threads / patch / 52902

patchrebase-interactive.c: silence format-zero-length warnings

Subject: [PATCH] rebase-interactive.c: silence format-zero-length warnings

## tl;dr

6 messages between Feb 27, 2020 and Mar 3, 2020. Diffs are folded; open one to read it.

replies: 5people: 4as markdown or json

Ralf Thielow via GitGitGadget· Feb 27, 2020, 20:25 UTC · lore
From: Ralf Thielow <ralf.thielow@gmail.com>
Fixes the following warnings:
rebase-interactive.c: In function ‘edit_todo_list’:
rebase-interactive.c:137:38: warning: zero-length gnu_printf format string [-Wformat-zero-length]
    write_file(rebase_path_dropped(), "");
rebase-interactive.c:144:37: warning: zero-length gnu_printf format string [-Wformat-zero-length]
   write_file(rebase_path_dropped(), "");
Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
---
    rebase-interactive.c: silence format-zero-length warnings
    
    I noticed these warnings a while ago and they're still there, so here's
    my fix.
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-567%2Fralfth%2Fformat-zero-length-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-567/ralfth/format-zero-length-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/567
 rebase-interactive.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
Show changes to rebase-interactive.c +2 −2
diff --git a/rebase-interactive.c b/rebase-interactive.c
index ac001dea588..0a4572e67ea 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -134,14 +134,14 @@ int edit_todo_list(struct repository *r, struct todo_list *todo_list,
 
 	if (incorrect) {
 		if (todo_list_check_against_backup(r, new_todo)) {
-			write_file(rebase_path_dropped(), "");
+			write_file(rebase_path_dropped(), "%s", "");
 			return -4;
 		}
 
 		if (incorrect > 0)
 			unlink(rebase_path_dropped());
 	} else if (todo_list_check(todo_list, new_todo)) {
-		write_file(rebase_path_dropped(), "");
+		write_file(rebase_path_dropped(), "%s", "");
 		return -4;
 	}
 

base-commit: 2d2118b814c11f509e1aa76cb07110f7231668dc

-- 
gitgitgadget
Jeff King· Feb 27, 2020, 23:54 UTC · re: Ralf Thielow via GitGitGadget · lore

[PATCH] config.mak.dev: re-enable -Wformat-zero-length

On Thu, Feb 27, 2020 at 08:25:30PM +0000, Ralf Thielow via GitGitGadget wrote:
Show 7 quoted lines
> Fixes the following warnings:
> 
> rebase-interactive.c: In function ‘edit_todo_list’:
> rebase-interactive.c:137:38: warning: zero-length gnu_printf format string [-Wformat-zero-length]
>     write_file(rebase_path_dropped(), "");
> rebase-interactive.c:144:37: warning: zero-length gnu_printf format string [-Wformat-zero-length]
>    write_file(rebase_path_dropped(), "");
Thanks, I think this is worth doing.

I had noticed them, too, but then they "went away" so I assumed they had already been fixed. It turns out that it's the difference between a build with and without the DEVELOPER Makefile knob set.

I think we should do this on top:
-- >8 --
Subject: [PATCH] config.mak.dev: re-enable -Wformat-zero-length

We recently triggered some -Wformat-zero-length warnings in the code, but no developers noticed because we suppress that warning in builds with the DEVELOPER=1 Makefile knob set. But we _don't_ suppress them in a non-developer build (and they're part of -Wall). So even though non-developers probably aren't using -Werror, they see the annoying warnings when they build.

We've had back and forth discussion over the years on whether this warning is useful or not. In most cases we've seen, it's not true that the call is a mistake, since we're using its side effects (like adding a newline status_printf_ln()) or writing an empty string to a destination which is handled by the function (as in write_file()). And so we end up working around it in the source by passing ("%s", "").

There's more discussion in the subthread starting at:
  https://lore.kernel.org/git/xmqqtwaod7ly.fsf@gitster.mtv.corp.google.com/

The short of it is that we probably can't just disable the warning for everybody because of portability issues. And ignoring it for developers puts us in the situation we're in now, where non-dev builds are annoyed.

Since the workaround is both rarely needed and fairly straight-forward, let's just commit to doing it as necessary, and re-enable the warning.

Signed-off-by: Jeff King <peff@peff.net>
---
I had totally forgotten about that thread until researching the history
just now. There's another option there involving #pragma, but it was too
gross for me to even suggest now as an alternative in the commit
message. ;) I think this is the most practical improvement.
 config.mak.dev | 1 -
 1 file changed, 1 deletion(-)
Show changes to config.mak.dev +0 −1
diff --git a/config.mak.dev b/config.mak.dev
index bf1f3fcdee..89b218d11a 100644
--- a/config.mak.dev
+++ b/config.mak.dev
@@ -9,7 +9,6 @@ endif
 DEVELOPER_CFLAGS += -Wall
 DEVELOPER_CFLAGS += -Wdeclaration-after-statement
 DEVELOPER_CFLAGS += -Wformat-security
-DEVELOPER_CFLAGS += -Wno-format-zero-length
 DEVELOPER_CFLAGS += -Wold-style-definition
 DEVELOPER_CFLAGS += -Woverflow
 DEVELOPER_CFLAGS += -Wpointer-arith

-- 
2.25.1.911.g022f5304bc
Junio C Hamano· Feb 28, 2020, 16:42 UTC · re: Jeff King · lore

Re: [PATCH] config.mak.dev: re-enable -Wformat-zero-length

Jeff King <peff@peff.net> writes:
> The short of it is that we probably can't just disable the warning for
> everybody because of portability issues. And ignoring it for developers
> puts us in the situation we're in now, where non-dev builds are annoyed.

"git blame" unfortunately is very bad at poing at a commit that removed something, so I do not offhand know how much it would help readers who later wonder "oh, I am sure we had thing to disable format-zero-length warning, and I want to learn the reason why we dropped it", but thanks for writing this down.

Show 25 quoted lines
> Since the workaround is both rarely needed and fairly straight-forward,
> let's just commit to doing it as necessary, and re-enable the warning.
>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
> I had totally forgotten about that thread until researching the history
> just now. There's another option there involving #pragma, but it was too
> gross for me to even suggest now as an alternative in the commit
> message. ;) I think this is the most practical improvement.
>
>  config.mak.dev | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/config.mak.dev b/config.mak.dev
> index bf1f3fcdee..89b218d11a 100644
> --- a/config.mak.dev
> +++ b/config.mak.dev
> @@ -9,7 +9,6 @@ endif
>  DEVELOPER_CFLAGS += -Wall
>  DEVELOPER_CFLAGS += -Wdeclaration-after-statement
>  DEVELOPER_CFLAGS += -Wformat-security
> -DEVELOPER_CFLAGS += -Wno-format-zero-length
>  DEVELOPER_CFLAGS += -Wold-style-definition
>  DEVELOPER_CFLAGS += -Woverflow
>  DEVELOPER_CFLAGS += -Wpointer-arith
Jeff King· Feb 28, 2020, 17:06 UTC · re: Junio C Hamano · lore

Re: [PATCH] config.mak.dev: re-enable -Wformat-zero-length

On Fri, Feb 28, 2020 at 08:42:47AM -0800, Junio C Hamano wrote:
Show 11 quoted lines
> Jeff King <peff@peff.net> writes:
> 
> > The short of it is that we probably can't just disable the warning for
> > everybody because of portability issues. And ignoring it for developers
> > puts us in the situation we're in now, where non-dev builds are annoyed.
> 
> "git blame" unfortunately is very bad at poing at a commit that
> removed something, so I do not offhand know how much it would help
> readers who later wonder "oh, I am sure we had thing to disable
> format-zero-length warning, and I want to learn the reason why we
> dropped it", but thanks for writing this down.

I often turn to "git log -Sformat-zero" for this (and in fact that was very useful for the research I did yesterday). But of course you have to first _know_ about the warning and wonder "hey, didn't used ignore it?" for that to be useful.

-Peff
Alban Gruin· Mar 3, 2020, 10:17 UTC · re: Ralf Thielow via GitGitGadget · lore

Re: [PATCH] rebase-interactive.c: silence format-zero-length warnings

Hi Ralf,
Le 27/02/2020 à 21:25, Ralf Thielow via GitGitGadget a écrit :
Show 48 quoted lines
> From: Ralf Thielow <ralf.thielow@gmail.com>
> 
> Fixes the following warnings:
> 
> rebase-interactive.c: In function ‘edit_todo_list’:
> rebase-interactive.c:137:38: warning: zero-length gnu_printf format string [-Wformat-zero-length]
>     write_file(rebase_path_dropped(), "");
> rebase-interactive.c:144:37: warning: zero-length gnu_printf format string [-Wformat-zero-length]
>    write_file(rebase_path_dropped(), "");
> 
> Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
> ---
>     rebase-interactive.c: silence format-zero-length warnings
>     
>     I noticed these warnings a while ago and they're still there, so here's
>     my fix.
> 
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-567%2Fralfth%2Fformat-zero-length-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-567/ralfth/format-zero-length-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/567
> 
>  rebase-interactive.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/rebase-interactive.c b/rebase-interactive.c
> index ac001dea588..0a4572e67ea 100644
> --- a/rebase-interactive.c
> +++ b/rebase-interactive.c
> @@ -134,14 +134,14 @@ int edit_todo_list(struct repository *r, struct todo_list *todo_list,
>  
>  	if (incorrect) {
>  		if (todo_list_check_against_backup(r, new_todo)) {
> -			write_file(rebase_path_dropped(), "");
> +			write_file(rebase_path_dropped(), "%s", "");
>  			return -4;
>  		}
>  
>  		if (incorrect > 0)
>  			unlink(rebase_path_dropped());
>  	} else if (todo_list_check(todo_list, new_todo)) {
> -		write_file(rebase_path_dropped(), "");
> +		write_file(rebase_path_dropped(), "%s", "");
>  		return -4;
>  	}
>  
> 
> base-commit: 2d2118b814c11f509e1aa76cb07110f7231668dc
> 
Ack.
On a tangent: what's wrong with empty format strings?

Cheers, Alban

Junio C Hamano· Mar 3, 2020, 14:20 UTC · re: Alban Gruin · lore

Re: [PATCH] rebase-interactive.c: silence format-zero-length warnings

Alban Gruin <alban.gruin@gmail.com> writes:
Show 8 quoted lines
>> Fixes the following warnings:
>> 
>> rebase-interactive.c: In function ‘edit_todo_list’:
>> rebase-interactive.c:137:38: warning: zero-length gnu_printf format string [-Wformat-zero-length]
>>     write_file(rebase_path_dropped(), "");
>> rebase-interactive.c:144:37: warning: zero-length gnu_printf format string [-Wformat-zero-length]
> ...
> On a tangent: what's wrong with empty format strings?

Those functions that are truly printf-like, such a call would be no-op and an indication of possible typo ("did you forget a %s or something?"), I presume.

But many of our functions that take printf-like format strings will do useful things even when an empty string is given, so the warning is unwanted.

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