Always close profiler output file.

Reported by Guilherme Batalheiro.

(cherry picked from commit fca6633)

Before the patch, a function `prof_finish` wrote a string
`No samples collected` to a profiler output file and then exited.
Due to early exit, the output file handle stay open. This patch
fixes the condition and the file handle is closed even if the
number of samples is equal to 0.

Sergey Bronnikov:
* added the description and the test for the problem

Part of tarantool/tarantool#11055

src/jit/p.lua

@@ -228,9 +228,7 @@ local function prof_finish()
     local samples = prof_samples
     if samples == 0 then
       if prof_raw ~= true then out:write("[No samples collected]\n") end
-      return
-    end
-    if prof_ann then
+    elseif prof_ann then
       prof_annotate(prof_count1, samples)
     else
       prof_top(prof_count1, prof_count2, samples, "")

test/tarantool-tests/lj-1304-close-profile-dump-with-0-samples.test.lua

@@ -0,0 +1,66 @@
+local tap = require('tap')
+-- Test file to demonstrate LuaJIT incorrect behaviour with missed
+-- closing a file handle for the profile output file.
+-- See also: https://github.com/LuaJIT/LuaJIT/issues/1304.
+local test = tap.test('lj-1304-close-profile-dump-with-0-samples')
+local profilename = require('utils').tools.profilename
+
+test:plan(2)
+
+local filename = profilename('sysprof')
+-- An interval of the profiling is set to a huge enough value to
+-- be sure that there are no samples collected.
+local jit_p_options = 'i9999999'
+
+local function close_profile_dump_with_0_samples(subtest)
+  local jit_p = require('jit.p')
+
+  subtest:plan(1)
+
+  collectgarbage('stop')
+
+  jit_p.start(jit_p_options, filename)
+  jit_p.stop()
+
+  local f = io.open(filename, 'r')
+  local p_content = f:read('a*')
+  subtest:is(p_content, '[No samples collected]\n',
+             'profile dump has no samples')
+  f:close()
+
+  -- Teardown.
+  collectgarbage('restart')
+  os.remove(filename)
+end
+
+local function close_profile_dump_with_0_samples_with_unload(subtest)
+  local jit_p = require('jit.p')
+
+  subtest:plan(1)
+
+  collectgarbage('stop')
+  jit_p.start(jit_p_options, filename)
+  jit_p.stop()
+
+  -- Unload the module and clean the local.
+  package.loaded['jit.p'] = nil
+  jit_p = nil -- luacheck: no unused
+  collectgarbage('collect')
+
+  local f = io.open(filename, 'r')
+  local p_content = f:read('a*')
+  subtest:is(p_content, '[No samples collected]\n',
+             'profile dump has no samples')
+  f.close()
+
+  -- Teardown.
+  collectgarbage('restart')
+  os.remove(filename)
+end
+
+test:test('close profile dump with 0 samples',
+          close_profile_dump_with_0_samples)
+test:test('close profile dump with 0 samples and profile module unload',
+          close_profile_dump_with_0_samples_with_unload)
+
+test:done(true)