Subject: Re: [PATCH v2] write-or-die: make GIT_FLUSH a Boolean environment variable

From: Taylor Blau <[email-masked]>
Date: Wed, 3 Jan 2024 12:15:26 -0500

On Wed, Jan 03, 2024 at 09:22:13AM +0100, Patrick Steinhardt wrote:
> On Wed, Jan 03, 2024 at 07:58:28AM +0000, Chandra Pratap via GitGitGadget wrote:
> [snip]
> > diff --git a/write-or-die.c b/write-or-die.c
> > index 42a2dc73cd3..a6acabd329f 100644
> > --- a/write-or-die.c
> > +++ b/write-or-die.c
> > @@ -20,15 +20,12 @@ void maybe_flush_or_die(FILE *f, const char *desc)
> >  {
> >  	static int skip_stdout_flush = -1;
> >  	struct stat st;
> > -	char *cp;
> >
> >  	if (f == stdout) {
> >  		if (skip_stdout_flush < 0) {
> > -			/* NEEDSWORK: make this a normal Boolean */
> > -			cp = getenv("GIT_FLUSH");
> > -			if (cp)
> > -				skip_stdout_flush = (atoi(cp) == 0);
> > -			else if ((fstat(fileno(stdout), &st) == 0) &&
> > +			if (!git_env_bool("GIT_FLUSH", -1))
> > +				skip_stdout_flush = 1;
>
> It's a bit surprising to pass `-1` as default value to `git_env_bool()`
> here, as this value would hint that the caller wants to explicitly
> handle the case where the "GIT_FLUSH" envvar is not set at all. We don't
> though, and essentially fall back to "GIT_FLUSH=1", so passing `1` as
> the fallback value would be less confusing.
>
> Anyway, the resulting behaviour is the same regardless of whether we
> pass `1` or `-1`, so I'm not sure whether this is worth a reroll.

Hmm. If we pass -1 as the default value in the call to git_env_bool(),
the only time we'll end up in the else branch is if the environment is
set to some false-y value.

I don't think that matches the existing behavior, since right now we'll
infer skip_stdout_flush based on whether or not stdout is a regular file
or something else.

I think you'd probably want something closer to:

--- 8< ---
diff --git a/write-or-die.c b/write-or-die.c
index 42a2dc73cd..f12e111688 100644
--- a/write-or-die.c
+++ b/write-or-die.c
@@ -19,20 +19,17 @@
 void maybe_flush_or_die(FILE *f, const char *desc)
 {
 	static int skip_stdout_flush = -1;
-	struct stat st;
-	char *cp;

 	if (f == stdout) {
 		if (skip_stdout_flush < 0) {
-			/* NEEDSWORK: make this a normal Boolean */
-			cp = getenv("GIT_FLUSH");
-			if (cp)
-				skip_stdout_flush = (atoi(cp) == 0);
-			else if ((fstat(fileno(stdout), &st) == 0) &&
-				 S_ISREG(st.st_mode))
-				skip_stdout_flush = 1;
-			else
-				skip_stdout_flush = 0;
+			skip_stdout_flush = git_env_bool("GIT_FLUSH", -1);
+			if (skip_stdout_flush < 0) {
+				struct stat st;
+				if (fstat(fileno(f), &st))
+					skip_stdout_flush = 0;
+				else
+					skip_stdout_flush = S_ISREG(st.st_mode);
+			}
 		}
 		if (skip_stdout_flush && !ferror(f))
 			return;
--- >8 ---

You could lose one level of indentation, but it costs an extra fstat()
call in the case where GIT_FLUSH is set to some explicit value. Doing
that would look like this ugly thing instead ;-):

--- 8< ---
diff --git a/write-or-die.c b/write-or-die.c
index 42a2dc73cd..b3275d7577 100644
--- a/write-or-die.c
+++ b/write-or-die.c
@@ -19,20 +19,11 @@
 void maybe_flush_or_die(FILE *f, const char *desc)
 {
 	static int skip_stdout_flush = -1;
-	struct stat st;
-	char *cp;

 	if (f == stdout) {
 		if (skip_stdout_flush < 0) {
-			/* NEEDSWORK: make this a normal Boolean */
-			cp = getenv("GIT_FLUSH");
-			if (cp)
-				skip_stdout_flush = (atoi(cp) == 0);
-			else if ((fstat(fileno(stdout), &st) == 0) &&
-				 S_ISREG(st.st_mode))
-				skip_stdout_flush = 1;
-			else
-				skip_stdout_flush = 0;
+			struct stat st;
+			skip_stdout_flush = git_env_bool("GIT_FLUSH", !fstat(fileno(f), &st) && S_ISREG(st.st_mode));
 		}
 		if (skip_stdout_flush && !ferror(f))
 			return;
--- >8 ---

Thanks,
Taylor