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

7 files changed, 41 insertions, 5 deletions

diff --git a/clang/test/Misc/warning-flags.c b/clang/test/Misc/warning-flags.c
index 98130c5..cdfb38f 100644
--- a/clang/test/Misc/warning-flags.c
+++ b/clang/test/Misc/warning-flags.c
@@ -17,7 +17,7 @@ This test serves two purposes:
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (242):
+CHECK: Warnings without flags (241):
 CHECK-NEXT:   ext_anonymous_struct_union_qualified
 CHECK-NEXT:   ext_binary_literal
 CHECK-NEXT:   ext_cast_fn_obj
@@ -26,7 +26,6 @@ CHECK-NEXT:   ext_designated_init
 CHECK-NEXT:   ext_duplicate_declspec
 CHECK-NEXT:   ext_ellipsis_exception_spec
 CHECK-NEXT:   ext_empty_fnmacro_arg
-CHECK-NEXT:   ext_empty_source_file
 CHECK-NEXT:   ext_enum_friend
 CHECK-NEXT:   ext_enum_value_not_int
 CHECK-NEXT:   ext_enumerator_list_comma
diff --git a/clang/test/PCH/empty-with-headers.c b/clang/test/PCH/empty-with-headers.c
new file mode 100644
index 0000000..751be1c
--- /dev/null
+++ b/clang/test/PCH/empty-with-headers.c
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c99 -pedantic-errors %s
+// RUN: %clang_cc1 -fsyntax-only -std=c99 -emit-pch -o %t %s
+// RUN: %clang_cc1 -fsyntax-only -std=c99 -pedantic-errors -include-pch %t %s
+
+// RUN: %clang_cc1 -fsyntax-only -std=c99 -pedantic-errors -DINCLUDED %s -verify
+// This last one should warn for -Wempty-translation-unit (C99 6.9p1).
+
+#if defined(INCLUDED)
+
+// empty except for the prefix header
+
+#elif defined(HEADER)
+
+typedef int my_int;
+#define INCLUDED
+
+#else
+
+#define HEADER
+#include "empty-with-headers.c"
+// empty except for the header
+
+#endif
+
+// This should only fire if the header is not included,
+// either explicitly or as a prefix header.
+// expected-error{{ISO C requires a translation unit to contain at least one declaration.}}
diff --git a/clang/test/Parser/completely-empty-header-file.h b/clang/test/Parser/completely-empty-header-file.h
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/clang/test/Parser/completely-empty-header-file.h
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.}}
diff --git a/clang/test/Parser/opencl-pragma.cl b/clang/test/Parser/opencl-pragma.cl
index 1946077..4c48b2a 100644
--- a/clang/test/Parser/opencl-pragma.cl
+++ b/clang/test/Parser/opencl-pragma.cl
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 %s -verify -pedantic -fsyntax-only
+// RUN: %clang_cc1 %s -verify -pedantic -Wno-empty-translation-unit -fsyntax-only
 
 #pragma OPENCL EXTENSION cl_khr_fp16 : enable
 
diff --git a/clang/test/Preprocessor/undef-error.c b/clang/test/Preprocessor/undef-error.c
index ad611de..959c163 100644
--- a/clang/test/Preprocessor/undef-error.c
+++ b/clang/test/Preprocessor/undef-error.c
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 %s -pedantic-errors -verify 
+// RUN: %clang_cc1 %s -pedantic-errors -Wno-empty-translation-unit -verify 
 // PR2045
 
 #define b
diff --git a/clang/test/Sema/c89-2.c b/clang/test/Sema/c89-2.c
index f6f6bd9..14b955a 100644
--- a/clang/test/Sema/c89-2.c
+++ b/clang/test/Sema/c89-2.c
@@ -1,4 +1,4 @@
-/* RUN: %clang_cc1 %s -std=c89 -pedantic-errors -verify
+/* RUN: %clang_cc1 %s -std=c89 -pedantic-errors -Wno-empty-translation-unit -verify
  */
 
 #if 1LL        /* expected-error {{long long}} */