clang-tidy: How to suppress warnings?

I have found another non-invasive (without adding // NOLINT to a third-party library) way to suppress warnings. For example, the current version of Google Test fails some cppcoreguidelines-* checks. The following code allows you to validate the current diff excluding lines that contain gtest's macros:

git diff -U3 | sed '
    s/^+\( *TEST(\)/ \1/;
    s/^+\( *EXPECT_[A-Z]*(\)/ \1/;
    s/^+\( *ASSERT_[A-Z]*(\)/ \1/;
' | recountdiff | interdiff -U0 /dev/null /dev/stdin | clang-tidy-diff.py -p1 -path build

It assumes that file build/compile_commands.json is generated before and clang-tidy-diff.py is available from your environment. recountdiff and interdiff from patchutils are the standard tools for manipulating patches.

The script works as follows:

1. git diff -U3 generates a patch with 3 context lines.
2. sed ... removes prefix + from the undesired lines, i.e. transform them to the context.
3. recountdiff correct offsets (in first ranges) in the chunk headers.
4. interdiff -U0 /dev/null /dev/stdin just removes all context lines from a patch. As a result, it splits the initial hunks.
5. clang-tidy-diff.py reads only second ranges from chunk headers and passes them to clang-tidy via -line-filter option.

UPD: It's important to provide interdiff with a sufficient number of context lines, otherwise it may produce some artifacts in the result. See the citation from man interdiff:

For best results, the diffs must have at least three lines of context.

Particularly, I have found that git diff -U0 | ... | interdiff generates some spurious literals $!otj after splitting chunks.

Use -isystem instead of -I to set your system and 3rd party include paths. -I should only be used to include code that is part of the project being built.

This is the only thing required to make clang-tidy ignore all errors in external code. All the other answers (at the point of writing) are just poor workarounds for something that is perfectly solved with -isystem.

If you use a build system like CMake or Meson it will automatically set -I and -isystem correctly for you.

-isystem is also the mechanism that is used for telling compilers, at least GCC and Clang, what's not your code. If you start to use -isystem you can also enable more compiler warnings without getting "false positives" from external code.

I solved the problem by adding // NOLINT to line 1790 of gmock-spec-builders.h

Here is the diff:

--- gmock-spec-builders.orig.h  2016-09-17 09:46:48.527313088 +0200
+++ gmock-spec-builders.h       2016-09-17 09:46:58.958353697 +0200
@@ -1787,7 +1787,7 @@
 #define ON_CALL(obj, call) GMOCK_ON_CALL_IMPL_(obj, call)

 #define GMOCK_EXPECT_CALL_IMPL_(obj, call) \
-    ((obj).gmock_##call).InternalExpectedAt(__FILE__, __LINE__, #obj, #call)
+    ((obj).gmock_##call).InternalExpectedAt(__FILE__, __LINE__, #obj, #call) // NOLINT
 #define EXPECT_CALL(obj, call) GMOCK_EXPECT_CALL_IMPL_(obj, call)

 #endif  // GMOCK_INCLUDE_GMOCK_GMOCK_SPEC_BUILDERS_H_

It would be nice to either upstream this patch (I see other NOLINT in the code) or post a bug report with the clang-tidy folks.