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git/Documentation/config/diff.txt
René Scharfe d7b97b7185 diff: let external diffs report that changes are uninteresting
The options --exit-code and --quiet instruct git diff to indicate
whether it found any significant changes by exiting with code 1 if it
did and 0 if there were none.  Currently this doesn't work if external
diff programs are involved, as we have no way to learn what they found.

Add that ability in the form of the new configuration options
diff.trustExitCode and diff.<driver>.trustExitCode and the environment
variable GIT_EXTERNAL_DIFF_TRUST_EXIT_CODE.  They pair with the config
options diff.external and diff.<driver>.command and the environment
variable GIT_EXTERNAL_DIFF, respectively.

The new options are off by default, keeping the old behavior.  Enabling
them indicates that the external diff returns exit code 1 if it finds
significant changes and 0 if it doesn't, like diff(1).

The name of the new options is taken from the git difftool and mergetool
options of similar purpose.  (There they enable passing on the exit code
of a diff tool and to infer whether a merge done by a merge tool is
successful.)

The new feature sets the diff flag diff_from_contents in
diff_setup_done() if we need the exit code and are allowed to call
external diffs.  This disables the optimization that avoids calling the
program with --quiet.  Add it back by skipping the call if the external
diff is not able to report empty diffs.  We can only do that check after
evaluating the file-specific attributes in run_external_diff().

If we do run the external diff with --quiet, send its output to
/dev/null.

I considered checking the output of the external diff to check whether
its empty.  It was added as 11be65cfa4 (diff: fix --exit-code with
external diff, 2024-05-05) and quickly reverted, as it does not work
with external diffs that do not write to stdout.  There's no reason why
a graphical diff tool would even need to write anything there at all.

I also considered using a non-zero exit code for empty diffs, which
could be done without adding new configuration options.  We'd need to
disable the optimization that allows git diff --quiet to skip calling
external diffs, though -- that might be quite surprising if graphical
diff programs are involved.  And assigning the opposite meaning of the
exit codes compared to diff(1) and git diff --exit-code to the external
diff can cause unnecessary confusion.

Suggested-by: Phillip Wood <phillip.wood123@gmail.com>
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2024-06-10 09:20:46 -07:00

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diff.autoRefreshIndex::
When using 'git diff' to compare with work tree
files, do not consider stat-only changes as changed.
Instead, silently run `git update-index --refresh` to
update the cached stat information for paths whose
contents in the work tree match the contents in the
index. This option defaults to true. Note that this
affects only 'git diff' Porcelain, and not lower level
'diff' commands such as 'git diff-files'.
diff.dirstat::
A comma separated list of `--dirstat` parameters specifying the
default behavior of the `--dirstat` option to linkgit:git-diff[1]
and friends. The defaults can be overridden on the command line
(using `--dirstat=<param1,param2,...>`). The fallback defaults
(when not changed by `diff.dirstat`) are `changes,noncumulative,3`.
The following parameters are available:
+
--
`changes`;;
Compute the dirstat numbers by counting the lines that have been
removed from the source, or added to the destination. This ignores
the amount of pure code movements within a file. In other words,
rearranging lines in a file is not counted as much as other changes.
This is the default behavior when no parameter is given.
`lines`;;
Compute the dirstat numbers by doing the regular line-based diff
analysis, and summing the removed/added line counts. (For binary
files, count 64-byte chunks instead, since binary files have no
natural concept of lines). This is a more expensive `--dirstat`
behavior than the `changes` behavior, but it does count rearranged
lines within a file as much as other changes. The resulting output
is consistent with what you get from the other `--*stat` options.
`files`;;
Compute the dirstat numbers by counting the number of files changed.
Each changed file counts equally in the dirstat analysis. This is
the computationally cheapest `--dirstat` behavior, since it does
not have to look at the file contents at all.
`cumulative`;;
Count changes in a child directory for the parent directory as well.
Note that when using `cumulative`, the sum of the percentages
reported may exceed 100%. The default (non-cumulative) behavior can
be specified with the `noncumulative` parameter.
<limit>;;
An integer parameter specifies a cut-off percent (3% by default).
Directories contributing less than this percentage of the changes
are not shown in the output.
--
+
Example: The following will count changed files, while ignoring
directories with less than 10% of the total amount of changed files,
and accumulating child directory counts in the parent directories:
`files,10,cumulative`.
diff.statNameWidth::
Limit the width of the filename part in --stat output. If set, applies
to all commands generating --stat output except format-patch.
diff.statGraphWidth::
Limit the width of the graph part in --stat output. If set, applies
to all commands generating --stat output except format-patch.
diff.context::
Generate diffs with <n> lines of context instead of the default
of 3. This value is overridden by the -U option.
diff.interHunkContext::
Show the context between diff hunks, up to the specified number
of lines, thereby fusing the hunks that are close to each other.
This value serves as the default for the `--inter-hunk-context`
command line option.
diff.external::
If this config variable is set, diff generation is not
performed using the internal diff machinery, but using the
given command. Can be overridden with the `GIT_EXTERNAL_DIFF'
environment variable. The command is called with parameters
as described under "git Diffs" in linkgit:git[1]. Note: if
you want to use an external diff program only on a subset of
your files, you might want to use linkgit:gitattributes[5] instead.
diff.trustExitCode::
If this boolean value is set to true then the
`diff.external` command is expected to return exit code
0 if it considers the input files to be equal or 1 if it
considers them to be different, like `diff(1)`.
If it is set to false, which is the default, then the command
is expected to return exit code 0 regardless of equality.
Any other exit code causes Git to report a fatal error.
diff.ignoreSubmodules::
Sets the default value of --ignore-submodules. Note that this
affects only 'git diff' Porcelain, and not lower level 'diff'
commands such as 'git diff-files'. 'git checkout'
and 'git switch' also honor
this setting when reporting uncommitted changes. Setting it to
'all' disables the submodule summary normally shown by 'git commit'
and 'git status' when `status.submoduleSummary` is set unless it is
overridden by using the --ignore-submodules command-line option.
The 'git submodule' commands are not affected by this setting.
By default this is set to untracked so that any untracked
submodules are ignored.
diff.mnemonicPrefix::
If set, 'git diff' uses a prefix pair that is different from the
standard "a/" and "b/" depending on what is being compared. When
this configuration is in effect, reverse diff output also swaps
the order of the prefixes:
`git diff`;;
compares the (i)ndex and the (w)ork tree;
`git diff HEAD`;;
compares a (c)ommit and the (w)ork tree;
`git diff --cached`;;
compares a (c)ommit and the (i)ndex;
`git diff HEAD:file1 file2`;;
compares an (o)bject and a (w)ork tree entity;
`git diff --no-index a b`;;
compares two non-git things (1) and (2).
diff.noPrefix::
If set, 'git diff' does not show any source or destination prefix.
diff.srcPrefix::
If set, 'git diff' uses this source prefix. Defaults to "a/".
diff.dstPrefix::
If set, 'git diff' uses this destination prefix. Defaults to "b/".
diff.relative::
If set to 'true', 'git diff' does not show changes outside of the directory
and show pathnames relative to the current directory.
diff.orderFile::
File indicating how to order files within a diff.
See the '-O' option to linkgit:git-diff[1] for details.
If `diff.orderFile` is a relative pathname, it is treated as
relative to the top of the working tree.
diff.renameLimit::
The number of files to consider in the exhaustive portion of
copy/rename detection; equivalent to the 'git diff' option
`-l`. If not set, the default value is currently 1000. This
setting has no effect if rename detection is turned off.
diff.renames::
Whether and how Git detects renames. If set to "false",
rename detection is disabled. If set to "true", basic rename
detection is enabled. If set to "copies" or "copy", Git will
detect copies, as well. Defaults to true. Note that this
affects only 'git diff' Porcelain like linkgit:git-diff[1] and
linkgit:git-log[1], and not lower level commands such as
linkgit:git-diff-files[1].
diff.suppressBlankEmpty::
A boolean to inhibit the standard behavior of printing a space
before each empty output line. Defaults to false.
diff.submodule::
Specify the format in which differences in submodules are
shown. The "short" format just shows the names of the commits
at the beginning and end of the range. The "log" format lists
the commits in the range like linkgit:git-submodule[1] `summary`
does. The "diff" format shows an inline diff of the changed
contents of the submodule. Defaults to "short".
diff.wordRegex::
A POSIX Extended Regular Expression used to determine what is a "word"
when performing word-by-word difference calculations. Character
sequences that match the regular expression are "words", all other
characters are *ignorable* whitespace.
diff.<driver>.command::
The custom diff driver command. See linkgit:gitattributes[5]
for details.
diff.<driver>.trustExitCode::
If this boolean value is set to true then the
`diff.<driver>.command` command is expected to return exit code
0 if it considers the input files to be equal or 1 if it
considers them to be different, like `diff(1)`.
If it is set to false, which is the default, then the command
is expected to return exit code 0 regardless of equality.
Any other exit code causes Git to report a fatal error.
diff.<driver>.xfuncname::
The regular expression that the diff driver should use to
recognize the hunk header. A built-in pattern may also be used.
See linkgit:gitattributes[5] for details.
diff.<driver>.binary::
Set this option to true to make the diff driver treat files as
binary. See linkgit:gitattributes[5] for details.
diff.<driver>.textconv::
The command that the diff driver should call to generate the
text-converted version of a file. The result of the
conversion is used to generate a human-readable diff. See
linkgit:gitattributes[5] for details.
diff.<driver>.wordRegex::
The regular expression that the diff driver should use to
split words in a line. See linkgit:gitattributes[5] for
details.
diff.<driver>.cachetextconv::
Set this option to true to make the diff driver cache the text
conversion outputs. See linkgit:gitattributes[5] for details.
include::../mergetools-diff.txt[]
diff.indentHeuristic::
Set this option to `false` to disable the default heuristics
that shift diff hunk boundaries to make patches easier to read.
diff.algorithm::
Choose a diff algorithm. The variants are as follows:
+
--
`default`, `myers`;;
The basic greedy diff algorithm. Currently, this is the default.
`minimal`;;
Spend extra time to make sure the smallest possible diff is
produced.
`patience`;;
Use "patience diff" algorithm when generating patches.
`histogram`;;
This algorithm extends the patience algorithm to "support
low-occurrence common elements".
--
+
diff.wsErrorHighlight::
Highlight whitespace errors in the `context`, `old` or `new`
lines of the diff. Multiple values are separated by comma,
`none` resets previous values, `default` reset the list to
`new` and `all` is a shorthand for `old,new,context`. The
whitespace errors are colored with `color.diff.whitespace`.
The command line option `--ws-error-highlight=<kind>`
overrides this setting.
diff.colorMoved::
If set to either a valid `<mode>` or a true value, moved lines
in a diff are colored differently, for details of valid modes
see '--color-moved' in linkgit:git-diff[1]. If simply set to
true the default color mode will be used. When set to false,
moved lines are not colored.
diff.colorMovedWS::
When moved lines are colored using e.g. the `diff.colorMoved` setting,
this option controls the `<mode>` how spaces are treated.
For details of valid modes see '--color-moved-ws' in linkgit:git-diff[1].