[PATCH 2/2] prompt: respect GIT_TERMINAL_PROMPT to disable terminal prompts

[Jeff King <peff@peff.net>]

If you run git as part of an automated system, you might
prefer git to die rather than try to issue a prompt on the
terminal (because there would be nobody to see it and
respond, and the process would hang forever).

This usually works out of the box because getpass() (and our
more featureful replacements) will fail when there is no
tty, but this does not cover all cases. For example, a batch
system run via ssh might have a tty, even when the user does
not expect it.

Let's provide an environment variable the user can set to
avoid even trying to touch the tty at all.

Signed-off-by: Jeff King <peff@peff.net>
---
I also considered adding a "git --[no-]terminal-prompt"
option, but it seemed like overkill to me. I imagine the
common use would be to just set this at the top of a script.
But it would be trivial to add if we want to.

No tests, because our lib-terminal.sh infrastructure is not
up to the challenge of fooling getpass(). Besides not
handling input at all, git will actually open /dev/tty
itself. So we would have to open a pty and then set it as
the controlling terminal for the sub-process.  It's probably
possible, but I'm not sure the portability headaches are
worth testing such a trivial feature.

 Documentation/git.txt |  4 ++++
 prompt.c              | 16 ++++++++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index afb48d3..54f7a1c 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -906,6 +906,10 @@ for further details.
 	and read the password from its STDOUT. See also the 'core.askpass'
 	option in linkgit:git-config[1].
 
+'GIT_TERMINAL_PROMPT'::
+	If this environment variable is set to `0`, git will not prompt
+	on the terminal (e.g., when asking for HTTP authentication).
+
 'GIT_CONFIG_NOSYSTEM'::
 	Whether to skip reading settings from the system-wide
 	`$(prefix)/etc/gitconfig` file.  This environment variable can
diff --git a/prompt.c b/prompt.c
index e5b4938..8181eeb 100644
--- a/prompt.c
+++ b/prompt.c
@@ -57,11 +57,19 @@ char *git_prompt(const char *prompt, int flags)
 			r = do_askpass(askpass, prompt);
 	}
 
-	if (!r)
-		r = git_terminal_prompt(prompt, flags & PROMPT_ECHO);
 	if (!r) {
-		/* prompts already contain ": " at the end */
-		die("could not read %s%s", prompt, strerror(errno));
+		const char *err;
+
+		if (git_env_bool("GIT_TERMINAL_PROMPT", 1)) {
+			r = git_terminal_prompt(prompt, flags & PROMPT_ECHO);
+			err = strerror(errno);
+		} else {
+			err = "terminal prompts disabled";
+		}
+		if (!r) {
+			/* prompts already contain ": " at the end */
+			die("could not read %s%s", prompt, err);
+		}
 	}
 	return r;
 }
-- 
2.2.0.390.gf60752d