On Fri, Apr 15, 2016 at 10:02 AM, Stefan Beller <sbeller@xxxxxxxxxx> wrote:
> On Fri, Apr 15, 2016 at 9:51 AM, Jacob Keller <jacob.e.keller@xxxxxxxxx> wrote:
>> From: Jacob Keller <jacob.keller@xxxxxxxxx>
>>
>> I took up Stefan's patch, and modified it to resolve a couple issues. I
>> also tried to implement the suggestions from Junio's review, as well as
>> the suggestions I had. It appears to produce equivalent output as Jeff's
>> script. This version is still missing a few things, and it is possible
>> Stefan is working on a v2 of his own, but I thought I'd submit this.
>>
>> There's still several TODOs:
>> * Add some tests
>> * better name for the heuristic(?)
>> * better patch description plus documentation
>> * is_emptyline should be more generic and handle CRLF
>>
>> Changes since Stefan's v1:
>> * Added a patch to implement xdl_hash_and_recmatch as Junio suggested.
>> * Fixed a segfault in Stefan's patch
>> * Added XDL flag to configure the behavior
>> * Used an int and counted empty lines via += instead of |=
>> * Renamed starts_with_emptyline to is_emptyline
>> * Added diff command line and config options
>>
>> For reviewer convenience, the interdiff between this and Stefan's version:
>>
>> diff --git a/Documentation/diff-config.txt b/Documentation/diff-config.txt
>> index edba56522bce..cebf82702d2a 100644
>> --- a/Documentation/diff-config.txt
>> +++ b/Documentation/diff-config.txt
>> @@ -170,6 +170,12 @@ diff.tool::
>>
>> include::mergetools-diff.txt[]
>>
>> +diff.emptyLineHeuristic::
>> + Set this option to true to enable the empty line chunk heuristic when
>> + producing diff output. This heuristic will attempt to shift hunks such
>> + that a common empty line occurs below the hunk with the rest of the
>> + context above it.
>> +
>
> This heuristic will attempt to shift hunks such that *the last* common
> empty line occurs below the hunk with the rest of the context above it.
>
> maybe?
>
That sounds reasonable.
>
>> diff.algorithm::
>> Choose a diff algorithm. The variants are as follows:
>> +
>> diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
>> index 4b0318e2ac15..6c1cd8b35584 100644
>> --- a/Documentation/diff-options.txt
>> +++ b/Documentation/diff-options.txt
>> @@ -63,6 +63,12 @@ ifndef::git-format-patch[]
>> Synonym for `-p --raw`.
>> endif::git-format-patch[]
>>
>> +--empty-line-heuristic::
>> +--no-empty-line-heuristic::
>> + When possible, shift common empty lines in diff hunks below the hunk
>> + such that the last common empty line for each hunk is below, with the
>> + rest of the context above the hunk.
>> +
>> --minimal::
>> Spend extra time to make sure the smallest possible
>> diff is produced.
>> diff --git a/diff.c b/diff.c
>> index 4dfe6609d059..8ab9a492928d 100644
>> --- a/diff.c
>> +++ b/diff.c
>> @@ -26,6 +26,7 @@
>> #endif
>>
>> static int diff_detect_rename_default;
>> +static int diff_empty_line_heuristic = 0;
>> static int diff_rename_limit_default = 400;
>> static int diff_suppress_blank_empty;
>> static int diff_use_color_default = -1;
>> @@ -189,6 +190,10 @@ int git_diff_ui_config(const char *var, const char *value, void *cb)
>> diff_detect_rename_default = git_config_rename(var, value);
>> return 0;
>> }
>> + if (!strcmp(var, "diff.emptylineheuristic")) {
>> + diff_empty_line_heuristic = git_config_bool(var, value);
>> + return 0;
>> + }
>> if (!strcmp(var, "diff.autorefreshindex")) {
>> diff_auto_refresh_index = git_config_bool(var, value);
>> return 0;
>> @@ -3278,6 +3283,8 @@ void diff_setup(struct diff_options *options)
>> options->use_color = diff_use_color_default;
>> options->detect_rename = diff_detect_rename_default;
>> options->xdl_opts |= diff_algorithm;
>> + if (diff_empty_line_heuristic)
>> + DIFF_XDL_SET(options, EMPTY_LINE_HEURISTIC);
>>
>> options->orderfile = diff_order_file_cfg;
>>
>> @@ -3798,6 +3805,10 @@ int diff_opt_parse(struct diff_options *options,
>> DIFF_XDL_SET(options, IGNORE_WHITESPACE_AT_EOL);
>> else if (!strcmp(arg, "--ignore-blank-lines"))
>> DIFF_XDL_SET(options, IGNORE_BLANK_LINES);
>> + else if (!strcmp(arg, "--empty-line-heuristic"))
>> + DIFF_XDL_SET(options, EMPTY_LINE_HEURISTIC);
>> + else if (!strcmp(arg, "--no-empty-line-heuristic"))
>> + DIFF_XDL_CLR(options, EMPTY_LINE_HEURISTIC);
>> else if (!strcmp(arg, "--patience"))
>> options->xdl_opts = DIFF_WITH_ALG(options, PATIENCE_DIFF);
>> else if (!strcmp(arg, "--histogram"))
>> diff --git a/xdiff/xdiff.h b/xdiff/xdiff.h
>> index 4fb7e79410c2..9195a5c0e958 100644
>> --- a/xdiff/xdiff.h
>> +++ b/xdiff/xdiff.h
>> @@ -41,6 +41,8 @@ extern "C" {
>>
>> #define XDF_IGNORE_BLANK_LINES (1 << 7)
>>
>> +#define XDF_EMPTY_LINE_HEURISTIC (1 << 8)
>> +
>> #define XDL_EMIT_FUNCNAMES (1 << 0)
>> #define XDL_EMIT_FUNCCONTEXT (1 << 2)
>>
>> diff --git a/xdiff/xdiffi.c b/xdiff/xdiffi.c
>> index 5f14beb98049..83984b90f82f 100644
>> --- a/xdiff/xdiffi.c
>> +++ b/xdiff/xdiffi.c
>> @@ -400,7 +400,7 @@ static xdchange_t *xdl_add_change(xdchange_t *xscr, long i1, long i2, long chg1,
>> }
>>
>>
>> -static int starts_with_emptyline(const char *recs)
>> +static int is_emptyline(const char *recs)
>> {
>> return recs[0] == '\n'; /* CRLF not covered here */
>> }
>> @@ -416,7 +416,7 @@ static int xdl_hash_and_recmatch(xrecord_t **recs, long ixs, long ix, long flags
>> int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
>> long ix, ixo, ixs, ixref, grpsiz, nrec = xdf->nrec;
>> char *rchg = xdf->rchg, *rchgo = xdfo->rchg;
>> - unsigned char has_emptyline;
>> + unsigned int emptylines;
>> xrecord_t **recs = xdf->recs;
>>
>> /*
>> @@ -450,7 +450,7 @@ int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
>>
>> do {
>> grpsiz = ix - ixs;
>> - has_emptyline = 0;
>> + emptylines = 0;
>>
>> /*
>> * If the line before the current change group, is equal to
>> @@ -458,11 +458,11 @@ int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
>> * the group.
>> */
>> while (ixs > 0 && xdl_hash_and_recmatch(recs, ixs - 1, ix - 1, flags)) {
>> + emptylines += is_emptyline(recs[ix - 1]->ptr);
>> +
>> rchg[--ixs] = 1;
>> rchg[--ix] = 0;
>>
>> - has_emptyline |=
>> - starts_with_emptyline(recs[ix]->ptr);
>
> How is this fixing the segfault bug?
> From my understanding ix should have the same value here as ix-1 above.
>
This change was for style reasons to check for empty lines first
thing, and it matches how we do "ix - 1" into xdl_hash_and_recmatch.
But as per your following comment, I think you're right and we don't
need this.
>> /*
>> * This change might have joined two change groups,
>> * so we try to take this scenario in account by moving
>> @@ -492,9 +492,6 @@ int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
>> rchg[ixs++] = 0;
>> rchg[ix++] = 1;
>>
>> - has_emptyline |=
>> - starts_with_emptyline(recs[ix]->ptr);
>> -
>
> Or would this fix the segfault bug?
> I think we would need to have the check for empty lines
> in both loops to be sure to cover the whole movable range.
>
This is the real segfault fix, I only changed the other in order to
make it appear consistent.
>
>> /*
>> * This change might have joined two change groups,
>> * so we try to take this scenario in account by moving
>> @@ -527,21 +524,12 @@ int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
>> * As we shifted the group forward as far as possible, we only
>> * need to shift it back if at all.
>> */
>> - if (has_emptyline) {
>> - while (ixs > 0 && recs[ixs - 1]->ha == recs[ix - 1]->ha &&
>> - xdl_recmatch(recs[ixs - 1]->ptr, recs[ixs - 1]->size, recs[ix - 1]->ptr, recs[ix - 1]->size, flags) &&
>> - !starts_with_emptyline(recs[ix - 1]->ptr)) {
>> + if ((flags & XDF_EMPTY_LINE_HEURISTIC) && emptylines) {
>> + while (ixs > 0 &&
>> + !is_emptyline(recs[ix - 1]->ptr) &&
>> + xdl_hash_and_recmatch(recs, ixs - 1, ix - 1, flags)) {
>> rchg[--ixs] = 1;
>> rchg[--ix] = 0;
>> -
>> - /*
>> - * This change did not join two change groups,
>> - * as we did that before already, so there is no
>> - * need to adapt the other-file, i.e.
>> - * running
>> - * for (; rchg[ixs - 1]; ixs--);
>> - * while (rchgo[--ixo]);
>> - */
>> }
>> }
>> }
>>
>> Jacob Keller (1):
>> xdiff: add xdl_hash_and_recmatch helper function
>>
>> Stefan Beller (1):
>> xdiff: implement empty line chunk heuristic
>>
>> Documentation/diff-config.txt | 6 ++++++
>> Documentation/diff-options.txt | 6 ++++++
>> diff.c | 11 +++++++++++
>> xdiff/xdiff.h | 2 ++
>> xdiff/xdiffi.c | 42 ++++++++++++++++++++++++++++++++++++++----
>> 5 files changed, 63 insertions(+), 4 deletions(-)
>>
>> --
>> 2.8.1.369.geae769a
>>
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