[PATCH] D125771: [clang-tidy] Add a useful note about -std=c++11-or-later

[Balázs Benics via Phabricator via cfe-commits]

steakhal created this revision.
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I and @whisperity spent some time debugging a LIT test case using the
`-std=c++11-or-later` `check_clang_tidy.py` flag when the test had
fixits.

It turns out if the test wants to report a diagnostic into a header
file AND into the test file as well, one needs to first copy the header
somewhere under the build directory.
It needs to be copied since `clang-tidy` sorts the reports into
alphabetical order, thus to have a deterministic order relative to the
diagnostic in the header AND the diagnostic in the test cpp file.

There is more to this story.

The `-std=c++11-or-later` turns out executes the test with multiple
`-std=XX` version substitution and each execution will also have the
`-fix` tidy parameter. This means that the freshly copied header file I
stated in the previous paragraph gets fixed up and the very next tidy
execution will fail miserably.

Following @whisperity's advice, I'm leaving a reminder about such
//shared// state in the related doc comment.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D125771

Files:
  clang-tools-extra/test/clang-tidy/check_clang_tidy.py


Index: clang-tools-extra/test/clang-tidy/check_clang_tidy.py
===================================================================
--- clang-tools-extra/test/clang-tidy/check_clang_tidy.py
+++ clang-tools-extra/test/clang-tidy/check_clang_tidy.py
@@ -19,11 +19,17 @@
     [-assume-filename=<file-with-source-extension>] \
     [-check-suffix=<comma-separated-file-check-suffixes>] \
     [-check-suffixes=<comma-separated-file-check-suffixes>] \
+    [-std=(c++11-or-later|c++17)] \
     <source-file> <check-name> <temp-file> \
     -- [optional clang-tidy arguments]
 
 Example:
   // RUN: %check_clang_tidy %s llvm-include-order %t -- -- -isystem %S/Inputs
+
+Notes:
+  -std=c++11-or-later:
+    This flag will cause multiple runs withing the same check_clang_tidy
+    execution. Make sure you don't have shared state across these runs.
 """
 
 import argparse


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