yocto-compat-layer: limit report of signature changes

Typically a single change cascades through the entire task dependency
chain. Developers had to figure that out themselves, based on hard to
read and interpret output (not sorted, no indention, no explanations):

   $ yocto-compat-layer.py -n meta-xxxx
   ...
   AssertionError: True is not false : Layer meta-xxxx changed signatures.
   webkitgtk:do_install changed fe2edc9082bc0da98f9cb1391c52f565 -> b3a44684c5cd9aacd3f7c6ed88eefab5
   gstreamer1.0-plugins-good:do_configure changed 3b2f8211be3fe08422bf6087f3af16d1 -> 7d80e42fa1f4f01ff4dfe2ea4477d382
   pulseaudio:do_package_qa changed 5d0a58ada66ff17f5576555302ac319a -> 0e13bcb96143d1ae54c451bc3de0aa30
   epiphany:do_prepare_recipe_sysroot changed 29e1b277dbcb005bd54950594c50d91b -> d3c45527b37677a0668ce483c6db3052
   ...
   gst-player:do_packagedata changed 9ce6efdd357dd74919bc4957458b1e95 -> d0c083ce629f37adfc9c4ba9eff81f83
   gstreamer1.0-plugins-base:do_install changed 1161cd867d15bea63e5dd5d9abf0519c -> 5bf2b652a2d77fee3eedb35af2f201a0
   gstreamer1.0-rtsp-server:do_packagedata changed 6781dc3070f80b843ed1970d74dd323e -> 454620c2e3b9fea87e525d14b6ed0344
   alsa-plugins:do_packagedata changed 1808c3f737cb805b169d004e948ea19c -> 480124b7fa5eab1f73bf96440d725231

Now the tool automates the problem analysis: it retrieves the depgraph
using the tinfoil API and only reports those tasks with modified
signatures whose dependencies have not changed, i.e. those tasks which
definitely introduce a change.

>From the previous example, that just leaves two tasks that need to be
checked:

   AssertionError: False is not true : Layer meta-xxxx changed 120 signatures, initial differences (first hash without, second with layer):
      gstreamer1.0-plugins-base:do_fetch: 76973f19f2e30d282152bdd7e4efe5bb -> e6e7c6fa9f2bd59d7d8d107f7c6ca1ac
      pulseaudio:do_install: 668eb1e30af129df9806b0aa0d7c10cd -> 1196bdb88eef56eeee4613bb06b9387e

This pruning might be a bit too aggressive in the sense that tasks
which inherit a change and then add more changes themselves won't be
reported initially. They will be found when fixing the reported tasks
and re-running the check.

For a developer it seems better to have something listed which
definitely is a problem and needs fixing instead of everything,
including the tasks which don't need fixes.

(From OE-Core rev: 7ab0e09de75bfd7e7498bfa72d1f2f5d02a96747)

Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/compatlayer/__init__.py

@@ -7,6 +7,8 @@ import os
 import subprocess
 from enum import Enum
 
+import bb.tinfoil
+
 class LayerType(Enum):
     BSP = 0
     DISTRO = 1
@@ -252,3 +254,33 @@ def get_signatures(builddir, failsafe=False):
         raise RuntimeError('Can\'t load signatures from %s' % sigs_file)
 
     return sigs
+
+def get_depgraph(targets=['world']):
+    '''
+    Returns the dependency graph for the given target(s).
+    The dependency graph is taken directly from DepTreeEvent.
+    '''
+    depgraph = None
+    with bb.tinfoil.Tinfoil() as tinfoil:
+        tinfoil.prepare(config_only=False)
+        tinfoil.set_event_mask(['bb.event.NoProvider', 'bb.event.DepTreeGenerated', 'bb.command.CommandCompleted'])
+        if not tinfoil.run_command('generateDepTreeEvent', targets, 'do_build'):
+            raise RuntimeError('starting generateDepTreeEvent failed')
+        while True:
+            event = tinfoil.wait_event(timeout=1000)
+            if event:
+                if isinstance(event, bb.command.CommandFailed):
+                    raise RuntimeError('Generating dependency information failed: %s' % event.error)
+                elif isinstance(event, bb.command.CommandCompleted):
+                    break
+                elif isinstance(event, bb.event.NoProvider):
+                    if event._reasons:
+                        raise RuntimeError('Nothing provides %s: %s' % (event._item, event._reasons))
+                    else:
+                        raise RuntimeError('Nothing provides %s.' % (event._item))
+                elif isinstance(event, bb.event.DepTreeGenerated):
+                    depgraph = event._depgraph
+
+    if depgraph is None:
+        raise RuntimeError('Could not retrieve the depgraph.')
+    return depgraph