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"""How much history a pane keeps, and the two settings that decide it.
lib-vt is handed no limit and picks its own: 10,000 *bytes*, which measured at 622
lines of an 80-column pane. Nobody chose that number, and nothing could change it
— D4 promised scrollback and then left the size to a library default.
"""
import os
import re
import sys
import tempfile
sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
from harness import Session, check, report
TOP = r"\x01\x1b[1~" # C-a Home: scroll to the oldest line
def spew(n):
"""A pane that prints `n` numbered lines and then waits."""
return [
"/bin/sh",
"-c",
'i=1; while [ $i -le %d ]; do echo "line-$i"; i=$((i+1)); done; read x' % n,
]
def conf(text):
f = tempfile.NamedTemporaryFile("w", suffix=".kdl", delete=False)
f.write(text)
f.close()
return f.name
def oldest(s):
"""The oldest line still in the pane, by scrolling to the top of it.
Measured from what is on screen rather than from a counter, because the
number a caller cares about is how far back they can *read*."""
s.settle(400)
s.send(TOP)
screen = s.snapshot().screen()
got = re.findall(r"line-(\d+)", screen)
return min(int(g) for g in got) if got else None
def kept(s, printed):
o = oldest(s)
return None if o is None else printed - o + 1
def test_a_pane_keeps_the_configured_number_of_lines():
"""Not the exact number: lib-vt prunes a page at a time, so what a pane keeps
is within a page's worth of what it was told. The property that matters is that
the setting is what decides it."""
cfg = conf("scrollback 400\n")
with Session(spew(3000), cols=80, rows=8, config=cfg) as s:
n = kept(s, 3000)
check(
"a small setting is honoured",
n is not None and 250 < n < 700,
"kept %s of 3000" % n,
)
os.unlink(cfg)
cfg = conf("scrollback 2000\n")
with Session(spew(3000), cols=80, rows=8, config=cfg) as s:
n = kept(s, 3000)
check(
"and a larger one keeps more",
n is not None and n > 1500,
"kept %s of 3000" % n,
)
os.unlink(cfg)
def test_zero_keeps_no_history_at_all():
"""The screen, and nothing behind it."""
cfg = conf("scrollback 0\n")
with Session(spew(3000), cols=80, rows=8, config=cfg) as s:
n = kept(s, 3000)
check(
"nothing is retained past the viewport",
n is not None and n <= 10,
"kept %s of 3000" % n,
)
check(
"and scrolling up says so",
"scrolled" not in s.snapshot().screen(),
s.snapshot().screen(),
)
os.unlink(cfg)
def test_the_default_is_not_a_library_accident():
"""622 lines was what lib-vt's 10,000-byte default bought. A `make` run is
longer than that, which is exactly when scrollback is wanted."""
with Session(spew(3000), cols=80, rows=8) as s:
n = kept(s, 3000)
check(
"the default keeps everything a 3000-line run printed",
n is not None and n > 2900,
"kept %s of 3000" % n,
)
def test_the_byte_ceiling_is_the_other_limit():
"""Either can be reached first and neither can see what the other depends on:
a line count cannot know how wide the terminal is, a byte count cannot know
how many lines that bought. lib-vt applies whichever bites."""
cfg = conf("scrollback 5000\nscrollback_bytes 500000\n")
with Session(spew(3000), cols=80, rows=8, config=cfg) as s:
n = kept(s, 3000)
check(
"a low ceiling clips a high line count",
n is not None and n < 1200,
"kept %s of 3000" % n,
)
os.unlink(cfg)
cfg = conf("scrollback 5000\nscrollback_bytes 0\n")
with Session(spew(3000), cols=80, rows=8, config=cfg) as s:
n = kept(s, 3000)
check(
"and no ceiling lets the line count stand",
n is not None and n > 2900,
"kept %s of 3000" % n,
)
os.unlink(cfg)
def test_a_negative_is_refused_rather_than_wrapped():
"""A signed value read into a size_t is how "unlimited" gets into a program by
accident: eighteen quintillion lines, and nobody asked for it."""
import subprocess
from harness import BIN
for line, word in (
("scrollback -1\n", "scrollback is a number of lines"),
("scrollback_bytes -1\n", "scrollback_bytes is a byte"),
):
cfg = conf(line)
out = subprocess.run([BIN, "--check", cfg], capture_output=True, text=True)
said = out.stderr + out.stdout
check("it says what it wanted: " + word, word in said, said)
check("and exits non-zero", out.returncode == 1, str(out.returncode))
os.unlink(cfg)
def test_it_applies_to_the_next_pane_not_the_ones_holding_history():
"""Same rule as `shell`, and for the same reason: retroactively shrinking a
pane's scrollback would throw away output somebody is reading."""
cfg = conf("scrollback 2000\n")
with Session(spew(3000), cols=80, rows=8, config=cfg) as s:
before = kept(s, 3000)
check(
"the pane has its history",
before is not None and before > 1500,
"kept %s" % before,
)
with open(cfg, "w") as f:
f.write("scrollback 0\n")
r = s.api("reload")
check("the config reloads", r["ok"], str(r))
after = kept(s, 3000)
check(
"and the pane already open keeps what it had",
after is not None and after > 1500,
"kept %s" % after,
)
os.unlink(cfg)
if __name__ == "__main__":
for name, fn in sorted(list(globals().items())):
if name.startswith("test_"):
fn()
sys.exit(report())
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