Add pedantic warning -Wempty-translation-unit (C11 6.9p1).

In standard C since C89, a 'translation-unit' is syntactically defined to have
at least one "external-declaration", which is either a decl or a function
definition. In Clang the latter gives us a declaration as well.

The tricky bit about this warning is that our predefines can contain external
declarations (__builtin_va_list and the 128-bit integer types). Therefore our
AST parser now makes sure we have at least one declaration that doesn't come
from the predefines buffer.

Also, remove bogus warning about empty source files. This doesn't catch source
files that only contain comments, and never fired anyway because of our
predefines.

PR12665 and <rdar://problem/9165548>

llvm-svn: 158085

1 files changed, 10 insertions, 0 deletions

diff --git a/clang/test/Parser/empty-translation-unit.c b/clang/test/Parser/empty-translation-unit.c
new file mode 100644
index 0000000..0dbf37e
--- /dev/null
+++ b/clang/test/Parser/empty-translation-unit.c
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c99 -pedantic -W -verify %s
+// RUN: %clang_cc1 -fsyntax-only -x c++ -std=c++03 -pedantic-errors -W %s
+
+#include "completely-empty-header-file.h"
+// no-warning -- an empty file is OK
+
+#define A_MACRO_IS_NOT_GOOD_ENOUGH 1
+
+// In C we should get this warning, but in C++ we shouldn't.
+// expected-warning{{ISO C requires a translation unit to contain at least one declaration.}}