
 228
 229       (t form))))
 230
 231 ;;;###autoload
 232 (defun macroexpand-all (form &optional environment)
 233   "Return result of expanding macros at all levels in FORM.
 234 If no macros are expanded, FORM is returned unchanged.
 235 The second optional arg ENVIRONMENT specifies an environment of macro
 236 definitions to shadow the loaded ones for use in file byte-compilation."
 237   (let ((macroexpand-all-environment environment))
 238     (macroexp--expand-all form)))
 239
 240 ;;; Handy functions to use in macros.
 241
 242 (defun macroexp-progn (exps)
 243   "Return an expression equivalent to `(progn ,@EXPS)."
 244   (if (cdr exps) `(progn ,@exps) (car exps)))
 245
 246 (defun macroexp-unprogn (exp)
 247   "Turn EXP into a list of expressions to execute in sequence."
 248   (if (eq (car-safe exp) 'progn) (cdr exp) (list exp)))
 249
 250 (defun macroexp-let* (bindings exp)
 251   "Return an expression equivalent to `(let* ,bindings ,exp)."
 252   (cond
 253    ((null bindings) exp)
 254    ((eq 'let* (car-safe exp)) `(let* (,@bindings ,@(cadr exp)) ,@(cddr exp)))
 255    (t `(let* ,bindings ,exp))))
 256
 257 (defun macroexp-if (test then else)
 258   "Return an expression equivalent to `(if ,test ,then ,else)."
 259   (cond
 260    ((eq (car-safe else) 'if)
 261     (if (equal test (nth 1 else))
 262         ;; Doing a test a second time: get rid of the redundancy.
 263         `(if ,test ,then ,@(nthcdr 3 else))
 264       `(cond (,test ,then)
 265              (,(nth 1 else) ,(nth 2 else))
 266              (t ,@(nthcdr 3 else)))))
 267    ((eq (car-safe else) 'cond)
 268     `(cond (,test ,then)
 269            ;; Doing a test a second time: get rid of the redundancy, as above.
 270            ,@(remove (assoc test else) (cdr else))))
 271    ;; Invert the test if that lets us reduce the depth of the tree.
 272    ((memq (car-safe then) '(if cond)) (macroexp-if `(not ,test) else then))
 273    (t `(if ,test ,then ,else))))
 274
 275 (defmacro macroexp-let2 (test var exp &rest exps)
 276   "Bind VAR to a copyable expression that returns the value of EXP.
 277 This is like `(let ((v ,EXP)) ,EXPS) except that `v' is a new generated
 278 symbol which EXPS can find in VAR.
 279 TEST should be the name of a predicate on EXP checking whether the `let' can
 280 be skipped; if nil, as is usual, `macroexp-const-p' is used."
 281   (declare (indent 3) (debug (sexp sexp form body)))
 282   (let ((bodysym (make-symbol "body"))
 283         (expsym (make-symbol "exp")))
 284     `(let* ((,expsym ,exp)
 285             (,var (if (funcall #',(or test #'macroexp-const-p) ,expsym)
 286                       ,expsym (make-symbol ,(symbol-name var))))
 287             (,bodysym ,(macroexp-progn exps)))
 288        (if (eq ,var ,expsym) ,bodysym
 289          (macroexp-let* (list (list ,var ,expsym))
 290                         ,bodysym)))))
 291
 292 (defun macroexp--maxsize (exp size)
 293   (cond ((< size 0) size)
 294         ((symbolp exp) (1- size))
 295         ((stringp exp) (- size (/ (length exp) 16)))
 296         ((vectorp exp)
 297          (dotimes (i (length exp))
 298            (setq size (macroexp--maxsize (aref exp i) size)))
 299          (1- size))
 300         ((consp exp)
 301          ;; We could try to be more clever with quote&function,
 302          ;; but it is difficult to do so correctly, and it's not obvious that
 303          ;; it would be worth the effort.
 304          (dolist (e exp)
 305            (setq size (macroexp--maxsize e size)))
 306          (1- size))
 307         (t -1)))
 308
 309 (defun macroexp-small-p (exp)
 310   "Return non-nil if EXP can be considered small."
 311   (> (macroexp--maxsize exp 10) 0))
 312
 313 (defsubst macroexp--const-symbol-p (symbol &optional any-value)
 314   "Non-nil if SYMBOL is constant.
 315 If ANY-VALUE is nil, only return non-nil if the value of the symbol is the
 316 symbol itself."
 317   (or (memq symbol '(nil t))
 318       (keywordp symbol)
 319       (if any-value
 320           (or (memq symbol byte-compile-const-variables)
 321               ;; FIXME: We should provide a less intrusive way to find out
 322               ;; if a variable is "constant".
 323               (and (boundp symbol)
 324                    (condition-case nil
 325                        (progn (set symbol (symbol-value symbol)) nil)
 326                      (setting-constant t)))))))
 327
 328 (defun macroexp-const-p (exp)
 329   "Return non-nil if EXP will always evaluate to the same value."
 330   (cond ((consp exp) (or (eq (car exp) 'quote)
 331                          (and (eq (car exp) 'function)
 332                               (symbolp (cadr exp)))))
 333         ;; It would sometimes make sense to pass `any-value', but it's not
 334         ;; always safe since a "constant" variable may not actually always have
 335         ;; the same value.
 336         ((symbolp exp) (macroexp--const-symbol-p exp))
 337         (t t)))
 338
 339 (defun macroexp-copyable-p (exp)
 340   "Return non-nil if EXP can be copied without extra cost."
 341   (or (symbolp exp) (macroexp-const-p exp)))
 342
 343 ;;; Load-time macro-expansion.
 344
 345 ;; Because macro-expansion used to be more lazy, eager macro-expansion
 346 ;; tends to bump into previously harmless/unnoticeable cyclic-dependencies.
 347 ;; So, we have to delay macro-expansion like we used to when we detect
 348 ;; such a cycle, and we also want to help coders resolve those cycles (since
 349 ;; they can be non-obvious) by providing a usefully trimmed backtrace
 350 ;; (hopefully) highlighting the problem.
 351
 352 (defun macroexp--backtrace ()
 353   "Return the Elisp backtrace, more recent frames first."
 354   (let ((bt ())
 355         (i 0))
 356     (while
 357         (let ((frame (backtrace-frame i)))
 358           (when frame
 359             (push frame bt)
 360             (setq i (1+ i)))))
 361     (nreverse bt)))
 362
 363 (defun macroexp--trim-backtrace-frame (frame)
 364   (pcase frame
 365     (`(,_ macroexpand (,head . ,_) . ,_) `(macroexpand (,head …)))
 366     (`(,_ internal-macroexpand-for-load (,head ,second . ,_) . ,_)
 367      (if (or (symbolp second)
 368              (and (eq 'quote (car-safe second))
 369                   (symbolp (cadr second))))
 370          `(macroexpand-all (,head ,second …))
 371        '(macroexpand-all …)))
 372     (`(,_ load-with-code-conversion ,name . ,_)
 373      `(load ,(file-name-nondirectory name)))))
 374
 375 (defvar macroexp--pending-eager-loads nil
 376   "Stack of files currently undergoing eager macro-expansion.")
 377
 378 (defun internal-macroexpand-for-load (form)
 379   ;; Called from the eager-macroexpansion in readevalloop.
 380   (cond
 381    ;; Don't repeat the same warning for every top-level element.
 382    ((eq 'skip (car macroexp--pending-eager-loads)) form)
 383    ;; If we detect a cycle, skip macro-expansion for now, and output a warning
 384    ;; with a trimmed backtrace.
 385    ((and load-file-name (member load-file-name macroexp--pending-eager-loads))
 386     (let* ((bt (delq nil
 387                      (mapcar #'macroexp--trim-backtrace-frame
 388                              (macroexp--backtrace))))
 389            (elem `(load ,(file-name-nondirectory load-file-name)))
 390            (tail (member elem (cdr (member elem bt)))))
 391       (if tail (setcdr tail (list '…)))
 392       (if (eq (car-safe (car bt)) 'macroexpand-all) (setq bt (cdr bt)))
 393       (message "Warning: Eager macro-expansion skipped due to cycle:\n  %s"
 394                (mapconcat #'prin1-to-string (nreverse bt) " => "))
 395       (push 'skip macroexp--pending-eager-loads)
 396       form))
 397    (t
 398     (condition-case err
 399         (let ((macroexp--pending-eager-loads
 400                (cons load-file-name macroexp--pending-eager-loads)))
 401           (macroexpand-all form))
 402       (error
 403        ;; Hopefully this shouldn't happen thanks to the cycle detection,
 404        ;; but in case it does happen, let's catch the error and give the
 405        ;; code a chance to macro-expand later.
 406        (message "Eager macro-expansion failure: %S" err)
 407        form)))))
 408
 409 ;; ¡¡¡ Big Ugly Hack !!!
 410 ;; src/bootstrap-emacs is mostly used to compile .el files, so it needs
 411 ;; macroexp, bytecomp, cconv, and byte-opt to be fast.  Generally this is done
 412 ;; by compiling those files first, but this only makes a difference if those
 413 ;; files are not preloaded.  But macroexp.el is preloaded so we reload it if
 414 ;; the current version is interpreted and there's a compiled version available.
 415 (eval-when-compile
 416   (add-hook 'emacs-startup-hook
 417             (lambda ()
 418               (and (not (byte-code-function-p
 419                          (symbol-function 'macroexpand-all)))
 420                    (locate-library "macroexp.elc")
 421                    (load "macroexp.elc")))))
 422
 423 (provide 'macroexp)
 424
 425 ;;; macroexp.el ends here