On Fri, Feb 17, 2023 at 12:21 PM John Cai via GitGitGadget <gitgitgadget@xxxxxxxxx> wrote: > > From: John Cai <johncai86@xxxxxxxxx> > > It can be useful to specify diff algorithms per file type. For example, > one may want to use the minimal diff algorithm for .json files, another > for .c files, etc. > > The diff machinery already checks attributes for a diff driver. Teach > the diff driver parser a new type "algorithm" to look for in the > config, which will be used if a driver has been specified through the > attributes. > > Enforce precedence of the diff algorithm by favoring the command line > option, then looking at the driver attributes & config combination, then > finally the diff.algorithm config. > > To enforce precedence order, use a new `ignore_driver_algorithm` member > during options pasing to indicate the diff algorithm was set via command > line args. s/pasing/parsing/ > Signed-off-by: John Cai <johncai86@xxxxxxxxx> > --- > Documentation/gitattributes.txt | 37 ++++++++++++++++++++++++++++++++ > diff.c | 33 ++++++++++++++++++++-------- > diff.h | 1 + > t/lib-diff-alternative.sh | 38 ++++++++++++++++++++++++++++++++- > userdiff.c | 4 +++- > userdiff.h | 1 + > 6 files changed, 103 insertions(+), 11 deletions(-) > > diff --git a/Documentation/gitattributes.txt b/Documentation/gitattributes.txt > index c19e64ea0ef..f212079a131 100644 > --- a/Documentation/gitattributes.txt > +++ b/Documentation/gitattributes.txt > @@ -758,6 +758,43 @@ with the above configuration, i.e. `j-c-diff`, with 7 > parameters, just like `GIT_EXTERNAL_DIFF` program is called. > See linkgit:git[1] for details. > > +Setting the internal diff algorithm > +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > + > +The diff algorithm can be set through the `diff.algorithm` config key, but > +sometimes it may be helpful to set the diff algorithm by path. For example, one > +might wish to set a diff algorithm automatically for all `.json` files such that > +the user would not need to pass in a separate command line `--diff-algorithm` > +flag each time. > + > +First, in `.gitattributes`, assign the `diff` attribute for paths. > + > +------------------------ > +*.json diff=<name> > +------------------------ > + > +Then, define a "diff.<name>.algorithm" configuration to specify the diff Should there be a link to `git-config` right after "configuration"? Otherwise, users may think that they are being told to specify additional configuration within the .gitattributes file. > +algorithm, choosing from `meyers`, `patience`, `minimal`, or `histogram`. s/meyers/myers/ > + > +---------------------------------------------------------------- > +[diff "<name>"] > + algorithm = histogram > +---------------------------------------------------------------- It's pretty easy to assume the above is meant to be part of the .gitattributes file instead of the .git/config file. Don't most users run `git config` commands directly rather than edit the .git/config file? Should we provide a sample command rather than showing what the config file will contain? > + > +This diff algorithm applies to user facing diff output like git-diff(1), > +git-show(1) and is used for the `--stat` output as well. The merge machinery > +will not use the diff algorithm set through this method. Yaay, thanks for including this! I'm still curious if this should this also include warnings/caveats, such as: * The diff attribute specified in .gitattributes will be ignored in a bare clone * The diff attribute specified in .gitattributes will be ignored if it is only specified in another branch (e.g. on a branch "special-file diff=patience" recorded in .gitattributes, then checkout master but run `git log -1 -p $branch`) * When a file is renamed, the diff attribute for the pre-image name is the only one the system pays attention to (thus adding "-R" can flip which diff algorithm is run for the renamed file). Also, since I tested the three items above to verify they are valid warnings, I'm a bit confused. I thought your intent was to use this server-side[1], so isn't the bare clone aspect a deal-breaker for your intended usecase? [1] https://lore.kernel.org/git/7852AC7B-7A4E-4DD0-ADEA-CFFD5D16C595@xxxxxxxxx/ > + > +NOTE: If the `command` key also exists, then Git will treat this as an external > +diff and attempt to use the value set for `command` as an external program. For > +instance, the following config, combined with the above `.gitattributes` file, > +will result in `command` favored over `algorithm`. > + > +---------------------------------------------------------------- > +[diff "<name>"] > + command = j-c-diff > + algorithm = histogram > +---------------------------------------------------------------- > > Defining a custom hunk-header > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > diff --git a/diff.c b/diff.c > index 5efc22ca06b..04469da6d34 100644 > --- a/diff.c > +++ b/diff.c > @@ -4456,15 +4456,13 @@ static void run_diff_cmd(const char *pgm, > const char *xfrm_msg = NULL; > int complete_rewrite = (p->status == DIFF_STATUS_MODIFIED) && p->score; > int must_show_header = 0; > + struct userdiff_driver *drv = NULL; > > - > - if (o->flags.allow_external) { > - struct userdiff_driver *drv; > - > + if (o->flags.allow_external || !o->ignore_driver_algorithm) > drv = userdiff_find_by_path(o->repo->index, attr_path); > - if (drv && drv->external) > - pgm = drv->external; > - } > + > + if (o->flags.allow_external && drv && drv->external) > + pgm = drv->external; > > if (msg) { > /* > @@ -4481,12 +4479,16 @@ static void run_diff_cmd(const char *pgm, > run_external_diff(pgm, name, other, one, two, xfrm_msg, o); > return; > } > - if (one && two) > + if (one && two) { > + if (drv && !o->ignore_driver_algorithm && drv->algorithm) > + set_diff_algorithm(o, drv->algorithm); > + > builtin_diff(name, other ? other : name, > one, two, xfrm_msg, must_show_header, > o, complete_rewrite); > - else > + } else { > fprintf(o->file, "* Unmerged path %s\n", name); > + } > } > > static void diff_fill_oid_info(struct diff_filespec *one, struct index_state *istate) > @@ -4583,6 +4585,14 @@ static void run_diffstat(struct diff_filepair *p, struct diff_options *o, > const char *name; > const char *other; > > + if (!o->ignore_driver_algorithm) { > + struct userdiff_driver *drv = userdiff_find_by_path(o->repo->index, p->one->path); > + > + if (drv && drv->algorithm) { > + set_diff_algorithm(o, drv->algorithm); > + } > + } > + > if (DIFF_PAIR_UNMERGED(p)) { > /* unmerged */ > builtin_diffstat(p->one->path, NULL, NULL, NULL, > @@ -5130,6 +5140,8 @@ static int diff_opt_diff_algorithm(const struct option *opt, > return error(_("option diff-algorithm accepts \"myers\", " > "\"minimal\", \"patience\" and \"histogram\"")); > > + options->ignore_driver_algorithm = 1; > + > return 0; > } > > @@ -5145,6 +5157,8 @@ static int diff_opt_diff_algorithm_no_arg(const struct option *opt, > BUG("available diff algorithms include \"myers\", " > "\"minimal\", \"patience\" and \"histogram\""); > > + options->ignore_driver_algorithm = 1; > + > return 0; > } > > @@ -5285,6 +5299,7 @@ static int diff_opt_patience(const struct option *opt, > for (i = 0; i < options->anchors_nr; i++) > free(options->anchors[i]); > options->anchors_nr = 0; > + options->ignore_driver_algorithm = 1; > > return set_diff_algorithm(options, "patience"); > } > diff --git a/diff.h b/diff.h > index 41eb2c3d428..8d770b1d579 100644 > --- a/diff.h > +++ b/diff.h > @@ -333,6 +333,7 @@ struct diff_options { > int prefix_length; > const char *stat_sep; > int xdl_opts; > + int ignore_driver_algorithm; > > /* see Documentation/diff-options.txt */ > char **anchors; > diff --git a/t/lib-diff-alternative.sh b/t/lib-diff-alternative.sh > index 8d1e408bb58..2dc02bca873 100644 > --- a/t/lib-diff-alternative.sh > +++ b/t/lib-diff-alternative.sh > @@ -105,10 +105,46 @@ index $file1..$file2 100644 > } > EOF > > + cat >expect_diffstat <<EOF > + file1 => file2 | 21 ++++++++++----------- > + 1 file changed, 10 insertions(+), 11 deletions(-) > +EOF > + > STRATEGY=$1 > > + test_expect_success "$STRATEGY diff from attributes" ' > + echo "file* diff=driver" >.gitattributes && > + git config diff.driver.algorithm "$STRATEGY" && > + test_must_fail git diff --no-index file1 file2 > output && > + cat expect && > + cat output && > + test_cmp expect output > + ' > + > + test_expect_success "$STRATEGY diff from attributes has valid diffstat" ' > + echo "file* diff=driver" >.gitattributes && > + git config diff.driver.algorithm "$STRATEGY" && > + test_must_fail git diff --stat --no-index file1 file2 > output && > + test_cmp expect_diffstat output > + ' > + > test_expect_success "$STRATEGY diff" ' > - test_must_fail git diff --no-index "--$STRATEGY" file1 file2 > output && > + test_must_fail git diff --no-index "--diff-algorithm=$STRATEGY" file1 file2 > output && > + test_cmp expect output > + ' > + > + test_expect_success "$STRATEGY diff command line precedence before attributes" ' > + echo "file* diff=driver" >.gitattributes && > + git config diff.driver.algorithm meyers && Is this misspelling of myers intentional? I think with the typo, the code falls back to the default algorithm, which happens to be myers, so I think the test works either way, but were you intending to test fallback behavior in case of a typo here, or was that accidental? > + test_must_fail git diff --no-index "--diff-algorithm=$STRATEGY" file1 file2 > output && > + test_cmp expect output > + ' > + > + test_expect_success "$STRATEGY diff attributes precedence before config" ' > + git config diff.algorithm default && > + echo "file* diff=driver" >.gitattributes && > + git config diff.driver.algorithm "$STRATEGY" && > + test_must_fail git diff --no-index file1 file2 > output && > test_cmp expect output > ' > > diff --git a/userdiff.c b/userdiff.c > index d71b82feb74..ff25cfc4b4c 100644 > --- a/userdiff.c > +++ b/userdiff.c > @@ -293,7 +293,7 @@ PATTERNS("scheme", > "|([^][)(}{[ \t])+"), > PATTERNS("tex", "^(\\\\((sub)*section|chapter|part)\\*{0,1}\\{.*)$", > "\\\\[a-zA-Z@]+|\\\\.|[a-zA-Z0-9\x80-\xff]+"), > -{ "default", NULL, -1, { NULL, 0 } }, > +{ "default", NULL, NULL, -1, { NULL, 0 } }, > }; > #undef PATTERNS > #undef IPATTERN > @@ -394,6 +394,8 @@ int userdiff_config(const char *k, const char *v) > return parse_bool(&drv->textconv_want_cache, k, v); > if (!strcmp(type, "wordregex")) > return git_config_string(&drv->word_regex, k, v); > + if (!strcmp(type, "algorithm")) > + return git_config_string(&drv->algorithm, k, v); > > return 0; > } > diff --git a/userdiff.h b/userdiff.h > index aee91bc77e6..24419db6973 100644 > --- a/userdiff.h > +++ b/userdiff.h > @@ -14,6 +14,7 @@ struct userdiff_funcname { > struct userdiff_driver { > const char *name; > const char *external; > + const char *algorithm; > int binary; > struct userdiff_funcname funcname; > const char *word_regex; > -- > gitgitgadget
