ci: ensure full sanitizer logs are shown in CI #39361

Problem:
When ASAN detects an error in a child process, the process may be killed
by test teardown before ASAN finishes writing its log file. This results
in truncated logs with no stack trace.

Also, the sanitizer log content was only written to stdout (which the
test runner may not display) and not included in the test_assert error
message.

Solution:
- Poll (up to 2s) for the ASAN "SUMMARY" line before reading, so the
  crashing process has time to finish writing.
- Include full log content in the test_assert error message, so it
  appears in CI output regardless of stdout handling.
- Warn when the log appears truncated (no SUMMARY line found).

test/testutil.lua

@@ -325,45 +325,73 @@ function M.glob(initial_path, re, exc_re)
   return ret
 end
 
+--- Reads sanitizer/valgrind log file lines, filtering out useless warnings.
+--- Waits briefly for the ASAN "SUMMARY" line so we don't read a truncated report
+--- (the crashing process may still be writing when we check).
+local function read_sanitizer_log(file)
+  local lines = {} --- @type string[]
+  local has_summary = false
+  -- Poll for up to 2 seconds for the log to be complete.
+  for _ = 1, 20 do
+    lines = {}
+    local warning_line = 0
+    local fd = assert(io.open(file))
+    for line in fd:lines() do
+      local cur_warning_line = check_logs_useless_lines[line]
+      if cur_warning_line == warning_line + 1 then
+        warning_line = cur_warning_line
+      else
+        lines[#lines + 1] = line
+      end
+      if line:find('SUMMARY') then
+        has_summary = true
+      end
+    end
+    fd:close()
+    if has_summary or #lines == 0 then
+      break
+    end
+    uv.sleep(100)
+  end
+  if not has_summary and #lines > 0 then
+    lines[#lines + 1] = '(WARNING: sanitizer log may be truncated, no SUMMARY line found)'
+  end
+  return lines
+end
+
 function M.check_logs()
   local log_dir = os.getenv('LOG_DIR')
-  local runtime_errors = {}
+  local runtime_errors = {} --- @type string[]
+  local runtime_errors_detail = {} --- @type string[]
   if log_dir and M.isdir(log_dir) then
     for tail in vim.fs.dir(log_dir) do
       if tail:sub(1, 30) == 'valgrind-' or tail:find('san%.') then
-        local file = log_dir .. '/' .. tail
-        local fd = assert(io.open(file))
-        local start_msg = ('='):rep(20) .. ' File ' .. file .. ' ' .. ('='):rep(20)
-        local lines = {} --- @type string[]
-        local warning_line = 0
-        for line in fd:lines() do
-          local cur_warning_line = check_logs_useless_lines[line]
-          if cur_warning_line == warning_line + 1 then
-            warning_line = cur_warning_line
-          else
-            lines[#lines + 1] = line
-          end
-        end
-        fd:close()
+        local file = ('%s/%s'):format(log_dir, tail)
+        local lines = read_sanitizer_log(file)
         if #lines > 0 then
+          local start_msg = ('%s File %s %s'):format(('='):rep(20), file, ('='):rep(20))
+          local end_msg = select(1, start_msg:gsub('.', '='))
+          local lines_str = ('= %s'):format(table.concat(lines, '\n= '))
+          local detail = ('%s\n%s\n%s'):format(start_msg, lines_str, end_msg)
           --- @type boolean?, file*?
           local status, f
-          local out = io.stdout
           if os.getenv('SYMBOLIZER') then
             status, f = pcall(M.repeated_read_cmd, os.getenv('SYMBOLIZER'), '-l', file)
           end
+          local out = io.stdout
           out:write(start_msg .. '\n')
           if status then
             assert(f)
             for line in f:lines() do
-              out:write('= ' .. line .. '\n')
+              out:write(('= %s\n'):format(line))
             end
             f:close()
           else
-            out:write('= ' .. table.concat(lines, '\n= ') .. '\n')
+            out:write(lines_str .. '\n')
           end
-          out:write(select(1, start_msg:gsub('.', '=')) .. '\n')
+          out:write(end_msg .. '\n')
           table.insert(runtime_errors, file)
+          table.insert(runtime_errors_detail, detail)
         end
         os.remove(file)
       end
@@ -371,7 +399,10 @@ function M.check_logs()
   end
   test_assert(
     0 == #runtime_errors,
-    string.format('Found runtime errors in logfile(s): %s', table.concat(runtime_errors, ', '))
+    string.format(
+      'Found runtime errors in logfile(s):\n%s',
+      table.concat(runtime_errors_detail, '\n')
+    )
   )
 end