fix(defaults): visual mode star (*,#) is fragile

Problem:
Visual mode "*", "#" mappings don't work on text with "/", "\", "?", and
newlines.

Solution:
Get the visual selection and escape it as a search pattern.
Add functions vim.get_visual_selection and _search_for_visual_selection.

Fix #21676

1 files changed, 19 insertions, 0 deletions

diff --git a/runtime/doc/lua.txt b/runtime/doc/lua.txt
index 77a89a123d..9d3a3dec71 100644
--- a/runtime/doc/lua.txt
+++ b/runtime/doc/lua.txt
@@ -1410,6 +1410,25 @@ deprecate({name}, {alternative}, {version}, {plugin}, {backtrace})
     Return: ~
         Deprecated message, or nil if no message was shown.
 
+                                                  *vim.get_visual_selection()*
+get_visual_selection({list}, {append_empty})
+    Gets the content of the visual selection.
+
+    The result is either a string or, if {list} is `true`, a list of strings.
+    If not in any |visual-mode|, `nil` is returned.
+
+    Parameters: ~
+      • {list}          boolean|nil Return a list of strings instead of a
+                        string. See |getreg()|. Defaults to `false`.
+      • {append_empty}  boolean|nil Append an empty string to the result when
+                        in |linewise-visual| mode and {list} is `true`. This
+                        will preserve the trailing newline of the selection
+                        when the result is concatenated with `"\n"`. Defaults
+                        to `false`.
+
+    Return: ~
+        string|table
+
 inspect({object}, {options})                                   *vim.inspect()*
     Gets a human-readable representation of the given object.