Fix utils.strip_luatest_trace

 * Strip uselss `...` and `eval` lines.
 * Scan the stack trace backwards so as to skip `[C]`, `...`, and `eval`
   lines that were called by luatest internal files, not vice versa.
 * Don't strip lines related to luatest test files (from luatest/test),
   even though they match the luatest internal file pattern, because
   we do want to see stack traces when we test luatest.

Needed for #396

CHANGELOG.md

@@ -20,6 +20,7 @@
 - Fix reporting of an assertion failure in `Server:exec()` in case verbose
   error serialization is enabled in Tarantool (gh-376).
 - Added `assert_items_exclude`.
+- Strip useless `...` lines from error trace.
 
 ## 1.0.1
 

luatest/utils.lua

@@ -61,23 +61,47 @@ end
 
 -- Check if line of stack trace comes from inside luatest.
 local function is_luatest_internal_line(s)
-    return s:find('[/\\]luatest[/\\]') or s:find('bin[/\\]luatest')
+    if s:find('bin[/\\]luatest') then
+        return true
+    end
+    if s:find('[/\\]luatest[/\\]') then
+        -- Do not strip lines originating from luatest test files because
+        -- we want to see stack traces when we test luatest.
+        return not s:find('[/\\]luatest[/\\]test[/\\]')
+    end
+    return false
 end
 
 function utils.strip_luatest_trace(trace)
     local lines = trace:split('\n')
-    local result = {lines[1]} -- always keep 1st line
+
+    -- Scan the stack trace backwards (from caller to callee) and strip all
+    -- frames related to luatest, as well as `[C]:`, `...`, `eval:` frames
+    -- called by them because they don't change context.
+    local result = {}
     local keep = true
-    for i = 2, table.maxn(lines) do
+    for i = table.maxn(lines), 2, -1 do
         local line = lines[i]
-        -- `[C]:` lines don't change context
-        if not line:find('^%s+%[C%]:') then
+        if not (line:find('^%s+%[C%]:') or
+                line:find('^%s+%.%.%.$') or
+                line:find('^%s+eval:')) then
             keep = not is_luatest_internal_line(line)
         end
         if keep then
             table.insert(result, line)
         end
     end
+
+    -- Always keep the 1st line because it's the header ('stack traceback:').
+    table.insert(result, lines[1])
+
+    -- Since we scanned the stack trace backwards, we need to reverse
+    -- the result.
+    for i = 1, math.floor(#result / 2) do
+        local v = result[#result - i + 1]
+        result[#result - i + 1] = result[i]
+        result[i] = v
+    end
     return table.concat(result, '\n')
 end
 

test/luaunit/utility_test.lua

@@ -847,6 +847,43 @@ function g.test_stripStackTrace()
         [[stack traceback:
     luaunit2/example_with_luaunit.lua:124: in function 'test1_withFailure']]
     )
+
+    t.assert_equals(subject([[stack traceback:
+    /tmp/luatest/luatest/utils.lua:55: in function 'luatest_error'
+    /tmp/luatest/luatest/assertions.lua:66: in function 'failure'
+    /tmp/luatest/luatest/assertions.lua:71: in function 'fail_fmt'
+    /tmp/luatest/luatest/assertions.lua:341: in function 'assert_le'
+    /tmp/luatest/test/example_test.lua:37: in function 'check'
+    /tmp/luatest/test/example_test.lua:40: in function </tmp/luatest/test/example_test.lua:34>
+    [C]: in function 'xpcall'
+    eval:9: in main chunk
+    [C]: at 0x5da8d110ced6
+    /tmp/luatest/luatest/server.lua:745: in function 'exec'
+    /tmp/luatest/test/example_test.lua:34: in function 'test.test_fail_server'
+    /tmp/luatest/luatest/runner.lua:472: in function </tmp/luatest/luatest/runner.lua:471>
+    [C]: in function 'xpcall'
+    /tmp/luatest/luatest/runner.lua:471: in function 'super'
+    /tmp/luatest/luatest/capturing.lua:106: in function 'protected_call'
+    /tmp/luatest/luatest/runner.lua:559: in function 'super'
+    /tmp/luatest/luatest/hooks.lua:290: in function 'invoke_test_function'
+    /tmp/luatest/luatest/runner.lua:554: in function 'super'
+    ...
+    [C]: in function 'xpcall'
+    /tmp/luatest/luatest/utils.lua:39: in function 'run_tests'
+    /tmp/luatest/luatest/runner.lua:381: in function </tmp/luatest/luatest/runner.lua:366>
+    [C]: in function 'xpcall'
+    /tmp/luatest/luatest/capturing.lua:74: in function </tmp/luatest/luatest/capturing.lua:72>
+    [C]: in function 'xpcall'
+    /tmp/luatest/luatest/runner.lua:55: in function 'fn'
+    .../vlad/src/tarantool/luatest/luatest/sandboxed_runner.lua:14: in function 'run'
+    /tmp/luatest/luatest/cli_entrypoint.lua:4: in function </tmp/luatest/luatest/cli_entrypoint.lua:3>
+    /tmp/luatest/bin/luatest:5: in main chunk]]
+        ),
+        [[stack traceback:
+    /tmp/luatest/test/example_test.lua:37: in function 'check'
+    /tmp/luatest/test/example_test.lua:40: in function </tmp/luatest/test/example_test.lua:34>
+    /tmp/luatest/test/example_test.lua:34: in function 'test.test_fail_server']]
+    )
 end
 
 function g.test_eps_value()