vim-patch:7.4.497 #2295

Problem:    With some regexp patterns the NFA engine uses many states and
            becomes very slow.  To the user it looks like Vim freezes.
Solution:   When the number of states reaches a limit fall back to the old
            engine. (Christian Brabandt)

https://github.com/vim/vim/releases/tag/v7-4-497

Helped-by: David Bürgin <676c7473@gmail.com>
Helped-by: Justin M. Keyes <justinkz@gmail.com>
Helped-by: Scott Prager <splinterofchaos@gmail.com>

test/benchmark/bench_re_freeze_spec.lua

@@ -0,0 +1,67 @@
+-- Test for benchmarking RE engine.
+
+local helpers = require('test.functional.helpers')
+local feed, insert, source = helpers.feed, helpers.insert, helpers.source
+local clear, execute, wait = helpers.clear, helpers.execute, helpers.wait
+
+-- Temporary file for gathering benchmarking results for each regexp engine.
+local result_file = 'benchmark.out'
+-- Fixture containing an HTML fragment that can make a search appear to freeze.
+local sample_file = 'test/benchmark/samples/re.freeze.txt'
+
+-- Vim script code that does both the work and the benchmarking of that work.
+local measure_cmd =
+    [[call Measure(%d, ']] .. sample_file .. [[', '\s\+\%%#\@<!$', '+5')]]
+local measure_script = [[
+    func! Measure(re, file, pattern, arg)
+      let sstart=reltime()
+    
+      execute 'set re=' . a:re
+      execute 'split' a:arg a:file
+      call search(a:pattern, '', '', 10000)
+      q!
+    
+      $put =printf('file: %s, re: %d, time: %s', a:file, a:re, reltimestr(reltime(sstart)))
+    endfunc]]
+
+describe('regexp search', function()
+  -- The test cases rely on a small Vim script, which we source here, and also
+  -- on a temporary result file, which we prepare and write to disk.
+  setup(function()
+    clear()
+    source(measure_script)
+    insert('" Benchmark_results:')
+    execute('write! ' .. result_file)
+  end)
+
+  -- At the end of the test run we just print the contents of the result file
+  -- for human inspection and promptly delete the file.
+  teardown(function()
+    print ''
+    for line in io.lines(result_file) do
+      print(line)
+    end
+    os.remove(result_file)
+  end)
+
+  it('is working with regexpengine=0', function()
+    local regexpengine = 0
+    execute(string.format(measure_cmd, regexpengine))
+    execute('write')
+    wait()
+  end)
+
+  it('is working with regexpengine=1', function()
+    local regexpengine = 1
+    execute(string.format(measure_cmd, regexpengine))
+    execute('write')
+    wait()
+  end)
+
+  it('is working with regexpengine=2', function()
+    local regexpengine = 2
+    execute(string.format(measure_cmd, regexpengine))
+    execute('write')
+    wait()
+  end)
+end)

test/benchmark/preload.lua

@@ -0,0 +1,4 @@
+-- Modules loaded here will not be cleared and reloaded by Busted.
+-- Busted started doing this to help provide more isolation.  See issue #62
+-- for more information about this.
+local helpers = require('test.functional.helpers')