Configurable tab label composition and minimum tab width

[aspiers]

idea / problem

Tab labels are composed in the renderer with a fixed four columns of padding, and every tab is floored at eight columns wide. Neither is reachable from config, so the only way to fit more tabs on a row is to shorten the tab names themselves.

On a narrow terminal, or with a lot of tabs open, that padding is most of what the tab bar is spending its width on. There is also no way to show the tab's index in the label, which makes prefix-number tab switching harder to use than it could be — you have to count positions rather than read the number off the tab.

This overlaps with #1176, which asks for a configurable tab bar more broadly and already has a prototype covering position, alignment and per-tab colours. I should have posted this there rather than opening a separate thread — apologies. What I am describing is one narrow axis of that: what the label is made of and how wide the tab is, rather than where the bar sits or how it is coloured. If #1176 grows a config surface for the tab bar, these two settings would fit naturally inside it. (#3195 raises a third axis again: label colours and hiding the + button.)

requested change

Two settings under [ui]:

• tab_format — a format string for the label, with {name}, {index} and {zoom} placeholders, where spaces in the format are the tab's padding. "{name}{zoom}" gives flush labels with no padding; " {index}:{name} " gives tmux-style numbering.
• tab_min_width — the floor below which a tab is not drawn, so short labels can be allowed to actually be short.

The defaults would render exactly as Herdr does today, including the centred labels and symmetric highlight padding from #2570.

why you want this

I run Herdr with many tabs on a laptop screen, and the fixed padding is a large share of each tab before any label is drawn — 4 of 11 columns for a tab named backend, 4 of 9 for herdr, and 7 of 8 for an unnamed tab showing just its number. Being able to set flush labels and a lower floor fits noticeably more tabs on screen without renaming anything.

The {index} placeholder is the other half of it: with the number visible in the label, prefix-number switching becomes something you can read rather than count.

existing implementation

I have both implemented, rebased on current master, with tests and defaults that render identically to today. The branch is on my fork if you want to build and try it:

master...aspiers:herdr:feat/configurable-tab-format

If this is a direction you would consider, I would like to contribute it: I am not currently an approved contributor, so I am raising this here first rather than opening a pull request, and would be glad to submit one if you would like the change and are happy for me to.

[jonaswindey]

A concrete case for the "what the label is made of" axis: per-tab agent state.

Herdr already derives a done state per tab — the agent finished and the tab has not been viewed yet, and it clears itself once you view it — and rolls it up to the workspace. The tab bar renders none of it: an inactive tab's style keys only off active and is_auto_named() (src/ui/tabs.rs:392-406 at v0.8.2), so there is no way to see from the tab row which tab has something waiting.

The only way to surface it today is to rename the tab, which has two side effects:

• Custom names never renumber, so a plugin that decorates labels has to re-implement positional numbering itself for every tab it has ever touched.
• The tab flips permanently to the non-DIM custom-name style, because custom_name can never be cleared again — Custom tab and workspace names can't be removed: no "Clear name" action, and saving an empty rename is a no-op #3252 asked for that reset and was closed as a feature request, and my No way to clear a tab's custom name: tab.rename permanently freezes auto-numbering and the dim tab-bar style #3470 was closed as a duplicate of it.

So the decoration is transient by intent but the rename is permanent in two independent ways.

Alongside {name}, {index} and {zoom}, a state token would cover this: {state_icon} / {state} for the tab's rolled-up agent status. Better still would be plugin-reported tokens, mirroring what the sidebar already does — workspace.report_metadata feeds $name tokens into [ui.sidebar.spaces] rows, and the tab equivalent would be a tab.report_metadata whose tokens are usable in tab_format. That would let a plugin show an unread marker, a progress counter or CI state on a tab without touching the stored name at all.

[zenhsieh]

I have a concrete dogfood case for tab-level metadata that should not consume tab-label width.

I run a sales-opportunity workspace with one short tab per opportunity. An LLM reports a separate business-attention state (red, orange, yellow, green, or unknown) plus an owner and reason through pane.report_metadata. The metadata path works, but rendering the token in the Agent sidebar puts the signal away from the object it describes. Renaming the tab is also the wrong tradeoff: horizontal tab space is scarce, and the business state changes frequently while the opportunity name does not.

The presentation I would actually use is an opt-in thin top edge on each tab, colored from one tab metadata token. It should not add an emoji, prefix, suffix, or status text to the label. Tab text, active background, click/drag target, scrolling, and width should otherwise remain unchanged. Tabs without the configured token should render exactly as they do today.

In the live workspace this immediately exposed seven overdue/committed opportunities and one non-overdue next action, while Herdr's existing agent-state indicator continued to answer the separate question of whether each agent was working, blocked, done, or idle.

This seems complementary to the tab.report_metadata idea already raised here and to the broader configurable-tab-bar discussion in #1176. The useful product question for me is whether a compact metadata-driven decorative edge fits Herdr's tab-bar direction; I am not proposing that Herdr interpret sales-specific states.

Environment: Herdr 0.8.0, Linux, named persistent session, desktop tab bar at the top.

[ericjahnel]

Same problem from the other end of the scale: I don't want shorter labels, I want none.

I run two to four tabs and always know what is where by position. The tab bar is currently the loudest element on my screen — the focused tab is a solid block of the accent colour, and every tab carries text I never read. My status bar shows workspaces as ● and ○, and I would like the tab bar to be just as quiet: a row of small indicators that tells me how many tabs exist and which one is focused, nothing more.

Both knobs proposed here would get me there, if they go one step further:

• the format may contain no {name} at all, so a tab can render as a static glyph
• the minimum width can go low enough for a single glyph plus padding

That turns the tab bar into a position indicator without changing anything for people who want labels. Happy to describe the use case further if that helps.