Test for a working -Wshadow

Makefile

@@ -275,6 +275,12 @@ endif
 CXX11_CHECK_CMD = $(CXX) -std=c++11 -o $(TMPOUT) -c test/build/c++11.cc
 HAS_CXX11 = $(shell $(CXX11_CHECK_CMD) 2> /dev/null && echo true || echo false)
 
+CHECK_SHADOW_WORKS_CMD = $(CC) -std=c99 -Werror -Wshadow -o $(TMPOUT) -c test/build/shadow.c
+HAS_WORKING_SHADOW = $(shell $(CHECK_SHADOW_WORKS_CMD) 2> /dev/null && echo true || echo false)
+ifeq ($(HAS_WORKING_SHADOW),true)
+W_SHADOW=-Wshadow
+endif
+
 CHECK_NO_SHIFT_NEGATIVE_VALUE_CMD = $(CC) -std=c99 -Werror -Wno-shift-negative-value -o $(TMPOUT) -c test/build/empty.c
 HAS_NO_SHIFT_NEGATIVE_VALUE = $(shell $(CHECK_NO_SHIFT_NEGATIVE_VALUE_CMD) 2> /dev/null && echo true || echo false)
 ifeq ($(HAS_NO_SHIFT_NEGATIVE_VALUE),true)
@@ -295,7 +301,7 @@ ifdef EXTRA_DEFINES
 DEFINES += $(EXTRA_DEFINES)
 endif
 
-CFLAGS += -std=c99 -Wsign-conversion -Wconversion -Wshadow
+CFLAGS += -std=c99 -Wsign-conversion -Wconversion $(W_SHADOW)
 ifeq ($(HAS_CXX11),true)
 CXXFLAGS += -std=c++11
 else

templates/Makefile.template

@@ -187,6 +187,12 @@
   CXX11_CHECK_CMD = $(CXX) -std=c++11 -o $(TMPOUT) -c test/build/c++11.cc
   HAS_CXX11 = $(shell $(CXX11_CHECK_CMD) 2> /dev/null && echo true || echo false)
 
+  CHECK_SHADOW_WORKS_CMD = $(CC) -std=c99 -Werror -Wshadow -o $(TMPOUT) -c test/build/shadow.c
+  HAS_WORKING_SHADOW = $(shell $(CHECK_SHADOW_WORKS_CMD) 2> /dev/null && echo true || echo false)
+  ifeq ($(HAS_WORKING_SHADOW),true)
+  W_SHADOW=-Wshadow
+  endif
+
   CHECK_NO_SHIFT_NEGATIVE_VALUE_CMD = $(CC) -std=c99 -Werror -Wno-shift-negative-value -o $(TMPOUT) -c test/build/empty.c
   HAS_NO_SHIFT_NEGATIVE_VALUE = $(shell $(CHECK_NO_SHIFT_NEGATIVE_VALUE_CMD) 2> /dev/null && echo true || echo false)
   ifeq ($(HAS_NO_SHIFT_NEGATIVE_VALUE),true)
@@ -207,7 +213,7 @@
   DEFINES += $(EXTRA_DEFINES)
   endif
 
-  CFLAGS += -std=c99 -Wsign-conversion -Wconversion -Wshadow
+  CFLAGS += -std=c99 -Wsign-conversion -Wconversion $(W_SHADOW)
   ifeq ($(HAS_CXX11),true)
   CXXFLAGS += -std=c++11
   else

test/build/boringssl.c

@@ -33,6 +33,7 @@
 
 // Check that boringssl is going to compile
 
+#include <stdio.h>
 #include <unistd.h>
 
 // boringssl uses anonymous unions

test/build/shadow.c

@@ -0,0 +1,43 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+// Check that boringssl is going to compile
+
+#include <stdio.h>
+#include <unistd.h>
+
+int main(void) {
+  const char *close = "this should not shadow";
+  printf("%s\n", close);
+  return 0;
+}