Hi Junio,

On Wed, 26 Dec 2018, Junio C Hamano wrote:

Paul-Sebastian Ungureanu [off-list ref] writes:

quoted

+static void set_env_if(const char *key, const char *value, int *given, int bit)
+{
+	if ((*given & bit) || getenv(key))
+		return; /* nothing to do */
+	setenv(key, value, 0);
+	*given |= bit;
+}

We call setenv(3) with overwrite=0 but we protect the call with a
check for existing value with getenv(3), which feels a bit like an
anti-pattern.  Wouldn't the following be simpler to follow, I wonder?

	if (!(*given & bit)) {
		setenv(key, value, 1);
		*given |= bit;
	}

The only case these two may behave differently is when '*given' does
not have the 'bit' set but the environment 'key' already exists.

Indeed, this is the case where your version would actually do the wrong
thing. Imagine that GIT_AUTHOR_NAME is set already. Your code would
*override* it. But that is not what we want to do here. We want to *fall
back* if there is no already-configured value.

And of course we won't set the `given` bit if we don't fall back here;
that should be done somewhere else, where that environment variable (that
we *refuse* to overwrite) is *actually* used.

Ciao,
Dscho

The proposed patch will leave 'bit' in '*given' unset, so when a
later code says "let's see if author_ident is explicitly given, and
complain otherwise", such a check will trigger and cause complaint.

On the other hand, the simplified version does not allow the
"explicitly-given" bits to be left unset, so it won't cause
complaint.

Isn't it a BUG() if *given lacks 'bit' when the corresponding
environment variable 'key' is missing?  IOW, I would understand
an implementation that is more elaborate than the simplified one I
just gave above were something like

	if (!(*given & bit)) {
		if (getenv(key))
			BUG("why does %s exist and no %x bit set???", key, bit);
		setenv(key, value, 0);
		*given |= bit;
	}

but I do not quite understand the reasoning behind the "check either
the bit, or the environment variable" in the proposed patch.

quoted

+void prepare_fallback_ident(const char *name, const char *email)
+{
+	set_env_if("GIT_AUTHOR_NAME", name,
+		   &author_ident_explicitly_given, IDENT_NAME_GIVEN);
+	set_env_if("GIT_AUTHOR_EMAIL", email,
+		   &author_ident_explicitly_given, IDENT_MAIL_GIVEN);
+	set_env_if("GIT_COMMITTER_NAME", name,
+		   &committer_ident_explicitly_given, IDENT_NAME_GIVEN);
+	set_env_if("GIT_COMMITTER_EMAIL", email,
+		   &committer_ident_explicitly_given, IDENT_MAIL_GIVEN);
+}

Introducing this function alone without a caller and without
function doc is a bit unfriendly to future callers, who must be
careful when to call it, I think.  For example, they must know that
it will be a disaster if they call this before they call
git_ident_config(), right?

quoted

+
 static int buf_cmp(const char *a_begin, const char *a_end,
 		   const char *b_begin, const char *b_end)
 {