chg: exec pager in child process

chg: exec pager in child process

Before this patch, chg uses the old pager behavior (pre 369741ef7253), which
executes pager in the main process. The user will see the exit code of the
pager, instead of the hg command.

Like 369741ef7253, this patch fixes the behavior by executing the pager in
the child process, and wait for it at the end of the main process.

--- a/contrib/chg/chg.c	Mon Jun 13 13:16:17 2016 +0100
+++ b/contrib/chg/chg.c	Sat Jun 11 20:25:49 2016 +0100
@@ -417,21 +417,22 @@
 	abortmsgerrno("failed to set up signal handlers");
 }
 
-/* This implementation is based on hgext/pager.py (pre 369741ef7253) */
-static void setuppager(hgclient_t *hgc, const char *const args[],
+/* This implementation is based on hgext/pager.py (post 369741ef7253)
+ * Return 0 if pager is not started, or pid of the pager */
+static pid_t setuppager(hgclient_t *hgc, const char *const args[],
 		       size_t argsize)
 {
 	const char *pagercmd = hgc_getpager(hgc, args, argsize);
 	if (!pagercmd)
-		return;
+		return 0;
 
 	int pipefds[2];
 	if (pipe(pipefds) < 0)
-		return;
+		return 0;
 	pid_t pid = fork();
 	if (pid < 0)
 		goto error;
-	if (pid == 0) {
+	if (pid > 0) {
 		close(pipefds[0]);
 		if (dup2(pipefds[1], fileno(stdout)) < 0)
 			goto error;
@@ -441,7 +442,7 @@
 		}
 		close(pipefds[1]);
 		hgc_attachio(hgc);  /* reattach to pager */
-		return;
+		return pid;
 	} else {
 		dup2(pipefds[0], fileno(stdin));
 		close(pipefds[0]);
@@ -451,13 +452,27 @@
 		if (r < 0) {
 			abortmsgerrno("cannot start pager '%s'", pagercmd);
 		}
-		return;
+		return 0;
 	}
 
 error:
 	close(pipefds[0]);
 	close(pipefds[1]);
 	abortmsgerrno("failed to prepare pager");
+	return 0;
+}
+
+static void waitpager(pid_t pid)
+{
+	/* close output streams to notify the pager its input ends */
+	fclose(stdout);
+	fclose(stderr);
+	while (1) {
+		pid_t ret = waitpid(pid, NULL, 0);
+		if (ret == -1 && errno == EINTR)
+			continue;
+		break;
+	}
 }
 
 /* Run instructions sent from the server like unlink and set redirect path
@@ -585,9 +600,12 @@
 	}
 
 	setupsignalhandler(hgc_peerpid(hgc));
-	setuppager(hgc, argv + 1, argc - 1);
+	pid_t pagerpid = setuppager(hgc, argv + 1, argc - 1);
 	int exitcode = hgc_runcommand(hgc, argv + 1, argc - 1);
 	hgc_close(hgc);
 	freecmdserveropts(&opts);
+	if (pagerpid)
+		waitpager(pagerpid);
+
 	return exitcode;
 }

--- a/tests/test-pager.t	Mon Jun 13 13:16:17 2016 +0100
+++ b/tests/test-pager.t	Sat Jun 11 20:25:49 2016 +0100
@@ -201,3 +201,24 @@
   paged! '1\n'
   $ A=2 hg --config pager.attend-printa=yes printa
   paged! '2\n'
+
+Pager should not override the exit code of other commands
+
+  $ cat >> $TESTTMP/fortytwo.py <<'EOF'
+  > from mercurial import cmdutil, commands
+  > cmdtable = {}
+  > command = cmdutil.command(cmdtable)
+  > @command('fortytwo', [], 'fortytwo', norepo=True)
+  > def fortytwo(ui, *opts):
+  >     ui.write('42\n')
+  >     return 42
+  > EOF
+
+  $ cat >> $HGRCPATH <<'EOF'
+  > [extensions]
+  > fortytwo = $TESTTMP/fortytwo.py
+  > EOF
+
+  $ hg fortytwo --pager=on
+  paged! '42\n'
+  [42]