windows: fix incorrect detection of broken pipe when writing to pager Paging e.g. hg incoming on Windows and quitting the pager before the output is consumed will print 'abort: Invalid argument'. This is because the windows error 0xE8 (ERROR_NO_DATA) is mapped to EINVAL even though it is documented as 'The pipe is being closed'. Note that this fix assumes that Windows' last error code is still valid in the exception handler. It works correctly in all my tests. A simpler fix would be to just map EINVAL to EPIPE, like was done is flush previously, but that would be less precise. This error was not observed previously, when pager was an extension.

test: stop passing --quiet in a run dedicated to debug output The goal of the run is to display some debug output. Passing --quiet in this case is strange.

acl: add bookmarks support Originally submitted at https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-March/080650.html as an RFC by timeless. .. feature:: The `acl` extension now has support for bookmarks as well as branches. Differential Revision: https://phab.mercurial-scm.org/D3750

repository: define manifest interfaces The long march towards declaring interfaces for repository primitives continues. This commit essentially defines interfaces based on the following types: * manifest.manifestdict -> imanifestdict * manifest.manifestlog -> imanifestlog * manifest.memmanifestctx -> imanifestrevisionwritable * manifest.manifestctx -> imanifestrevisionstored * manifest.memtreemanifestctx -> imanifestrevisionwritable * manifest.treemanifestctx -> imanifestrevisionstored * util.dirs -> idirs The interfaces are thoroughly documented. Their documentation is now better than the documentation in manifest.py in many cases. With the exception of util.dirs, classes have been annotated with their interfaces. (I didn't feel like util.dirs needed the proper interface treatment.) Tests have been added demonstrating that all classes and instances conform to their interfaces. This work was much easier than filelogs. That's because Durham did an excellent job formalizing the manifest API a while back. There are still some minor kludges with the interfaces that should probably be addressed. But the primary goal with interface declarations is getting something established. Once we have an interface, we can modify it later easily enough. Differential Revision: https://phab.mercurial-scm.org/D3869

narrowbundle2: when we handle a widen, mark the operation as unsafe We have to manually drive the context manager here since the logic is awkwardly split between a couple of places. Differential Revision: https://phab.mercurial-scm.org/D3719

narrow: mark the critical chunks of narrowing/widening as unsafe I'm _mostly_ sure these are the only unsafe chunks here. Differential Revision: https://phab.mercurial-scm.org/D3718

repair: mark the critical section of strip() as unsafe When our experimental nointerrupt feature is enabled, this will help prevent users from corrupting their repo during a strip. Differential Revision: https://phab.mercurial-scm.org/D3717

ui: add an uninterruptable context manager that can block SIGINT The blocking of SIGINT is not done by default, but my hope is that we will one day. This was inspired by Facebook's "nointerrupt" extension, which is a bit more heavy-handed than this (whole commands are treated as unsafe to interrupt). A future patch will enable this for varying bits of Mercurial that are performing unsafe operations. It's intentional that the KeyboardInterrupt is raised as the context manager exits: during the span of the context manager interrupting Mercurial could lead to data loss, but typically those spans are fairly narrow, so we can let the unsafe block complete and then terminate hg (which will leave the repo in a consistent state, even if it's not the user's desired state). .. api:: New context manager ``ui.uninterruptable()`` to mark portions of a command as potentially unsafe places to interrupt Mercurial with Control-C or similar. Differential Revision: https://phab.mercurial-scm.org/D3716

merge with stable

Added signature for changeset 0b63a6743010

Added tag 4.6.2 for changeset 0b63a6743010

revset: add partial support for ancestor(wdir()) It's easy, so let's make it happen. I'm not certain if 'wdir() &' should be required. ancestors(wdir()) works without it, but ancestor(wdir()) doesn't as of now. That's the issue of fullreposet.__contains__() vs __and__().

context: also accept diff option directly For now we accept both diff option and dictionary. This will let us upgrade internal users gradually before we drop the old API at the end of this series.

context: also take all other arguments than `patch.diff` accept This is needed to use `context.diff` as a full replacement of `patch.diff`

context: explicitly take diffopts in `context.diff` (API) To provide a proper replacement for the `patch.diff(…)` function, the `context.diff(…)` method needs to be able to take more parameters. To distinguish the diff options from the new other arguments, we upgrade the diff options to its own explicit argument.

rebase: check whether the rebasestate exists or not a bit early Converted the else part into `if True` because that part will soon be under a except part. Differential Revision: https://phab.mercurial-scm.org/D3876

rebase: use staeobj to check whether interrupted rebase exists This cleans up the code a bit. Differential Revision: https://phab.mercurial-scm.org/D3875

rebase: add a stateobj variable to rebaseruntime class The stateobj variable is an object of state.cmdstate() and will be used in upcoming patches to clean up the logic a bit and also use cbor format to write data to rebasestate class. Differential Revision: https://phab.mercurial-scm.org/D3874

rebase: refactor logic to read rebasestate in a separate function This will help us in plugging the use of state.cmdstate() to read rebasestate. Differential Revision: https://phab.mercurial-scm.org/D3873

revlog: reuse 'descendant' implemention in 'isancestor' The two functions do the same thing, but one takes nodes while the other takes revs. Using one to implement the other make sense. We should probably cleanup the API at some point to avoid having so many similar functions. However, we focus on an efficient implementation for now.

revlog: efficient implementation of 'descendant' Iterating over descendants is costly, because there are no "parent -> children" pointers. Walking the other way around is much more efficient, especially on large repositories, where descendant walks can cost seconds. And the other hand, common ancestors code follows links in the right direction and has a compiled implementation. In real life usage, this saved up to 80s during some pull operations, where descendant test happens in extension code.

revlog: refactor out the rev-oriented part of commonancestorheads We plan to use this in a function taking revs as argument. Round trips to nodes seem silly.

revlog: do inclusive descendant testing (API) In many other places, a revision is considered a descendant of itself. We update the behavior of `revlog.descendant()` to match this. (for example. `revlog.isancestor` does inclusive testing). No tests break, so it seems safe to do so. This will make it easier to use a more efficient implementation in a later changeset.

manifest: make cachesize a private attribute AFAICT this isn't accessed outside the class. It is a private attribute and its naming should reflect that. Differential Revision: https://phab.mercurial-scm.org/D3868

repository: document that file() return value conforms to interface Differential Revision: https://phab.mercurial-scm.org/D3867

cleanup: pass in overwrite flag to hg.updaterepo() as named argument For clarity.

histedit: use self.stateobj to check whether interrupted histedit exists self.stateobj is an instance of state.cmdstate() class which has an .exists() function which is used to check whether there exists an interrupted statefile or not. Differential Revision: https://phab.mercurial-scm.org/D3865

histedit: add a stateobj variable to histeditstate class The stateobj variable will be an instance of state.cmdstate() class. The stateobj variable will be used in upcoming patches to simplify the code a bit and start using cbor to write state files. Differential Revision: https://phab.mercurial-scm.org/D3864

histedit: factor out logic of processing state data in separate fn The new function will serve as the point from where we always get a dictionary of data stored in the statefile and will be helpful in integrating state.cmdstate.read() to write statefile in cbor. Differential Revision: https://phab.mercurial-scm.org/D3863

histedit: use hg.updaterepo() to avoid ui.{push|pop}buffer() hack In some parts of code, we call hg.update() and surround that with ui.pushbuffer() and ui.popbuffer() to suppress the output returned by hg.update(). We have hg.updaterepo() which does not writes to UI and can be used instead. Differential Revision: https://phab.mercurial-scm.org/D3862

scmutil: fix __enter__ in progress context manager Differential Revision: https://phab.mercurial-scm.org/D3861

httppeer: fix use of uninitialized variable with devel logging If the request fails, "res" was uninitialized. Differential Revision: https://phab.mercurial-scm.org/D3860

rebase: convert opts dict to bytes at once

rebase: isolate command options from internal flags I want to get rid of per-function byteskwargs(opts).

rebase: suppress warning thrown when aborting rebase in case of dryrun Before this patch dryrun output contained "rebase aborted" every time we run rebase in dryrun mode and this warning does not sound safe from a user prespective. Differential Revision: https://phab.mercurial-scm.org/D3857

rebase: no need to store backup in case of dryrun While aborting an unfinished rebase in case of dryrun there is no need to store backup for those rebased csets. Differential Revision: https://phab.mercurial-scm.org/D3827

rebase: split _origrebase() for conveniece in dryrun This patch split _origrebase() method by extracting rbsrt part from that to make it easy to implement dryrun in more elegant way than before. Differential Revision: https://phab.mercurial-scm.org/D3856

rebase: extract dryrun as a function To avoid more number of indented blocks and make it easier to add additional functionality in dryrun, extracted as a function. Differential Revision: https://phab.mercurial-scm.org/D3855

rebase: add lock to cover whole dryrun process Before this patch it is easy for another hg to interrupt the dryrun. This patch make sure that dryrun will complete without any interruption. Differential Revision: https://phab.mercurial-scm.org/D3854

merge: add a 'keepconflictparent' argument to graft Before this change, `merge.graft` was always dropping the "grafted" changeset from the parent. This is impractical in case of conflict as the second parent can be useful to help with conflict resolution. We add a new boolean parameter to control this behavior. This will make using `merge.graft` directly in shelve practicable. Differential Revision: https://phab.mercurial-scm.org/D3692

unlinkpath: make empty directory removal optional (issue5901) (issue5826) There are known cases where performing operations such as rebase from a directory that is newly created can fail or at least lead to being in a directory handle that no longer exists. This is even reproducible by just doing something as simple as: cd foo; hg rm * The behavior is different if you use `hg addremove`, the directory is not removed until we attempt to go back to the node after committing it: cd foo; rm *; hg addremove; hg ci -m'bye foo'; hg co .^; hg co tip Differential Revision: https://phab.mercurial-scm.org/D3859

py3: convert opts keys to bytes using pycompat.byteskwargs() This fixes the py3 build broken due to 56b2074114b19e12abd9cd4c378d58b702232705. Differential Revision: https://phab.mercurial-scm.org/D3853

procutil: add a shim for translating shell commands to native commands

revset: move lookup of first ancestor() candidate out of the loop

revset: leverage orset() to flatten ancestor() arguments This also makes orset() accept an empty argument because nullary ancestor() call is valid. That's not the case for orset(), but should be okay.

revset: remove orphan i18n comment from ancestor()

grep: deprecates `--all` flag As the name "all" is a misnomer for an option that searches on diffs of revisions, we are moving to diff flag from all, deprecating it in the process. Differential Revision: https://phab.mercurial-scm.org/D3825

namespaces: let namespaces override singlenode() definition Some namespaces have multiple nodes per name (meaning that their namemap() returns multiple nodes). One such namespace is the "topics" namespace (from the evolve repo). We also have our own internal namespace at Google (for review units) that has multiple nodes per name. These namespaces may not want to use the default "pick highest revnum" resolution that we currently use when resolving a name to a single node. As an example, they may decide that `hg co <name>` should check out a commit that's last in some sense even if an earlier commit had just been amended and thus had a higher revnum [1]. This patch gives the namespace the option to continue to return multiple nodes and to override how the best node is picked. Allowing namespaces to override that may also be useful as an optimization (it may be cheaper for the namespace to find just that node). I have been arguing (in D3715) for using all the nodes returned from namemap() when resolving the symbol to a revset, so e.g. `hg log -r stable` would resolve to *all* nodes on stable, not just the one with the highest revnum (except that I don't actually think we should change it for the branch namespace because of BC). Most people seem opposed to that. If we decide not to do it, I think we can deprecate the namemap() function in favor of the new singlenode() (I find it weird to have namespaces, like the branch namespace, where namemap() isn't nodemap()'s inverse). I therefore think this patch makes sense regardless of what we decide on that issue. [1] Actually, even the branch namespace would have wanted to override singlenode() if it had supported multiple nodes. That's because closes branch heads are mostly ignored, so "hg co default" will not check out the highest-revnum node if that's a closed head. Differential Revision: https://phab.mercurial-scm.org/D3852

rebase: refactor dryrun implementation This patch refactor dry-run code to make it easy to add additional functionality in dryrun. Otherwise we had to add every functionality through _origrebase() which does not seem a good implementation. Differential Revision: https://phab.mercurial-scm.org/D3849

hooks: allow Unix style environment variables on external Windows hooks This will help making common hooks between Windows and non-Windows platforms. Having to build the shellenviron dict here and in procutil.system() is a bit unfortunate, but the only other option is to fix up the command inside procutil.system(). It seems more important that the note about the hook being run reflects what is actually run. The patch from last summer added the hooks on the command line, but it looks like HG_ARGS has since learned about --config args, and the output was just confusing. Therefore, it's now loaded from a file in the histedit test for clarity.

windows: add a method to convert Unix style command lines to Windows style This started as a copy/paste of `os.path.expandvars()`, but limited to a given dictionary of variables, converting `foo = foo + bar` to `foo += bar`, and adding 'b' string prefixes. Then code was added to make sure that a value being substituted in wouldn't itself be expanded by cmd.exe. But that left inconsistent results between `$var1` and `%var1%` when its value was '%foo%'- since neither were touched, `$var1` wouldn't expand but `%var1%` would. So instead, this just converts the Unix style to Windows style (if the variable exists, because Windows will leave `%missing%` as-is), and lets cmd.exe do its thing. I then dropped the %% -> % conversion (because Windows doesn't do this), and added the ability to escape the '$' with '\'. The escape character is dropped, for consistency with shell handling. After everything seemed stable and working, running the whole test suite flagged a problem near the end of test-bookmarks.t:1069. The problem is cmd.exe won't pass empty variables to its child, so defined but empty variables are now skipped. I can't think of anything better, and it seems like a pre-existing violation of the documentation, which calls out that HG_OLDNODE is empty on bookmark creation. Future additions could potentially be replacing strong quotes with double quotes (cmd.exe doesn't know what to do with the former), escaping a double quote, and some tilde expansion via os.path.expanduser(). I've got some doubts about replacing the strong quotes in case sh.exe is run, but it seems like the right thing to do the vast majority of the time. The original form of this was discussed about a year ago[1]. [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-July/100735.html

hgweb: add archive entries to graph page Changelog page has them, so it makes sense to add them to graph page too.

hgweb: add z-index for search field tooltip On graph page, search field tooltip sometimes goes down to the graph area, where it used to be covered by foreground element of graph entries (.fg) because they have z-index: 10. To prevent the tooltip from being covered, z-index: 15 is enough.

tests: pass "rev" argument to commands.update() as string commands.update() normally gets its "rev" argument as a string, but test-basic.t was passing an integer. That happened to work, but we shouldn't rely on it. Differential Revision: https://phab.mercurial-scm.org/D3851

revset: fix heads() order to always follow the input set (BC) An argument expression should never affect the order of the result set. That's the rule of the revset predicates.

test-revset: show that order of heads() can be wrong

stringutil: update list of re-special characters to include &~ I missed this because I was looking at the change that refactored re.escape, and these characters were added in https://github.com/python/cpython/commit/05cb728d68a278d11466f9a6c8258d914135c96c. Differential Revision: https://phab.mercurial-scm.org/D3850

tests: fix up some lax escaping in test-template-basic.t These misfired escapes turn into hard errors in Python 3.7, and I'd really rather we not work around it. We should *probably* try and find a way to proactively warn users about invalid escape sequences. There's one more failure of this type in this file on Python 3.7, but I can't figure out the issue. It'll need to be corrected in a follow-up. Differential Revision: https://phab.mercurial-scm.org/D3843

cleanup: migrate from re.escape to stringutil.reescape This has consistent behavior on Python 2.7, 3.6, and 3.7 and has the benefit of probably being a little faster. Test output changes are largely because / used to be pointlessly escaped. Differential Revision: https://phab.mercurial-scm.org/D3842

stringutil: add a new function to do minimal regex escaping Per https://bugs.python.org/issue29995, re.escape() used to over-escape regular expression strings, but in Python 3.7 that's been fixed, which also improved the performance of re.escape(). Since it's both an output change for us *and* a perfomance win, let's just effectively backport the new behavior to hg on all Python versions. Differential Revision: https://phab.mercurial-scm.org/D3841

graft: add no-commit mode (issue5631) This patch adds a new flag --no-commit in graft command. This feature grafts the changes but do not create commits for those changes, grafted changes will be added in the working directory. Also added tests to reflect the expected behavior. Differential Revision: https://phab.mercurial-scm.org/D2409

patchbomb: use email.mime.base instead of email.MIMEBase The later was removed on Python 3. On python 2: >>> email.MIMEBase.MIMEBase is email.mime.base.MIMEBase True Differential Revision: https://phab.mercurial-scm.org/D3836

patchbomb: use email.mime.multipart instead of email.MIMEMultipart The later was removed in Python 3. On python 2: >>> email.MIMEMultipart.MIMEMultipart is email.mime.multipart.MIMEMultipart True Differential Revision: https://phab.mercurial-scm.org/D3835

py3: add b'' prefixes in tests/test-bundle2-pushback.t This makes the test run on Python 3. # skip-blame because just b'' prefixes. Differential Revision: https://phab.mercurial-scm.org/D3834

py3: make tests/test-diff-antipatience.t work with python 3 On python3, if we do list(b'abcd'), we get [97, 98, 99, 100]. So this patch does the list() operation on unicodes and then convert things to bytes. This also adds `and None` to suppress return values of .write() calls. Differential Revision: https://phab.mercurial-scm.org/D3833

terse: pass "clean" and "unknown" booleans by name for clarity Differential Revision: https://phab.mercurial-scm.org/D3838

terse: add tests of running from subdirectory I also included comments explaining what I think the output should be (discussion started on D3628). Differential Revision: https://phab.mercurial-scm.org/D3837

convert: don't pass --no-files to "darcs show repo" command The test fails with darcs 2.14.0 because --no-files is no longer supported. It was removed at the patch 97973a52bf496657558412562d6fad2ee651b1e0, which says "show repo: removed --files option, removed manual flags parsing." As far as I can tell, --no-files was specified just for optimization, so old darcs should work without it.

shelve: stop testing missing rebase state file We no longer use the file. Neither during rebase not during continue. Differential Revision: https://phab.mercurial-scm.org/D3691

shelve: actually test corrupted shelve state The test was previous moving the corrupted shelve state file as an histedit state file. Differential Revision: https://phab.mercurial-scm.org/D3690

shelve: directly handle `--continue` Shelve is currently sub-contracting some of its work to the rebase extension. In order to make shelve more independent and flexible we would like shelve to handle the parent alignment directly. This changeset takes on the next step, handling the abort process. Same as for --abort. It turns out we have all the necessary bits in the `shelvestate` file. So we do not need anything from the interrupted rebase. Differential Revision: https://phab.mercurial-scm.org/D3689

shelve: directly handle the abort process Shelve is currently sub-contracting some of its work to the rebase extension. In order to make shelve more independent and flexible we would like shelve to handle the parent alignment directly. This change starts with the simplest bits, handling the abort process. It turns out we have all the necessary bits in the `shelvestate` file. So we do not need anything from the interrupted rebase. As a nice side effect, a test about missing `shelverebasestate` state file now behave better. Differential Revision: https://phab.mercurial-scm.org/D3688

shelve: check the actual shelvestate in morestatus The rebasestate is a lower level implementation details that we are trying to remove. Differential Revision: https://phab.mercurial-scm.org/D3687

packaging: dynamically define make targets We currently have make boilerplate for each instance of a distro's release. This is redundant, annoying to maintain, and prone to errors. This commit defines variables holding available releases for various distros. We then iterate through the list and dynamically define make targets. Differential Revision: https://phab.mercurial-scm.org/D3761

packaging: don't write files for templatized Dockerfiles Now that Docker image building is implemented in Python and we can perform template substitution in memory, we don't need to write out produced Dockerfiles to disk. Differential Revision: https://phab.mercurial-scm.org/D3760

packaging: replace dockerlib.sh with a Python script I want to do some more advanced things with Docker in upcoming commits. Trying to do that with shell scripts will be a bit too painful for my liking. Implementing things in Python will be vastly simpler in the long run. This commit essentially ports dockerlib.sh to a Python script. dockerdeb and dockerrpm have been ported to use the new hg-docker script. hg-docker requires Python 3. I've only tested on Python 3.5. Unlike the local packaging scripts which may need to run on old distros, the Docker packaging scripts don't have these constraints. So I think it is acceptable to require Python 3.5. As part of the transition, the Docker image tags changed slightly. I don't think that's a big deal: the Docker image names are effectively arbitrary and are a means to an end to achieve running commands in Docker containers. The code for resolving the Dockerfile content allows substituting values passed as arguments. This will be used in a subsequent commit. Differential Revision: https://phab.mercurial-scm.org/D3759

packaging: consistently create build user in Dockerfiles Previously, dockerlib.sh appended some commands to create a "build" user in each Docker image. The resulting Docker images could be inconsistent depending on the execution environment and base image. With this change, we explicitly create our custom user and group as the first action in each Dockerfile. The user always has user:group 1000:1000 and all built images are consistent. We also create a home directory for the user under /build. This directory is currently ignored. As part of this, we stop setting the DBUILDUSER variable in dockerlib.sh and instead set it in the respective scripts that call it. This is in preparation for further refactoring of dockerlib.sh. Differential Revision: https://phab.mercurial-scm.org/D3758

scmutil: move construction of instability count message to separate fn When the commad we are running, introduces new instabilities, we show a message like `5 new orphan changesets`, `2 new content-divergent changesets`, `1 new phase-divergent changesets` etc which is very nice. Now taking a step ahead, we want users to show how to fix them too. Something like: `5 new orphan changesets (run 'hg evolve' to resolve/stabilize them)` `2 new content-divergent changesets (run 'hg evolve --content-divergent' to resolve them)` and maybe telling user a way to understand more about those new instabilities like `hg evolve --list` or `hg log -r 'orphan()'` something like that. The idea came from issue5855 which I want to fix because fixing that will result in a nice UI. Taking the construction logic out will allow extensions like evolve (maybe rebase too) to wrap that and add information about how to resolve and how to understand the instability more. Differential Revision: https://phab.mercurial-scm.org/D3734

procutil: use unbuffered stdout on Windows Windows doesn't support line buffering, treating it as fully buffered. This causes output of slow commands to stutter. We use unbuffered instead.

procutil: use unbuffered stdout on Windows Windows doesn't support line buffering, treating it as fully buffered. This causes output of slow commands to stutter. We use unbuffered instead.

graft: introduce --abort flag to abort interrupted graft This patch introduces a new --abort flag to `hg graft` command which aborts an interrupted graft and rollbacks to the state before graft. The behavior when some of grafted changeset get's published while interrupted graft or we have new descendants on grafted changesets is same as that of rebase which is warn the user, don't strip and abort the abort the graft. Tests are added for the new flag. .. feature:: `hg graft` now has a `--abort` flag which aborts the interrupted graft and rollbacks to state before the graft. Differential Revision: https://phab.mercurial-scm.org/D3754

graft: move `if continue` to elif and add new line This will make upcoming patch where we introduce a new elif for the abort case more readable. Also added a new line before the if-else starts. Differential Revision: https://phab.mercurial-scm.org/D3752

graft: start storing new nodes formed in graftstate This patch starts storing the new nodes formed during the ongoing graft operation in the graftstate. We need the list of new nodes formed while implmenting `graft --abort` which will strip out the new nodes. Differential Revision: https://phab.mercurial-scm.org/D3751

show: use filter() function to strip "tip" tag Before, an empty tag "" was inserted in place of "tip", resulting in double spaces.

templater: extend filter() to accept template expression for emptiness test This utilizes the pass-by-name nature of template arguments.

templater: introduce filter() function to remove empty items from list The primary use case is to filter out "tip" from a list of tags.

templater: fix truth testing of integer 0 taken from a list/dict Broken at f9c426385853. bool(python_value) shouldn't be used here since an integer 0 has to be truthy for backward compatibility.

formatter: look for template symbols from the associated name Otherwise symbolsused() would fail if a named template is specified with -T.

py3: add b'' prefixes in tests/test-obsolete-divergent.t This makes the test pass on Python 3. # skip-blame because just b'' prefixes. Differential Revision: https://phab.mercurial-scm.org/D3832

py3: use stringutil.pprint() to print NoneType Before this patch, when running test-debugcommands.t, we get a TypeError because NoneType can't be converted into bytes. This patch uses stringutil.pprint() to print the ui._colormode. We are now close to getting test-debugcommands.t passing on Python 3. Differential Revision: https://phab.mercurial-scm.org/D3831

rebase: make dry-run return 1 or 0 according to result In dry-run mode, if there is no conflict return 0, if any then return 1 Differential Revision: https://phab.mercurial-scm.org/D3829

relink: use context manager for lock management

censor: use context manager for lock management

templater: remove redundant member variables from templater class We no longer need them since the engine is instantiated in __init__().

templater: resurrect cache of engine instance The engine-level cache was effectively disabled at 48289eafb37d "templater: drop extension point of engine classes (API)" by mistake, which made template rendering quite slow. Spotted by Martin von Zweigbergk.

templater: extract template loader to separate class This avoids reference cycle in the subsequent patch: templater -> _proc -> templater.load -> templater The templater class will be a thin wrapper around the loader and the engine.