classes/waf: Set WAFLOCK

Sets the WAFLOCK environment variable. This controls the name of the
lock file that waf uses to pass the build configuration from 'configure'
to 'build' and 'install'. Using a uniquely generated name based on the
parameters passed to 'configure' ensures that the source directory can
be configured for multiple different builds without conflicting (since
the lock file is stored in ${S})

(From OE-Core rev: 29419141a42e6b6664f72d085288ba03c74f90a6)

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/waf.bbclass

@@ -5,6 +5,32 @@ B = "${WORKDIR}/build"
 
 EXTRA_OECONF_append = " ${PACKAGECONFIG_CONFARGS}"
 
+def waflock_hash(d):
+    # Calculates the hash used for the waf lock file. This should include
+    # all of the user controllable inputs passed to waf configure. Note
+    # that the full paths for ${B} and ${S} are used; this is OK and desired
+    # because a change to either of these should create a unique lock file
+    # to prevent collisions.
+    import hashlib
+    h = hashlib.sha512()
+    def update(name):
+        val = d.getVar(name)
+        if val is not None:
+            h.update(val.encode('utf-8'))
+    update('S')
+    update('B')
+    update('prefix')
+    update('EXTRA_OECONF')
+    return h.hexdigest()
+
+# Use WAFLOCK to specify a separate lock file. The build is already
+# sufficiently isolated by setting the output directory, this ensures that
+# bitbake won't step on toes of any other configured context in the source
+# directory (e.g. if the source is coming from externalsrc and was previously
+# configured elsewhere).
+export WAFLOCK = ".lock-waf_oe_${@waflock_hash(d)}_build"
+BB_HASHBASE_WHITELIST += "WAFLOCK"
+
 python waf_preconfigure() {
     import subprocess
     from distutils.version import StrictVersion