view mercurial/help/flags.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

Most Mercurial commands accept various flags.

Flag names
==========

Flags for each command are listed in :hg:`help` for that command.
Additionally, some flags, such as --repository, are global and can be used with
any command - those are seen in :hg:`help -v`, and can be specified before or
after the command.

Every flag has at least a long name, such as --repository. Some flags may also
have a short one-letter name, such as the equivalent -R. Using the short or long
name is equivalent and has the same effect.

Flags that have a short name can also be bundled together - for instance, to
specify both --edit (short -e) and --interactive (short -i), one could use::

    hg commit -ei

If any of the bundled flags takes a value (i.e. is not a boolean), it must be
last, followed by the value::

    hg commit -im 'Message'

Flag types
==========

Mercurial command-line flags can be strings, numbers, booleans, or lists of
strings.

Specifying flag values
======================

The following syntaxes are allowed, assuming a flag 'flagname' with short name
'f'::

    --flagname=foo
    --flagname foo
    -f foo
    -ffoo

This syntax applies to all non-boolean flags (strings, numbers or lists).

Specifying boolean flags
========================

Boolean flags do not take a value parameter. To specify a boolean, use the flag
name to set it to true, or the same name prefixed with 'no-' to set it to
false::

    hg commit --interactive
    hg commit --no-interactive

Specifying list flags
=====================

List flags take multiple values. To specify them, pass the flag multiple times::

    hg files --include mercurial --include tests

Setting flag defaults
=====================

In order to set a default value for a flag in an hgrc file, it is recommended to
use aliases::

    [alias]
    commit = commit --interactive

For more information on hgrc files, see :hg:`help config`.

Overriding flags on the command line
====================================

If the same non-list flag is specified multiple times on the command line, the
latest specification is used::

    hg commit -m "Ignored value" -m "Used value"

This includes the use of aliases - e.g., if one has::

    [alias]
    committemp = commit -m "Ignored value"

then the following command will override that -m::

    hg committemp -m "Used value"

Overriding flag defaults
========================

Every flag has a default value, and you may also set your own defaults in hgrc
as described above.
Except for list flags, defaults can be overridden on the command line simply by
specifying the flag in that location.

Hidden flags
============

Some flags are not shown in a command's help by default - specifically, those
that are deemed to be experimental, deprecated or advanced. To show all flags,
add the --verbose flag for the help command::

    hg help --verbose commit