Implement the readability-const-return-type check.

This check flags function top-level const-qualified return types and suggests removing the mostly-superfluous const qualifier where possible.

Patch by Yitzhak Mandelbaum.

3 files changed, 33 insertions, 0 deletions

diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 5987c3c47d9..45dffb92978 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -142,6 +142,12 @@ Improvements to clang-tidy
   Detects local variable declarations declaring more than one variable and
   tries to refactor the code to one statement per declaration.
 
+- New :doc:`readability-const-return-type
+  <clang-tidy/checks/readability-const-return-type>` check.
+
+  Checks for functions with a ``const``-qualified return type and recommends
+  removal of the ``const`` keyword.
+
 - New :doc:`readability-magic-numbers
   <clang-tidy/checks/readability-magic-numbers>` check.
 
diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index 082ec276af4..f33130b5e46 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -225,6 +225,7 @@ Clang-Tidy Checks
    portability-simd-intrinsics
    readability-avoid-const-params-in-decls
    readability-braces-around-statements
+   readability-const-return-type
    readability-container-size-empty
    readability-delete-null-pointer
    readability-deleted-default
diff --git a/clang-tools-extra/docs/clang-tidy/checks/readability-const-return-type.rst b/clang-tools-extra/docs/clang-tidy/checks/readability-const-return-type.rst
new file mode 100644
index 00000000000..e236d8d00e6
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/readability-const-return-type.rst
@@ -0,0 +1,26 @@
+.. title:: clang-tidy - readability-const-return-type
+
+readability-const-return-type
+=============================
+
+Checks for functions with a ``const``-qualified return type and recommends
+removal of the ``const`` keyword. Such use of `const` is usually superfluous,
+and can prevent valuable compiler optimizations.  Does not (yet) fix trailing
+return types.
+
+Examples:
+
+.. code-block:: c++
+		
+  const int foo();
+  const Clazz foo();
+  Clazz *const foo();
+
+Note that this applies strictly to top-level qualification, which excludes
+pointers or references to const values. For example, these are fine:
+
+.. code-block:: c++
+
+   const int* foo();
+   const int& foo();
+   const Clazz* foo();