sidebar: the new-tab button says what it is, given a row to say it on

The mark went bare because in the strip it sits at the end of a row of
tabs, where the company it keeps says what it does and columns are
scarce. A sidebar row is neither: it is a row of its own with columns
to spare, and a lone glyph on it reads as decoration -- the hint under
the pointer cannot help, since you have to suspect a thing is a button
before you hover it.

So with the room it reads '+ new tab', in the word hint_for already
gives this action rather than a second name for the same thing, and
falls back to the bare mark when the sidebar is too narrow. The strip
is untouched. The row fills and hits like a tab's, so hover and the
drop-target fill cover the row rather than the word on it.

3 files changed, 84 insertions, 17 deletions

diff --git a/docs/panes.md b/docs/panes.md
index 329e017..ab9bd08 100644
--- a/docs/panes.md
+++ b/docs/panes.md
@@ -62,7 +62,8 @@ tab_bar_chrome true   // frame it like a pane
 A **sidebar lists one tab per row** down the chosen edge, and the panes trade
 the strip's row for its columns. Everything the strip does travels with it:
 click to switch, double-click to rename in place, drag a pane onto a tab or
-onto the `+`, drag tabs to reorder. The pane count and the prefix badge move
+onto the `+` — which, given a row of its own and the columns to spare, spells
+itself out as `+ new tab`. The pane count and the prefix badge move
 to the sidebar's bottom rows; the [status line](config.md) along the bottom
 keeps the full width. A terminal too narrow to give up the columns falls back
 to the top row until it grows.
diff --git a/src/app_draw.c b/src/app_draw.c
index 7614582..54b8950 100644
--- a/src/app_draw.c
+++ b/src/app_draw.c
@@ -1903,29 +1903,50 @@ static uint16_t draw_tab_cell(app_t *a, screen_t *s, size_t i, uint16_t x,
   return hit_w;
 }
 
-/* A bare mark, spaced like the frame's own buttons rather than spelled out.
- * It used to read "+tab", because a pane frame carried a "+" for splitting
- * and two verbs that look identical is a UI bug the fork shipped. That "+"
- * went when the border became the button, so the collision it was avoiding
- * no longer exists and the word was left explaining itself to nobody.
+/* In the strip, a bare mark, spaced like the frame's own buttons rather than
+ * spelled out. It used to read "+tab", because a pane frame carried a "+" for
+ * splitting and two verbs that look identical is a UI bug the fork shipped.
+ * That "+" went when the border became the button, so the collision it was
+ * avoiding no longer exists and the word was left explaining itself to
+ * nobody: in the strip the mark sits at the end of a row of tabs, where what
+ * it does is plain from the company it keeps.
  *
- * Padded to three cells for the same reason the frame's buttons are: a
- * one-cell target is a thing you miss with a mouse. What it does is said by
- * the hint under the pointer, which is where every other one-character
- * affordance here says it. */
+ * A sidebar row is not that. It is a row of its own with columns to spare,
+ * and a lone glyph on it reads as decoration rather than as a button -- the
+ * hint under the pointer cannot rescue it either, because you have to suspect
+ * a thing is a button before you hover it. So given the room it says the
+ * word, and the word is the one `hint_for` already gives this action rather
+ * than a second name for the same thing.
+ *
+ * `max_w` is the row to fill; 0 is the strip's natural width. Three cells at
+ * minimum for the same reason the frame's buttons are: a one-cell target is a
+ * thing you miss with a mouse. */
 static void draw_newtab_button(app_t *a, screen_t *s, uint16_t x, uint16_t y,
-                               bool dragging_pane) {
-  char btn[24];
-  snprintf(btn, sizeof btn, " %s ", CFG.newtab_mark);
+                               uint16_t max_w, bool dragging_pane) {
+  char btn[64];
+  if (max_w && (uint16_t)(cells(CFG.newtab_mark) + 10) <= max_w)
+    snprintf(btn, sizeof btn, " %s new tab ", CFG.newtab_mark);
+  else
+    snprintf(btn, sizeof btn, " %s ", CFG.newtab_mark);
+  /* Padded out on a sidebar row for the same reason a tab's label is: the
+   * hover and the drop fill are the row, not the word sitting on it. */
+  if (max_w) {
+    size_t len = strlen(btn);
+    while (cells(btn) < max_w && len + 1 < sizeof btn) {
+      btn[len++] = ' ';
+      btn[len] = 0;
+    }
+  }
   uint16_t w = screen_text(s, x, y, btn, TAB_IDLE, NO_COLOR, 0);
-  if (ptr_on(a, x, y, w, 1))
+  uint16_t hit_w = max_w ? max_w : w;
+  if (ptr_on(a, x, y, hit_w, 1))
     screen_text(s, x, y, btn, TAB_HOVER, NO_COLOR, ATTR_BOLD);
   /* The button that makes a tab is also a place to drop a pane into one. */
   if (dragging_pane)
     screen_text(s, x, y, btn,
                 a->drag.new_tab_target ? TAB_ACTIVE_HOVER_FG : DROP_C,
                 a->drag.new_tab_target ? DROP_C : NO_COLOR, ATTR_BOLD);
-  hit_add(&s->hits, x, y, w, 1, "newtab");
+  hit_add(&s->hits, x, y, hit_w, 1, "newtab");
 }
 
 void draw_tab_strip(app_t *a, screen_t *s) {
@@ -1968,7 +1989,7 @@ void draw_tab_strip(app_t *a, screen_t *s) {
   {
     uint16_t bw = (uint16_t)(cells(CFG.newtab_mark) + 2);
     if (bw > 2 && x + bw <= right)
-      draw_newtab_button(a, s, x, y, dragging_pane);
+      draw_newtab_button(a, s, x, y, 0, dragging_pane);
   }
 }
 
@@ -2126,7 +2147,7 @@ void draw_tab_sidebar(app_t *a, screen_t *s) {
   }
 
   if (cells(CFG.newtab_mark) && y < limit)
-    draw_newtab_button(a, s, cx, y, dragging_pane);
+    draw_newtab_button(a, s, cx, y, cw, dragging_pane);
 }
 
 /* The space between two of a split's children, or false if they are flush.
diff --git a/tests/test_tab_bar.py b/tests/test_tab_bar.py
index eab817a..ce3ad9b 100644
--- a/tests/test_tab_bar.py
+++ b/tests/test_tab_bar.py
@@ -303,6 +303,48 @@ def test_chrome_false_gives_the_columns_back():
         )
 
 
+def test_the_sidebar_button_says_what_it_does():
+    with Session(SH, cols=90, rows=20, config=LEFT) as s:
+        s.settle(40)
+        snap = s.snapshot()
+        row = _row(snap, Y0 + 1)
+        check("a row of its own spells the verb out", "new tab" in row, repr(row))
+        check(
+            "and the whole row is the target, like a tab's",
+            snap.hit_at(CX + CW - 1, Y0 + 1) == "newtab",
+            str(snap.hit_at(CX + CW - 1, Y0 + 1)),
+        )
+
+
+def test_a_narrow_sidebar_keeps_the_bare_mark():
+    narrow = _cfg('tab_bar_side "left"\ntab_bar_width 10\n')
+    with Session(SH, cols=90, rows=20, config=narrow) as s:
+        s.settle(40)
+        snap = s.snapshot()
+        row = snap.line(Y0 + 1)[CX : CX + 8]
+        check(
+            "no room for the word, so it is not said", "new tab" not in row, repr(row)
+        )
+        check(
+            "...but the button is still there",
+            snap.hit_at(CX, Y0 + 1) == "newtab",
+            str(snap.hit_at(CX, Y0 + 1)),
+        )
+
+
+def test_the_strip_keeps_its_bare_mark():
+    """The word is a sidebar's affordance, not a new spelling everywhere: in
+    the strip the mark sits at the end of a row of tabs, where columns are
+    scarce and the company it keeps says what it is."""
+    with Session(SH, cols=90, rows=20) as s:
+        s.settle(40)
+        check(
+            "the strip is unchanged",
+            "new tab" not in s.snapshot().line(1),
+            repr(s.snapshot().line(1)),
+        )
+
+
 def test_narrow_terminal_falls_back_to_top():
     # 40 < width + min_pane cols + 4: the sidebar would leave no room for the
     # pane it is chrome for, so the strip goes back to the top row.
@@ -347,6 +389,9 @@ if __name__ == "__main__":
     test_the_sidebar_is_framed_like_a_pane()
     test_compact_shares_its_lines_with_the_ring()
     test_chrome_false_gives_the_columns_back()
+    test_the_sidebar_button_says_what_it_does()
+    test_a_narrow_sidebar_keeps_the_bare_mark()
+    test_the_strip_keeps_its_bare_mark()
     test_narrow_terminal_falls_back_to_top()
     test_growing_back_restores_the_sidebar()
     sys.exit(report())