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, 8 insertions, 0 deletions

diff --git a/config/config.kdl b/config/config.kdl
index 147b709..47473f0 100644
--- a/config/config.kdl
+++ b/config/config.kdl
@@ -283,6 +283,14 @@ bell_mark "[!]"
 // The one-row bar with tabs, the new-tab button and the pane count.
 status_bar true
 
+// Where a tab's number sits. "prefix" writes it against the name (`1:api`);
+// "right" puts it at the far end of the row, so every name starts in the same
+// column and the numbers line up in one of their own -- which a sidebar has
+// room for and the top strip has not, a tab there being exactly as wide as
+// its label. Sidebars only for that reason, and a row too narrow to spare the
+// columns keeps the prefix: the name is the part you came for.
+tab_bar_index "prefix"
+
 // The line along the bottom: which session and tab you are in, what the
 // focused pane calls itself, and whether it is in a state worth knowing about
 // - scrolled back, on an alternate screen, or not started yet. On the right it