sidebar: the tab number at the far edge (tab_bar_index)

`1:api` puts a number at the start of every row, and in a sidebar that is a
column of digits in front of the thing you are actually reading -- the names
start one, two or three cells in depending on how many tabs you have, and the
numbers are only wanted at the moment you reach for C-a 2.

tab_bar_index "right" moves them:

    │ tests        1 │        │ 1:tests        │
    │ verylongproj 2 │   vs   │ 2:verylongproje│
    │ api          3 │        │ 3:api          │

Every name starts in the same column and the numbers line up in one of their
own, which costs a column of sidebar and buys the list a shape. "prefix" stays
the default, because it is what the strip has always drawn and the strip is
where most people meet it.

Sidebars only, and not by omission: a tab in the top strip is exactly as wide
as its label, so there is no far end to align against and a number floating
after a name it does not belong to would be worse than the prefix it replaced.
The setting is ignored there rather than half-honoured. A row too narrow to
spare the columns (under the number plus five) also keeps the prefix, since
the name is the part you came for, and the rename editor keeps the whole cell
as it always did.

A name long enough to reach the number stops one cell short of it, because
`verylongproje2` is a tab called verylongproje2 as far as any reader can tell.
The cell comes back as padding, so the plate is unbroken and the hit is still
the whole row -- clicking the number is clicking the tab, and the number
brightens with the label under the pointer rather than leaving half a row lit.
The bell mark keeps its place between them, budgeted first as before, so a
long name cannot eat either of the two things that are not the name.

1 files changed, 105 insertions, 0 deletions

diff --git a/tests/test_tab_bar.py b/tests/test_tab_bar.py
index d7ff86f..fca4742 100644
--- a/tests/test_tab_bar.py
+++ b/tests/test_tab_bar.py
@@ -158,6 +158,105 @@ def _status(s, text):
     s.settle(30)
 
 
+RIGHT_IDX = _cfg(f'tab_bar_side "left"\ntab_bar_width {W}\ntab_bar_index "right"\n')
+
+
+def test_the_index_can_sit_at_the_far_end():
+    """`tab_bar_index "right"`: names all start in one column, numbers line up
+    in another. A sidebar row is wider than the name on it, and the prefix
+    spends the start of every row on a number nobody reads until they want to
+    press it."""
+    with Session(SH, cols=90, rows=20, config=RIGHT_IDX) as s:
+        s.settle(30)
+        s.api("new-tab", name="api")
+        s.settle(30)
+        rows = [_row(snap := s.snapshot(), Y0), _row(snap, Y0 + 1)]
+        check(
+            "the number is against the right edge",
+            [r.rstrip()[-1] for r in rows] == ["1", "2"],
+            str(rows),
+        )
+        check(
+            "...and every name starts in the same column",
+            rows[1].index("api") == rows[0].index("tests"),
+            str(rows),
+        )
+        check("no prefix is left behind", "1:" not in rows[0], str(rows))
+
+
+def test_a_long_name_stops_short_of_the_number():
+    """Otherwise `verylongproje2` is a tab called verylongproje2, and nothing
+    on the row says otherwise."""
+    with Session(SH, cols=90, rows=20, config=RIGHT_IDX) as s:
+        s.settle(30)
+        s.api("new-tab", name="verylongprojectname")
+        s.settle(30)
+        row = _row(s.snapshot(), Y0 + 1)
+        check("the number survived the long name", row.rstrip()[-1] == "2", repr(row))
+        check(
+            "...with a cell of air before it",
+            row.rstrip()[-2] == " ",
+            repr(row),
+        )
+        check("and the row is still one plate wide", len(row) == CW, repr(row))
+
+
+def test_a_narrow_row_keeps_the_prefix():
+    """The name is the part you came for: at eight columns there is nothing to
+    align and the number goes back in front, where it costs two cells."""
+    narrow = _cfg('tab_bar_side "left"\ntab_bar_width 8\ntab_bar_index "right"\n')
+    with Session(SH, cols=90, rows=20, config=narrow) as s:
+        s.settle(30)
+        row = s.snapshot().line(Y0)[1:7]
+        check("the prefix is back", "1:" in row, repr(row))
+
+
+def test_the_top_strip_ignores_it():
+    """A strip tab is as wide as its label, so there is no far end to align
+    against -- and a number floating after a name it does not belong to would
+    be worse than the prefix it replaced."""
+    top = _cfg('tab_bar_index "right"\n')
+    with Session(SH, cols=60, rows=10, config=top) as s:
+        s.settle(30)
+        check(
+            "the strip still writes 1:name",
+            "1:tests" in s.snapshot().screen(),
+            s.snapshot().line(1),
+        )
+
+
+def test_the_whole_row_is_still_one_door():
+    with Session(SH, cols=90, rows=20, config=RIGHT_IDX) as s:
+        s.settle(30)
+        s.api("new-tab", name="api")
+        s.settle(30)
+        snap = s.snapshot()
+        at_name = snap.hit_at(CX + 1, Y0 + 1)
+        at_number = snap.hit_at(CX + CW - 2, Y0 + 1)
+        check(
+            "clicking the number is clicking the tab",
+            at_name and at_name == at_number,
+            f"{at_name} vs {at_number}",
+        )
+        st = snap.style_at(CX + CW - 2, Y0 + 1)
+        check(
+            "and the number sits on the tab's own plate",
+            st and st["bg"] == (snap.style_at(CX + 1, Y0 + 1) or {}).get("bg"),
+            str(st),
+        )
+
+
+def test_a_bad_index_mode_is_a_line_and_no_more():
+    bad = _cfg(f'tab_bar_side "left"\ntab_bar_width {W}\ntab_bar_index "middle"\n')
+    with Session(SH, cols=90, rows=20, config=bad) as s:
+        s.settle(30)
+        check(
+            "the session runs, with the default",
+            "1:tests" in s.snapshot().screen(),
+            _row(s.snapshot(), Y0),
+        )
+
+
 def test_every_tab_sits_on_a_plate():
     """The tab you are in is the accent; the others are `tab_idle_bg`. The
     quiet fill is what gives a tab edges -- and what the active fill is
@@ -858,6 +957,12 @@ if __name__ == "__main__":
     test_sidebar_rows_click_like_the_strip()
     test_right_sidebar_takes_the_other_edge()
     test_pad_pushes_the_list_down()
+    test_the_index_can_sit_at_the_far_end()
+    test_a_long_name_stops_short_of_the_number()
+    test_a_narrow_row_keeps_the_prefix()
+    test_the_top_strip_ignores_it()
+    test_the_whole_row_is_still_one_door()
+    test_a_bad_index_mode_is_a_line_and_no_more()
     test_every_tab_sits_on_a_plate()
     test_an_old_theme_gets_an_idle_plate_in_its_own_family()
     test_a_theme_can_have_the_bare_tabs_back()