[clang-tidy] new check 'readability-redundant-preprocessor'

Finds potentially redundant preprocessor directives.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D54349

3 files changed, 67 insertions, 0 deletions

diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index f6cdc3efbdc..8731dc73c64 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -244,6 +244,11 @@ Improvements to clang-tidy
   Detects usage of magic numbers, numbers that are used as literals instead of
   introduced via constants or symbols.
 
+- New :doc:`readability-redundant-preprocessor
+  <clang-tidy/checks/readability-redundant-preprocessor>` check.
+
+  Finds potentially redundant preprocessor directives.
+
 - New :doc:`readability-uppercase-literal-suffix
   <clang-tidy/checks/readability-uppercase-literal-suffix>` check.
 
diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index b4a60e76c8e..080e747bdfa 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -254,6 +254,7 @@ Clang-Tidy Checks
    readability-redundant-declaration
    readability-redundant-function-ptr-dereference
    readability-redundant-member-init
+   readability-redundant-preprocessor
    readability-redundant-smartptr-get
    readability-redundant-string-cstr
    readability-redundant-string-init
diff --git a/clang-tools-extra/docs/clang-tidy/checks/readability-redundant-preprocessor.rst b/clang-tools-extra/docs/clang-tidy/checks/readability-redundant-preprocessor.rst
new file mode 100644
index 00000000000..f013a3417d3
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/readability-redundant-preprocessor.rst
@@ -0,0 +1,61 @@
+.. title:: clang-tidy - readability-redundant-preprocessor
+
+readability-redundant-preprocessor
+==================================
+
+Finds potentially redundant preprocessor directives. At the moment the
+following cases are detected:
+
+* `#ifdef` .. `#endif` pairs which are nested inside an outer pair with the
+  same condition. For example:
+
+.. code-block:: c++
+
+  #ifdef FOO
+  #ifdef FOO // inner ifdef is considered redundant
+  void f();
+  #endif
+  #endif
+
+* Same for `#ifndef` .. `#endif` pairs. For example:
+
+.. code-block:: c++
+
+  #ifndef FOO
+  #ifndef FOO // inner ifndef is considered redundant
+  void f();
+  #endif
+  #endif
+
+* `#ifndef` inside an `#ifdef` with the same condition:
+
+.. code-block:: c++
+
+  #ifdef FOO
+  #ifndef FOO // inner ifndef is considered redundant
+  void f();
+  #endif
+  #endif
+
+* `#ifdef` inside an `#ifndef` with the same condition:
+
+.. code-block:: c++
+
+  #ifndef FOO
+  #ifdef FOO // inner ifdef is considered redundant
+  void f();
+  #endif
+  #endif
+
+* `#if` .. `#endif` pairs which are nested inside an outer pair with the same
+  condition. For example:
+
+.. code-block:: c++
+
+  #define FOO 4
+  #if FOO == 4
+  #if FOO == 4 // inner if is considered redundant
+  void f();
+  #endif
+  #endif
+