sstate: Implement a setscene dependency validation routine to allow skipping of some sstate installation

This is a first attempt at logic to determine when a sstate dependency needs
to be installed and when it does not. Its a start at the logic and errs on the
side of caution, as it gets wider testing, we can refine the logic as needed.

This code should allow a significant performance speedup to certain workflows, for
example "bitbake xxx-image -c rootfs" will not populate the target sysroot.

(From OE-Core rev: b43faba37816817edc5240a139361d16e07c6131)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/sstate.bbclass

@@ -620,3 +620,55 @@ def sstate_checkhashes(sq_fn, sq_task, sq_hash, sq_hashfn, d):
 
     return ret
 
+BB_SETSCENE_DEPVALID = "setscene_depvalid"
+
+def setscene_depvalid(task, taskdependees, notneeded, d):
+    # taskdependees is a dict of tasks which depend on task, each being a 3 item list of [PN, TASKNAME, FILENAME]
+    # task is included in taskdependees too
+
+    bb.debug(2, "Considering setscene task: %s" % (str(taskdependees[task])))
+
+    def isNative(x):
+        return x.endswith("-native")
+    def isNativeCross(x):
+        return x.endswith("-native") or x.endswith("-cross") or x.endswith("-cross-initial")
+    def isSafeDep(x):
+        if x in ["quilt-native", "autoconf-native", "automake-native", "gnu-config-native", "libtool-native", "pkgconfig-native", "gcc-cross", "binutils-cross"]:
+            return True
+        return False
+
+    # We can skip these "safe" dependencies since the aren't runtime dependencies, just build time
+    if isSafeDep(taskdependees[task][0]) and taskdependees[task][1] == "do_populate_sysroot":
+        return True
+
+    # We only need to trigger populate_lic through direct dependencies
+    if taskdependees[task][1] == "do_populate_lic":
+        return True
+
+    for dep in taskdependees:
+        bb.debug(2, "  considering dependency: %s" % (str(taskdependees[dep])))
+        if task == dep:
+            continue
+        if dep in notneeded:
+            continue
+        # do_package_write_* and do_package doesn't need do_package
+        if taskdependees[task][1] == "do_package" and taskdependees[dep][1] in ['do_package', 'do_package_write_deb', 'do_package_write_ipk', 'do_package_write_rpm']:
+            continue
+        # do_package_write_* and do_package doesn't need do_populate_sysroot
+        if taskdependees[task][1] == "do_populate_sysroot" and taskdependees[dep][1] in ['do_package', 'do_package_write_deb', 'do_package_write_ipk', 'do_package_write_rpm']:
+            continue
+        # Native/Cross packages don't exist and are noexec anyway
+        if isNativeCross(taskdependees[dep][0]) and taskdependees[dep][1] in ['do_package_write_deb', 'do_package_write_ipk', 'do_package_write_rpm']:
+            continue
+        # Native/Cross populate_sysroot need their dependencies
+        if isNativeCross(taskdependees[task][0]) and isNativeCross(taskdependees[dep][0]) and taskdependees[task][1] == 'do_populate_sysroot' and taskdependees[dep][1] == 'do_populate_sysroot':
+            return False
+        # Target populate_sysroot do not need their dependencies
+        if taskdependees[task][1] == 'do_populate_sysroot' and taskdependees[dep][1] == 'do_populate_sysroot':
+            continue
+
+        # Safe fallthrough default
+        bb.debug(2, " Default setscene dependency fall through due to dependency: %s" % (str(taskdependees[dep])))
+        return False
+    return True
+