[PATCH 1 of 5] pager: stdout is line buffered by default

[Simon Farnsworth]

# HG changeset patch
# User Simon Farnsworth <simonfar at fb.com>
# Date 1484835774 28800
#      Thu Jan 19 06:22:54 2017 -0800
# Node ID 76123ae2e0ccaa58db3d4fc26b75b7251e13ad16
# Parent  036c37bd3ec189480647ff568cee9e0b43a5bc81
pager: stdout is line buffered by default

pager only starts when ui.formatted() is true. In normal operation,
when ui.formatted() is true, stdout is line buffered anyway.

The code here doesn't actually do what the commit message in changeset
62c5e937 claims it will do; sys.stdout is not yet pager.stdin when we
reopen, so we affect the original sys.stdout's buffering mode. It's the dup2
that puts pager.stdin's fd into sys.stdout's fd, and that doesn't affect
buffering.

diff --git a/hgext/pager.py b/hgext/pager.py
--- a/hgext/pager.py
+++ b/hgext/pager.py
@@ -87,14 +87,10 @@
                              close_fds=util.closefds, stdin=subprocess.PIPE,
                              stdout=util.stdout, stderr=util.stderr)
 
-    # back up original file objects and descriptors
-    olduifout = ui.fout
-    oldstdout = util.stdout
+    # back up original file descriptors
     stdoutfd = os.dup(util.stdout.fileno())
     stderrfd = os.dup(util.stderr.fileno())
 
-    # create new line-buffered stdout so that output can show up immediately
-    ui.fout = util.stdout = newstdout = os.fdopen(util.stdout.fileno(), 'wb', 1)
     os.dup2(pager.stdin.fileno(), util.stdout.fileno())
     if ui._isatty(util.stderr):
         os.dup2(pager.stdin.fileno(), util.stderr.fileno())
@@ -103,15 +99,12 @@
     def killpager():
         if util.safehasattr(signal, "SIGINT"):
             signal.signal(signal.SIGINT, signal.SIG_IGN)
-        pager.stdin.close()
-        ui.fout = olduifout
-        util.stdout = oldstdout
-        # close new stdout while it's associated with pager; otherwise stdout
-        # fd would be closed when newstdout is deleted
-        newstdout.close()
-        # restore original fds: stdout is open again
+        # restore original fds
         os.dup2(stdoutfd, util.stdout.fileno())
         os.dup2(stderrfd, util.stderr.fileno())
+        # close pager's stdin so that it knows we're not going to send any more
+        # data
+        pager.stdin.close()
         pager.wait()
 
 def uisetup(ui):