Mercurial > hg
view mercurial/help/merge-tools.txt @ 40626:87a872555e90
revlog: detect incomplete revlog reads
_readsegment() is supposed to return N bytes of revlog revision
data starting at a file offset. Surprisingly, its behavior before
this patch never verified that it actually read and returned N
bytes! Instead, it would perform the read(), then return whatever
data was available. And even more surprisingly, nothing in the
call chain appears to have been validating that it received all
the data it was expecting.
This behavior could lead to partial or incomplete revision chunks
being operated on. This could result in e.g. cached deltas being
applied against incomplete base revisions. The delta application
process would happily perform this operation. Only hash
verification would detect the corruption and save us.
This commit changes the behavior of raw revlog reading to validate
that we actually read() the number of bytes that were requested.
We will raise a more specific error faster, rather than possibly
have it go undetected or manifest later in the call stack, at
delta application or hash verification.
Differential Revision: https://phab.mercurial-scm.org/D5266
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Tue, 13 Nov 2018 12:30:59 -0800 |
parents | 0dfcc348d383 |
children |
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To merge files Mercurial uses merge tools. A merge tool combines two different versions of a file into a merged file. Merge tools are given the two files and the greatest common ancestor of the two file versions, so they can determine the changes made on both branches. Merge tools are used both for :hg:`resolve`, :hg:`merge`, :hg:`update`, :hg:`backout` and in several extensions. Usually, the merge tool tries to automatically reconcile the files by combining all non-overlapping changes that occurred separately in the two different evolutions of the same initial base file. Furthermore, some interactive merge programs make it easier to manually resolve conflicting merges, either in a graphical way, or by inserting some conflict markers. Mercurial does not include any interactive merge programs but relies on external tools for that. Available merge tools ===================== External merge tools and their properties are configured in the merge-tools configuration section - see hgrc(5) - but they can often just be named by their executable. A merge tool is generally usable if its executable can be found on the system and if it can handle the merge. The executable is found if it is an absolute or relative executable path or the name of an application in the executable search path. The tool is assumed to be able to handle the merge if it can handle symlinks if the file is a symlink, if it can handle binary files if the file is binary, and if a GUI is available if the tool requires a GUI. There are some internal merge tools which can be used. The internal merge tools are: .. internaltoolsmarker Internal tools are always available and do not require a GUI but will by default not handle symlinks or binary files. See next section for detail about "actual capabilities" described above. Choosing a merge tool ===================== Mercurial uses these rules when deciding which merge tool to use: 1. If a tool has been specified with the --tool option to merge or resolve, it is used. If it is the name of a tool in the merge-tools configuration, its configuration is used. Otherwise the specified tool must be executable by the shell. 2. If the ``HGMERGE`` environment variable is present, its value is used and must be executable by the shell. 3. If the filename of the file to be merged matches any of the patterns in the merge-patterns configuration section, the first usable merge tool corresponding to a matching pattern is used. 4. If ui.merge is set it will be considered next. If the value is not the name of a configured tool, the specified value is used and must be executable by the shell. Otherwise the named tool is used if it is usable. 5. If any usable merge tools are present in the merge-tools configuration section, the one with the highest priority is used. 6. If a program named ``hgmerge`` can be found on the system, it is used - but it will by default not be used for symlinks and binary files. 7. If the file to be merged is not binary and is not a symlink, then internal ``:merge`` is used. 8. Otherwise, ``:prompt`` is used. For historical reason, Mercurial treats merge tools as below while examining rules above. ==== =============== ====== ======= step specified via binary symlink ==== =============== ====== ======= 1. --tool o/o o/o 2. HGMERGE o/o o/o 3. merge-patterns o/o(*) x/?(*) 4. ui.merge x/?(*) x/?(*) ==== =============== ====== ======= Each capability column indicates Mercurial behavior for internal/external merge tools at examining each rule. - "o": "assume that a tool has capability" - "x": "assume that a tool does not have capability" - "?": "check actual capability of a tool" If ``merge.strict-capability-check`` configuration is true, Mercurial checks capabilities of merge tools strictly in (*) cases above (= each capability column becomes "?/?"). It is false by default for backward compatibility. .. note:: After selecting a merge program, Mercurial will by default attempt to merge the files using a simple merge algorithm first. Only if it doesn't succeed because of conflicting changes will Mercurial actually execute the merge program. Whether to use the simple merge algorithm first can be controlled by the premerge setting of the merge tool. Premerge is enabled by default unless the file is binary or a symlink. See the merge-tools and ui sections of hgrc(5) for details on the configuration of merge tools.