From 85ee736a938bc882ee8cb2eb312c9b4c66f53a6c Mon Sep 17 00:00:00 2001
From: Andreas Herrmann <andreas.herrmann@tweag.io>
Date: Tue, 24 Nov 2020 10:34:55 +0100
Subject: [PATCH 1/2] Test C and C++ compilation explicitly

---
 tests/BUILD.bazel | 5 +++++
 tests/c-test.c    | 7 +++++++
 tests/cc-test.cc  | 6 +++++-
 3 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 tests/c-test.c

diff --git a/tests/BUILD.bazel b/tests/BUILD.bazel
index 077c0c845..6c80584fd 100644
--- a/tests/BUILD.bazel
+++ b/tests/BUILD.bazel
@@ -82,6 +82,11 @@ cc_binary(
     srcs = ["cc-test.cc"],
 )
 
+cc_binary(
+    name = "c-test",
+    srcs = ["c-test.c"],
+)
+
 # Test that nixpkgs_cc_configure is selected.
 cc_toolchain_test(
     name = "cc-toolchain",
diff --git a/tests/c-test.c b/tests/c-test.c
new file mode 100644
index 000000000..304d0d872
--- /dev/null
+++ b/tests/c-test.c
@@ -0,0 +1,7 @@
+#include "stdio.h"
+int main() {
+        puts("Hello world\n");
+        // Ensure that this is compiled as C, template is a keyword in C++.
+        int template = 0;
+        return template;
+}
diff --git a/tests/cc-test.cc b/tests/cc-test.cc
index 76e819701..0e7f60bbd 100644
--- a/tests/cc-test.cc
+++ b/tests/cc-test.cc
@@ -1 +1,5 @@
-int main() { return 0; }
+#include <iostream>
+int main() {
+        std::cout << "Hello world\n";
+        return 0;
+}

From 6d6fc1b608a79ac2036688d640c3d13c68e158f2 Mon Sep 17 00:00:00 2001
From: Andreas Herrmann <andreas.herrmann@tweag.io>
Date: Tue, 24 Nov 2020 12:07:35 +0100
Subject: [PATCH 2/2] Clang compatibility

Add `-x c++` to `CXX_FLAGS` to enable C++ compilcation with `clang`.
Shift `-lstdc++` and `-lm` into `LINK_LIBS` to avoid missing symbol
errors when linking C++ with `clang`.
---
 nixpkgs/toolchains/cc.nix | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/nixpkgs/toolchains/cc.nix b/nixpkgs/toolchains/cc.nix
index a234e3276..e2c766a0d 100644
--- a/nixpkgs/toolchains/cc.nix
+++ b/nixpkgs/toolchains/cc.nix
@@ -160,7 +160,10 @@ in
         # Keep stack frames for debugging, even in opt mode.
         -fno-omit-frame-pointer
       )
-      CXX_FLAGS=(-std=c++0x)
+      CXX_FLAGS=(
+        -x c++
+        -std=c++0x
+      )
       LINK_FLAGS=(
         $(
           if [[ -x ${cc}/bin/ld.gold ]]; then echo -fuse-ld=gold; fi
@@ -176,10 +179,11 @@ in
           # Have gcc return the exit code from ld.
           add_compiler_option_if_supported -pass-exit-codes
         )
+      )
+      LINK_LIBS=(
         -lstdc++
         -lm
       )
-      LINK_LIBS=()
       OPT_COMPILE_FLAGS=(
         # No debug symbols.
         # Maybe we should enable https://gcc.gnu.org/wiki/DebugFission for opt or