1 Ikiwiki currently only has one type of dependency between pages
2 (plus wikilinks special cased in on the side). This has resulted in various
3 problems, and it's seemed for a long time to me that ikiwiki needs to get
4 smarter about what types of dependencies are supported.
8 The current single dependency type causes the depending page to be rebuilt
9 whenever a matching dependency is added, removed, or *modified*. But a
10 great many things don't care about the modification case, and often cause
11 unnecessary page rebuilds:
13 * map only cares if the pages are added or removed. Content change does
14 not matter (unless show=title is used).
15 * brokenlinks, orphans, pagecount, ditto (generally)
16 * inline in archive mode cares about page title, author changing, but
17 not content. (Ditto for meta with show=title.)
18 * Causes extra work when solving the [[bugs/transitive_dependencies]]
21 ### two types of dependencies needed for [[tracking_bugs_with_dependencies]]
23 >> it seems that there are two types of dependency, and ikiwiki
24 >> currently only handles one of them. The first type is "Rebuild this
25 >> page when any of these other pages changes" - ikiwiki handles this.
26 >> The second type is "rebuild this page when set of pages referred to by
27 >> this pagespec changes" - ikiwiki doesn't seem to handle this. I
28 >> suspect that named pagespecs would make that second type of dependency
29 >> more important. I'll try to come up with a good example. -- [[Will]]
31 >>> Hrm, I was going to build an example of this with backlinks, but it
32 >>> looks like that is handled as a special case at the moment (line 458 of
33 >>> render.pm). I'll see if I can breapk
34 >>> things another way. Fixing this properly would allow removal of that special case. -- [[Will]]
36 >>>> I can't quite understand the distinction you're trying to draw
37 >>>> between the two types of dependencies. Backlinks are a very special
38 >>>> case though and I'll be suprised if they fit well into pagespecs.
41 >>>>> The issue is that the existential pagespec matching allows you to build things that have similar
42 >>>>> problems to backlinks.
43 >>>>> e.g. the following inline:
45 \[[!inline pages="define(~done, link(done)) and link(~done)" archive=yes]]
47 >>>>> includes any page that links to a page that links to done. Now imagine I add a new link to 'done' on
48 >>>>> some random page somewhere - a page which some other page links to which didn't previously get included - the set of pages accepted by the pagespec, and hence the set of
49 >>>>> pages inlined, will change. But, there is no dependency anywhere on the page that I altered, so
50 >>>>> ikiwiki will not rebuild the page with the inline in it. What is happening is that the page that I altered affects
51 >>>>> the set of pages matched by the pagespec without itself being matched by the pagespec, and hence included in the dependency list.
53 >>>>> To make this work well, I think you need to recognise two types of dependencies for each page (and no
54 >>>>> special cases for particular types of links, eg backlinks). The first type of dependency says, "The content of
55 >>>>> this page depends upon the content of these other pages". The `add_depends()` in the shortcuts
56 >>>>> plugin is of this form: any time the shortcuts page is edited, any page with a shortcut on it
57 >>>>> is rebuilt. The inline plugin also needs to add dependencies of this form to detect when the inlined
58 >>>>> content changes. By contrast, the map plugin does not need a dependency of this form, because it
59 >>>>> doesn't actually care about the content of any pages, just which pages it needs to include (which we'll handle next).
61 >>>>> The second type of dependency says, "The content of this page depends upon the exact set of pages matched
62 >>>>> by this pagespec". The first type of dependency was about the content of some pages, the second type is about
63 >>>>> which pages get matched by a pagespec. This is the type of dependency tracking that the map plugin needs.
64 >>>>> If the set of pages matched by map pagespec changes, then the page with the map on it needs to be rebuilt to show a different list of pages.
65 >>>>> Inline needs this type of dependency as well as the previous type - This type handles a change in which pages
66 >>>>> are inlined, the previous type handles a change in the content of any of those pages. Shortcut does not need this type of
67 >>>>> dependency. Most of the places that use `add_depends()` seem to need this type of dependency rather than the first type.
69 >>>>>> Note that inline and map currently achieve the second type of dependency by
70 >>>>>> explicitly calling `add_depends` for each page the displayed.
71 >>>>>> If any of those pages are removed, the regular pagespec would not
72 >>>>>> match them -- since they're gone. However, the explicit dependency
73 >>>>>> on them does cause them to match. It's an ugly corner I'd like to
74 >>>>>> get rid of. --[[Joey]]
76 >>>>> Implementation Details: The first type of dependency can be handled very similarly to the current
77 >>>>> dependency system. You just need to keep a list of pages that the content depends upon. You could
78 >>>>> keep that list as a pagespec, but if you do this you might want to check that the pagespec doesn't change,
79 >>>>> possibly by adding a dependency of the second type along with the dependency of the first type.
81 >>>>>> An example of the current system not tracking enough data is
82 >>>>>> described in [[bugs/transitive_dependencies]].
85 >>>>> The second type of dependency is a little more tricky. For each page, we'd need a list of pagespecs that
86 >>>>> the page depended on, and for each pagespec you'd want to store the list of pages that currently match it.
87 >>>>> On refresh, you'd need to check each pagespec to see if the set of pages that match it has changed, and if
88 >>>>> that set has changed, then rebuild the dependent page(s). Oh, and for this second type of dependency, I
89 >>>>> don't think you can merge pagespecs. If I wanted to know if either "\*" or "link(done)" changes, then just checking
90 >>>>> to see if the set of pages matched by "\* or link(done)" changes doesn't work.
92 >>>>> The current system works because even though you usually want dependencies of the second type, the set of pages
93 >>>>> referred to by a pagespec can only change if one of those pages itself changes. i.e. A dependency check of the
94 >>>>> first type will catch a dependency change of the second type with current pagespecs.
95 >>>>> This doesn't work with backlinks, and it doesn't work with existential matching. Backlinks are currently special-cased. I don't know
96 >>>>> how to special-case existential matching - I suspect you're better off just getting the dependency tracking right.
98 >>>>> I also tried to come up with other possible solutions: e.g. can we find the dependencies for a pagespec? That
99 >>>>> would be the set of pages where a change on one of those pages could lead to a change in the set of pages matched by the pagespec.
100 >>>>> For old-style pagespecs without backlinks, the dependency set for a pagespec is the same as the set of pages the pagespec matches.
101 >>>>> Unfortunately, with existential matching, the set of pages that each
102 >>>>> pagespec depends upon can quickly become "*", which is not very useful. -- [[Will]]
106 I propose the following. --[[Joey]]
108 * Add a second type of dependency, call it an "presence dependency".
109 * `add_depends` defaults to adding a regular ("full") dependency, as
110 before. (So nothing breaks.)
111 * `add_depends($page, $spec, presence => 0)` adds an presence dependency.
112 * `refresh` only looks at added/removed pages when resolving presence
115 This seems straightforwardly doable. I'd like [[Will]]'s feedback on it, if
116 possible. The type types of dependencies I am proposing are not identical
117 to the two types he talks about above, but I hope are close enough that
120 This doesn't deal with the stuff that only depend on the metadata of a
121 page, as collected in the scan pass, changing. But it does leave a window
122 open for adding such a dependency type later.
126 I implemented the above in a branch.
127 [[!template id=gitbranch branch=origin/dependency-types author="[[joey]]"]]
129 Then I found some problems:
131 * Something simple like pagecount, that seems like it could use a
132 presence dependency, can have a pagespec that uses metadata, like
133 `author()` or `copyright()`.
134 * pagestats, orphans and brokenlinks cannot use presence dependencies
135 because they need to update when links change.
137 Now I'm thinking about having a special dependency look at page
138 metadata, and fire if the metadata changes. And it seems links should
139 either be included in that, or there should be a way to make a dependency
140 that fires when a page's links change. (And what about backlinks?)
142 It's easy to see when a page's links change, since there is `%oldlinks`.
143 To see when metadata is changed is harder, since it's stored in the
144 pagestate by the meta plugin. Also, there are many different types of
145 metadata, that would need to be matched with the pagespecs somehow.
147 Quick alternative: Make add_depends look at the pagespec. Ie, if it
148 is a simple page name, or a glob, we know a presence dependency
149 can be valid. If's more complex, convert the dependency from
152 There is a lot to dislike about this method. Its parsing of the pagespec,
153 as currently implemented, does not let plugins add new types of pagespecs
154 that only care about presence. Its pagespec parsing is also subject to
155 false negatives (though these should be somewhat rare, and no false
156 positives). Still, it does work, and it makes things like simple maps and
157 pagecounts much more efficient.
161 #### Will's first pass feedback.
163 If the API is going to be updated, then it would be good to make it forward compatible.
164 I'd like for the API to be extendible to what is useful for complex pagespecs, even if we
165 that is a little redundant at the moment.
167 My attempt to play with this is in my git repo. [[!template id=gitbranch branch=origin/depends-spec author="[[will]]"]]
168 That branch is a little out of date, but if you just look at the changes in IkiWiki.pm you'll see the concept I was looking at.
169 I added an "add_depends_spec()" function that adds a dependency on the pagespec passed to it. If the set of matched pages
170 changes, then the dependent page is rebuilt. At the moment the implementation uses the same hack used by map and inline -
171 just add all the pages that currently exist as traditional content dependencies.
173 > As I note below, a problem with this approach is that it has to try
174 > matching the pagespec against every page, redundantly with the work done
175 > by the plugin. (But there are ways to avoid that redundant matching.)
178 Getting back to commenting on your proposal:
180 Just talking about the definition of a "presence dependency" for the moment, and ignoring implementation. Is a
181 "presence dependency" supposed to cause an update when a page disappears? I assume so. Is a presence dependency
182 supposed to cause an update when a pages existence hasn't changed, but it no longer matches the pagespec.
183 (e.g. you use `created_before(test_page)` in a pagespec, and there was a page, `new_page`, that was created
184 after `test_page`. `new_page` will not match the spec. Now we'll delete and then re-create `test_page`. Now
185 `new_page` will match the spec, and yet `new_page` itself hasn't changed. Nor has its 'presence' - it was present
186 before and it is present now. Should this cause a re-build of any page that has a 'presence' dependency on the spec?
188 > Yes, a presence dep will trigger when a page is added, or removed.
190 > Your example is valid.. but it's also not handled right by normal,
191 > (content) dependencies, for the same reasons. Still, I think I've
192 > addressed it with the pagespec influence stuff below. --[[Joey]]
194 I think that is another version of the problem you encountered with meta-data.
196 In the longer term I was thinking we'd have to introduce a concept of 'internal pagespec dependencies'. Note that I'm
197 defining 'internal' pagespec dependencies differently to the pagespec dependencies I defined above. Perhaps an example:
198 If you had a pagespec that was `created_before(test_page)`, then you could list all pages created before `test_page`
199 with a `map` directive. The map directive would add a pagespec dependency on `created_before(test_page)`.
200 Internally, there would be a second page-spec parsing function that discovers which pages a given pagespec
201 depends on. As well as the function `match_created_before()`, we'd have to add a new function `depend_created_before()`.
202 This new function would return a list of pages, which when any of them change, the output of `match_created_before()`
203 would change. In this example, it would just return `test_page`.
205 These lists of dependent pages could just be concatenated for every `match_...()` function in a pagespec - you can ignore
206 the boolean formula aspects of the pagespec for this. If a content dependency were added on these pages, then I think
207 the correct rebuilds would occur.
209 In all, this is a surprisingly difficult problem to solve perfectly. Consider the following case:
217 > Doesn't shave self.
221 > [!include pages="!link(ShavesSelf)"]
223 Does ShavedByBob.mdwn include itself?
225 (Yeah - in IkiWiki currently links are *not* included by include, but the idea holds. I had a good example a while back, but I can't think of it right now.)
231 > I have also been thinking about some sort of analysis pass over pagespecs
232 > to determine what metadata, pages, etc they depend on. It is indeed
233 > tricky to do. More thoughts on influence lists a bit below. --[[Joey]]
235 >> The big part of what makes this tricky is that there may be cycles in the
236 >> dependency graph. This can lead to situations where the result is just not
237 >> well defined. This is what I was trying to get at above. -- [[Will]]
239 >>> Hmm, I'm not seeing cycles be a problem, at least with the current
240 >>> pagespec terms. --[[Joey]]
242 >>>> Oh, they're not with current pagespec terms. But this is really close to extending to handle
243 >>>> functional pagespecs, etc. And I think I'd like to think about that now.
245 >>>> Having said that, I don't want to hold you up - you seem to be making progress. The best is
246 >>>> the enemy of the good, etc. etc.
248 >>>> For my part, I'm imagining we have two more constructs in IkiWiki:
250 >>>> * A map directive that actually wikilinks to the pages it links to, and
251 >>>> * A `match_sharedLink(pageX)` matching function that matches pageY if both pageX and pageY each have links to any same third page, pageZ.
253 >>>> With those two constructs, one page changing might change the set of pages included in a map somewhere, which might then change the set of pages matched by some other pagespec, which might then...
257 >>>>> I think that should be supported by [[bugs/transitive_dependencies]].
258 >>>>> At least in the current implementation, which considers each page
259 >>>>> that is rendered to be changed, and rebuilds pages that are dependent
260 >>>>> on it, in a loop. An alternate implementation, which could be faster,
261 >>>>> is to construct a directed graph and traverse it just once. Sounds
262 >>>>> like that would probably not support what you want to do.
265 >>>>>> Yes - that's what I'm talking about - I'll add some comments there. -- [[Will]]
269 ### Link dependencies
271 * `add_depends($page, $spec, links => 1, presence => 1)`
272 adds a links + presence dependency.
273 * Use backlinks change code to detect changes to link dependencies too.
274 * So, brokenlinks can fire whenever any links in any of the
275 pages it's tracking change, or when pages are added or
277 * To determine if a pagespec is valid to be used with a links dependency,
278 use the same set that are valid for presence dependencies. But also
279 allow `backlinks()` to be used in it, since that matches pages
280 that the page links to, which is just what link dependencies are
285 ### the removal problem
287 So far I have not addressed fixing the removal problem (which Will
290 Summary of problem: A has a dependency on a pagespec such as
291 "bugs/* and !link(done)". B currently matches. Then B is updated,
292 in a way that makes A's dependency not match it (ie, it links to done).
293 Now A is not updated, because ikiwiki does not realize that it
294 depended on B before.
296 This was worked around to fix [[bugs/inline_page_not_updated_on_removal]]
297 by inline and map adding explicit dependencies on each page that appears
298 on them. Then a change to B triggers the explicit dep. While this works,
299 it's 1) ugly 2) probably not implemented by all plugins that could
300 be affected by this problem (ie, linkmap) and 3) is most of the reason why
301 we grew the complication of `depends_simple`.
303 One way to fix this is to include with each dependency, a list of pages
304 that currently match it. If the list changes, the dependency is triggered.
306 Should be doable, but may involve more work than
307 currently. Consider that a dependency on `bugs/*` currently
308 is triggered by just checking until *one* page is found to match it.
309 But to store the list, *every* page would have to be tried against it.
310 Unless the list can somehow be intelligently updated, looking at only the
315 Found a further complication in presence dependencies. Map now uses
316 presence dependencies when adding its explicit dependencies on pages. But
317 this defeats the purpose of the explicit dependencies! Because, now,
318 when B is changed to not match a pagespec, the A's presence dep does
321 I didn't think things through when switching it to use presence
322 dependencies there. But, if I change it to use full dependencies, then all
323 the work that was done to allow map to use presence dependencies for its
324 main pagespec is for naught. The map will once again have to update
325 whenever *any* content of the page changes.
327 This points toward the conclusion that explicit dependencies, however they
328 are added, are not the right solution at all. Some other approach, such as
329 maintaining the list of pages that match a dependency, and noticing when it
334 ### pagespec influence lists
336 I'm using this term for the concept of a list of pages whose modification
337 can indirectly influence what pages a pagespec matches.
339 > Trying to make a formal definition of this: (Note, I'm using the term sets rather than lists, but they're roughly equivalent)
341 > * Let the *matching set* for a pagespec be the set of existing pages that the pagespec matches.
342 > * Let the *missing document matching set* be the set of pages that would match the spec if they didn't exist. These pages may or may not currently exist. Note that membership of this set depends upon how the `match_()` functions react to non-existant pages.
343 > * Let the *indirect influence set* for a pagespec be the set of all pages, *p*, whose alteration might:
344 > * cause the pagespec to include or exclude a page other than *p*, or
345 > * cause the pagespec to exclude *p*, unless the alteration is the removal of *p* and *p* is in the missing document matching set.
347 > Justification: The 'base dependency mechanism' is to compare changed pages against each pagespec. If the page matches, then rebuild the spec. For this comparison, creation and removal
348 > of pages are both considered changes. This base mechanism will catch:
350 > * The addition of any page to the matching set through its own modification/creation
351 > * The removal of any page *that would still match while non-existant* from the matching set through its own removal. (Note: The base mechanism cannot remove a page from the matching set because of that page's own modification (not deletion). If the page should be removed matching set, then it obviously cannot match the spec after the change.)
352 > * The modification (not deletion) of any page that still matches after the modification.
354 > The base mechanism may therefore not catch:
356 > * The addition or removal of any page from the matching set through the modification/addition/removal of any other page.
357 > * The removal of any page from the matching set through its own modification/removal if it does not still match after the change.
359 > The indirect influence set then should handle anything that the base mechanism will not catch.
363 >> I appreciate the formalism!
365 >> Only existing pages need to be in these sets, because if a page is added
366 >> in the future, the existing dependency code will always test to see
367 >> if it matches. So it will be in the maching set (or not) at that point.
369 >>> Hrm, I agree with you in general, but I think I can come up with nasty counter-examples. What about a pagespec
370 >>> of "!backlink(bogus)" where the page bogus doesn't exist? In this case, the page 'bogus' needs to be in the influence
371 >>> set even though it doesn't exist.
373 >>>> I think you're right, this is a case that the current code is not
374 >>>> handling. Actually, I made all the pagespecs return influences
375 >>>> even if the influence was not present or did not match. But, it
376 >>>> currently only records influences as dependencies when a pagespec
377 >>>> successfully matches. Now I'm sure that is wrong, and I've removed
378 >>>> that false optimisation. I've updated some of the below. --[[Joey]]
380 >>> Also, I would really like the formalism to include the whole dependency system, not just any additions to it. That will make
381 >>> the whole thing much easier to reason about.
383 >> The problem with your definition of direct influence set seems to be
384 >> that it doesn't allow `link()` and `title()` to have as an indirect
385 >> influence, the page that matches. But I'm quite sure we need those.
388 >>> I see what you mean. Does the revised definition capture this effectively?
389 >>> The problem with this revised definition is that it still doesn't match your examples below.
390 >>> My revised definition will include pretty much all currently matching pages to be in the influence list
391 >>> because deletion of any of them would cause a change in which pages are matched - the removal problem.
396 * The pagespec "created_before(foo)" has an indirect influence list that contains foo.
397 The removal or (re)creation of foo changes what pages match it. Note that
398 this is true even if the pagespec currently fails to match.
400 >>> This is an annoying example (hence well worth having :) ). I think the
401 >>> indirect influence list must contain 'foo' and all currently matching
402 >>> pages. `created_before(foo)` will not match
403 >>> a deleted page, and so the base mechanism would not cause a rebuild. The
404 >>> removal problem strikes. -- [[Will]]
406 >>>> But `created_before` can in fact match a deleted page. Because the mtime
407 >>>> of a deleted page is temporarily set to 0 while the base mechanism runs to
408 >>>> find changes in deleted pages. (I verified this works by experiment,
409 >>>> also that `created_after` is triggered by a deleted page.) --[[Joey]]
411 >>>>> Oh, okie. I looked at the source, saw the `if (exists $IkiWiki::pagectime{$testpage})` and assumed it would fail.
412 >>>>> Of course, having it succeed doesn't cure all the issues -- just moves them. With `created_before()` succeeding
413 >>>>> for deleted files, this pagespec will be match any removal in the entire wiki with the base mechanism. Whether this is
414 >>>>> better or worse than the longer indirect influence list is an empirical question. -- [[Will]]
416 * The pagespec "foo" has an empty influence list. This is because a
417 modification/creation/removal of foo directly changes what the pagespec
420 * The pagespec "*" has an empty influence list, for the same reason.
421 Avoiding including every page in the wiki into its influence list is
424 >>> So, why don't the above influence lists contain the currently matched pages?
425 >>> Don't you need this to handle the removal problem? -- [[Will]]
427 >>>> The removal problem is slightly confusingly named, since it does not
428 >>>> affect pages that were matched by a glob and have been removed. Such
429 >>>> pages can be handled without being influences, because ikiwiki knows
430 >>>> they have been removed, and so can still match them against the
431 >>>> pagespec, and see they used to match; and thus knows that the
432 >>>> dependency has triggered.
434 >>>>> IkiWiki can only see that they used to match if they're in the glob matching set. -- [[Will]]
436 >>>> Maybe the thing to do is consider this an optimisation, where such
437 >>>> pages are influences, but ikiwiki is able to implicitly find them,
438 >>>> so they do not need to be explicitly stored. --[[Joey]]
440 * The pagespec "title(foo)" has an influence list that contains every page
441 that currently matches it. A change to any matching page can change its
442 title, making it not match any more, and so the list is needed due to the
443 removal problem. A page that does not have a matching title is not an
444 influence, because modifying the page to change its title directly
445 changes what the pagespec matches.
447 * The pagespec "backlink(index)" has an influence list
448 that contains index (because a change to index changes the backlinks).
449 Note that this is true even if the backlink currently fails.
451 >>> This is another interesting example. The missing document matching set contains all links on the page index, and so
452 >>> the influence list only needs to contain 'index' itself. -- [[Will]]
454 * The pagespec "link(done)" has an influence list that
455 contains every page that it matches. A change to any matching page can
456 remove a link and make it not match any more, and so the list is needed
457 due to the removal problem.
459 >> Why doesn't this include every page? If I change a page that doesn't have a link to
460 >> 'done' to include a link to 'done', then it will now match... or is that considered a
461 >> 'direct match'? -- [[Will]]
463 >>> The regular dependency calculation code will check if every changed
464 >>> page matches every dependency. So it will notice the link was added.
467 #### Low-level Calculation
469 One way to calculate a pagespec's influence would be to
470 expand the SuccessReason and FailReason objects used and returned
471 by `pagespec_match`. Make the objects be created with an
472 influence list included, and when the objects are ANDed or ORed
473 together, combine the influence lists.
475 That would have the benefit of allowing just using the existing `match_*`
476 functions, with minor changes to a few of them to gather influence info.
478 But does it work? Let's try some examples:
480 Consider "bugs/* and link(done) and backlink(index)".
482 Its influence list contains index, and it contains all pages that the whole
483 pagespec matches. It should, ideally, not contain all pages that link
484 to done. There are a lot of such pages, and only a subset influence this
487 When matching this pagespec against a page, the `link` will put the page
488 on the list. The `backlink` will put index on the list, and they will be
489 anded together and combined. If we combine the influences from each
490 successful match, we get the right result.
492 Now consider "bugs/* and link(done) and !backlink(index)".
494 It influence list is the same as the previous one, even though a term has
495 been negated. Because a change to index still influences it, though in a
498 If negation of a SuccessReason preserves the influence list, the right
499 influence list will be calculated.
501 Consider "bugs/* and (link(done) or backlink(index))"
502 and "bugs/* and (backlink(index) or link(done))'
504 Its clear that the influence lists for these are identical. And they
505 contain index, plus all matching pages.
507 When matching the first against page P, the `link` will put P on the list.
508 The OR needs to be a non-short-circuiting type. (In perl, `or`, not `||` --
509 so, `pagespec_translate` will need to be changed to not use `||`.)
510 Given that, the `backlink` will always be evalulated, and will put index
511 onto the influence list. If we combine the influences from each
512 successful match, we get the right result.
514 > This is implemented, seems to work ok. --[[Joey]]
516 > `or` short-circuits too, but the implementation correctly uses `|`,
517 > which I assume is what you meant. --[[smcv]]
519 >> Er, yeah. --[[Joey]]
523 What about: "!link(done)"
525 Specifically, I want to make sure it works now that I've changed
526 `match_link` to only return a page as an influence if it *does*
529 So, when matching against page P, that does not link to done,
530 there are no influences, and the pagespec matches. If P is later
531 changed to add a link to done, then the dependency resolver will directly
534 When matching against page P, that does link to done, P
535 is an influence, and the pagespec does not match. If P is later changed
536 to not link to done, the influence will do its job.
542 Here is a case where this approach has some false positives.
544 "bugs/* and link(patch)"
546 This finds as influences all pages that link to patch, even
547 if they are not under bugs/, and so can never match.
549 To fix this, the influence calculation would need to consider boolean
550 operators. Currently, this turns into roughly:
552 `FailReason() & SuccessReason(patch)`
554 Let's say that the glob instead returns a HardFailReason, which when
555 ANDed with another object, blocks their influences. (But when ORed,
558 Question: Are all pagespec terms that return reason objects w/o any
559 influence info, suitable to block influence in this way?
561 To be suitable to block, a term should never change from failing to match a
562 page to successfully matching it, unless that page is directly changed in a
563 way that influences are not needed for ikiwiki to notice. But, if a term
564 did not meet these criteria, it would have an influence. QED.
568 Note that influences can also have types, same as dependency types.
569 For example, "backlink(foo)" has an influence of foo, of type links.
570 "created_before(foo)" also is influenced by foo, but it's a presence
573 > This is an interesting concept that I hadn't considered. It might
574 > allow significant computational savings, but I suspect will be tricky
575 > to implement. -- [[Will]]
577 >> It was actually really easy to implement it, assuming I picked the right
578 >> dependency types of course. --[[Joey]]
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