Allow a new syntax in a module requires-declaration:

  requires ! feature

The purpose of this is to allow (for instance) the module map for /usr/include
to exclude <tgmath.h> and <complex.h> when building in C++ (these headers are
instead provided by the C++ standard library in this case, and the glibc C
<tgmath.h> header would otherwise try to include <complex.h>, resulting in a
module cycle).

llvm-svn: 193549

1 files changed, 5 insertions, 2 deletions

diff --git a/clang/docs/Modules.rst b/clang/docs/Modules.rst
index bcb71c27d45..9fb4c774874 100644
--- a/clang/docs/Modules.rst
+++ b/clang/docs/Modules.rst
@@ -320,9 +320,12 @@ A *requires-declaration* specifies the requirements that an importing translatio
     ``requires`` *feature-list*
 
   *feature-list*:
-    *identifier* (',' *identifier*)*
+    *feature* (',' *feature*)*
+
+  *feature*:
+    ``!``:sub:`opt` *identifier*
 
-The requirements clause allows specific modules or submodules to specify that they are only accessible with certain language dialects or on certain platforms. The feature list is a set of identifiers, defined below. If any of the features is not available in a given translation unit, that translation unit shall not import the module.
+The requirements clause allows specific modules or submodules to specify that they are only accessible with certain language dialects or on certain platforms. The feature list is a set of identifiers, defined below. If any of the features is not available in a given translation unit, that translation unit shall not import the module. The optional ``!`` indicates that a feature is incompatible with the module.
 
 The following features are defined: