Joincol with no column to the right and Theme with no such theme say so

Both did nothing without a word, from a click or a ctl write alike, and a
script could not tell a no-op from success. Joincol in the rightmost column
now fails 'Joincol: no column to the right'. A Theme name that is none says so
and names the themes sharing its first letter, since all of them (ThemeSel
lists them) are too many for a message or a refused write; a startup config
line still fails quietly, as its other bad lines do.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/colors.zig b/src/colors.zig
index bb366fc0..8e608590 100644
--- a/src/colors.zig
+++ b/src/colors.zig
@@ -316,6 +316,19 @@ fn invalidateThemeDependentRasters(p: *Pardes) void {
     };
 }
 
+/// Themes whose names share `name`'s first letter, a line of them, for a
+/// Theme given a name there is none of: all of them (ThemeSel) are too many
+/// for a message or a refused write.
+pub fn themesNear(buf: []u8, name: []const u8) []const u8 {
+    var w = std.Io.Writer.fixed(buf);
+    for (themes) |t| {
+        if (name.len > 0 and std.ascii.toLower(t.name[0]) != std.ascii.toLower(name[0])) continue;
+        if (w.buffered().len + t.name.len + 1 > buf.len) break;
+        w.print("{s}{s}", .{ if (w.buffered().len > 0) " " else "", t.name }) catch break;
+    }
+    return w.buffered();
+}
+
 pub fn setThemeIndex(p: *Pardes, index: usize) void {
     if (index >= themes.len or
         (p.custom_theme == null and p.theme_file_path.get().len == 0 and