Subject: Re: [PATCH] add -p: introduce 'w' command to view hunk with --word-diff

From: Phillip Wood <[email-masked]>
Date: Thu, 7 May 2026 14:24:24 +0100

Hi Javier

On 07/05/2026 00:54, Javier Bassi wrote:
> When using `git add --patch`, reviewing changes in long lines can be
> difficult with the default line-based diff. This is particularly
> noticeable in formats such as JSONP, CSV, LaTeX, Markdown, or other
> plain text where small inline edits can be hard to spot.
> 
> Added `w - print the current hunk with word-diff` during hunk selection
> to re-display the current hunk using `--word-diff`. This provides a
> clearer inline view of changes without modifying the hunk or affecting
> how patches are applied or staged.

I think this is useful. While one can set interactive.diffFilter to 
highlight intraline differences with "diff-highlight" or "delta" they do 
not cope well if the text has been reflowed.

I think the approach of using the current hunk text, rather than running 
"git diff --diff-words" is sensible because it works correctly if the 
user has edited the hunk and it makes it easy to handle hunks that have 
been split. It would be good to propagate the filename when creating the 
filespec so that we use the correct word diff regex for the file. We 
should also propagate the context and inter-hunk context settings from 
struct interactive_options. It would also be a good idea to reuse the 
hunk header from the unified diff so that the line numbers and hunk 
fragment are correct.

Thanks

Phillip

> Signed-off-by: Javier Bassi <[email-masked]>
> ---
>   Documentation/git-add.adoc |   1 +
>   add-patch.c                | 105 ++++++++++++++++++++++++++++++++++++-
>   t/t3701-add-interactive.sh |  59 +++++++++++++--------
>   3 files changed, 142 insertions(+), 23 deletions(-)
> 
> diff --git a/Documentation/git-add.adoc b/Documentation/git-add.adoc
> index 941135dc63..d2ee1cf9a9 100644
> --- a/Documentation/git-add.adoc
> +++ b/Documentation/git-add.adoc
> @@ -351,6 +351,7 @@ patch::
>          K - go to the previous hunk, roll over at the top
>          s - split the current hunk into smaller hunks
>          e - manually edit the current hunk
> +       w - print the current hunk with word-diff
>          p - print the current hunk
>          P - print the current hunk using the pager
>          ? - print help
> diff --git a/add-patch.c b/add-patch.c
> index f27edcbe8d..0364f4bc97 100644
> --- a/add-patch.c
> +++ b/add-patch.c
> @@ -7,6 +7,7 @@
>   #include "commit.h"
>   #include "config.h"
>   #include "diff.h"
> +#include "diffcore.h"
>   #include "editor.h"
>   #include "environment.h"
>   #include "gettext.h"
> @@ -1508,6 +1509,105 @@ static void summarize_hunk(struct add_p_state *s, struct hunk *hunk,
>   	strbuf_complete_line(out);
>   }
>   
> +static void trim_trailing_lf(struct strbuf *buf)
> +{
> +	if (buf->len && buf->buf[buf->len - 1] == '\n')
> +		strbuf_setlen(buf, buf->len - 1);
> +}
> +
> +static void add_word_diff_line(struct strbuf *old, struct strbuf *new,
> +			       const char *line, size_t len, char marker)
> +{
> +	if (marker == '-' || marker == '+' || *line == ' ') {
> +		line++;
> +		len--;
> +	}
> +
> +	if (marker != '+')
> +		strbuf_add(old, line, len);
> +	if (marker != '-')
> +		strbuf_add(new, line, len);
> +}
> +
> +static void build_word_diff_files(struct add_p_state *s, struct hunk *hunk,
> +				  struct strbuf *old, struct strbuf *new)
> +{
> +	size_t i;
> +	char last_marker = '\0';
> +
> +	for (i = hunk->start; i < hunk->end; i = find_next_line(&s->plain, i)) {
> +		size_t next = find_next_line(&s->plain, i);
> +		char marker = normalize_marker(s->plain.buf + i);
> +
> +		if (marker == '\\') {
> +			if (last_marker != '+')
> +				trim_trailing_lf(old);
> +			if (last_marker != '-')
> +				trim_trailing_lf(new);
> +			continue;
> +		}
> +
> +		if (marker != ' ' && marker != '-' && marker != '+')
> +			BUG("unhandled diff marker: '%c'", marker);
> +
> +		add_word_diff_line(old, new, s->plain.buf + i, next - i,
> +				   marker);
> +		last_marker = marker;
> +	}
> +}
> +
> +static struct diff_filespec *word_diff_filespec(struct repository *r,
> +						const char *name,
> +						struct strbuf *buf)
> +{
> +	struct diff_filespec *spec = alloc_filespec(name);
> +	size_t size;
> +
> +	fill_filespec(spec, null_oid(r->hash_algo), 0, 0100644);
> +	spec->data = strbuf_detach(buf, &size);
> +	spec->size = size;
> +	spec->should_free = 1;
> +	spec->is_stdin = 1;
> +
> +	return spec;
> +}
> +
> +static void show_hunk_word_diff(struct add_p_state *s, struct hunk *hunk,
> +				int colored)
> +{
> +	struct hunk_header *header = &hunk->header;
> +	struct strbuf old = STRBUF_INIT, new = STRBUF_INIT;
> +	struct diff_options opts;
> +	struct diff_queue_struct queue;
> +
> +	if (!header->old_offset && !header->new_offset) {
> +		strbuf_reset(&s->buf);
> +		render_hunk(s, hunk, 0, colored, &s->buf);
> +		fputs(s->buf.buf, stdout);
> +		return;
> +	}
> +
> +	build_word_diff_files(s, hunk, &old, &new);
> +
> +	repo_diff_setup(s->r, &opts);
> +	opts.output_format = DIFF_FORMAT_PATCH;
> +	opts.use_color = colored ? s->cfg.use_color_diff : GIT_COLOR_NEVER;
> +	opts.word_diff = DIFF_WORDS_PLAIN;
> +	opts.context = header->old_count > header->new_count ?
> +		header->old_count : header->new_count;
> +	opts.flags.suppress_diff_headers = 1;
> +	diff_setup_done(&opts);
> +
> +	memcpy(&queue, &diff_queued_diff, sizeof(diff_queued_diff));
> +	diff_queue_init(&diff_queued_diff);
> +	diff_queue(&diff_queued_diff,
> +		   word_diff_filespec(s->r, "a", &old),
> +		   word_diff_filespec(s->r, "b", &new));
> +	diffcore_std(&opts);
> +	diff_flush(&opts);
> +	memcpy(&diff_queued_diff, &queue, sizeof(diff_queued_diff));
> +}
> +
>   #define DISPLAY_HUNKS_LINES 20
>   static size_t display_hunks(struct add_p_state *s,
>   			    struct file_diff *file_diff, size_t start_index)
> @@ -1540,6 +1640,7 @@ N_("j - go to the next undecided hunk, roll over at the bottom\n"
>      "/ - search for a hunk matching the given regex\n"
>      "s - split the current hunk into smaller hunks\n"
>      "e - manually edit the current hunk\n"
> +   "w - print the current hunk with word-diff\n"
>      "p - print the current hunk\n"
>      "P - print the current hunk using the pager\n"
>      "> - go to the next file, roll over at the bottom\n"
> @@ -1731,7 +1832,7 @@ static size_t patch_update_file(struct add_p_state *s,
>   				permitted |= ALLOW_GOTO_PREVIOUS_FILE;
>   				strbuf_addstr(&s->buf, ",<");
>   			}
> -			strbuf_addstr(&s->buf, ",p,P");
> +			strbuf_addstr(&s->buf, ",w,p,P");
>   		}
>   		if (file_diff->deleted)
>   			prompt_mode_type = PROMPT_DELETION;
> @@ -1953,6 +2054,8 @@ static size_t patch_update_file(struct add_p_state *s,
>   				hunk->use = USE_HUNK;
>   				goto soft_increment;
>   			}
> +		} else if (s->answer.buf[0] == 'w') {
> +			show_hunk_word_diff(s, hunk, colored);
>   		} else if (ch == 'p') {
>   			rendered_hunk_index = -1;
>   			use_pager = (s->answer.buf[0] == 'P') ? 1 : 0;
> diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
> index 6e120a4001..e1ce98d62b 100755
> --- a/t/t3701-add-interactive.sh
> +++ b/t/t3701-add-interactive.sh
> @@ -48,8 +48,8 @@ test_expect_success 'unknown command' '
>   	git add -N command &&
>   	git diff command >expect &&
>   	cat >>expect <<-EOF &&
> -	(1/1) Stage addition [y,n,q,a,d,e,p,P,?]? Unknown command ${SQ}W${SQ} (use ${SQ}?${SQ} for help)
> -	(1/1) Stage addition [y,n,q,a,d,e,p,P,?]?$SP
> +	(1/1) Stage addition [y,n,q,a,d,e,w,p,P,?]? Unknown command ${SQ}W${SQ} (use ${SQ}?${SQ} for help)
> +	(1/1) Stage addition [y,n,q,a,d,e,w,p,P,?]?$SP
>   	EOF
>   	git add -p -- command <command >actual 2>&1 &&
>   	test_cmp expect actual
> @@ -332,9 +332,9 @@ test_expect_success 'different prompts for mode change/deleted' '
>   	git -c core.filemode=true add -p >actual &&
>   	sed -n "s/^\(([0-9/]*) Stage .*?\).*/\1/p" actual >actual.filtered &&
>   	cat >expect <<-\EOF &&
> -	(1/1) Stage deletion [y,n,q,a,d,p,P,?]?
> -	(1/2) Stage mode change [y,n,q,a,d,k,K,j,J,g,/,p,P,?]?
> -	(2/2) Stage this hunk [y,n,q,a,d,K,J,g,/,e,p,P,?]?
> +	(1/1) Stage deletion [y,n,q,a,d,w,p,P,?]?
> +	(1/2) Stage mode change [y,n,q,a,d,k,K,j,J,g,/,w,p,P,?]?
> +	(2/2) Stage this hunk [y,n,q,a,d,K,J,g,/,e,w,p,P,?]?
>   	EOF
>   	test_cmp expect actual.filtered
>   '
> @@ -521,13 +521,13 @@ test_expect_success 'split hunk setup' '
>   test_expect_success 'goto hunk 1 with "g 1"' '
>   	test_when_finished "git reset" &&
>   	tr _ " " >expect <<-EOF &&
> -	(2/2) Stage this hunk [y,n,q,a,d,K,J,g,/,e,p,P,?]? + 1:  -1,2 +1,3          +15
> +	(2/2) Stage this hunk [y,n,q,a,d,K,J,g,/,e,w,p,P,?]? + 1:  -1,2 +1,3          +15
>   	_ 2:  -2,4 +3,8          +21
>   	go to which hunk? @@ -1,2 +1,3 @@
>   	_10
>   	+15
>   	_20
> -	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]?_
> +	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]?_
>   	EOF
>   	test_write_lines s y g 1 | git add -p >actual &&
>   	tail -n 7 <actual >actual.trimmed &&
> @@ -540,7 +540,7 @@ test_expect_success 'goto hunk 1 with "g1"' '
>   	_10
>   	+15
>   	_20
> -	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]?_
> +	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]?_
>   	EOF
>   	test_write_lines s y g1 | git add -p >actual &&
>   	tail -n 4 <actual >actual.trimmed &&
> @@ -550,11 +550,11 @@ test_expect_success 'goto hunk 1 with "g1"' '
>   test_expect_success 'navigate to hunk via regex /pattern' '
>   	test_when_finished "git reset" &&
>   	tr _ " " >expect <<-EOF &&
> -	(2/2) Stage this hunk [y,n,q,a,d,K,J,g,/,e,p,P,?]? @@ -1,2 +1,3 @@
> +	(2/2) Stage this hunk [y,n,q,a,d,K,J,g,/,e,w,p,P,?]? @@ -1,2 +1,3 @@
>   	_10
>   	+15
>   	_20
> -	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]?_
> +	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]?_
>   	EOF
>   	test_write_lines s y /1,2 | git add -p >actual &&
>   	tail -n 5 <actual >actual.trimmed &&
> @@ -567,7 +567,7 @@ test_expect_success 'navigate to hunk via regex / pattern' '
>   	_10
>   	+15
>   	_20
> -	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]?_
> +	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]?_
>   	EOF
>   	test_write_lines s y / 1,2 | git add -p >actual &&
>   	tail -n 4 <actual >actual.trimmed &&
> @@ -579,27 +579,42 @@ test_expect_success 'print again the hunk' '
>   	tr _ " " >expect <<-EOF &&
>   	+15
>   	 20
> -	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]? @@ -1,2 +1,3 @@
> +	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]? @@ -1,2 +1,3 @@
>   	 10
>   	+15
>   	 20
> -	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]?_
> +	(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]?_
>   	EOF
>   	test_write_lines s y g 1 p | git add -p >actual &&
>   	tail -n 7 <actual >actual.trimmed &&
>   	test_cmp expect actual.trimmed
>   '
>   
> +test_expect_success 'print hunk with word-diff' '
> +	test_when_finished "rm -rf word-diff-repo" &&
> +	git init word-diff-repo &&
> +	(
> +		cd word-diff-repo &&
> +		test_write_lines "alpha old beta" context >word-diff &&
> +		git add word-diff &&
> +		git commit -m word-diff &&
> +		test_write_lines "alpha new beta" context >word-diff &&
> +		test_write_lines w n | git add -p word-diff >actual &&
> +		test_grep "alpha \\[-old-\\]{+new+} beta" actual &&
> +		git diff --cached --exit-code
> +	)
> +'
> +
>   test_expect_success TTY 'print again the hunk (PAGER)' '
>   	test_when_finished "git reset" &&
>   	cat >expect <<-EOF &&
>   	<GREEN>+<RESET><GREEN>15<RESET>
>   	 20<RESET>
> -	<BOLD;BLUE>(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]? <RESET>PAGER <CYAN>@@ -1,2 +1,3 @@<RESET>
> +	<BOLD;BLUE>(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]? <RESET>PAGER <CYAN>@@ -1,2 +1,3 @@<RESET>
>   	PAGER  10<RESET>
>   	PAGER <GREEN>+<RESET><GREEN>15<RESET>
>   	PAGER  20<RESET>
> -	<BOLD;BLUE>(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]? <RESET>
> +	<BOLD;BLUE>(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]? <RESET>
>   	EOF
>   	test_write_lines s y g 1 P |
>   	(
> @@ -796,21 +811,21 @@ test_expect_success 'colors can be overridden' '
>   	<BLUE>+<RESET><BLUE>new<RESET>
>   	<CYAN> more-context<RESET>
>   	<BLUE>+<RESET><BLUE>another-one<RESET>
> -	<YELLOW>(1/1) Stage this hunk [y,n,q,a,d,s,e,p,P,?]? <RESET><BOLD>Split into 2 hunks.<RESET>
> +	<YELLOW>(1/1) Stage this hunk [y,n,q,a,d,s,e,w,p,P,?]? <RESET><BOLD>Split into 2 hunks.<RESET>
>   	<MAGENTA>@@ -1,3 +1,3 @@<RESET>
>   	<CYAN> context<RESET>
>   	<BOLD>-old<RESET>
>   	<BLUE>+<RESET><BLUE>new<RESET>
>   	<CYAN> more-context<RESET>
> -	<YELLOW>(1/2) Stage this hunk [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]? <RESET><MAGENTA>@@ -3 +3,2 @@<RESET>
> +	<YELLOW>(1/2) Stage this hunk [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]? <RESET><MAGENTA>@@ -3 +3,2 @@<RESET>
>   	<CYAN> more-context<RESET>
>   	<BLUE>+<RESET><BLUE>another-one<RESET>
> -	<YELLOW>(2/2) Stage this hunk [y,n,q,a,d,K,J,g,/,e,p,P,?]? <RESET><MAGENTA>@@ -1,3 +1,3 @@<RESET>
> +	<YELLOW>(2/2) Stage this hunk [y,n,q,a,d,K,J,g,/,e,w,p,P,?]? <RESET><MAGENTA>@@ -1,3 +1,3 @@<RESET>
>   	<CYAN> context<RESET>
>   	<BOLD>-old<RESET>
>   	<BLUE>+new<RESET>
>   	<CYAN> more-context<RESET>
> -	<YELLOW>(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]? <RESET>
> +	<YELLOW>(1/2) Stage this hunk (was: y) [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]? <RESET>
>   	EOF
>   	test_cmp expect actual
>   '
> @@ -1424,9 +1439,9 @@ test_expect_success 'invalid option s is rejected' '
>   	test_write_lines j s q | git add -p >out &&
>   	sed -ne "s/ @@.*//" -e "s/ \$//" -e "/^(/p" <out >actual &&
>   	cat >expect <<-EOF &&
> -	(1/2) Stage this hunk [y,n,q,a,d,k,K,j,J,g,/,s,e,p,P,?]?
> -	(2/2) Stage this hunk [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]? Sorry, cannot split this hunk
> -	(2/2) Stage this hunk [y,n,q,a,d,k,K,j,J,g,/,e,p,P,?]?
> +	(1/2) Stage this hunk [y,n,q,a,d,k,K,j,J,g,/,s,e,w,p,P,?]?
> +	(2/2) Stage this hunk [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]? Sorry, cannot split this hunk
> +	(2/2) Stage this hunk [y,n,q,a,d,k,K,j,J,g,/,e,w,p,P,?]?
>   	EOF
>   	test_cmp expect actual
>   '