fix(lua): vim.regex():match_str abort in Luv callback #41008

runtime/doc/lua.txt

@@ -5033,8 +5033,10 @@ vim.re.updatelocale()                                  *vim.re.updatelocale()*
 ==============================================================================
 Lua module: vim.regex                                              *vim.regex*
 
-Vim regexes can be used directly from Lua. Currently they only allow matching
-within a single line.
+The `vim.regex` interface allows Lua code to use Vim regexes.
+• Matches within a single line.
+• Does not check for interrupts (CTRL-C), so can be used from an |api-fast|
+  context.
 
 
                                                           *regex:match_line()*

runtime/lua/vim/_meta/regex.lua

@@ -4,8 +4,9 @@ error('Cannot require a meta file')
 
 -- luacheck: no unused args
 
---- @brief Vim regexes can be used directly from Lua. Currently they only allow
---- matching within a single line.
+--- @brief The `vim.regex` interface allows Lua code to use Vim regexes.
+--- - Matches within a single line.
+--- - Does not check for interrupts (CTRL-C), so can be used from an |api-fast| context.
 
 --- Parses the Vim regex `re` and returns a regex object. Regexes are "magic" and case-sensitive by
 --- default, regardless of 'magic' and 'ignorecase'. They can be controlled with flags, see |/magic|

src/nvim/lua/stdlib.c

@@ -304,7 +304,8 @@ int nlua_regex(lua_State *lstate)
   regprog_T *prog = NULL;
 
   TRY_WRAP(&err, {
-    prog = vim_regcomp(text, RE_AUTO | RE_MAGIC | RE_STRICT);
+    // RE_NOBREAK: so vim.regex() works in api-fast context. #18111
+    prog = vim_regcomp(text, RE_AUTO | RE_MAGIC | RE_STRICT | RE_NOBREAK);
   });
 
   if (ERROR_SET(&err)) {

test/functional/lua/vim_spec.lua

@@ -1814,6 +1814,29 @@ describe('lua stdlib', function()
     -- vim.regex() error inside :silent! should not crash. #20546
     command([[silent! lua vim.regex('\\z')]])
     assert_alive()
+
+    -- match_str() in a fast (luv) callback does not abort. #18111
+    eq(
+      { true, true },
+      exec_lua(function()
+        local re = vim.regex('^.*\\.go$')
+        local res
+        local timer = assert(vim.uv.new_timer())
+        timer:start(10, 0, function()
+          -- Enough matches to reach BREAKCHECK_SKIP, which would abort (reentrant event loop).
+          local ok = true
+          for _ = 1, 3000 do
+            ok = ok and re:match_str('internal/config/config.go') ~= nil
+          end
+          res = { ok, vim.in_fast_event() }
+          timer:close()
+        end)
+        vim.wait(1000, function()
+          return res ~= nil
+        end)
+        return res
+      end)
+    )
   end)
 
   it('vim.defer_fn', function()