[clang-tidy] Skip user headers named like C headers in `modernize-deprecated-headers` (#195507) Previously `modernize-deprecated-headers` would match on any header with the same name as standard library headers. This commit fixes the problem by checking whether the include resolves to a system header. Closes #45991 --------- Co-authored-by: Victor Chernyakin <chernyakin.victor.j@outlook.com>

diff --git a/clang-tools-extra/clang-tidy/modernize/DeprecatedHeadersCheck.cpp b/clang-tools-extra/clang-tidy/modernize/DeprecatedHeadersCheck.cpp
index eff7c2f..88c411f 100644
--- a/clang-tools-extra/clang-tidy/modernize/DeprecatedHeadersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/DeprecatedHeadersCheck.cpp

@@ -175,6 +175,10 @@
   if (SM.isInSystemHeader(HashLoc))
     return;
 
+  // Skip headers that happen to use the same name as a standard library header.
+  if (!File || !SrcMgr::isSystem(FileType))
+    return;
+
   // FIXME: Take care of library symbols from the global namespace.
   //
   // Reasonable options for the check:

diff --git a/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp b/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp
index 81df26f..861f3a7 100644
--- a/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp
+++ b/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp

@@ -318,12 +318,13 @@
     }
   )cpp");
   auto TU = TestTU::withCode(Test.code());
-  TU.HeaderFilename = "assert.h"; // Suppress "not found" error.
+  TU.AdditionalFiles["system/assert.h"] = ""; // Suppress "not found" error.
   TU.ClangTidyProvider = addTidyChecks("bugprone-sizeof-expression,"
                                        "bugprone-macro-repeated-side-effects,"
                                        "modernize-deprecated-headers,"
                                        "modernize-use-trailing-return-type,"
                                        "misc-no-recursion");
+  TU.ExtraArgs.push_back("-isystem" + testPath("system"));
   TU.ExtraArgs.push_back("-Wno-unsequenced");
   EXPECT_THAT(
       TU.build().getDiagnostics(),

diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index d4b81d0..9d35533 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst

@@ -408,6 +408,11 @@
   Because it only sees one file at a time, the check can't be sure
   such entities aren't referenced in any other files of that module.
 
+- Improved :doc:`modernize-deprecated-headers
+  <clang-tidy/checks/modernize/deprecated-headers>` check by avoiding false
+  positives on project headers that use the same name as a standard library
+  header.
+
 - Improved :doc:`modernize-pass-by-value
   <clang-tidy/checks/modernize/pass-by-value>` check by adding `IgnoreMacros`
   option to suppress warnings in macros.

diff --git a/clang-tools-extra/test/clang-tidy/checkers/modernize/Inputs/deprecated-headers/user/assert.h b/clang-tools-extra/test/clang-tidy/checkers/modernize/Inputs/deprecated-headers/user/assert.h
new file mode 100644
index 0000000..1038e93
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/modernize/Inputs/deprecated-headers/user/assert.h

@@ -0,0 +1 @@
+#define USER_ASSERT_H 1

diff --git a/clang-tools-extra/test/clang-tidy/checkers/modernize/deprecated-headers-user.cpp b/clang-tools-extra/test/clang-tidy/checkers/modernize/deprecated-headers-user.cpp
new file mode 100644
index 0000000..ff24ffd
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/modernize/deprecated-headers-user.cpp

@@ -0,0 +1,9 @@
+// RUN: %check_clang_tidy -std=c++11-or-later %s modernize-deprecated-headers %t -- -extra-arg-before=-iquote%S/Inputs/deprecated-headers/user -extra-arg-before=-isystem%S/Inputs/deprecated-headers
+
+#include "assert.h"
+
+#include <assert.h>
+// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: inclusion of deprecated C++ header 'assert.h'; consider using 'cassert' instead [modernize-deprecated-headers]
+// CHECK-FIXES: #include <cassert>
+
+int user_header = USER_ASSERT_H;