buildstats-summary.bbclass: Import useful bbclass from meta-mentor

This class summarizes sstate reuse at the end of the build, so you know how
much of your build was done from scratch.

(From OE-Core rev: 0069c06cc9c929de7e7d29b0381fcb36049a4401)

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Christopher Larson <kergoth@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/buildstats-summary.bbclass

@@ -0,0 +1,39 @@
+# Summarize sstate usage at the end of the build
+python buildstats_summary () {
+    if not isinstance(e, bb.event.BuildCompleted):
+        return
+
+    import collections
+    import os.path
+
+    bn = get_bn(e)
+    bsdir = os.path.join(e.data.getVar('BUILDSTATS_BASE', True), bn)
+    if not os.path.exists(bsdir):
+        return
+
+    sstatetasks = (e.data.getVar('SSTATETASKS', True) or '').split()
+    built = collections.defaultdict(lambda: [set(), set()])
+    for pf in os.listdir(bsdir):
+        taskdir = os.path.join(bsdir, pf)
+        if not os.path.isdir(taskdir):
+            continue
+
+        tasks = os.listdir(taskdir)
+        for t in sstatetasks:
+            no_sstate, sstate = built[t]
+            if t in tasks:
+                no_sstate.add(pf)
+            elif t + '_setscene' in tasks:
+                sstate.add(pf)
+
+    header_printed = False
+    for t in sstatetasks:
+        no_sstate, sstate = built[t]
+        if no_sstate | sstate:
+            if not header_printed:
+                header_printed = True
+                bb.note("Build completion summary:")
+
+            bb.note("  {0}: {1}% sstate reuse ({2} setscene, {3} scratch)".format(t, 100*len(sstate)/(len(sstate)+len(no_sstate)), len(sstate), len(no_sstate)))
+}
+addhandler buildstats_summary