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Revset null/wdir Plan

How to handle null and wdir() in revset?

Contents

Status of revset functions
Status of commands
Expected behavior
Possible use cases
Possible implementation
See also

1. Status of revset functions

A list of revset functions and operators sorted by category.

(TODO: add current/expected behavior of wdir())

works as expected
not determined, but seems correct
not determined, but seems wrong or unsure
wrong

1.1. Set

common set operation or intersection with computed set
should have no problem with null and wdir()
but several functions use None (= wdir()) for different meanings

Predicate	null
`not x`	`null: & !0:tip -> -1`
	`null:0 & !null -> 0`
`x and y`	`null:tip & null -> -1`
`x or y`	`0 + null -> -1`
`x - y`	`null:tip - 0: -> -1`
`all()`	`null & all() -> ()`
`bundle()`	bundle won't have null
`first(set, [n])`, `limit(...)`	`first(null:) -> ()`
	`null: & first(null:) -> -1`
`hidden()`	null won't be hidden
`last(set, [n])`	`last(tip:null) -> ()`
	`null: & last(tip:null) -> -1`
`outgoing([path])`	null won't appear
`remote([id [,path]])`	null won't appear
`reverse(set)`	`reverse(null:0) -> 0, -1`

1.2. Ancestor / Descendant

operation that interacts with DAG or revlog
wdir() can't live in it
null sometimes goes wrong because p2() = null
4905

Predicate	null
`x::y`	`null::0 -> -1, 0`
`x^n`, `x^`	`0^1 -> -1`
`x^`	`0^ -> ()`
`x~n`	`0~1 -> -1`
`ancestor(*changeset)`	`ancestor(*roots) -> ()`
	`ancestor(null) -> ()`
	`null: & ancestor(*roots) -> -1`
`ancestors(set)`	`ancestors(null:0) -> -1, 0`
`branchpoint()`	`null & branchpoint() -> -1`
`children(set)`	`children(null) -> roots`
`descendants(set)`	`descendants(null) -> *`
`follow()`	`null & follow() -> ()`
`follow(file)`	null should have no file
`heads(set)`	`heads(null) -> -1`
	`null: & heads(0) -> 0`
`merge()`	`null & merge() -> ()`
`only(set, [set])`	null won't appear
`p1([set])`	`p1(0) -> ()`
	`null & p1(0) -> ()`
`p2([set])`	`p2(0) -> ()`
`parents([set])`	`parents(0) -> ()`
	`null & parents(0) -> ()`
`roots(set)`	`roots(null:0) -> -1, 0`

1.3. Arithmetic

integer comparison, increment or decrement
null should work, but wdir() can't because of None

Predicate	null
`x:y`	`null:0 -> -1, 0`
`max(set)`	`max(null) -> ()`
	`null: & max(null) -> -1`
`min(set)`	`min(null) -> ()`
	`null: & min(null) -> -1`
`sort(set[, [-]key...])` key=rev	`sort(0:null) -> -1, 0`

1.4. Changectx attribute

filter by ctx attributes
should have no problem with null and wdir()

Predicate	null
`author(string)`, `user(string)`	`null & author("") -> -1`
`closed()`	null won't be closed
`converted([id])`	null won't be converted
`date(interval)`	`null & date(-99999) -> -1`
`desc(string)`	`null & desc("") -> -1`
`destination([set])`	null won't be rebased
`extra(label, [value])`	`null & extra(branch, default) -> -1`
`grep(regex)`	`null & grep("") -> -1`
`keyword(string)`	`null & keyword("") -> -1`
`matching(revision [, field])`	`null & matching(null) -> -1`
`origin([set])`	null won't be rebased
`sort(set[, [-]key...])` key!=rev	`sort(0:null, date) -> -1, 0`

1.5. File status / manifest

filter by match, etc.
should have no problem with null and wdir()

Predicate	null
`adds(pattern)`	null should have no file
`contains(pattern)`
`file(pattern)`
`modifies(pattern)`
`removes(pattern)`
`subrepo([pattern])`

1.6. Misc revision data

filter by miscellaneous data that requires a real revision
tend to crash by wdir()

Predicate	null
`bisect(string)`	null won't appear
`bookmark([name])`	null won't be bookmarked
`branch(string)`	`null & branch(default)`
`branch(set)`	`branch(null) -> 0, ...`
`bumped()`	null won't appear
`divergent()`	null won't appear
`draft()`	null should be public
`extinct()`	null won't appear
`filelog(pattern)`	null should have no file
`head()`	`null & head() -> ()` in empty repo
`named(namespace)`	null won't be named
`obsolete()`	null won't be obsoleted
`public()`	`null & public() -> -1`
`secret()`	null should be public
`tag([name])`	null won't be tagged
`unstable()`	null won't appear

1.7. Trivial identifier / wrapper

Predicate	null
`id(string)`	`id(000000000000) -> -1`
`present(set)`	`present(null) -> -1`
`rev(number)`	`rev(-1) -> -1`

2. Status of commands

finished
$/!\$ partially implemented
not yet finished

(TODO: commands that should reject wdir(), subrepo, largefiles?)

Command	Default	wdir
`annotate`	`p1`
`archive`	`p1`	3ec8351fa6ed
`cat`	`p1`	$/!\$
`diff`	`p1:wdir`	$/!\$
`export`	`p1`	$/!\$ 5438
`files`	`wdir`
`grep`	`tip:0`
`identify`	`wdir`
`locate`	`wdir`
`log`	`tip:0`
`parents`	`wdir`
`status`	`wdir`

3. Expected behavior

General guidelines (from 4691)

null should not appear in the general case
We need a simple and consitent rules for it to appear
It must not be an implementation hell revset side
It should be simple enough to support it when writing revset in extension
We want similar rules for wdir()

marmoute:

null should not survive combination (and) with anything.

1) The following include null in the result
- "null"
- "null + 2"
- "null::" (probably)
- "::null" (probably)

2) the following does not includes it
- "null and (::2)"
- "null and date(-9001)"
- "null and all()"
(replaces null by any of the variant in (1))

"all()" could maybe take and argument to accept null.

yuja:

null should work just like other revisions once appeared

- "null and (:2)" -> ()       # because :2 = 0:2
- "null and (::2)" -> (null,)
- "null and date(-100000)" -> (null,)
- "null and all()" -> ()      # if all() = 0:tip
                   or (null)  # if all() = everything in sets (like "and true")
- "wdir() and draft()" -> (wdir,)

4. Possible use cases

(TODO: I don't have good example in mind)

hg log -Gr ":wdir() and branch(name)" to show DAG of the specified branch including working directory
hg log -r "wdir():0 and modifies(pattern)"

5. Possible implementation

how null and wdir() appear in set:

fullreposet allows us to populate a set containing null and wdir() only if specified (d2de20e1451f, backed out by e16456831516)
this magic should be disabled once fullreposet is evaluated
- .filter() -> spanset().filter()

None is itchy:

map None to len(repo) or INT_MAX
1. always integer in set: repo[len(repo)] -> wctx, but wctx.rev() -> None
2. use integer representation only in revset: wrap result by a proxy set
  that converts between None and len(repo)
len(repo)
- will allow us to handle wdir as contiguous revision
- but it is likely to hide bugs
INT_MAX
- is constant, which will cause less bugs
- but it can't appear in spanset, will require more special cases
changelog, rbc, etc.
- null should be handled in the same way as regular revisions because changelog knows it.
- but wdir() isn't. what should we do?
- https://selenic.com/pipermail/mercurial-devel/2015-July/071768.html

ff... hash:

have to exist in base-16 trie (nodetree) so that short ff... hash can be resolved correctly.
- but nodetree uses INT_MAX for nullrev.

6. See also

CategoryDeveloper CategoryNewFeatures