[PATCH] clean: explicitly `fflush` stdout

[PATCH] clean: explicitly `fflush` stdout

[Johannes Schindelin via GitGitGadget]

From: =?UTF-8?q?=EB=A7=88=EB=88=84=EC=97=98?= <nalla@hamal.uberspace.de>

For performance reasons `stdout` is buffered by default. That leads to
problems if after printing to `stdout` a read on `stdin` is performed.

For that reason interactive commands like `git clean -i` do not function
properly anymore if the `stdout` is not flushed by `fflush(stdout)` before
trying to read from `stdin`.

So let's precede all reads on `stdin` in `git clean -i` by flushing
`stdout`.

Signed-off-by: 마누엘 <nalla@hamal.uberspace.de>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
    Explicitly fflush stdout in git clean
    
    This is yet another patch that was funneled through a Git for Windows
    PR. It has served us well for almost five years now, and it is beyond
    time that it find its final home in core Git.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-755%2Fdscho%2Ffflush-in-git-clean-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-755/dscho/fflush-in-git-clean-v1
Pull-Request: https://github.com/git/git/pull/755

 builtin/clean.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/builtin/clean.c b/builtin/clean.c
index 5abf087e7c4..2bd06d13395 100644
--- a/builtin/clean.c
+++ b/builtin/clean.c
@@ -580,6 +580,7 @@ static int *list_and_choose(struct menu_opts *opts, struct menu_stuff *stuff)
 			       clean_get_color(CLEAN_COLOR_RESET));
 		}
 
+		fflush(stdout);
 		if (strbuf_getline_lf(&choice, stdin) != EOF) {
 			strbuf_trim(&choice);
 		} else {
@@ -662,6 +663,7 @@ static int filter_by_patterns_cmd(void)
 		clean_print_color(CLEAN_COLOR_PROMPT);
 		printf(_("Input ignore patterns>> "));
 		clean_print_color(CLEAN_COLOR_RESET);
+		fflush(stdout);
 		if (strbuf_getline_lf(&confirm, stdin) != EOF)
 			strbuf_trim(&confirm);
 		else
@@ -760,6 +762,7 @@ static int ask_each_cmd(void)
 			qname = quote_path_relative(item->string, NULL, &buf);
 			/* TRANSLATORS: Make sure to keep [y/N] as is */
 			printf(_("Remove %s [y/N]? "), qname);
+			fflush(stdout);
 			if (strbuf_getline_lf(&confirm, stdin) != EOF) {
 				strbuf_trim(&confirm);
 			} else {

base-commit: 9fadedd637b312089337d73c3ed8447e9f0aa775
-- 
gitgitgadget

Re: [PATCH] clean: explicitly `fflush` stdout

[Jeff King]

On Wed, Apr 08, 2020 at 07:33:00PM +0000, Johannes Schindelin via GitGitGadget wrote:

> From: =?UTF-8?q?=EB=A7=88=EB=88=84=EC=97=98?= <nalla@hamal.uberspace.de>
> 
> For performance reasons `stdout` is buffered by default. That leads to
> problems if after printing to `stdout` a read on `stdin` is performed.

This first paragraph left me scratching my head. It's only a problem for
interactive uses, right? Would:

  This can lead to problems for interactive commands which write a
  prompt to `stdout` and then read user input on `stdin`. If the prompt
  is left in the buffer, the user will not realize the program is
  waiting for their input.

make sense?

> For that reason interactive commands like `git clean -i` do not function
> properly anymore if the `stdout` is not flushed by `fflush(stdout)` before
> trying to read from `stdin`.

I'm not sure I understand this "anymore". Did the buffering change at
some point, introducing a regression?

> So let's precede all reads on `stdin` in `git clean -i` by flushing
> `stdout`.

This (and the patch) make sense to me. It might be worth factoring out a
"read input from user" function and putting the flush there, but with
only three affected call sites, I'm OK with it either way.

>     This is yet another patch that was funneled through a Git for Windows
>     PR. It has served us well for almost five years now, and it is beyond
>     time that it find its final home in core Git.

Agreed. I guess it didn't affect people on other platforms much because
stdout to a terminal is generally line-buffered on POSIX systems. But
it's better not to rely on that, plus it could create confusion if
somebody tried to manipulate the interactive operation through a pipe
(e.g., driving it from a GUI or something).

-Peff

Re: [PATCH] clean: explicitly `fflush` stdout

[Junio C Hamano]

Jeff King <peff@peff.net> writes:

> This (and the patch) make sense to me. It might be worth factoring out a
> "read input from user" function and putting the flush there, but with
> only three affected call sites, I'm OK with it either way.
>
>>     This is yet another patch that was funneled through a Git for Windows
>>     PR. It has served us well for almost five years now, and it is beyond
>>     time that it find its final home in core Git.
>
> Agreed. I guess it didn't affect people on other platforms much because
> stdout to a terminal is generally line-buffered on POSIX systems. But
> it's better not to rely on that, plus it could create confusion if
> somebody tried to manipulate the interactive operation through a pipe
> (e.g., driving it from a GUI or something).

Hmph, I thought it was more common to do prompts etc. on the
standard error stream, which tends to make the buffering of the
output less of a problem, but apparently these prompts are given to
the standard output.  I am also OK to sprinkle fflush(stdout) but in
the longer term, it would probably be a good idea to introduce a
helper to "prompt then grab input" or "read user input" (if the
former, we'd be able to bring consistency into "which between the
standard output or the standard error does a prompt come?", and if
the latter we'd do fflush(NULL) before reading), especially if there
are many git subcommands that go interactive.

Thanks.

Re: [PATCH] clean: explicitly `fflush` stdout

[Jeff King]

On Wed, Apr 08, 2020 at 02:51:11PM -0700, Junio C Hamano wrote:

> > Agreed. I guess it didn't affect people on other platforms much because
> > stdout to a terminal is generally line-buffered on POSIX systems. But
> > it's better not to rely on that, plus it could create confusion if
> > somebody tried to manipulate the interactive operation through a pipe
> > (e.g., driving it from a GUI or something).
> 
> Hmph, I thought it was more common to do prompts etc. on the
> standard error stream, which tends to make the buffering of the
> output less of a problem, but apparently these prompts are given to
> the standard output.

The prompts in git-add--interactive.perl go to stdout, as do the ones
for "am --interactive". I think that's reasonable, if you think of it as
the main output of the program.

At one point the "am" ones actually went to /dev/tty, but IMHO that's a
mistake. In 99% of cases it behaves the same as looking at stdin/stdout
(because they're connected to the terminal anyway), and in the other 1%
it's just as likely to be the wrong thing as the right. Plus it makes
testing much harder.

> I am also OK to sprinkle fflush(stdout) but in
> the longer term, it would probably be a good idea to introduce a
> helper to "prompt then grab input" or "read user input" (if the
> former, we'd be able to bring consistency into "which between the
> standard output or the standard error does a prompt come?", and if
> the latter we'd do fflush(NULL) before reading), especially if there
> are many git subcommands that go interactive.

Agreed. There is git_prompt(), but that does the tty thing, which I
think we'd want to avoid in most cases. It's used by the credential
code, which really does want to use a terminal to do things like turn
off character echoing. Plus it's not the main function of the program,
but rather a side effect (so we have to avoid disrupting the main
stdin/stdout).

-Peff

[PATCH v2 0/2] Explicitly fflush stdout in git clean

[Johannes Schindelin via GitGitGadget]

This is yet another patch that was funneled through a Git for Windows PR,
read: it has been battle-tested.

Of course, the current iteration of this patch series has not been
battle-tested, so please do review carefully, so that we can prevent bugs
from slipping in during the review process.

Changes since v1:

 * Added a preparatory patch that refactors all interactive input reading
   via strbuf_getline(..., stdin).
 * Adjusted the patch and its commit message accordingly.

Johannes Schindelin (1):
  Refactor code asking the user for input interactively

마누엘 (1):
  Explicitly `fflush` stdout before expecting interactive input

 add-interactive.c |  4 ++--
 add-patch.c       |  4 ++--
 builtin/clean.c   | 14 ++++----------
 prompt.c          | 12 ++++++++++++
 prompt.h          |  2 ++
 shell.c           |  4 ++--
 6 files changed, 24 insertions(+), 16 deletions(-)


base-commit: 9fadedd637b312089337d73c3ed8447e9f0aa775
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-755%2Fdscho%2Ffflush-in-git-clean-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-755/dscho/fflush-in-git-clean-v2
Pull-Request: https://github.com/git/git/pull/755

Range-diff vs v1:

 1:  21acd883b94 < -:  ----------- clean: explicitly `fflush` stdout
 -:  ----------- > 1:  9d2ee78a9e4 Refactor code asking the user for input interactively
 -:  ----------- > 2:  d3949e42004 Explicitly `fflush` stdout before expecting interactive input

-- 
gitgitgadget

[PATCH v2 1/2] Refactor code asking the user for input interactively

[Johannes Schindelin via GitGitGadget]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

There are quite a few code locations (e.g. `git clean --interactive`)
where Git asks the user for an answer. In preparation for fixing a bug
shared by all of them, and also to DRY up the code, let's refactor it.

Please note that most of these callers trimmed white-space both at the
beginning and at the end of the answer, instead of trimming only the
end (as the caller in `add-patch.c` does).

THerefore, technically speaking, we change behavior in this patch. At
the same time, it can be argued that this is actually a bug fix.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 add-interactive.c |  4 ++--
 add-patch.c       |  4 ++--
 builtin/clean.c   | 14 ++++----------
 prompt.c          | 10 ++++++++++
 prompt.h          |  2 ++
 shell.c           |  4 ++--
 6 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/add-interactive.c b/add-interactive.c
index 4a9bf85cac0..29cd2fe0201 100644
--- a/add-interactive.c
+++ b/add-interactive.c
@@ -9,6 +9,7 @@
 #include "lockfile.h"
 #include "dir.h"
 #include "run-command.h"
+#include "prompt.h"
 
 static void init_color(struct repository *r, struct add_i_state *s,
 		       const char *slot_name, char *dst,
@@ -289,13 +290,12 @@ static ssize_t list_and_choose(struct add_i_state *s,
 		fputs(singleton ? "> " : ">> ", stdout);
 		fflush(stdout);
 
-		if (strbuf_getline(&input, stdin) == EOF) {
+		if (git_read_line_interactively(&input) == EOF) {
 			putchar('\n');
 			if (immediate)
 				res = LIST_AND_CHOOSE_QUIT;
 			break;
 		}
-		strbuf_trim(&input);
 
 		if (!input.len)
 			break;
diff --git a/add-patch.c b/add-patch.c
index d8dafa8168d..d8bfe379be4 100644
--- a/add-patch.c
+++ b/add-patch.c
@@ -7,6 +7,7 @@
 #include "color.h"
 #include "diff.h"
 #include "compat/terminal.h"
+#include "prompt.h"
 
 enum prompt_mode_type {
 	PROMPT_MODE_CHANGE = 0, PROMPT_DELETION, PROMPT_HUNK,
@@ -1158,9 +1159,8 @@ static int read_single_character(struct add_p_state *s)
 		return res;
 	}
 
-	if (strbuf_getline(&s->answer, stdin) == EOF)
+	if (git_read_line_interactively(&s->answer) == EOF)
 		return EOF;
-	strbuf_trim_trailing_newline(&s->answer);
 	return 0;
 }
 
diff --git a/builtin/clean.c b/builtin/clean.c
index 5abf087e7c4..c8c011d2ddf 100644
--- a/builtin/clean.c
+++ b/builtin/clean.c
@@ -18,6 +18,7 @@
 #include "color.h"
 #include "pathspec.h"
 #include "help.h"
+#include "prompt.h"
 
 static int force = -1; /* unset */
 static int interactive;
@@ -420,7 +421,6 @@ static int find_unique(const char *choice, struct menu_stuff *menu_stuff)
 	return found;
 }
 
-
 /*
  * Parse user input, and return choice(s) for menu (menu_stuff).
  *
@@ -580,9 +580,7 @@ static int *list_and_choose(struct menu_opts *opts, struct menu_stuff *stuff)
 			       clean_get_color(CLEAN_COLOR_RESET));
 		}
 
-		if (strbuf_getline_lf(&choice, stdin) != EOF) {
-			strbuf_trim(&choice);
-		} else {
+		if (git_read_line_interactively(&choice) == EOF) {
 			eof = 1;
 			break;
 		}
@@ -662,9 +660,7 @@ static int filter_by_patterns_cmd(void)
 		clean_print_color(CLEAN_COLOR_PROMPT);
 		printf(_("Input ignore patterns>> "));
 		clean_print_color(CLEAN_COLOR_RESET);
-		if (strbuf_getline_lf(&confirm, stdin) != EOF)
-			strbuf_trim(&confirm);
-		else
+		if (git_read_line_interactively(&confirm) == EOF)
 			putchar('\n');
 
 		/* quit filter_by_pattern mode if press ENTER or Ctrl-D */
@@ -760,9 +756,7 @@ static int ask_each_cmd(void)
 			qname = quote_path_relative(item->string, NULL, &buf);
 			/* TRANSLATORS: Make sure to keep [y/N] as is */
 			printf(_("Remove %s [y/N]? "), qname);
-			if (strbuf_getline_lf(&confirm, stdin) != EOF) {
-				strbuf_trim(&confirm);
-			} else {
+			if (git_read_line_interactively(&confirm) == EOF) {
 				putchar('\n');
 				eof = 1;
 			}
diff --git a/prompt.c b/prompt.c
index 6d5885d0096..098dcfb7cf9 100644
--- a/prompt.c
+++ b/prompt.c
@@ -74,3 +74,13 @@ char *git_prompt(const char *prompt, int flags)
 	}
 	return r;
 }
+
+int git_read_line_interactively(struct strbuf *line)
+{
+	int ret = strbuf_getline_lf(line, stdin);
+
+	if (ret != EOF)
+		strbuf_trim_trailing_newline(line);
+
+	return ret;
+}
diff --git a/prompt.h b/prompt.h
index e04cced030c..e294e93541c 100644
--- a/prompt.h
+++ b/prompt.h
@@ -6,4 +6,6 @@
 
 char *git_prompt(const char *prompt, int flags);
 
+int git_read_line_interactively(struct strbuf *line);
+
 #endif /* PROMPT_H */
diff --git a/shell.c b/shell.c
index 54cca7439de..cef7ffdc9e1 100644
--- a/shell.c
+++ b/shell.c
@@ -4,6 +4,7 @@
 #include "strbuf.h"
 #include "run-command.h"
 #include "alias.h"
+#include "prompt.h"
 
 #define COMMAND_DIR "git-shell-commands"
 #define HELP_COMMAND COMMAND_DIR "/help"
@@ -76,12 +77,11 @@ static void run_shell(void)
 		int count;
 
 		fprintf(stderr, "git> ");
-		if (strbuf_getline_lf(&line, stdin) == EOF) {
+		if (git_read_line_interactively(&line) == EOF) {
 			fprintf(stderr, "\n");
 			strbuf_release(&line);
 			break;
 		}
-		strbuf_trim(&line);
 		rawargs = strbuf_detach(&line, NULL);
 		split_args = xstrdup(rawargs);
 		count = split_cmdline(split_args, &argv);
-- 
gitgitgadget

[PATCH v2 2/2] Explicitly `fflush` stdout before expecting interactive input

[마누엘 via GitGitGadget]

From: =?UTF-8?q?=EB=A7=88=EB=88=84=EC=97=98?= <nalla@hamal.uberspace.de>

At least one interactive command writes a prompt to `stdout` and then
reads user input on `stdin`: `git clean --interactive`. If the prompt is
left in the buffer, the user will not realize the program is waiting for
their input.

So let's just flush `stdout` before reading the user's input.

Signed-off-by: 마누엘 <nalla@hamal.uberspace.de>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 prompt.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/prompt.c b/prompt.c
index 098dcfb7cf9..5ded21a017f 100644
--- a/prompt.c
+++ b/prompt.c
@@ -77,8 +77,10 @@ char *git_prompt(const char *prompt, int flags)
 
 int git_read_line_interactively(struct strbuf *line)
 {
-	int ret = strbuf_getline_lf(line, stdin);
+	int ret;
 
+	fflush(stdout);
+	ret = strbuf_getline_lf(line, stdin);
 	if (ret != EOF)
 		strbuf_trim_trailing_newline(line);
 
-- 
gitgitgadget

Re: [PATCH v2 1/2] Refactor code asking the user for input interactively

[Derrick Stolee]

On 4/10/2020 7:27 AM, Johannes Schindelin via GitGitGadget wrote:
> From: Johannes Schindelin <johannes.schindelin@gmx.de>
> 
> There are quite a few code locations (e.g. `git clean --interactive`)
> where Git asks the user for an answer. In preparation for fixing a bug
> shared by all of them, and also to DRY up the code, let's refactor it.
> 
> Please note that most of these callers trimmed white-space both at the
> beginning and at the end of the answer, instead of trimming only the
> end (as the caller in `add-patch.c` does).

add-patch also only trims the newline! This is still a good change.

> THerefore, technically speaking, we change behavior in this patch. At

Strange capitalization here.

> the same time, it can be argued that this is actually a bug fix.
> 

> @@ -1158,9 +1159,8 @@ static int read_single_character(struct add_p_state *s)
>  		return res;
>  	}
>  
> -	if (strbuf_getline(&s->answer, stdin) == EOF)
> +	if (git_read_line_interactively(&s->answer) == EOF)
>  		return EOF;
> -	strbuf_trim_trailing_newline(&s->answer);

(Pointing out the trailing newline trim here.)

> +
> +int git_read_line_interactively(struct strbuf *line)
> +{
> +	int ret = strbuf_getline_lf(line, stdin);
> +
> +	if (ret != EOF)
> +		strbuf_trim_trailing_newline(line);
> +
> +	return ret;
> +}

This looks good. Do we need a trailing newline or something?
The way the diff ends abruptly after the "}" line made me
think so.

Thanks,
-Stolee

Re: [PATCH v2 2/2] Explicitly `fflush` stdout before expecting interactive input

[Derrick Stolee]

On 4/10/2020 7:27 AM, 마누엘 via GitGitGadget wrote:
> From: =?UTF-8?q?=EB=A7=88=EB=88=84=EC=97=98?= <nalla@hamal.uberspace.de>
> 
> At least one interactive command writes a prompt to `stdout` and then
> reads user input on `stdin`: `git clean --interactive`. If the prompt is
> left in the buffer, the user will not realize the program is waiting for
> their input.
> 
> So let's just flush `stdout` before reading the user's input.
> 
> Signed-off-by: 마누엘 <nalla@hamal.uberspace.de>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  prompt.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/prompt.c b/prompt.c
> index 098dcfb7cf9..5ded21a017f 100644
> --- a/prompt.c
> +++ b/prompt.c
> @@ -77,8 +77,10 @@ char *git_prompt(const char *prompt, int flags)
>  
>  int git_read_line_interactively(struct strbuf *line)
>  {
> -	int ret = strbuf_getline_lf(line, stdin);
> +	int ret;
>  
> +	fflush(stdout);
> +	ret = strbuf_getline_lf(line, stdin);
>  	if (ret != EOF)
>  		strbuf_trim_trailing_newline(line);

Nice and "clean" ;)

LGTM
-Stolee

Re: [PATCH v2 1/2] Refactor code asking the user for input interactively

[Johannes Schindelin]

Hi Dr Stolee,

On Fri, 10 Apr 2020, Derrick Stolee wrote:

> On 4/10/2020 7:27 AM, Johannes Schindelin via GitGitGadget wrote:
> > From: Johannes Schindelin <johannes.schindelin@gmx.de>
> >
> > There are quite a few code locations (e.g. `git clean --interactive`)
> > where Git asks the user for an answer. In preparation for fixing a bug
> > shared by all of them, and also to DRY up the code, let's refactor it.
> >
> > Please note that most of these callers trimmed white-space both at the
> > beginning and at the end of the answer, instead of trimming only the
> > end (as the caller in `add-patch.c` does).
>
> add-patch also only trims the newline! This is still a good change.
>
> > THerefore, technically speaking, we change behavior in this patch. At
>
> Strange capitalization here.

I fixed it and force-pushed, waiting a little with submitting it in case
there are more things reviewers point out.

> > the same time, it can be argued that this is actually a bug fix.
> >
>
> > @@ -1158,9 +1159,8 @@ static int read_single_character(struct add_p_state *s)
> >  		return res;
> >  	}
> >
> > -	if (strbuf_getline(&s->answer, stdin) == EOF)
> > +	if (git_read_line_interactively(&s->answer) == EOF)
> >  		return EOF;
> > -	strbuf_trim_trailing_newline(&s->answer);
>
> (Pointing out the trailing newline trim here.)
>
> > +
> > +int git_read_line_interactively(struct strbuf *line)
> > +{
> > +	int ret = strbuf_getline_lf(line, stdin);
> > +
> > +	if (ret != EOF)
> > +		strbuf_trim_trailing_newline(line);
> > +
> > +	return ret;
> > +}
>
> This looks good. Do we need a trailing newline or something?
> The way the diff ends abruptly after the "}" line made me
> think so.

No, this file ends in that line, therefore it ends abruptly ;-)

If I add another newline, `git diff` shows a red `+` at the end, i.e. we
consider it a white-space problem.

Thank you for your review!
Dscho

>
> Thanks,
> -Stolee
>
>

Re: [PATCH] clean: explicitly `fflush` stdout

[Johannes Schindelin]

Hi Peff,

On Wed, 8 Apr 2020, Jeff King wrote:

> On Wed, Apr 08, 2020 at 07:33:00PM +0000, Johannes Schindelin via GitGitGadget wrote:
>
> > From: =?UTF-8?q?=EB=A7=88=EB=88=84=EC=97=98?= <nalla@hamal.uberspace.de>
> >
> > For performance reasons `stdout` is buffered by default. That leads to
> > problems if after printing to `stdout` a read on `stdin` is performed.
>
> This first paragraph left me scratching my head. It's only a problem for
> interactive uses, right? Would:
>
>   This can lead to problems for interactive commands which write a
>   prompt to `stdout` and then read user input on `stdin`. If the prompt
>   is left in the buffer, the user will not realize the program is
>   waiting for their input.
>
> make sense?

Thank you, yes, that makes sense.

Based on another suggestion of yours, I did refactor the code a bit more
and already sent out the result as v2.

Thank you,
Dscho

>
> > For that reason interactive commands like `git clean -i` do not function
> > properly anymore if the `stdout` is not flushed by `fflush(stdout)` before
> > trying to read from `stdin`.
>
> I'm not sure I understand this "anymore". Did the buffering change at
> some point, introducing a regression?
>
> > So let's precede all reads on `stdin` in `git clean -i` by flushing
> > `stdout`.
>
> This (and the patch) make sense to me. It might be worth factoring out a
> "read input from user" function and putting the flush there, but with
> only three affected call sites, I'm OK with it either way.
>
> >     This is yet another patch that was funneled through a Git for Windows
> >     PR. It has served us well for almost five years now, and it is beyond
> >     time that it find its final home in core Git.
>
> Agreed. I guess it didn't affect people on other platforms much because
> stdout to a terminal is generally line-buffered on POSIX systems. But
> it's better not to rely on that, plus it could create confusion if
> somebody tried to manipulate the interactive operation through a pipe
> (e.g., driving it from a GUI or something).
>
> -Peff
>

Re: [PATCH v2 1/2] Refactor code asking the user for input interactively

[Jeff King]

On Fri, Apr 10, 2020 at 11:27:50AM +0000, Johannes Schindelin via GitGitGadget wrote:

> diff --git a/prompt.h b/prompt.h
> index e04cced030c..e294e93541c 100644
> --- a/prompt.h
> +++ b/prompt.h
> @@ -6,4 +6,6 @@
>  
>  char *git_prompt(const char *prompt, int flags);
>  
> +int git_read_line_interactively(struct strbuf *line);
> +

It might be worth adding some comments discussing why one would use
git_prompt() versus git_read_line_interactively().

Other than that, both patches look good to me. Thanks for calling out
the changed trimming behavior preemptively. I agree it should not be a
big deal either way.

-Peff

Re: [PATCH v2 1/2] Refactor code asking the user for input interactively

[Junio C Hamano]

"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
writes:

> -		if (strbuf_getline(&input, stdin) == EOF) {
> +		if (git_read_line_interactively(&input) == EOF) {

It's not like we are mimicking or giving a thin wrapper to improve
an existing read_line_interactively() from a third-party, so I do
not see much point in giving "git_" prefix here.  On the other hand,
"strbuf_" prefix may not hurt (but the type of its first parameter
is sufficient so it is not exactly required).

>  			printf(_("Remove %s [y/N]? "), qname);
> -			if (strbuf_getline_lf(&confirm, stdin) != EOF) {
> -				strbuf_trim(&confirm);
> -			} else {
> +			if (git_read_line_interactively(&confirm) == EOF) {
>  				putchar('\n');
>  				eof = 1;

A fat-finger that gave an answer " yes <RET>" used to be still taken
as a yes but now it is interpreted as "no", because the new helper
trims a lot less.  In general, the existing code should be already
choosing the safer default, so such a change in behaviour brought in
by this change, even if they were not intentional, should probably
be safe.

Thanks.

[PATCH v3 0/2] Explicitly fflush stdout in git clean

[Johannes Schindelin via GitGitGadget]

This is yet another patch that was funneled through a Git for Windows PR,
read: it has been battle-tested.

Of course, the current iteration of this patch series has not been
battle-tested, so please do review carefully, so that we can prevent bugs
from slipping in during the review process.

Changes since v2:

 * Fixed the capitalization of "THerefore" in the commit message.

Changes since v1:

 * Added a preparatory patch that refactors all interactive input reading
   via strbuf_getline(..., stdin).
 * Adjusted the patch and its commit message accordingly.

Johannes Schindelin (1):
  Refactor code asking the user for input interactively

마누엘 (1):
  Explicitly `fflush` stdout before expecting interactive input

 add-interactive.c |  4 ++--
 add-patch.c       |  4 ++--
 builtin/clean.c   | 14 ++++----------
 prompt.c          | 12 ++++++++++++
 prompt.h          |  2 ++
 shell.c           |  4 ++--
 6 files changed, 24 insertions(+), 16 deletions(-)


base-commit: 9fadedd637b312089337d73c3ed8447e9f0aa775
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-755%2Fdscho%2Ffflush-in-git-clean-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-755/dscho/fflush-in-git-clean-v3
Pull-Request: https://github.com/git/git/pull/755

Range-diff vs v2:

 1:  9d2ee78a9e4 ! 1:  072f95090ae Refactor code asking the user for input interactively
     @@ Commit message
          beginning and at the end of the answer, instead of trimming only the
          end (as the caller in `add-patch.c` does).
      
     -    THerefore, technically speaking, we change behavior in this patch. At
     +    Therefore, technically speaking, we change behavior in this patch. At
          the same time, it can be argued that this is actually a bug fix.
      
          Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
 2:  d3949e42004 = 2:  063d2aaa401 Explicitly `fflush` stdout before expecting interactive input

-- 
gitgitgadget

[PATCH v3 1/2] Refactor code asking the user for input interactively

[Johannes Schindelin via GitGitGadget]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

There are quite a few code locations (e.g. `git clean --interactive`)
where Git asks the user for an answer. In preparation for fixing a bug
shared by all of them, and also to DRY up the code, let's refactor it.

Please note that most of these callers trimmed white-space both at the
beginning and at the end of the answer, instead of trimming only the
end (as the caller in `add-patch.c` does).

Therefore, technically speaking, we change behavior in this patch. At
the same time, it can be argued that this is actually a bug fix.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 add-interactive.c |  4 ++--
 add-patch.c       |  4 ++--
 builtin/clean.c   | 14 ++++----------
 prompt.c          | 10 ++++++++++
 prompt.h          |  2 ++
 shell.c           |  4 ++--
 6 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/add-interactive.c b/add-interactive.c
index 4a9bf85cac0..29cd2fe0201 100644
--- a/add-interactive.c
+++ b/add-interactive.c
@@ -9,6 +9,7 @@
 #include "lockfile.h"
 #include "dir.h"
 #include "run-command.h"
+#include "prompt.h"
 
 static void init_color(struct repository *r, struct add_i_state *s,
 		       const char *slot_name, char *dst,
@@ -289,13 +290,12 @@ static ssize_t list_and_choose(struct add_i_state *s,
 		fputs(singleton ? "> " : ">> ", stdout);
 		fflush(stdout);
 
-		if (strbuf_getline(&input, stdin) == EOF) {
+		if (git_read_line_interactively(&input) == EOF) {
 			putchar('\n');
 			if (immediate)
 				res = LIST_AND_CHOOSE_QUIT;
 			break;
 		}
-		strbuf_trim(&input);
 
 		if (!input.len)
 			break;
diff --git a/add-patch.c b/add-patch.c
index d8dafa8168d..d8bfe379be4 100644
--- a/add-patch.c
+++ b/add-patch.c
@@ -7,6 +7,7 @@
 #include "color.h"
 #include "diff.h"
 #include "compat/terminal.h"
+#include "prompt.h"
 
 enum prompt_mode_type {
 	PROMPT_MODE_CHANGE = 0, PROMPT_DELETION, PROMPT_HUNK,
@@ -1158,9 +1159,8 @@ static int read_single_character(struct add_p_state *s)
 		return res;
 	}
 
-	if (strbuf_getline(&s->answer, stdin) == EOF)
+	if (git_read_line_interactively(&s->answer) == EOF)
 		return EOF;
-	strbuf_trim_trailing_newline(&s->answer);
 	return 0;
 }
 
diff --git a/builtin/clean.c b/builtin/clean.c
index 5abf087e7c4..c8c011d2ddf 100644
--- a/builtin/clean.c
+++ b/builtin/clean.c
@@ -18,6 +18,7 @@
 #include "color.h"
 #include "pathspec.h"
 #include "help.h"
+#include "prompt.h"
 
 static int force = -1; /* unset */
 static int interactive;
@@ -420,7 +421,6 @@ static int find_unique(const char *choice, struct menu_stuff *menu_stuff)
 	return found;
 }
 
-
 /*
  * Parse user input, and return choice(s) for menu (menu_stuff).
  *
@@ -580,9 +580,7 @@ static int *list_and_choose(struct menu_opts *opts, struct menu_stuff *stuff)
 			       clean_get_color(CLEAN_COLOR_RESET));
 		}
 
-		if (strbuf_getline_lf(&choice, stdin) != EOF) {
-			strbuf_trim(&choice);
-		} else {
+		if (git_read_line_interactively(&choice) == EOF) {
 			eof = 1;
 			break;
 		}
@@ -662,9 +660,7 @@ static int filter_by_patterns_cmd(void)
 		clean_print_color(CLEAN_COLOR_PROMPT);
 		printf(_("Input ignore patterns>> "));
 		clean_print_color(CLEAN_COLOR_RESET);
-		if (strbuf_getline_lf(&confirm, stdin) != EOF)
-			strbuf_trim(&confirm);
-		else
+		if (git_read_line_interactively(&confirm) == EOF)
 			putchar('\n');
 
 		/* quit filter_by_pattern mode if press ENTER or Ctrl-D */
@@ -760,9 +756,7 @@ static int ask_each_cmd(void)
 			qname = quote_path_relative(item->string, NULL, &buf);
 			/* TRANSLATORS: Make sure to keep [y/N] as is */
 			printf(_("Remove %s [y/N]? "), qname);
-			if (strbuf_getline_lf(&confirm, stdin) != EOF) {
-				strbuf_trim(&confirm);
-			} else {
+			if (git_read_line_interactively(&confirm) == EOF) {
 				putchar('\n');
 				eof = 1;
 			}
diff --git a/prompt.c b/prompt.c
index 6d5885d0096..098dcfb7cf9 100644
--- a/prompt.c
+++ b/prompt.c
@@ -74,3 +74,13 @@ char *git_prompt(const char *prompt, int flags)
 	}
 	return r;
 }
+
+int git_read_line_interactively(struct strbuf *line)
+{
+	int ret = strbuf_getline_lf(line, stdin);
+
+	if (ret != EOF)
+		strbuf_trim_trailing_newline(line);
+
+	return ret;
+}
diff --git a/prompt.h b/prompt.h
index e04cced030c..e294e93541c 100644
--- a/prompt.h
+++ b/prompt.h
@@ -6,4 +6,6 @@
 
 char *git_prompt(const char *prompt, int flags);
 
+int git_read_line_interactively(struct strbuf *line);
+
 #endif /* PROMPT_H */
diff --git a/shell.c b/shell.c
index 54cca7439de..cef7ffdc9e1 100644
--- a/shell.c
+++ b/shell.c
@@ -4,6 +4,7 @@
 #include "strbuf.h"
 #include "run-command.h"
 #include "alias.h"
+#include "prompt.h"
 
 #define COMMAND_DIR "git-shell-commands"
 #define HELP_COMMAND COMMAND_DIR "/help"
@@ -76,12 +77,11 @@ static void run_shell(void)
 		int count;
 
 		fprintf(stderr, "git> ");
-		if (strbuf_getline_lf(&line, stdin) == EOF) {
+		if (git_read_line_interactively(&line) == EOF) {
 			fprintf(stderr, "\n");
 			strbuf_release(&line);
 			break;
 		}
-		strbuf_trim(&line);
 		rawargs = strbuf_detach(&line, NULL);
 		split_args = xstrdup(rawargs);
 		count = split_cmdline(split_args, &argv);
-- 
gitgitgadget

[PATCH v3 2/2] Explicitly `fflush` stdout before expecting interactive input

[마누엘 via GitGitGadget]

From: =?UTF-8?q?=EB=A7=88=EB=88=84=EC=97=98?= <nalla@hamal.uberspace.de>

At least one interactive command writes a prompt to `stdout` and then
reads user input on `stdin`: `git clean --interactive`. If the prompt is
left in the buffer, the user will not realize the program is waiting for
their input.

So let's just flush `stdout` before reading the user's input.

Signed-off-by: 마누엘 <nalla@hamal.uberspace.de>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 prompt.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/prompt.c b/prompt.c
index 098dcfb7cf9..5ded21a017f 100644
--- a/prompt.c
+++ b/prompt.c
@@ -77,8 +77,10 @@ char *git_prompt(const char *prompt, int flags)
 
 int git_read_line_interactively(struct strbuf *line)
 {
-	int ret = strbuf_getline_lf(line, stdin);
+	int ret;
 
+	fflush(stdout);
+	ret = strbuf_getline_lf(line, stdin);
 	if (ret != EOF)
 		strbuf_trim_trailing_newline(line);
 
-- 
gitgitgadget