classes/sanity: check for case-sensitive file systems

Case-insensitive file systems fail during builds in very mysterious ways, such
as mpfr:

  ERROR: patch_do_patch: Not a directory

The problem here being that mpfr has a PATCHES file, so when we try to copy the
patches into ${S}/patches/ it fails.

We can't and won't support case-insensitive file systems so add a sanity check
to abort the build if one is found.

(From OE-Core rev: 20ce04fb64f559e64490d53678fa00644a92894a)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/sanity.bbclass

@@ -350,6 +350,14 @@ def check_not_nfs(path, name):
         return "The %s: %s can't be located on nfs.\n" % (name, path)
     return ""
 
+# Check that the path is on a case-sensitive file system
+def check_case_sensitive(path, name):
+    import tempfile
+    with tempfile.NamedTemporaryFile(prefix='TmP', dir=path) as tmp_file:
+        if os.path.exists(tmp_file.name.lower()):
+            return "The %s (%s) can't be on a case-insensitive file system.\n" % (name, path)
+        return ""
+
 # Check that path isn't a broken symlink
 def check_symlink(lnk, data):
     if os.path.islink(lnk) and not os.path.exists(lnk):
@@ -672,6 +680,10 @@ def check_sanity_version_change(status, d):
     # Check that TMPDIR isn't located on nfs
     status.addresult(check_not_nfs(tmpdir, "TMPDIR"))
 
+    # Check for case-insensitive file systems (such as Linux in Docker on
+    # macOS with default HFS+ file system)
+    status.addresult(check_case_sensitive(tmpdir, "TMPDIR"))
+
 def sanity_check_locale(d):
     """
     Currently bitbake switches locale to en_US.UTF-8 so check that this locale actually exists.