diffcore-pickaxe doc: document -S and -G properly
The documentation of -S and -G is very sketchy. Completely rewrite the sections in Documentation/diff-options.txt and Documentation/gitdiffcore.txt. References: 52e9578 ([PATCH] Introducing software archaeologist's tool "pickaxe".) f506b8e (git log/diff: add -G<regexp> that greps in the patch text) Inputs-from: Phil Hord <phil.hord@gmail.com> Co-authored-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Ramkumar Ramachandra committed
May 31, 2013 at 17:42 UTC
5bc3f0b56779d189aaf7cab7e5d307aa4e7c0887
2 files changed
+57
-26
Documentation/diff-options.txt
+30
-8
@@ -383,14 +383,36 @@ ifndef::git-format-patch[]
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that matches other criteria, nothing is selected.
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-S<string>::
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- Look for differences that introduce or remove an instance of
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- <string>. Note that this is different than the string simply
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- appearing in diff output; see the 'pickaxe' entry in
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- linkgit:gitdiffcore[7] for more details.
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+ Look for differences that change the number of occurrences of
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+ the specified string (i.e. addition/deletion) in a file.
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+ Intended for the scripter's use.
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++
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+It is useful when you're looking for an exact block of code (like a
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+struct), and want to know the history of that block since it first
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+came into being: use the feature iteratively to feed the interesting
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+block in the preimage back into `-S`, and keep going until you get the
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+very first version of the block.
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-G<regex>::
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- Look for differences whose added or removed line matches
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- the given <regex>.
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+ Look for differences whose patch text contains added/removed
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+ lines that match <regex>.
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++
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+To illustrate the difference between `-S<regex> --pickaxe-regex` and
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+`-G<regex>`, consider a commit with the following diff in the same
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+file:
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++
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+----
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++ return !regexec(regexp, two->ptr, 1, ®match, 0);
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+...
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+- hit = !regexec(regexp, mf2.ptr, 1, ®match, 0);
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+----
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++
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+While `git log -G"regexec\(regexp"` will show this commit, `git log
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+-S"regexec\(regexp" --pickaxe-regex` will not (because the number of
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+occurrences of that string did not change).
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++
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+See the 'pickaxe' entry in linkgit:gitdiffcore[7] for more
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+information.
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--pickaxe-all::
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When `-S` or `-G` finds a change, show all the changes in that
@@ -398,8 +420,8 @@ ifndef::git-format-patch[]
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in <string>.
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--pickaxe-regex::
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- Make the <string> not a plain string but an extended POSIX
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- regex to match.
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+ Treat the <string> given to `-S` as an extended POSIX regular
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+ expression to match.
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endif::git-format-patch[]
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-O<orderfile>::
Documentation/gitdiffcore.txt
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-18
@@ -222,26 +222,35 @@ version prefixed with '+'.
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diffcore-pickaxe: For Detecting Addition/Deletion of Specified String
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---------------------------------------------------------------------
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-This transformation is used to find filepairs that represent
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-changes that touch a specified string, and is controlled by the
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--S option and the `--pickaxe-all` option to the 'git diff-*'
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-commands.
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-
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-When diffcore-pickaxe is in use, it checks if there are
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-filepairs whose "result" side and whose "origin" side have
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-different number of specified string. Such a filepair represents
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-"the string appeared in this changeset". It also checks for the
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-opposite case that loses the specified string.
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-
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-When `--pickaxe-all` is not in effect, diffcore-pickaxe leaves
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-only such filepairs that touch the specified string in its
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-output. When `--pickaxe-all` is used, diffcore-pickaxe leaves all
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-filepairs intact if there is such a filepair, or makes the
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-output empty otherwise. The latter behaviour is designed to
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-make reviewing of the changes in the context of the whole
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+This transformation limits the set of filepairs to those that change
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+specified strings between the preimage and the postimage in a certain
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+way. -S<block of text> and -G<regular expression> options are used to
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+specify different ways these strings are sought.
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+
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+"-S<block of text>" detects filepairs whose preimage and postimage
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+have different number of occurrences of the specified block of text.
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+By definition, it will not detect in-file moves. Also, when a
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+changeset moves a file wholesale without affecting the interesting
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+string, diffcore-rename kicks in as usual, and `-S` omits the filepair
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+(since the number of occurrences of that string didn't change in that
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+rename-detected filepair). When used with `--pickaxe-regex`, treat
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+the <block of text> as an extended POSIX regular expression to match,
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+instead of a literal string.
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+
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+"-G<regular expression>" (mnemonic: grep) detects filepairs whose
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+textual diff has an added or a deleted line that matches the given
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+regular expression. This means that it will detect in-file (or what
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+rename-detection considers the same file) moves, which is noise. The
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+implementation runs diff twice and greps, and this can be quite
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+expensive.
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+
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+When `-S` or `-G` are used without `--pickaxe-all`, only filepairs
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+that match their respective criterion are kept in the output. When
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+`--pickaxe-all` is used, if even one filepair matches their respective
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+criterion in a changeset, the entire changeset is kept. This behavior
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+is designed to make reviewing changes in the context of the whole
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changeset easier.
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-
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diffcore-order: For Sorting the Output Based on Filenames
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---------------------------------------------------------
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