TODO 32.6 KB
Newer Older
* Decree that versions older than 2 years are not supported;
2 3
  yet, keep supporting an upgrade from whatever vendors provide
  — so push them to provide recent stuff.
4 5 6
** Already, swank-asdf doesn't support anything older than 2.014.6
   (as provided by the first 2011 iteration of Quicklisp), and
   I (fare) am pushing for swank-asdf to not support anything older
7 8 9
   than 3.1.2 (since no maintained implementation has anything older,
   with the LispWorks 7.0 release being last to upgrade, in May 2015;
   or CLISP hg in May 2016, though it hasn't been released since 2010).
10 11 12 13 14 15 16
** Maybe remove old versions from upgrade tests; or maybe not:
   if we support old versions in any way,
   it should be for upgrade only, and "punt" is acceptable.
** Maybe remove upgrade from antique ASDF altogether.
   Clear all the code in the header, and/or
   move a few elements to asdf/upgrade.
** Upgrade tests might be split in two test sets: short and long.
17 18
** Make tests stateless and/or make any modifications private,
   so that they can be run in parallel.

20 21 22 23 24 25 26
* Testing support
** Replace test-op with run-test-op and test-report-op ?

* Implement a style-checker, that will issue STYLE-WARNINGs
  when you don't follow all the recommended guidelines.

* Moving toward cross-compilation (ASDF 3.4? 4?)
   This would allow to get most of the benefits of XCVB
28 29
   (reproducibility, scalability, applicability to mobile platforms, etc.),
   except without the backward incompatibility of XCVB.
   NB: the MOCL author would benefit a lot, and might chip in.
31 32
** Need to further split asdf:perform in two parts:
   A part that runs on the host and specifies (as SEXP or string to read)
   forms that must be evaluated on the target machine, not the host:
   (asdf:perform-forms target operation component &key input-files output-files)
   The default implementation can fallback to running the
36 37 38 39 40 41 42 43
   (asdf:perform operation component) on the target.
   To ensure isolation, it would run in an isolated process in which
   just the specially crafted operation and component objects are defined,
   though the defsystem-depends-on dependencies are also loaded;
   the action would be run in a temporary directory, that would contain
   only a read-only copy of the declared input-files, and some writable
   output directory for the output files, that would afterwards be
   copied to their actual destination.

45 46 47 48 49 50 51 52 53 54 55 56 57
   ;; null means the target is the current host.
   ;; Or should the base class be plan-traversal or such?
   (defmethod perform-form ((target null) operation component)
     ;; :host means execute on the host. () is empty options.
     `(:host () (asdf:perform ',op ',comp)))

   ;; external-target means a cross compiler that we spawn.
   (defmethod perform-form ((target external-target) operation component)
     `(:target ;; who is to execute that? the target Lisp.
       ;; options for the performing system:
       (:depends-on ,(defsystem-dependencies
                      (component-system component)))
       ;; The actual forms to evaluate
58 59 60
       (asdf:perform ,(fake-operation-form operation)
                     ,(fake-component-form component))))

61 62 63 64
   By specifying :host-common-lisp you can have forms run on the host.
   By specifying :run-program, you can spawn a subprocess without
   having to first spawn a Lisp that will call run-program. etc.

65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89
   The other way around the default perform method could be:

   (defmethod perform ((o t) (c t))
     (let ((forms (perform-forms nil o c)))
       (if (equal forms
                  `((asdf:perform ',o ',c)))
           (error "Missing perform method on ..." ...)
           (map () 'eval-thunk forms))))

   Note that in the general case, there are multiple forms,
   that must be provided on the command line somehow
   (see the lisp-invocation system and also how cl-launch does it),
   with packages necessary to read latter forms being
   created by former forms, so you cannot read everything in one go.
   ASDF or at least UIOP should probably be provided in the target
   image by default, anyway, without needing to be explicitly specified.
   A more declarative interface to needing the defsystem-deps
   is probably useful.
** A real cross-compiling backend that works the way of XCVB
   would need to compute a complete graph for the plan,
   which could be achieved by inheriting from the code in POIU.
   Thinking about it, the cross-compiling target object
   could actually be the same as the plan object.
   The basic case of in-image execution would need to be in ASDF,
   while the actual cross-compilation case would be in an extension.
Francois-Rene Rideau committed
** Audit all the current specializers of perform, and offer them a new way;
   they can keep the perform method to run on older versions of ASDF.
Francois-Rene Rideau committed
92 93
** Modify SBCL and other implementations so they provide UIOP
   independently from ASDF?
94 95 96 97 98 99 100
** The default perform-plan method could iterate over pre-computed forms,
   in a way that does not involve the ASDF object model anymore,
   making ASDF friendlier to self-upgrades.
   Then, ASDF wouldn't need to be concatenated during upgrade
   — but should still concatenate for bootstrap purposes,
   when require'ing it as an implementation-provided module,
   compiling from ASDF 2, or otherwise distributing as a single file.

Francois-Rene Rideau committed
102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
* Implementation bugs
** CMUCL has bugs:
*** In ASDF 2.32.13, sibling-dependencies is renamed to sideway-dependencies
    in defclass component, a superclass of system, and upgrade from
    2.32 or earlier thus fails with
    Error in function KERNEL:CLASS-TYPEP:  Class is currently invalid:
    in a direct call from ASDF/FIND-SYSTEM:LOCATE-SYSTEM,
    which suggests CMUCL's PCL fails to finalize classes properly.
*** Non-default optimize settings may or may not subtly break PCL.
    For the longest time (from 2.26.136 to, ASDF had:
    (declaim (optimize (speed 1) (safety 3) (debug 3)))
    This form may or may not work around that breakage in some cases:
    (setf c::top-level-lambda-max 0)
*** At some point there was massive breakage due to uninitialized slots
    as revealed in with
    make t l=cmucl t=test-encodings.script
    which was a different PCL bug from the above (without same workaround)
    but possibly also triggered by the non-standard declaim.
121 122
*** `#5(1 ,@\`(2 3)))` returns `#(1 2 3)`,
     rather than `#(1 2 3 2 3 2 3 2 3)` or even better `#(1 2 3 3 3)`.
Francois-Rene Rideau committed
123 124
*** It purports to support Unicode, but it has only 16-bit characters.
   Note that (subtypep 'character 'base-char) says T -- everything is a base char(!)
Francois-Rene Rideau committed

126 127
** SCL has bugs:
*** it doesn't like run-program from a modified directory?
*** it somehow pushes `:non-base-chars-exist-p` even though `+non-base-chars-exist-p+` is `NIL`???

Francois-Rene Rideau committed
** XCL has bad bugs:
131 132 133 134 135 136 137 138 139 140 141 142 143
*** make-pathname doesn't handle :type nil properly and
    has massive lossage in logical-pathname support.
*** If using block () and return in search-for-system-definition
    instead of return-from, XCL mistakenly has the return jump
    to the end of the try function or something.
*** It also takes a long time for errors to propagate into a debugging REPL —
     Maybe O(n^3) behavior or worse in walking the C++ stack?
*** The backtrace frames may contains unprintable objects.
*** make-pathname fails to copy the version from the defaults.
*** (make-pathname :host "ASDFTEST" :directory '(:absolute "system2" "module4")
      :name nil :type nil) fails to handle the logical-pathname-ness of ASDFTEST.
*** `#5(1 ,@`(2 3)))` returns #(1 2 3),
     rather than #(1 2 3 2 3 2 3 2 3) or even better #(1 2 3 3 3).
144 145 146 147
*** XCL recognizes :unspecific for a pathname type,
   but prints the namestring with a dot separator!
   (make-pathname :name "foo" :type :unspecific) ==> #P"foo."
    If bug is ever fixed, upgrade *unspecific-pathname-type* in uiop/pathname.
*** XCL doesn't properly process files the name of which contains a *
*** XCL fails to recognize that specialized method parameters are implicitly ignorable.
Francois-Rene Rideau committed
150 151

** GCL is almost working again; but implementation bugs remain.
152 153 154 155 156 157 158 159 160 161
   See Francois-Rene Rideau's messages on gcl-devel starting November 2013.
*** Missing support for many UIOP functions:
   combine-fasls, get-optimization-settings...
*** ASDF may now be included for (require "asdf") and (require "ASDF"),
    but how to compile it properly?
*** GCL fails to properly compile ASDF with the default compilation settings,
   but works with those in script-support.lisp.
   Symptoms when trying to load asdf.o:
   Signalled by "AN ANONYMOUS FUNCTION".
   INTERNAL-SIMPLE-ERROR: The package named ASDF/INTERFACE, does not exist
162 163
*** Another GCL compiler bug:
   when I changed the definition of getcwd from
164 165
   `(let ((*default-pathname-defaults* #p"")) (truename #p""))` to
   `(let ((*default-pathname-defaults* *nil-pathname*)) (truename *nil-pathname*))`
   to guard against e.g. a logical-pathname context while loading asdf
   and parsing `#p""`, calls to `getcwd` result in a segfault.
*** An another bug: gcl refuses dynamic-extent declaration on functions.
169 170 171 172
   ```uiop/stream.lisp:         #-gcl (declare (dynamic-extent ,@(when
   before `(#',beforef)) ,@(when after `(#',afterf))))```
*** `(typep p 'logical-pathname)` should be T if p has a logical-pathname host.
*** `apropos` is case-sensitive and returns a same symbol many times
173 174
   (presumably once per package where it is present,
   instead of just once for its home package)
175 176
*** `compile-file` fails to return proper secondary values in case of non-style `WARNING`.
*** `(pathname-directory #p"foo/")` is incorrectly `("foo")` instead of `(:RELATIVE "foo")`
*** Do whatever it takes to pass the asdf tests, add the above?
178 179 180
*** Trying to `uiop:slurp-stream-forms` from a stream with `#+(or) :foo`
   (or `read-file-forms` from an file with same) results in an error,
   rather than `nil`. This is probably a bug in `#+` processing.
   Unhappily, debian creates such a file in
183 184
*** Tests that try to catch an error fail (but catching a warning succeeds),
   which suggests brokenness in handler-bind and/or error.
185 186 187 188 189 190
*** `COMPILE-FILE*` fails due to handler-bind error in
   `with-muffled-compiler-conditions` or so.
*** `#5(1 ,@`(2 3)))` returns `#(1 2 3)`,
     rather than `#(1 2 3 2 3 2 3 2 3)` or even better `#(1 2 3 3 3)`.
*** `(DIRECTORY #p"*.*")` fails to match files with pathname-type `NIL`.
*** GCL doesn't properly process files the name of which contains a `*`
Francois-Rene Rideau committed

192 193 194 195
** ABCL has a few bugs.
*** ABCL fails the timestamp propagation test.
*** `#5(1 ,@`(2 3)))` returns #(1 2 3),
   rather than #(1 2 3 2 3 2 3 2 3) or even better #(1 2 3 3 3).
*** ABCL doesn't properly process files the name of which contains a *

198 199
** ECL has issues with its bundles.
   On MacOS X, test-bundle.script fails.
*** ECL doesn't properly process files the name of which contains a *

Francois-Rene Rideau committed
202 203 204
** Allegro fails to parse argv the correct Windows way wrt C++ escaping conventions.
   Is this (still) the case? What about LispWorks? Other implementations?

Francois-Rene Rideau committed
205 206
* Design & Implement some out-of-line configuration mechanism for various options?
  i.e. let configuration files override some variables around some actions.
** Could be used to override new backward-incompatible defaults
Francois-Rene Rideau committed
   (e.g. for operation propagation, deferred warnings, etc.)
** Use the above to bind variable around performing of actions.

211 212 213 214 215 216 217
* Improve robustness
** Fix bugs on
*** fix directory-files to not return directories on CCL, etc. Add tests.
*** have a better defsystem form verifier - see lp#1007335
*** have a function verify-strict-asd that can verify a asd is pure lp#541562
   Then if it passes, use load-strict-asd.
   If not, optionally issue a warning. Start migrating people toward that.
218 219 220
** Include tests for prebuilt-system in test-bundle and in test-program.
** Test that a package-system secondary system is properly superseded
   when the primary system is redefined.

222 223 224 225
* Learn to use cl-grid-test
** So we can easily make sure ASDF changes don't break stuff,
   and that breakage gets fixed quickly.
** So we see if ASDF-USER can :use most (all?) of UIOP.
226 227 228 229 230
  SB-GROVEL used (until 25c1769 from 2013-02-23) to :use both ASDF and
  SB-EXT, which prevents ASDF from exporting RUN-PROGRAM, but
  should not be a problem with ASDF-USER :use'ing UIOP.
  A run of quicklisp is necessary, with an eye also for warnings
  from .asd's that might be overriding definitions in UIOP(!)

232 233 234 235 236 237 238 239 240
* Diagnostics
** have a mode to explain WHY a component needs to be recompiled.
** A ``dry run'' of an operation can be made with the following form:
     (let ((asdf:*verbose-out* *standard-output*))
       (loop :for (op . comp) :in
          (asdf/plan:make-plan nil '<operation-name> '<system-name> :force t))
         :do (asdf:explain op comp)))
   What would be a nice interface for this functionality?

* have with-input-file use the encodings mechanism?
** Import asdf-encodings into UIOP? Sounds a lot of code for no users.

* have a single test .asd that tests as many features as possible, use it for upgrade test.

* Bug found by fe[nl]ix: infinite loop if the definitions in an asd file
248 249
  are not in strict defsystem-depends-on dependency order.
** At least document the issue.
250 251
** Real solution: defer parsing and evaluation of defsystem forms?
   Or simply detect circularity and issue an appropriate error?
252 253

* Include some ABL test for stassats's (now obsolete?) thing:
   :centralize-lisp-binaries t :default-toplevel-directory *fasl-dir*)
Francois-Rene Rideau committed
** Or deprecate and remove ABL compatibility altogether? Move it to contrib?
257 258 259 260
   No one has been using ASDF1 for years.
   There is no ABL to be compatible with —
   is anyone still using the compatibility mode?
   Maybe issue a warning, then a cerror, before to remove the code?

Francois-Rene Rideau committed
* Make load-op a generic operation that selects the proper strategy?
Francois-Rene Rideau committed
  for each system, module or file, according to component properties and user-configuration:
  compile the lisp file then load the fasl (load-fasl-op on a cl-source-file),
Francois-Rene Rideau committed
  load the lisp file without compiling (load-source-op),
266 267
  compile all files for the system, link them and load the result
   (load-fasl-op on the system),
Francois-Rene Rideau committed
268 269 270 271
  compile all files for the system *and* its dependencies, link and load (monolithic-load-fasl-op),
  concatenate all files for the system, then load the result (load-concatenated-source-op),
  concatenate all files for the system, then link them and load the result (load-compiled-concatenated-op),
  concatenate all files for the system *and* its dependencies, link and load (monolithic-load-compiled-concatenated-op).

273 274
* operation cleanup?
** Kill backward-compat functions after all clients have moved on.
Francois-Rene Rideau committed
** Kill original-initargs -- BEWARE, it currently has clients!
276 277 278 279
*** current ECL users used to depend on it for bundles, and may or may
   not be satisfied with how it's not propagated anymore.
*** SLIME uses it (!)
*** weblocks uses it (!)
280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306
** To allow semantically distinct operations of the same class:
You'd need to have a protocol to canonicalize them
in the *OPERATIONS* memoization table, not by class name,
but by CONS of the class name and some CANONICAL-OPERATION-INITARGS.
The latter would be a generic function called on the initargs,
where any parasite initargs such as FORCE and FORCE-NOT have been removed,
since they below to the PLAN, not the OPERATION:
the OPERATE protocol would be refined to explicit split
arguments to be passed to MAKE-PLAN or to MAKE-OPERATION.
would SORT (a plist->alist of) the initargs,
and that would replace the current ORIGINAL-INITARGS slot.
For this scheme to work even in presence of undisciplined users
using MAKE-INSTANCE on an operation class,
the OPERATION class would have an extra slot EFFECTIVE-OPERATION,
uninitialized by default (nil or unbound), whose accessor initializes it
if it's uninitialized, by looking up a canonical instance in *OPERATIONS*,
and if unfound registering the current operation as canonical.
Then, each component's COMPONENT-OPERATION-TIME hash-table
would be indexed by canonicalized operation object
rather than by operation class,
and POIU would have to be changed accordingly.
Of course, this entire cleanup is incompatible
with how SWANK and GBBopen currently abuse slots of operation,
so these would have to be fixed first.
And that's why I didn't do it.
It looks like SWANK can be fixed soon, though, so we'll see.

308 309
* Hunt systems that use obsolete APIs

310 311 312 313 314 315 316 317 318 319 320
* Get rid of component-properties
** directly use component-properties:
*** yaclml.asd => misguided :features for version comparison
*** amazon-ecs-20110418-git/amazon-ecs.asd => :website property
*** hemlock.asd => bad implementation of latin1 encodings
** .asd use :properties
*** arnesi, arnesi+ => :features, misguided for version comparison and pseudo #+features
*** lkcas, thopter => :long-name
*** cl-irc cliki-bot rss cl-syslog com.informatimago.clext
   com.informatimago.clisp com.informatimago.clmisc
322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380
   com.informatimago.common-lisp com.informatimago.common-lisp.csv
   => (uninterned!)
   #:author-email #:date
   (#:albert #:output-dirs)
   (#:albert #:formats)
   (#:albert #:docbook #:template)
   (#:albert #:docbook #:bgcolor)
   (#:albert #:docbook #:textcolor)
   (#:albert #:docbook #:dtd)
*** portableaserve
   ("system" "author" "email")
   ("albert" "presentation" "output-dir")
   ("albert" "presentation" "formats")
   ("albert" "docbook" "dtd")
   ("albert" "docbook" "template")
*** com.clearly-useful.generic-collection-interface => :com.clearly-useful
*** metatilities
   => :ait-timeout :system-applicable-p
*** ucw ucw-core
382 383
384 385

* ASDF4: search for this tag, rename things (incompatibly, thus) and cleanup code.
386 387 388 389 390 391 392 393 394 395 396 397 398 399
** Migrate from component-depends-on to action-depends-on
*** I contend a future version of ASDF will replace
`(component-depends-on operation component)`
with `(action-depends-on plan operation component)`.
This allows for different normalization strategies for dependencies
(including strategies that avoid resolving things to NIL),
a reified context for featurep checks, etc.
*** Easy but long backward-compatible transition:
**** get all users to use the new gf and keep extending both new and old gf,
   meanwhile the new gf has an around method that actually calls the old gf
   except in testing mode and/or if we can check that they're using the new convention
**** when everyone has migrated, remove the old mode and the short-circuit.
*** However, we cannot deprecate component-depends-on yet — not until we have
   some transition in place to a better interface.

401 402
* Documentation
** See message from 2014-01-27 05:26:44 GMT for stuff to document.
** style guide for .asd files
Francois-Rene Rideau committed

406 407 408 409 410 411 412
** deferred-warnings support probably needs to be redone better.
*** implement deferred warnings support on lispworks
*** turn undefined function style-warnings into full warnings(?)
*** work with cl-test-grid to eliminate deferred warnings from quicklisp libraries
*** rewrote part of deferred warnings support.
   Ask him to release the code he implemented at Google under QITAB.

415 416 417 418 419 420 421 422
** Ensure all run-program issues on Windows are solved.
*** SBCL cannot do raw CMD.EXE command-lines
*** We don't seem to properly escape CRLF in escape-windows-token,
   or maybe it is, but CMD.EXE does the wrong thing in them,
   so the semantics depend on whether it's used,
   or maybe it's CCL eating them while parsing, or maybe not, etc.
   In any case, this requires clarification.

423 424 425 426 427 428 429 430 431 432 433
** define-package cannot deal with symbols moving "forward".
*** document that THOU SHALT NOT USE :RECYCLE with packages previously
   defined by define-package when building from scratch.
*** Maybe add a check? But how to tell whether you're building from scratch?
*** Add some :moved-to directive to define-package, such that
   (:moved-to forward-package symbols...)
   will declare symbols as moved forward: when the symbol already exists,
   it is moved to the forward package if that package already exists,
   after the package created if it doesn't exist yet (!)
*** There again, a check that a forward-package is not backward
   would be very nice.
Francois-Rene Rideau committed

* Faster source-registry:
** In addition and/or as a substitute to the .cl-source-registry.cache,
437 438 439 440 441 442 443 444 445 446 447 448 449
   that is meant to be semi-automatically managed, there could be
   a cl-source-registry.conf meant for manual management:
   when recursing into a source-registry :tree, if such file is present
   (or if not, if a hidden .cl-source-registry.conf is present instead?),
   its contents is read as a (:source-registry ...) specification, and
   replaces the actual or notional (:tree ...) for the current directory;
   it may then include :file entries as well as :directory and :tree entries,
   whereby the programmer can explicitly give a definitive list of
   systems exported by his software, while excluding any test system
   that he doesn't want to export. This means that developers have
   both a way of speeding up the build of their software and of
   avoiding pollution by test systems that should remain private,
   and that they can otherwise explicitly enable when they need them.
450 451 452 453 454
** The .cl-source-registry.cache should avoid recursing into
   directories that themselves already have a cache or a .conf file,
   but instead store the name of these directories,
   so these files will be read recursively by asdf, allowing for
   semi-modular updates.
455 456 457 458

* Properly deprecate all that needs to go
** Get lisa, readable, bourbaki to NOT include ASDF 1 anymore in their sources.
** Identify all the things in ASDF that we want to deprecate, and make
   sure we deprecate them all in 3.4.
460 461 462 463 464 465
** Implement support for deprecating old packages,
   by having all functions and macros under the old package name be
   proxies to those in the new package name?
   (Exception: special variables can't be proxies, have to be imported.)
** Eradicate Quicklisp systems that depend on asdf-driver or
   asdf-package-system, make them depend on uiop and asdf3.1 instead.
466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628

* Fix plan
** Goal: Implement proper incrementality for defsystem-depends-on.
Fix the bug wherein ASDF fails to properly handle incrementality for `defsystem-depends-on`.
Some discussion about ASDF at

** DONE Items
*** Add `DEFINE-OP` for loading system definitions.
*** A `DEFINE-OP` will depend on other `DEFINE-OP`s
*** A `DEFINE-OP` depends on all `LOAD-OP` in the file.
Whether via defsystem-depends-on or manual `LOAD-OP`s.
*** Store timestamps in `DEFINE-OP` entries, not `*DEFINED-SYSTEMS*`.
*** In find-system, add condition that all dependencies are up-to-date.
*** This necessitates another layer of visit states,
that do not plan, just check planning...
*** `LOAD-ASD` calls `PERFORM DEFINE-OP` (not the other way around)
*** Systems probably need depend on `(DEFINE-OP . PRIMARY-SYSTEM)`
*** These dynamically-discovered dependencies are stored in a slot of `SYSTEM`.
*** Have a special kind of definition-depends-on dependency.
Before we reuse a node from a previous session,
we must make sure it is still properly defined.
This matters because we do reuse (at least *some* nodes, e.g. system nodes)
from previous sessions, and the control structure may have changed
(i.e. the system hasn't been redefined, but one of its defsystem-depends-on
dependencies has changed).
*** Handle incomplete definitions properly
Don't just let the incompletely parsed system be registered
in a false positive success as if it were an empty system.
Solution: It is registered, but considered out-of-date,
so next attempt to use it will cause a refresh attempt.
*** Handle nested calls to `OPERATE`
We must accept that ASDF isn't really plan-then-perform,
as the ASDF1 model claimed to be.
It's an arbitrary nesting of plan-and-perform, like a parenthesization
with plan (steps) as left parenthesis and perform (steps) as right parenthesis,
and with operate being a maximal balanced span of plan and perform steps.
*** What goes in a shared dynamic `*SESSION*`, what in a private lexical `PLAN`?
Memoization CACHE of various functions, Status of VISITED-NODES, FORCING parameters.
The session will contain not just the current `*CACHE*`, but also
all or most of the graph traversal, thus the `:force` options, etc.
The `*PLAN*` may or may not contain some work queueing.
But even, e.g. a table of "nodes still directly blocking us"
is shared at the shared traversal level.
*** It is an error for a nested `OPERATE` to contradict session flags.
This raises the question of `:force` and `:force-not` flags.
An actual operate cannot contradict them and cause things to be performed
with a wrong subset of dependencies loaded.
Yet, `REQUIRED-COMPONENTS` (that does cause anything to be performed —
except via nested `OPERATE` from `defsystem-depends-on`)
must be able to skip some dependencies
(though maybe only _in addition_ to the global ones).
*** What timestamp for `forced` and `forced-not` actions?
If an action is forced-not, it should be returned with an action stamp from this cache,
and not with `nil` as is currently wrongly done
(unless of course the cache entry is missing,
at which point `nil` is the correct answer).
Conversely, a force means the stamp should be `t`
(indicating it needs to be done in the future)
(that part asdf gets right).
*** Handle planning things that are now done but were done in a previous phase of the build,
so dependency on them should trigger the build.
*** Protocol to not re-perform an action twice
In PERFORM-PLAN, check that an action wasn't already DONE-P due to
being needed in a previous phase of recursively calling OPERATE,
before to PERFORM it.
To correctly propagate timestamps in across nested calls,
the graph traversal and timestamp propagation is shared at the session level
between all nested calls to `OPERATE`.
During a session and across phases, every action has a status made of
a stamp and three bits: KEEP-P, DONE-P, NEED-P.
The stamp also survives across sessions, in `COMPONENT-OPERATION-TIMES`.
*** Detect circularities across nested calls to `OPERATE`
This means the circularity detection data is part of the session.
Notably, the visiting list and set.
The top of the list can also serve to record the dependencies from `OPERATE` to `DEPEND-OP`.
*** In UIOP, RECORD-DEPENDENCY must not cross to an upper plan and/or it should
record the dependency in said upper plan (that matters because
parallel plans doing extra checking, and this is a problem
whereby some links to extra actions are left unresolved).
Maybe in the future, record the dependency in the session, not in a plan.

** TODO items
*** find-system should probably cause a dependency on define-op, especially inside another define-op
*** Is it worth it trying to optimize away a dependency on a define-op
when an action already depends on another operation that "obviously" depends on that define-op?
*** Document DEFINE-OP and the design in asdf.texinfo and/or in some article.

** Future developments
*** Grovel all .asd files in Quicklisp and collect all violations of declarativeness,
where declarativeness is having only defsystem forms. Specially classify in-package,
maybe also defpackage. Then we can assess the impact of requiring declarativeness.
*** Also grovel Quicklisp for all extensions to ASDF:
see if there are new methods on perform, input-files, output-files, operate, etc.
*** To allow defsystem-depends-on to another secondary system within the
same file, I can imagine some system to dynamically create a separate action
(DEFINE-OP foo/x) for each form defsystem foo/x, and have it depend on
all the preceding actions operated in the .asd file.
Plus a last action for dangling load-system or operate statements?
Or one action for every operate statement?
There would be no action of the entire load-asd, but a separate mechanism
to detect circularity?
What about dangling statements? They would be a bit like xcvb weakly-ordered
run-time dependencies that CAN have circularities? Ouch. Really ugly.
Each statement would need its own action? Ouch.
*** Have load-asd clear any invalidated previous secondary system
before loading, which supposes remembering what these systems are.
Then, you're not allowed to forward-reference a secondary system that
hasn't been defined yet while you're loading the .asd, whereas you
can load the asd if you aren't loading it yet.
*** Maybe split DEFINE-OP into PREPARE-DEFINE-OP and DEFINE-OP, so that
secondary systems can be properly loaded?
*** Add mapping from files to action that creates it and/or uses it?
Then we can detect conflict between multiple actions creating one file.
Forbid direct use of files not listed as inputs? What about transitive inputs?
Build in a container that has only the proper files...
*** What data structure for scheduling planned actions?
A doubly-linked to remove entire chunks of the plan after a sub-operate?
That won't do, because later-discovered defsystem dependency can refer to
systems that were planned but not performed, so there need be no contiguity
in the chunks that are performed by subcalls to operate.
Actually, if we otherwise forbid reference to another system
from non-system components, then we could move things with system granularity,
which is one thing; but we still need a general mechanism at the system level.
So, whether it's an explicit queue or an implicit traversal of the dependency graph,
we must check whether an action has already been done before we try to perform it.
And an implicit traversal has the advantage that you can avoid entire subtrees
when you find that the current node has already been performed during
a previous phase of the plan.
In conclusion: "just" traverse the graph at the last minute, and
perform things serially, and/or if you want some parallelism,
build a queue dynamically at the last minute for the "now" jobs
while keeping most of the plan as graph structures.

*** Merging in parts of POIU?
ASDF internals are nothing to be proud of:
ASDF1 was optimized for "smallest code that kind of works in the usual case",
and ASDF3 was optimized for "smallest code that fixes ASDF1 in the general case
while mostly maintaining backward compatibility".

Because of its optimization constraint, ASDF1 was using and abusing lists a lot,
rather than defining nice data structures.
ASDF3 uses somewhat more structured data, with a few more classes, and
algorithms that are O(n) instead of O(n**3) in simple cases and
exponential in carefully crafted examples;
yet it has shunned any definition of more advanced or general data structures.
By contrast, POIU has a dequeue to represent queued compilation jobs, and
a general graph representation for the action graph
(though the original POIU was also O(n**3) because it lacked PREPARE-OP).

I could import the POIU queue and graph representations into ASDF, and
that would add about 100 lines of code to UIOP for the queue, and
200 lines to ASDF for the graph, maybe a bit more if the code is
generalized, commented and largely put in UIOP.

Then, there's the support for actual forking and using forks,
that would be about 400 lines added to UIOP, and
the using it in ASDF to consume the plan, which would be under 200 lines.
But those parts are probably better left out of ASDF itself.
That said, it all was a lot when ASDF was < 1000 lines of code,
but isn't all that much now that it is > 12000 lines of code.