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30e12b924b
Patch id changes if users reorder file diffs that make up a patch. As the result is functionally equivalent, a different patch id is surprising to many users. In particular, reordering files using diff -O is helpful to make patches more readable (e.g. API header diff before implementation diff). Add an option to change patch-id behaviour making it stable against these kinds of patch change: calculate SHA1 hash for each hunk separately and sum all hashes (using a symmetrical sum) to get patch id We use a 20byte sum and not xor - since xor would give 0 output for patches that have two identical diffs, which isn't all that unlikely (e.g. append the same line in two places). The new behaviour is enabled - when patchid.stable is true - when --stable flag is present Using a new flag --unstable or setting patchid.stable to false force the historical behaviour. In the documentation, clarify that patch ID can now be a sum of hashes, not a hash. Document how command line and config options affect the behaviour. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
62 lines
2.1 KiB
Text
62 lines
2.1 KiB
Text
git-patch-id(1)
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===============
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NAME
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----
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git-patch-id - Compute unique ID for a patch
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SYNOPSIS
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--------
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[verse]
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'git patch-id' [--stable | --unstable] < <patch>
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DESCRIPTION
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-----------
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A "patch ID" is nothing but a sum of SHA-1 of the file diffs associated with a
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patch, with whitespace and line numbers ignored. As such, it's "reasonably
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stable", but at the same time also reasonably unique, i.e., two patches that
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have the same "patch ID" are almost guaranteed to be the same thing.
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IOW, you can use this thing to look for likely duplicate commits.
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When dealing with 'git diff-tree' output, it takes advantage of
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the fact that the patch is prefixed with the object name of the
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commit, and outputs two 40-byte hexadecimal strings. The first
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string is the patch ID, and the second string is the commit ID.
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This can be used to make a mapping from patch ID to commit ID.
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OPTIONS
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-------
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--stable::
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Use a "stable" sum of hashes as the patch ID. With this option:
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- Reordering file diffs that make up a patch does not affect the ID.
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In particular, two patches produced by comparing the same two trees
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with two different settings for "-O<orderfile>" result in the same
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patch ID signature, thereby allowing the computed result to be used
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as a key to index some meta-information about the change between
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the two trees;
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- Result is different from the value produced by git 1.9 and older
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or produced when an "unstable" hash (see --unstable below) is
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configured - even when used on a diff output taken without any use
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of "-O<orderfile>", thereby making existing databases storing such
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"unstable" or historical patch-ids unusable.
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This is the default if patchid.stable is set to true.
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--unstable::
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Use an "unstable" hash as the patch ID. With this option,
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the result produced is compatible with the patch-id value produced
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by git 1.9 and older. Users with pre-existing databases storing
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patch-ids produced by git 1.9 and older (who do not deal with reordered
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patches) may want to use this option.
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This is the default.
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<patch>::
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The diff to create the ID of.
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GIT
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---
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Part of the linkgit:git[1] suite
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