selftest/sstatetests: add tests for 'bitbake -S printdiff'

'bitbake -S printdiff' is a useful diagnostic facility for finding out
why sstate is not being reused, but until now it had no tests that would
ensure it works. This commit adds three basic scenarios:

1. make a change in a really basic, common recipe that is at the very root
of dependency trees (quilt-native), and ensure that change is correctly discovered when
building an image.

2. make a change in gcc-source recipe, which is somewhat special
(operates in work-shared), and ensure that gcc-runtime builds track
that down as well.

3. make a change in base_do_configure() definition from base.bbclass,
which is not recipe-specific, but affects many basic recipes, and ensure that
is correctly reported as well.

The test itself actually runs twice:
- first against a fully populated build directory, where
the printdiff code is guaranteed to find the correct previous
stamp that can be compared with in a predictable manner.

- then in an empty build directory where the printdiff code
goes to look in the sstate cache, and so the existence of the
previous signature can be tested, but not the difference with it
(what the exact difference would be is unpredictable as the
sstate cache is indeed shared between many builds).

(From OE-Core rev: 7a7d76aa8a8d590ebc99156f9f4b9535cdf868c7)

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-selftest/classes/base-do-configure-modified.bbclass

@@ -0,0 +1,3 @@
+base_do_configure:append () {
+	echo "this changes base_do_configure() definiton"
+}

meta-selftest/recipes-test/gcc-source/gcc-source_%.bbappend

@@ -0,0 +1,2 @@
+# This bbappend is used to alter the recipe using the test_recipe.inc file created by tests.
+include test_recipe.inc

meta-selftest/recipes-test/quilt-native/quilt-native_%.bbappend

@@ -0,0 +1,2 @@
+# This bbappend is used to alter the recipe using the test_recipe.inc file created by tests.
+include test_recipe.inc

meta/lib/oeqa/selftest/cases/sstatetests.py

@@ -773,3 +773,116 @@ addtask tmptask2 before do_tmptask1
                 latestfiles = sorted(filedates.keys(), key=lambda f: filedates[f])[-2:]
                 bb.siggen.compare_sigfiles(latestfiles[-2], latestfiles[-1], recursecb)
                 self.assertEqual(recursecb_count,1)
+
+class SStatePrintdiff(SStateBase):
+    # FIXME: OEBasicHash setting is necessary for now as otherwise the following error can occur:
+    # ERROR: Can't find a task we're supposed to have written out? (hash: e79d70b9c2cc72030c1ce822525510699a1eeb1ddf5986271d3217422244366a)?
+    # The underlying issue should be investigated and addressed.
+    def run_test_printdiff_changerecipe(self, target, change_recipe, change_bbtask, change_content, expected_sametmp_output, expected_difftmp_output):
+        self.write_config("""
+TMPDIR = "${TOPDIR}/tmp-sstateprintdiff"
+BB_SIGNATURE_HANDLER = "OEBasicHash"
+""")
+        self.track_for_cleanup(self.topdir + "/tmp-sstateprintdiff")
+        bitbake(target)
+        bitbake("-S none {}".format(target))
+        bitbake(change_bbtask)
+        self.write_recipeinc(change_recipe, change_content)
+        result_sametmp = bitbake("-S printdiff {}".format(target))
+
+        self.write_config("""
+TMPDIR = "${TOPDIR}/tmp-sstateprintdiff-2"
+BB_SIGNATURE_HANDLER = "OEBasicHash"
+""")
+        self.track_for_cleanup(self.topdir + "/tmp-sstateprintdiff-2")
+        result_difftmp = bitbake("-S printdiff {}".format(target))
+
+        self.delete_recipeinc(change_recipe)
+        for item in expected_sametmp_output:
+            self.assertIn(item, result_sametmp.output)
+        for item in expected_difftmp_output:
+            self.assertIn(item, result_difftmp.output)
+
+    def run_test_printdiff_changeconfig(self, target, change_content, expected_sametmp_output, expected_difftmp_output):
+        self.write_config("""
+TMPDIR = "${TOPDIR}/tmp-sstateprintdiff"
+BB_SIGNATURE_HANDLER = "OEBasicHash"
+""")
+        self.track_for_cleanup(self.topdir + "/tmp-sstateprintdiff")
+        bitbake(target)
+        bitbake("-S none {}".format(target))
+        self.append_config(change_content)
+        result_sametmp = bitbake("-S printdiff {}".format(target))
+
+        self.write_config("""
+TMPDIR = "${TOPDIR}/tmp-sstateprintdiff-2"
+BB_SIGNATURE_HANDLER = "OEBasicHash"
+""")
+        self.append_config(change_content)
+        self.track_for_cleanup(self.topdir + "/tmp-sstateprintdiff-2")
+        result_difftmp = bitbake("-S printdiff {}".format(target))
+
+        for item in expected_sametmp_output:
+            self.assertIn(item, result_sametmp.output)
+        for item in expected_difftmp_output:
+            self.assertIn(item, result_difftmp.output)
+
+
+    # Check if printdiff walks the full dependency chain from the image target to where the change is in a specific recipe
+    def test_image_minimal_vs_quilt(self):
+        expected_output = ("Task quilt-native:do_install couldn't be used from the cache because:",
+"We need hash",
+"most recent matching task was")
+        expected_sametmp_output = expected_output + ("Variable do_install value changed",'+    echo "this changes the task signature"')
+        expected_difftmp_output = expected_output
+
+        self.run_test_printdiff_changerecipe("core-image-minimal", "quilt-native", "-c do_install quilt-native",
+"""
+do_install:append() {
+    echo "this changes the task signature"
+}
+""",
+expected_sametmp_output, expected_difftmp_output)
+
+    # Check if changes to gcc-source (which uses tmp/work-shared) are correctly discovered
+    def test_gcc_runtime_vs_gcc_source(self):
+        gcc_source_pn = 'gcc-source-%s' % get_bb_vars(['PV'], 'gcc')['PV']
+
+        expected_output = ("Task {}:do_preconfigure couldn't be used from the cache because:".format(gcc_source_pn),
+"We need hash",
+"most recent matching task was")
+        expected_sametmp_output = expected_output + ("Variable do_preconfigure value changed",'+    print("this changes the task signature")')
+        #FIXME: printdiff is supposed to find at least one preconfigure task signature in the sstate cache, but isn't able to
+        #expected_difftmp_output = expected_output
+        expected_difftmp_output = ()
+
+        self.run_test_printdiff_changerecipe("gcc-runtime", "gcc-source", "-c do_preconfigure {}".format(gcc_source_pn),
+"""
+python do_preconfigure:append() {
+    print("this changes the task signature")
+}
+""",
+expected_sametmp_output, expected_difftmp_output)
+
+    # Check if changing a really base task definiton is reported against multiple core recipes using it
+    def test_image_minimal_vs_base_do_configure(self):
+        expected_output = ("Task zstd-native:do_configure couldn't be used from the cache because:",
+"Task texinfo-dummy-native:do_configure couldn't be used from the cache because:",
+"Task ldconfig-native:do_configure couldn't be used from the cache because:",
+"Task gettext-minimal-native:do_configure couldn't be used from the cache because:",
+"Task tzcode-native:do_configure couldn't be used from the cache because:",
+"Task makedevs-native:do_configure couldn't be used from the cache because:",
+"Task pigz-native:do_configure couldn't be used from the cache because:",
+"Task update-rc.d-native:do_configure couldn't be used from the cache because:",
+"Task unzip-native:do_configure couldn't be used from the cache because:",
+"Task gnu-config-native:do_configure couldn't be used from the cache because:",
+"We need hash",
+"most recent matching task was")
+        expected_sametmp_output = expected_output + ("Variable base_do_configure value changed",'+	echo "this changes base_do_configure() definiton"')
+        expected_difftmp_output = expected_output
+
+        self.run_test_printdiff_changeconfig("core-image-minimal",
+"""
+INHERIT += "base-do-configure-modified"
+""",
+expected_sametmp_output, expected_difftmp_output)