Reland r371785: Add -Wpoison-system-directories warning

When using clang as a cross-compiler, we should not use system
headers to do the compilation.
This CL adds support of a new warning flag -Wpoison-system-directories which
emits warnings if --sysroot is set and headers from common host system location
are used.
By default the warning is disabled.

The intention of the warning is to catch bad includes which are usually
generated by third party build system not targeting cross-compilation.
Such cases happen in Chrome OS when someone imports a new package or upgrade
one to a newer version from upstream.

This is reland of r371785 with a fix to test file.

Patch by: denik (Denis Nikitin)

llvm-svn: 371878

6 files changed, 29 insertions, 0 deletions

diff --git a/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/lib/.keep b/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/lib/.keep
new file mode 100644
index 00000000000..e69de29bb2d
--- /dev/null
+++ b/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/lib/.keep
diff --git a/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/include/c++/.keep b/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/include/c++/.keep
new file mode 100644
index 00000000000..e69de29bb2d
--- /dev/null
+++ b/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/include/c++/.keep
diff --git a/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/lib/gcc/.keep b/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/lib/gcc/.keep
new file mode 100644
index 00000000000..e69de29bb2d
--- /dev/null
+++ b/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/lib/gcc/.keep
diff --git a/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/local/include/.keep b/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/local/include/.keep
new file mode 100644
index 00000000000..e69de29bb2d
--- /dev/null
+++ b/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/local/include/.keep
diff --git a/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/local/lib/.keep b/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/local/lib/.keep
new file mode 100644
index 00000000000..e69de29bb2d
--- /dev/null
+++ b/clang/test/Frontend/Inputs/sysroot_x86_64_cross_linux_tree/usr/local/lib/.keep
diff --git a/clang/test/Frontend/warning-poison-system-directories.c b/clang/test/Frontend/warning-poison-system-directories.c
new file mode 100644
index 00000000000..ba4c0e1990e
--- /dev/null
+++ b/clang/test/Frontend/warning-poison-system-directories.c
@@ -0,0 +1,29 @@
+// REQUIRES: x86-registered-target
+
+// System directory and sysroot option causes warning.
+// RUN: %clang -Wpoison-system-directories -target x86_64 -I/usr/include --sysroot %S/Inputs/sysroot_x86_64_cross_linux_tree -c -o - %s 2> %t.1.stderr
+// RUN: FileCheck -check-prefix=WARN < %t.1.stderr %s
+// RUN: %clang -Wpoison-system-directories -target x86_64 -cxx-isystem/usr/include --sysroot %S/Inputs/sysroot_x86_64_cross_linux_tree -c -o - %s 2> %t.1.stderr
+// RUN: FileCheck -check-prefix=WARN < %t.1.stderr %s
+// RUN: %clang -Wpoison-system-directories -target x86_64 -iquote/usr/local/include --sysroot %S/Inputs/sysroot_x86_64_cross_linux_tree -c -o - %s 2> %t.1.stderr
+// RUN: FileCheck -check-prefix=WARN < %t.1.stderr %s
+// RUN: %clang -Wpoison-system-directories -target x86_64 -isystem/usr/local/include --sysroot %S/Inputs/sysroot_x86_64_cross_linux_tree -c -o - %s 2> %t.1.stderr
+// RUN: FileCheck -check-prefix=WARN < %t.1.stderr %s
+
+// Missing target but included sysroot still causes the warning.
+// RUN: %clang -Wpoison-system-directories -I/usr/include --sysroot %S/Inputs/sysroot_x86_64_cross_linux_tree -c -o - %s 2> %t.2.stderr
+// RUN: FileCheck -check-prefix=WARN < %t.2.stderr %s
+
+// With -Werror the warning causes the failure.
+// RUN: not %clang -Werror=poison-system-directories -target x86_64 -I/usr/include --sysroot %S/Inputs/sysroot_x86_64_cross_linux_tree -c -o - %s 2> %t.3.stderr
+// RUN: FileCheck -check-prefix=ERROR < %t.3.stderr %s
+
+// Cros target without sysroot causes no warning.
+// RUN: %clang -Wpoison-system-directories -Werror -target x86_64 -I/usr/include -c -o - %s
+
+// By default the warning is off.
+// RUN: %clang -Werror -target x86_64 -I/usr/include --sysroot %S/Inputs/sysroot_x86_64_cross_linux_tree -c -o - %s
+
+// WARN: warning: include location {{[^ ]+}} is unsafe for cross-compilation [-Wpoison-system-directories]
+
+// ERROR: error: include location {{[^ ]+}} is unsafe for cross-compilation [-Werror,-Wpoison-system-directories]