fix(float): title/footer shows printable control chars #40047

Problem:
Literal tab (or other control char) in a float title/footer is
not made printable, so it renders incorrectly instead of as "^I".

Solution:
Normalize title/footer text for display like 'statusline'
tab to "^I", parameterize parse_virt_text() with untab
and recompute the width.

src/nvim/api/deprecated.c

@@ -234,7 +234,7 @@ Integer nvim_buf_set_virtual_text(Buffer buffer, Integer src_id, Integer line, A
   uint32_t ns_id = src2ns(&src_id);
   int width;
 
-  VirtText virt_text = parse_virt_text(chunks, err, &width);
+  VirtText virt_text = parse_virt_text(chunks, err, &width, false);
   if (ERROR_SET(err)) {
     return 0;
   }

src/nvim/api/extmark.c

@@ -669,7 +669,7 @@ Integer nvim_buf_set_extmark(Buffer buf, Integer ns_id, Integer line, Integer co
   }
 
   if (HAS_KEY(opts, set_extmark, virt_text)) {
-    virt_text.data.virt_text = parse_virt_text(opts->virt_text, err, &virt_text.width);
+    virt_text.data.virt_text = parse_virt_text(opts->virt_text, err, &virt_text.width, false);
     if (ERROR_SET(err)) {
       goto error;
     }
@@ -742,7 +742,7 @@ Integer nvim_buf_set_extmark(Buffer buf, Integer ns_id, Integer line, Integer co
         goto error;
       });
       int dummig;
-      VirtText jtem = parse_virt_text(a.items[j].data.array, err, &dummig);
+      VirtText jtem = parse_virt_text(a.items[j].data.array, err, &dummig, false);
       kv_push(virt_lines.data.virt_lines, ((struct virt_line){ jtem, virt_lines_flags }));
       if (ERROR_SET(err)) {
         goto error;
@@ -1192,7 +1192,7 @@ static bool extmark_get_index_from_obj(buf_T *buf, Integer ns_id, Object obj, in
   }
 }
 
-VirtText parse_virt_text(Array chunks, Error *err, int *width)
+VirtText parse_virt_text(Array chunks, Error *err, int *width, bool untab)
 {
   VirtText virt_text = KV_INITIAL_VALUE;
   int w = 0;
@@ -1230,7 +1230,7 @@ VirtText parse_virt_text(Array chunks, Error *err, int *width)
       }
     }
 
-    char *text = transstr(str.size > 0 ? str.data : "", false);  // allocates
+    char *text = transstr(str.size > 0 ? str.data : "", untab);  // allocates
     w += (int)mb_string2cells(text);
 
     kv_push(virt_text, ((VirtTextChunk){ .text = text, .hl_id = hl_id }));

src/nvim/api/win_config.c

@@ -15,6 +15,7 @@
 #include "nvim/autocmd_defs.h"
 #include "nvim/buffer.h"
 #include "nvim/buffer_defs.h"
+#include "nvim/charset.h"
 #include "nvim/decoration_defs.h"
 #include "nvim/drawscreen.h"
 #include "nvim/errors.h"
@@ -1021,38 +1022,27 @@ static void parse_bordertext(Object bordertext, BorderTextType bordertext_type,
     return;
   });
 
-  bool *is_present;
-  VirtText *chunks;
-  int *width;
-  switch (bordertext_type) {
-  case kBorderTextTitle:
-    is_present = &fconfig->title;
-    chunks = &fconfig->title_chunks;
-    width = &fconfig->title_width;
-    break;
-  case kBorderTextFooter:
-    is_present = &fconfig->footer;
-    chunks = &fconfig->footer_chunks;
-    width = &fconfig->footer_width;
-    break;
-  }
+  bool is_title = bordertext_type == kBorderTextTitle;
+  bool *is_present = is_title ? &fconfig->title : &fconfig->footer;
+  VirtText *chunks = is_title ? &fconfig->title_chunks : &fconfig->footer_chunks;
+  int *width = is_title ? &fconfig->title_width : &fconfig->footer_width;
 
   if (bordertext.type == kObjectTypeString) {
     if (bordertext.data.string.size == 0) {
       *is_present = false;
       return;
     }
+    char *text = transstr(bordertext.data.string.data, true);
     kv_init(*chunks);
-    kv_push(*chunks, ((VirtTextChunk){ .text = xstrdup(bordertext.data.string.data),
-                                       .hl_id = -1 }));
-    *width = (int)mb_string2cells(bordertext.data.string.data);
-    *is_present = true;
-    return;
+    kv_push(*chunks, ((VirtTextChunk){ .text = text, .hl_id = -1 }));
+    *width = (int)mb_string2cells(text);
+  } else {
+    *chunks = parse_virt_text(bordertext.data.array, err, width, true);
+    if (ERROR_SET(err)) {
+      return;
+    }
   }
 
-  *width = 0;
-  *chunks = parse_virt_text(bordertext.data.array, err, width);
-
   *is_present = true;
 }