Support tests in freestanding

Summary:
Freestanding is *weird*. The standard allows it to differ in a bunch of odd
manners from regular C++, and the committee would like to improve that
situation. I'd like to make libc++ behave better with what freestanding should
be, so that it can be a tool we use in improving the standard. To do that we
need to try stuff out, both with "freestanding the language mode" and
"freestanding the library subset".

Let's start with the super basic: run the libc++ tests in freestanding, using
clang as the compiler, and see what works. The easiest hack to do this:

In utils/libcxx/test/config.py add:

  self.cxx.compile_flags += ['-ffreestanding']

Run the tests and they all fail.

Why? Because in freestanding `main` isn't special. This "not special" property
has two effects: main doesn't get mangled, and main isn't allowed to omit its
`return` statement. The first means main gets mangled and the linker can't
create a valid executable for us to test. The second means we spew out warnings
(ew) and the compiler doesn't insert the `return` we omitted, and main just
falls of the end and does whatever undefined behavior (if you're luck, ud2
leading to non-zero return code).

Let's start my work with the basics. This patch changes all libc++ tests to
declare `main` as `int main(int, char**` so it mangles consistently (enabling us
to declare another `extern "C"` main for freestanding which calls the mangled
one), and adds `return 0;` to all places where it was missing. This touches 6124
files, and I apologize.

The former was done with The Magic Of Sed.

The later was done with a (not quite correct but decent) clang tool:

  https://gist.github.com/jfbastien/793819ff360baa845483dde81170feed

This works for most tests, though I did have to adjust a few places when e.g.
the test runs with `-x c`, macros are used for main (such as for the filesystem
tests), etc.

Once this is in we can create a freestanding bot which will prevent further
regressions. After that, we can start the real work of supporting C++
freestanding fairly well in libc++.

<rdar://problem/47754795>

Reviewers: ldionne, mclow.lists, EricWF

Subscribers: christof, jkorous, dexonsmith, arphaman, miyuki, libcxx-commits

Differential Revision: https://reviews.llvm.org/D57624

llvm-svn: 353086

7 files changed, 21 insertions, 7 deletions

diff --git a/libcxx/test/std/strings/string.view/string.view.template/ends_with.char.pass.cpp b/libcxx/test/std/strings/string.view/string.view.template/ends_with.char.pass.cpp
index c89fdb8e4e8..c0373307427 100644
--- a/libcxx/test/std/strings/string.view/string.view.template/ends_with.char.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.template/ends_with.char.pass.cpp
@@ -17,7 +17,7 @@
 #include "test_macros.h"
 #include "constexpr_char_traits.hpp"
 
-int main()
+int main(int, char**)
 {
     {
     typedef std::string_view SV;
@@ -43,4 +43,6 @@ int main()
     static_assert (!sv2.ends_with('x'), "" );
     }
 #endif
+
+  return 0;
 }
diff --git a/libcxx/test/std/strings/string.view/string.view.template/ends_with.ptr.pass.cpp b/libcxx/test/std/strings/string.view/string.view.template/ends_with.ptr.pass.cpp
index 4ef1c8e2f98..64caf5cc0d5 100644
--- a/libcxx/test/std/strings/string.view/string.view.template/ends_with.ptr.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.template/ends_with.ptr.pass.cpp
@@ -17,7 +17,7 @@
 #include "test_macros.h"
 #include "constexpr_char_traits.hpp"
 
-int main()
+int main(int, char**)
 {
     {
     typedef std::string_view SV;
@@ -100,4 +100,6 @@ int main()
     static_assert ( svNot.ends_with("def"), "" );
     }
 #endif
+
+  return 0;
 }
diff --git a/libcxx/test/std/strings/string.view/string.view.template/ends_with.string_view.pass.cpp b/libcxx/test/std/strings/string.view/string.view.template/ends_with.string_view.pass.cpp
index 2d115c104b4..b5f67f8ddd1 100644
--- a/libcxx/test/std/strings/string.view/string.view.template/ends_with.string_view.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.template/ends_with.string_view.pass.cpp
@@ -17,7 +17,7 @@
 #include "test_macros.h"
 #include "constexpr_char_traits.hpp"
 
-int main()
+int main(int, char**)
 {
     {
     typedef std::string_view SV;
@@ -100,4 +100,6 @@ int main()
     static_assert ( svNot.ends_with(svNot), "" );
     }
 #endif
+
+  return 0;
 }
diff --git a/libcxx/test/std/strings/string.view/string.view.template/nothing_to_do.pass.cpp b/libcxx/test/std/strings/string.view/string.view.template/nothing_to_do.pass.cpp
index 3f07051d03a..45edec7f4b0 100644
--- a/libcxx/test/std/strings/string.view/string.view.template/nothing_to_do.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.template/nothing_to_do.pass.cpp
@@ -8,4 +8,6 @@
 
 #include <string_view>
 
-int main () {}
+int main(int, char**) {
+  return 0;
+}
diff --git a/libcxx/test/std/strings/string.view/string.view.template/starts_with.char.pass.cpp b/libcxx/test/std/strings/string.view/string.view.template/starts_with.char.pass.cpp
index d35222bbf87..d43944fdec7 100644
--- a/libcxx/test/std/strings/string.view/string.view.template/starts_with.char.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.template/starts_with.char.pass.cpp
@@ -17,7 +17,7 @@
 #include "test_macros.h"
 #include "constexpr_char_traits.hpp"
 
-int main()
+int main(int, char**)
 {
     {
     typedef std::string_view SV;
@@ -43,4 +43,6 @@ int main()
     static_assert (!sv2.starts_with('x'), "" );
     }
 #endif
+
+  return 0;
 }
diff --git a/libcxx/test/std/strings/string.view/string.view.template/starts_with.ptr.pass.cpp b/libcxx/test/std/strings/string.view/string.view.template/starts_with.ptr.pass.cpp
index a3ffde5c584..ce651ec57e0 100644
--- a/libcxx/test/std/strings/string.view/string.view.template/starts_with.ptr.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.template/starts_with.ptr.pass.cpp
@@ -17,7 +17,7 @@
 #include "test_macros.h"
 #include "constexpr_char_traits.hpp"
 
-int main()
+int main(int, char**)
 {
     {
     typedef std::string_view SV;
@@ -100,4 +100,6 @@ int main()
     static_assert ( svNot.starts_with("def"), "" );
     }
 #endif
+
+  return 0;
 }
diff --git a/libcxx/test/std/strings/string.view/string.view.template/starts_with.string_view.pass.cpp b/libcxx/test/std/strings/string.view/string.view.template/starts_with.string_view.pass.cpp
index 5a5adbd8470..3d184bae0eb 100644
--- a/libcxx/test/std/strings/string.view/string.view.template/starts_with.string_view.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.template/starts_with.string_view.pass.cpp
@@ -17,7 +17,7 @@
 #include "test_macros.h"
 #include "constexpr_char_traits.hpp"
 
-int main()
+int main(int, char**)
 {
     {
     typedef std::string_view SV;
@@ -100,4 +100,6 @@ int main()
     static_assert ( svNot.starts_with(svNot), "" );
     }
 #endif
+
+  return 0;
 }