mdw@git.distorted.org.uk Git - sod/blob - src/c-types-parse.lisp

   1 ;;; -*-lisp-*-
   2 ;;;
   3 ;;; Parser for C types
   4 ;;;
   5 ;;; (c) 2009 Straylight/Edgeware
   6 ;;;
   7
   8 ;;;----- Licensing notice ---------------------------------------------------
   9 ;;;
  10 ;;; This file is part of the Sensble Object Design, an object system for C.
  11 ;;;
  12 ;;; SOD is free software; you can redistribute it and/or modify
  13 ;;; it under the terms of the GNU General Public License as published by
  14 ;;; the Free Software Foundation; either version 2 of the License, or
  15 ;;; (at your option) any later version.
  16 ;;;
  17 ;;; SOD is distributed in the hope that it will be useful,
  18 ;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  19 ;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20 ;;; GNU General Public License for more details.
  21 ;;;
  22 ;;; You should have received a copy of the GNU General Public License
  23 ;;; along with SOD; if not, write to the Free Software Foundation,
  24 ;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  25
  26 (cl:in-package #:sod)
  27
  28 ;;;--------------------------------------------------------------------------
  29 ;;; Declaration specifiers.
  30 ;;;
  31 ;;; This stuff is distressingly complicated.
  32 ;;;
  33 ;;; Parsing a (single) declaration specifier is quite easy, and a declaration
  34 ;;; is just a sequence of these things.  Except that there are a stack of
  35 ;;; rules about which ones are allowed to go together, and the language
  36 ;;; doesn't require them to appear in any particular order.
  37 ;;;
  38 ;;; A collection of declaration specifiers is carried about in a purpose-made
  39 ;;; object with a number of handy operations defined on it, and then I build
  40 ;;; some parsers in terms of them.  The basic strategy is to parse
  41 ;;; declaration specifiers while they're valid, and keep track of what we've
  42 ;;; read.  When I've reached the end, we'll convert what we've got into a
  43 ;;; `canonical form', and then convert that into a C type object of the
  44 ;;; appropriate kind.  The whole business is rather more complicated than it
  45 ;;; really ought to be.
  46
  47 ;; Firstly, a table of interesting things about the various declaration
  48 ;; specifiers that I might encounter.  I categorize declaration specifiers
  49 ;; into four kinds.
  50 ;;
  51 ;;   * `Type specifiers' describe the actual type, whether that's integer,
  52 ;;     character, floating point, or some tagged or user-named type.
  53 ;;
  54 ;;   * `Size specifiers' distinguish different sizes of the same basic type.
  55 ;;       This is how we tell the difference between `int' and `long'.
  56 ;;
  57 ;;   * `Sign specifiers' distinguish different signednesses.  This is how we
  58 ;;     tell the difference between `int' and `unsigned'.
  59 ;;
  60 ;;   * `Qualifiers' are our old friends `const', `restrict' and `volatile'.
  61 ;;
  62 ;; These groupings are for my benefit here, in determining whether a
  63 ;; particular declaration specifier is valid in the current context.  I don't
  64 ;; accept `function specifiers' (of which the only current example is
  65 ;; `inline') since it's meaningless to me.
  66
  67 (defclass declspec ()
  68   ;; Despite the fact that it looks pretty trivial, this can't be done with
  69   ;; `defstruct' for the simple reason that we add more methods to the
  70   ;; accessor functions later.
  71   ((label :type keyword :initarg :label :reader ds-label)
  72    (name :type string :initarg :name :reader ds-name)
  73    (kind :type (member type sign size qualifier)
  74          :initarg :kind :reader ds-kind)
  75    (taggedp :type boolean :initarg :taggedp
  76             :initform nil :reader ds-taggedp))
  77   (:documentation
  78    "Represents the important components of a declaration specifier.
  79
  80     The only interesting instances of this class are in the table
  81     `*declspec-map*'."))
  82
  83 (defmethod shared-initialize :after ((ds declspec) slot-names &key)
  84   "If no name is provided then derive one from the label.
  85
  86    Most declaration specifiers have simple names for which this works well."
  87   (default-slot (ds 'name slot-names)
  88     (string-downcase (ds-label ds))))
  89
  90 (defparameter *declspec-map*
  91   (let ((map (make-hash-table :test #'equal)))
  92     (dolist (item '((type :void :char :int :float :double)
  93                     ((type :taggedp t) :enum :struct :union)
  94                     (size :short :long (:long-long :name "long long"))
  95                     (sign :signed :unsigned)
  96                     (qualifier :const :restrict :volatile)))
  97       (destructuring-bind (kind &key (taggedp nil))
  98           (let ((spec (car item)))
  99             (if (consp spec) spec (list spec)))
 100         (dolist (spec (cdr item))
 101           (destructuring-bind (label
 102                                &key
 103                                (name (string-downcase label))
 104                                (taggedp taggedp))
 105               (if (consp spec) spec (list spec))
 106             (let ((ds (make-instance 'declspec
 107                                      :label label
 108                                      :name name
 109                                      :kind kind
 110                                      :taggedp taggedp)))
 111               (setf (gethash name map) ds
 112                     (gethash label map) ds))))))
 113     map)
 114   "Maps symbolic labels and textual names to `declspec' instances.")
 115
 116 ;; A collection of declaration specifiers, and how to merge them together.
 117
 118 (defclass declspecs ()
 119   ;; This could have been done with `defstruct' just as well, but a
 120   ;; `defclass' can be tweaked interactively, which is a win at the moment.
 121   ((type :initform nil :initarg :type :reader ds-type)
 122    (sign :initform nil :initarg :sign :reader ds-sign)
 123    (size :initform nil :initarg :size :reader ds-size)
 124    (qualifier :initform nil :initarg :qualifiers :reader ds-qualifiers))
 125   (:documentation
 126    "Represents a collection of declaration specifiers.
 127
 128     This is used during type parsing to represent the type under
 129     construction.  Instances are immutable: we build new ones rather than
 130     modifying existing ones.  This leads to a certain amount of churn, but
 131     we'll just have to live with that.
 132
 133     (Why are instances immutable?  Because it's much easier to merge a new
 134     specifier into an existing collection and then check that the resulting
 135     thing is valid, rather than having to deal with all of the possible
 136     special cases of what the new thing might be.  And if the merged
 137     collection isn't good, I must roll back to the previous version.  So I
 138     don't get to take advantage of a mutable structure.)"))
 139
 140 (defmethod ds-label ((ty c-type)) :c-type)
 141 (defmethod ds-name ((ty c-type)) (princ-to-string ty))
 142 (defmethod ds-kind ((ty c-type)) 'type)
 143
 144 (defparameter *good-declspecs*
 145   '(((:int) (:signed :unsigned) (:short :long :long-long))
 146     ((:char) (:signed :unsigned) ())
 147     ((:double) () (:long))
 148     (t () ()))
 149   "List of good collections of declaration specifiers.
 150
 151    Each item is a list of the form (TYPES SIGNS SIZES).  Each of TYPES, SIGNS
 152    and SIZES is either a list of acceptable specifiers of the appropriate
 153    kind, or T, which matches any specifier.")
 154
 155 (defun good-declspecs-p (specs)
 156   "Are SPECS a good collection of declaration specifiers?"
 157   (let ((speclist (list (ds-type specs) (ds-sign specs) (ds-size specs))))
 158     (some (lambda (it)
 159             (every (lambda (spec pat)
 160                      (or (eq pat t) (null spec)
 161                          (member (ds-label spec) pat)))
 162                    speclist it))
 163           *good-declspecs*)))
 164
 165 (defun combine-declspec (specs ds)
 166   "Combine the declspec DS with the existing SPECS.
 167
 168    Returns new DECLSPECS if they're OK, or `nil' if not.  The old SPECS are
 169    not modified."
 170
 171   (let* ((kind (ds-kind ds))
 172          (old (slot-value specs kind)))
 173     (multiple-value-bind (ok new)
 174         (case kind
 175           (qualifier (values t (adjoin ds old)))
 176           (size (cond ((not old) (values t ds))
 177                       ((and (eq (ds-label old) :long) (eq ds old))
 178                        (values t (gethash :long-long *declspec-map*)))
 179                       (t (values nil nil))))
 180           (t (values (not old) ds)))
 181       (if ok
 182           (let ((copy (copy-instance specs)))
 183             (setf (slot-value copy kind) new)
 184             (and (good-declspecs-p copy) copy))
 185           nil))))
 186
 187 (defun declspecs-type (specs)
 188   "Convert `declspecs' SPECS into a standalone C type object."
 189   (let ((type (ds-type specs))
 190         (size (ds-size specs))
 191         (sign (ds-sign specs))
 192         (quals (mapcar #'ds-label (ds-qualifiers specs))))
 193     (cond ((typep type 'c-type)
 194            (qualify-c-type type quals))
 195           ((or type size sign)
 196            (when (and sign (eq (ds-label sign) :signed)
 197                       (eq (ds-label type) :int))
 198              (setf sign nil))
 199            (cond ((and (or (null type) (eq (ds-label type) :int))
 200                        (or size sign))
 201                   (setf type nil))
 202                  ((null type)
 203                   (setf type (gethash :int *declspec-map*))))
 204            (make-simple-type (format nil "~{~@[~A~^ ~]~}"
 205                                      (mapcar #'ds-name
 206                                              (remove nil
 207                                                      (list sign size type))))
 208                              quals))
 209           (t
 210            nil))))
 211
 212 ;; Parsing declaration specifiers.
 213
 214 (define-indicator :declspec "<declaration-specifier>")
 215
 216 (defun scan-declspec
 217     (scanner &key (predicate (constantly t)) (indicator :declspec))
 218   "Scan a `declspec' from SCANNER.
 219
 220    If PREDICATE is provided then only succeed if (funcall PREDICATE DECLSPEC)
 221    is true, where DECLSPEC is the raw declaration specifier or C-type object,
 222    so we won't have fetched the tag for a tagged type yet.  If the PREDICATE
 223    returns false then the scan fails without consuming input.
 224
 225    If we couldn't find an acceptable declaration specifier then issue
 226    INDICATOR as the failure indicator.  Value on success is either a
 227    `declspec' object or a `c-type' object."
 228
 229   ;; Turns out to be easier to do this by hand.
 230   (let ((ds (and (eq (token-type scanner) :id)
 231                  (let ((kw (token-value scanner)))
 232                    (or (gethash kw *module-type-map*)
 233                        (gethash kw *declspec-map*))))))
 234     (cond ((or (not ds) (and predicate (not (funcall predicate ds))))
 235            (values (list indicator) nil nil))
 236           ((ds-taggedp ds)
 237            (scanner-step scanner)
 238            (if (eq (token-type scanner) :id)
 239                (let ((ty (make-c-tagged-type (ds-label ds)
 240                                              (token-value scanner))))
 241                  (scanner-step scanner)
 242                  (values ty t t))
 243                (values :tag nil t)))
 244           (t
 245            (scanner-step scanner)
 246            (values ds t t)))))
 247
 248 (defun scan-and-merge-declspec (scanner specs)
 249   "Scan a declaration specifier and merge it with SPECS.
 250
 251    This is a parser function.  If it succeeds, it returns the merged
 252    `declspecs' object.  It can fail either if no valid declaration specifier
 253    is found or it cannot merge the declaration specifier with the existing
 254    SPECS."
 255
 256   (with-parser-context (token-scanner-context :scanner scanner)
 257     (if-parse (:consumedp consumedp) (scan-declspec scanner)
 258       (aif (combine-declspec specs it)
 259            (values it t consumedp)
 260            (values (list :declspec) nil consumedp)))))
 261
 262 (export 'parse-c-type)
 263 (defun parse-c-type (scanner)
 264   "Parse a C type from declaration specifiers.
 265
 266    This is a parser function.  If it succeeds then the result is a `c-type'
 267    object representing the type it found.  Note that this function won't try
 268    to parse a C declarator."
 269
 270   (with-parser-context (token-scanner-context :scanner scanner)
 271     (if-parse (:result specs :consumedp cp)
 272               (many (specs (make-instance 'declspecs) it :min 1)
 273                 (peek (scan-and-merge-declspec scanner specs)))
 274               (let ((type (declspecs-type specs)))
 275                 (if type (values type t cp)
 276                     (values (list :declspec) nil cp))))))
 277
 278 ;;;--------------------------------------------------------------------------
 279 ;;; Parsing declarators.
 280 ;;;
 281 ;;; The syntax of declaration specifiers was horrific.  Declarators are a
 282 ;;; very simple expression syntax, but this time the semantics are awful.  In
 283 ;;; particular, they're inside-out.  If <> denotes mumble of foo, then op <>
 284 ;;; is something like mumble of op of foo.  Unfortunately, the expression
 285 ;;; parser engine wants to apply op of mumble of foo, so I'll have to do some
 286 ;;; work to fix the impedance mismatch.
 287 ;;;
 288 ;;; The currency we'll use is a pair (FUNC . NAME), with the semantics that
 289 ;;; (funcall FUNC TYPE) returns the derived type.  The result of
 290 ;;; `parse-declarator' will be of this form.
 291
 292 (export 'parse-declarator)
 293 (defun parse-declarator (scanner base-type &key kernel abstractp)
 294   "Parse a C declarator, returning a pair (C-TYPE . NAME).
 295
 296    The SCANNER is a token scanner to read from.  The BASE-TYPE is the type
 297    extracted from the preceding declaration specifiers, as parsed by
 298    `parse-c-type'.
 299
 300    The result contains both the resulting constructed C-TYPE (with any
 301    qualifiers etc. as necessary), and the name from the middle of the
 302    declarator.  The name is parsed using the KERNEL parser provided, and
 303    defaults to matching a simple identifier `:id'.  This might, e.g., be
 304    (? :id) to parse an `abstract declarator' which has optional names.
 305
 306    There's an annoying ambiguity in the syntax, if an empty KERNEL is
 307    permitted.  In this case, you must ensure that ABSTRACTP is true so that
 308    the appropriate heuristic can be applied.  As a convenience, if ABSTRACTP
 309    is true then `(? :id)' is used as the default KERNEL."
 310   (with-parser-context (token-scanner-context :scanner scanner)
 311     (let ((kernel-parser (cond (kernel kernel)
 312                                (abstractp (parser () (? :id)))
 313                                (t (parser () :id)))))
 314
 315       (labels ((qualifiers ()
 316                  ;; qualifier*
 317
 318                  (parse
 319                    (seq ((quals (list ()
 320                                   (scan-declspec
 321                                    scanner
 322                                    :indicator :qualifier
 323                                    :predicate (lambda (ds)
 324                                                 (and (typep ds 'declspec)
 325                                                      (eq (ds-kind ds)
 326                                                          'qualifier)))))))
 327                      (mapcar #'ds-label quals))))
 328
 329                (star ()
 330                  ;; Prefix: `*' qualifiers
 331
 332                  (parse (seq (#\* (quals (qualifiers)))
 333                           (preop "*" (state 9)
 334                             (cons (lambda (type)
 335                                     (funcall (car state)
 336                                              (make-pointer-type type quals)))
 337                                   (cdr state))))))
 338
 339                (next-declspec-p ()
 340                  ;; Ansert whether the next token is a valid declaration
 341                  ;; specifier, without consuming it.
 342                  (and (eq (token-type scanner) :id)
 343                       (let ((id (token-value scanner)))
 344                         (or (gethash id *module-type-map*)
 345                             (gethash id *declspec-map*)))))
 346
 347                (prefix-lparen ()
 348                  ;; Prefix: `('
 349                  ;;
 350                  ;; Opening parentheses are treated as prefix operators by
 351                  ;; the expression parsing engine.  There's an annoying
 352                  ;; ambiguity in the syntax if abstract declarators are
 353                  ;; permitted: a `(' might be either the start of a nested
 354                  ;; subdeclarator or the start of a postfix function argument
 355                  ;; list.  The two are disambiguated by stating that if the
 356                  ;; token following the `(' is a `)' or a declaration
 357                  ;; specifier, then we have a postfix argument list.
 358                  (parse
 359                    (peek (seq (#\(
 360                                (nil (if (and abstractp (next-declspec-p))
 361                                         (values nil nil nil)
 362                                         (values t t nil))))
 363                            (lparen #\))))))
 364
 365                (kernel ()
 366                  (parse (seq ((name (funcall kernel-parser)))
 367                           (cons #'identity name))))
 368
 369                (argument-list ()
 370                  ;; [ argument [ `,' argument ]* ]
 371
 372                  (parse (list (:min 0)
 373                           (seq ((base-type (parse-c-type scanner))
 374                                 (dtor (parse-declarator scanner
 375                                                         base-type
 376                                                         :abstractp t)))
 377                                (make-argument (cdr dtor) (car dtor)))
 378                           #\,)))
 379
 380                (postfix-lparen ()
 381                  ;; Postfix: `(' argument-list `)'
 382
 383                  (parse (seq (#\( (args (argument-list)) #\))
 384                           (postop "()" (state 10)
 385                             (cons (lambda (type)
 386                                     (funcall (car state)
 387                                              (make-function-type type args)))
 388                                   (cdr state))))))
 389
 390                (dimension ()
 391                  ;; `[' c-fragment ']'
 392
 393                  (parse (seq ((frag (parse-delimited-fragment
 394                                      scanner #\[ #\])))
 395                           (c-fragment-text frag))))
 396
 397                (lbracket ()
 398                  ;; Postfix: dimension+
 399
 400                  (parse (seq ((dims (list (:min 1) (dimension))))
 401                           (postop "[]" (state 10)
 402                             (cons (lambda (type)
 403                                     (funcall (car state)
 404                                              (make-array-type type dims)))
 405                                   (cdr state)))))))
 406
 407         ;; And now we actually do the declarator parsing.
 408         (parse (seq ((value (expr (:nestedp nestedp)
 409
 410                               ;; An actual operand.
 411                               (kernel)
 412
 413                               ;; Binary operators.  There aren't any.
 414                               nil
 415
 416                               ;; Prefix operators.
 417                               (or (star)
 418                                   (prefix-lparen))
 419
 420                               ;; Postfix operators.
 421                               (or (postfix-lparen)
 422                                   (lbracket)
 423                                   (when nestedp (seq (#\)) (rparen #\))))))))
 424                  (cons (funcall (car value) base-type) (cdr value))))))))
 425
 426 ;;;----- That's all, folks --------------------------------------------------