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Diffstat (limited to 'doc/todo')
| -rw-r--r-- | doc/todo/dependency_types.mdwn | 206 |
1 files changed, 191 insertions, 15 deletions
diff --git a/doc/todo/dependency_types.mdwn b/doc/todo/dependency_types.mdwn index 479cc95cc..d9e68841d 100644 --- a/doc/todo/dependency_types.mdwn +++ b/doc/todo/dependency_types.mdwn @@ -222,7 +222,7 @@ ShavedByBob.mdwn: Does ShavedByBob.mdwn include itself? -(Yeah - in IkiWiki currently links are included by include, but the idea holds. I had a good example a while back, but I can't think of it right now.) +(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.) sigh. @@ -232,6 +232,36 @@ sigh. > to determine what metadata, pages, etc they depend on. It is indeed > tricky to do. More thoughts on influence lists a bit below. --[[Joey]] +>> The big part of what makes this tricky is that there may be cycles in the +>> dependency graph. This can lead to situations where the result is just not +>> well defined. This is what I was trying to get at above. -- [[Will]] + +>>> Hmm, I'm not seeing cycles be a problem, at least with the current +>>> pagespec terms. --[[Joey]] + +>>>> Oh, they're not with current pagespec terms. But this is really close to extending to handle +>>>> functional pagespecs, etc. And I think I'd like to think about that now. +>>>> +>>>> Having said that, I don't want to hold you up - you seem to be making progress. The best is +>>>> the enemy of the good, etc. etc. +>>>> +>>>> For my part, I'm imagining we have two more constructs in IkiWiki: +>>>> +>>>> * A map directive that actually wikilinks to the pages it links to, and +>>>> * A `match_sharedLink(pageX)` matching function that matches pageY if both pageX and pageY each have links to any same third page, pageZ. +>>>> +>>>> 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... +>>>> +>>>> --[[Will]] + +>>>>> I think that should be supported by [[bugs/transitive_dependencies]]. +>>>>> At least in the current implementation, which considers each page +>>>>> that is rendered to be changed, and rebuilds pages that are dependent +>>>>> on it, in a loop. An alternate implementation, which could be faster, +>>>>> is to construct a directed graph and traverse it just once. Sounds +>>>>> like that would probably not support what you want to do. +>>>>> --[[Joey]] + ---- ### Link dependencies @@ -273,7 +303,7 @@ One way to fix this is to include with each dependency, a list of pages that currently match it. If the list changes, the dependency is triggered. Should be doable, but may involve more work than -currently. Consider that a dependency on "bugs/*" currently +currently. Consider that a dependency on `bugs/*` currently is triggered by just checking until *one* page is found to match it. But to store the list, *every* page would have to be tried against it. Unless the list can somehow be intelligently updated, looking at only the @@ -305,10 +335,53 @@ changes, is needed. I'm using this term for the concept of a list of pages whose modification can indirectly influence what pages a pagespec matches. +> Trying to make a formal definition of this: (Note, I'm using the term sets rather than lists, but they're roughly equivalent) +> +> * Let the *matching set* for a pagespec be the set of existing pages that the pagespec matches. +> * Let a *influence set* for a pagespec be the set of all pages, *p*, whose alteration might: +> * cause the pagespec to include or exclude a page other than *p*, or +> * cause the pagespec to exclude *p*. +> +>> \[Will snipped some stuff and edited the formal definition] +> +> --[[Will]] + +>> I appreciate the formalism! +>> +>> Only existing pages need to be in these sets, because if a page is added +>> in the future, the existing dependency code will always test to see +>> if it matches. So it will be in the maching set (or not) at that point. +>> +>>> Hrm, I agree with you in general, but I think I can come up with nasty counter-examples. What about a pagespec +>>> of "!backlink(bogus)" where the page bogus doesn't exist? In this case, the page 'bogus' needs to be in the influence +>>> set even though it doesn't exist. +>>> +>>>> I think you're right, this is a case that the current code is not +>>>> handling. Actually, I made all the pagespecs return influences +>>>> even if the influence was not present or did not match. But, it +>>>> currently only records influences as dependencies when a pagespec +>>>> successfully matches. Now I'm sure that is wrong, and I've removed +>>>> that false optimisation. I've updated some of the below. --[[Joey]] +>>> +>>> Also, I would really like the formalism to include the whole dependency system, not just any additions to it. That will make +>>> the whole thing much easier to reason about. +>> +>> The problem with your definition of direct influence set seems to be +>> that it doesn't allow `link()` and `title()` to have as an indirect +>> influence, the page that matches. But I'm quite sure we need those. +>> --[[Joey]] + +>>> I see what you mean. Does the revised definition capture this effectively? +>>> The problem with this revised definition is that it still doesn't match your examples below. +>>> My revised definition will include pretty much all currently matching pages to be in the influence list +>>> because deletion of any of them would cause a change in which pages are matched - the removal problem. +>>> -- [[Will]] + #### Examples * The pagespec "created_before(foo)" has an influence list that contains foo. - The removal or (re)creation of foo changes what pages match it. + The removal or (re)creation of foo changes what pages match it. Note that + this is true even if the pagespec currently fails to match. * The pagespec "foo" has an empty influence list. This is because a modification/creation/removal of foo directly changes what the pagespec @@ -318,20 +391,44 @@ can indirectly influence what pages a pagespec matches. Avoiding including every page in the wiki into its influence list is very important! +>>> So, why don't the above influence lists contain the currently matched pages? +>>> Don't you need this to handle the removal problem? -- [[Will]] + +>>>> The removal problem is slightly confusingly named, since it does not +>>>> affect pages that were matched by a glob and have been removed. Such +>>>> pages can be handled without being influences, because ikiwiki knows +>>>> they have been removed, and so can still match them against the +>>>> pagespec, and see they used to match; and thus knows that the +>>>> dependency has triggered. +>>>> +>>>> Maybe the thing to do is consider this an optimisation, where such +>>>> pages are influences, but ikiwiki is able to implicitly find them, +>>>> so they do not need to be explicitly stored. --[[Joey]] + * The pagespec "title(foo)" has an influence list that contains every page that currently matches it. A change to any matching page can change its - title. Why is that considered an indirect influence? Well, the pagespec - might be used in a presence dependency, and so its title changing - would not directly affect the dependency. + title, making it not match any more, and so the list is needed due to the + removal problem. A page that does not have a matching title is not an + influence, because modifying the page to change its title directly + changes what the pagespec matches. * The pagespec "backlink(index)" has an influence list that contains index (because a change to index changes the backlinks). + Note that this is true even if the backlink currently fails. * The pagespec "link(done)" has an influence list that contains every page that it matches. A change to any matching page can remove a link and make it not match any more, and so the list is needed due to the removal problem. +>> Why doesn't this include every page? If I change a page that doesn't have a link to +>> 'done' to include a link to 'done', then it will now match... or is that considered a +>> 'direct match'? -- [[Will]] + +>>> The regular dependency calculation code will check if every changed +>>> page matches every dependency. So it will notice the link was added. +>>> --[[Joey]] + #### Low-level Calculation One way to calculate a pagespec's influence would be to @@ -379,17 +476,89 @@ Given that, the `backlink` will always be evalulated, and will put index onto the influence list. If we combine the influences from each successful match, we get the right result. -> This is implemented, seems to work ok. --[[Joey]] +> This is implemented, seems to work ok. --[[Joey]] -#### High-level Calculation and Storage +> `or` short-circuits too, but the implementation correctly uses `|`, +> which I assume is what you meant. --[[smcv]] -Calculating the full influence list for a pagespec requires trying to match -it against every page in the wiki. +>> Er, yeah. --[[Joey]] -I'd like to avoid doing such expensive matching redundantly. So add a -`pagespec_match_all`, which returns a list of all pages in the whole -wiki that match the pagespec, and also adds the pagespec as a dependency, -and while it's at it, calculates and stores the influence list. +---- + +What about: "!link(done)" + +Specifically, I want to make sure it works now that I've changed +`match_link` to only return a page as an influence if it *does* +link to done. + +So, when matching against page P, that does not link to done, +there are no influences, and the pagespec matches. If P is later +changed to add a link to done, then the dependency resolver will directly +notice that. + +When matching against page P, that does link to done, P +is an influence, and the pagespec does not match. If P is later changed +to not link to done, the influence will do its job. + +Looks good! + +---- + +Here is a case where this approach has some false positives. + +"bugs/* and link(patch)" + +This finds as influences all pages that link to patch, even +if they are not under bugs/, and so can never match. + +To fix this, the influence calculation would need to consider boolean +operators. Currently, this turns into roughly: + +`FailReason() & SuccessReason(patch)` + +Let's say that the glob instead returns a HardFailReason, which when +ANDed with another object, drops their influences. (But when ORed, combines +them.) Fixes the above, but does it always work? + +"(bugs/* or link(patch)) and backlink(index)" => +`( HardFailReason() | SuccessReason(page) ) & SuccessReason(index)`` => +`SuccessReason(page & SuccessReason(index)` => +SuccessReason(page, index) => right + +"(bugs/* and link(patch)) or backlink(index)" => +`( HardFailReason() & SuccessReason(page) ) | SuccessReason(index)`` => +`HardFailReason() | SuccessReason(index)` => +`SuccessReason(index)` => right + +"!bugs/* and link(patch)" => +`HardFailReason() | SuccessReason(bugs/foo)` => +`HardFailReason()` => right + +#### High-level Calculation and Storage + +Naively calculating the full influence list for a pagespec requires trying +to match it against every page in the wiki. I'd like to avoid doing such +expensive matching redundantly. + +It may be possible, for some types of pagespecs, to just try matching a +single, arbitrary page against it, and know the full influence list has +been obtained. It seems to be that case that if a pagespec has any +influences, matching any page will return at least one. So if none are +returned, we can skip trying other pages. + +If the influence list does not include the page that was tried, we know +that the pagespec does not things like `link()` and `title()`, that are +influenced by the page's own content. So it *might* be safe to not try +matching any more pages in this case too. I think it would work for all +current pagespec terms. There might be a hypothetical term where this +optimisation doesn't work. We could add a special case to ensure it can +work: If a term declares it is unfluenced by "", then it means it is +always influenced by the matching page. + +Anyway, this seems worth doing: Add a `pagespec_match_all`, which returns a +list of all pages in the whole wiki that match the pagespec, and also adds +the pagespec as a dependency, and while it's at it, calculates and stores +the influence list. It could have an optional sort parameter, and limit parameter, to control how many items to return and the sort order. So when inline wants to @@ -414,7 +583,7 @@ it's calculated more smartly, and is added automatically. > I've implemented influence calculation in `add_depends`. As expected, > it means rather a lot more work, and makes some things much slower. -> Optimisation via `pagespec_match_depends` next.. --[[Joey]] +> Optimisations next.. --[[Joey]] #### Influence types @@ -422,3 +591,10 @@ Note that influences can also have types, same as dependency types. For example, "backlink(foo)" has an influence of foo, of type links. "created_before(foo)" also is influenced by foo, but it's a presence type. Etc. + +> This is an interesting concept that I hadn't considered. It might +> allow significant computational savings, but I suspect will be tricky +> to implement. -- [[Will]] + +>> It was actually really easy to implement it, assuming I picked the right +>> dependency types of course. --[[Joey]] |