LogReader: print number of missing rlogs (#32830)

* count rlogs

* minimization changes

* cache to avoid duplicate checks

* no real point in checking qlogs to just show the warning

---------

Co-authored-by: Shane Smiskol <shane@smiskol.com>

tools/lib/logreader.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 import bz2
-from functools import partial
+from functools import cache, partial
 import multiprocessing
 import capnp
 import enum
@@ -87,18 +87,21 @@ Source = Callable[[SegmentRange, ReadMode], LogPaths]
 
 InternalUnavailableException = Exception("Internal source not available")
 
+
+@cache
 def default_valid_file(fn: LogPath) -> bool:
   return fn is not None and file_exists(fn)
 
 
 def auto_strategy(rlog_paths: LogPaths, qlog_paths: LogPaths, interactive: bool, valid_file: ValidFileCallable) -> LogPaths:
   # auto select logs based on availability
-  if any(rlog is None or not valid_file(rlog) for rlog in rlog_paths) and all(qlog is not None and valid_file(qlog) for qlog in qlog_paths):
+  missing_rlogs = [rlog is None or not valid_file(rlog) for rlog in rlog_paths].count(True)
+  if missing_rlogs != 0:
     if interactive:
-      if input("Some rlogs were not found, would you like to fallback to qlogs for those segments? (y/n) ").lower() != "y":
+      if input(f"{missing_rlogs} rlogs were not found, would you like to fallback to qlogs for those segments? (y/n) ").lower() != "y":
         return rlog_paths
     else:
-      cloudlog.warning("Some rlogs were not found, falling back to qlogs for those segments...")
+      cloudlog.warning(f"{missing_rlogs} rlogs were not found, falling back to qlogs for those segments...")
 
     return [rlog if valid_file(rlog) else (qlog if valid_file(qlog) else None)
             for (rlog, qlog) in zip(rlog_paths, qlog_paths, strict=True)]