Problem: Custom ui2 window tracks 'fillchars' option to adjust to the
  change of `msgsep` flag. However, 'fillchars' is `:h global-local`
  window option. If it is set locally to the window, ui2 reacts to its
  `msgsep` value and keeps using it afterwards even in other windows.

Solution: Use and react to only global value of 'fillchars'.

Problem:
When repeating search using a semicolon (e.g. `/pat1/;/pat2`), `pat`
advances past both the semicolon and the delimiter ('/' or '?'),
consuming 2 characters, but `patlen` was only decremented by 1.
Consequently, `patlen` in the subsequent search is 1 byte too long and
includes the trailing NUL byte, corrupting `msgbuf` and causing ui2's
search_count handler to fail with 'attempt to concatenate a nil value'.

Solution:
Decrement `patlen` by 2 when skipping ';' and delimiter. Also ensure
ui2 safely guards search_count messages when extracting the search stat.

Fixes #41929

AI-assisted

Problem:

- annotation-usage-error and code-style-check are disabled.
- vim.inspect relies on a dummy self-assignment for docgen, and its help
  omits parameter and option details.
- LuaLS fallback types obscure iterator inference.
- Docgen hardcodes public function names and appends separately sorted
  files, leaving shared helpers under the inspector heading.

Solution:

- Enable annotation-usage-error and code-style-check, and fix misplaced
  annotations.
- Document vim.inspect's callable module directly, removing the dummy
  assignment. Describe its parameters, option defaults and process
  callback.
- Remove LuaLS iterator fallbacks, correct iterator signatures and check
  values that the improved inference identifies as optional.
- Parse callable modules, require bindings and parent module references.
  Derive public names and inherited function docs from these links,
  including missing help for vim.async.semaphore() and vim.version().
- Export vim.lsp.tagfunc directly with lazy loading and document its
  implementation instead of maintaining a wrapper.
- Group files in section_order, replacing append_only and merge_files.
  Merge declarations before sorting each section, placing shared helpers
  in the main vim section and keeping vim.inspect in alphabetical order.
- Add basic parser coverage for callable modules and module links.

AI-assisted

Problem: Argument type mismatches are excluded from EmmyLua checks.

Solution: Correct runtime annotations and calls, document local checker
workarounds, and enable the diagnostic.

AI-assisted

Enable EmmyLua's assign-type-mismatch diagnostic after correcting the
runtime annotations and assignments it flags.

Correct option, tuple, and return types, and use separate locals when a
value changes representation. Add guards and narrow casts where needed
so the runtime passes the stricter check. Regenerate the affected docs.

AI-assisted

Enable EmmyLua's need-check-nil diagnostic and resolve nullable values
through more precise types, explicit invariants, and guards for missing
runtime state. Keep analyzer-specific workarounds local and update the
affected API documentation.

Exclude the bundled re.lua from analysis so its nil-check warnings do
not fail CI.

AI-assisted

Problem:
expand_msg() derives its start row from the pager buffer even when the
target is the cmd or dialog buffer, so the copied lines are appended
instead of replacing, and the copied extmarks are placed at pager rows in
a smaller buffer: "Invalid 'end_col': out of range", thrown inside a UI
event handler.

Solution:
Offset only when appending to a visible pager, and read the line count
after msg_clear(), whose autocmds may write to the pager. Copy marks with
`strict = false`, since the rows and columns are recomputed for a
different buffer and should clamp rather than raise.

AI-assisted

- call-non-callable
- missing-fields
- redefined-label
- redefined-local
- undefined-field
- unreachable-code

Promote redefined-local and unreachable-code to warnings.

Fix DOS line-ending handling for multiline semantic tokens, and support
intersection types in the help parser.

AI-assisted

Problem: LuaLS struggles with the generics used in Nvim's runtime,
requiring broad diagnostic suppressions. Indexing is also slow.

Solution: Use EmmyLua for type checks in the build and CI. It offers
more sophisticated type checking, substantially better support for
generics, and much better flow analysis.

Correct the affected annotations. Use `@internal`, supported directly by
EmmyLua, instead of `@nodoc` for shared internal declarations, and
support it in the help parser.

AI-assisted