Re: SConsignFile(None) + Decider('MD5-timestamp')

I've dug more into this issue, and have attached a proposed patch against scons-4.0.1.

The general idea is to pass the parent node to _build_dependency_map, to then correlate "children" to signatures the same way Node/__init__.py changed() does, rather than using bsources/etc.  This fixes the pathing issues, and should perform the same when building from the same directory repeatedly.

Can anyone verify the bug, or provide feedback on the proposed patch?

Should I open a bug report instead?

Thanks,
Trevor

________________________________
From: Scons-users <[email protected]> on behalf of trevor fitzsimmons <[email protected]>
Sent: Wednesday, July 29, 2020 11:52 AM
To: [email protected] <[email protected]>
Subject: [Scons-users] SConsignFile(None) + Decider('MD5-timestamp')

Since scons-3.0.2 (through the current scons-4.0.1), using SConsignFile(None) in conjunction with Decider('MD5-timestamp') causes scons to rebuild targets when invoked from different directories in the source code hierarchy.

Attached is a simple example to illustrate the issue.  Building from test/src will cause an initial build as expecting.  Building again from test/src will do nothing, as expected, and report everything is up-to-date.  However, if you build from test, everything in test/src will be rebuilt, even though it is already up-to-date.  Building again from test will do nothing, as expected, and report everything is up-to-date.  Building from test/src will then cause another full rebuild, even though everything is up-to-date, and the cycle continues.

This has something to do with the dependency_map which was added in Node/FS.py in scons-3.0.2, but I do not know enough about the inner workings of scons to propose a fix.  FS.py changed_timestamp_then_content(self, target, prev_ni, node=None) calls prev_ni = self._get_previous_signatures(dependency_map).  Depending on the starting directory, self is either main.cpp or src/main.cpp, while the key in dependency_map is the other.

In our full code-base, it's quite usual to build in a subdirectory while changing code, to avoid waiting on a full build, so the current work-around is to not use Decider('MD5-timestamp').  It would be ideal to have a patch that could eventually be applied to scons, to fix the issue in a future version.

Thanks

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--- FS.py	2020-08-12 08:33:01.907999875 -0400
+++ FS_new.py	2020-08-12 08:32:49.311341846 -0400
@@ -3310,7 +3310,7 @@
     __dmap_sig_cache = {}
 
 
-    def _build_dependency_map(self, binfo):
+    def _build_dependency_map(self, binfo, node):
         """
         Build mapping from file -> signature
 
@@ -3322,13 +3322,16 @@
             dictionary of file->signature mappings
         """
 
+        if node is None:
+            node = self
+
         # For an "empty" binfo properties like bsources
         # do not exist: check this to avoid exception.
         if (len(binfo.bsourcesigs) + len(binfo.bdependsigs) +
             len(binfo.bimplicitsigs)) == 0:
             return {}
 
-        binfo.dependency_map = { child:signature for child, signature in zip(chain(binfo.bsources, binfo.bdepends, binfo.bimplicit),
+        binfo.dependency_map = { child:signature for child, signature in zip(node.children(),
                                      chain(binfo.bsourcesigs, binfo.bdependsigs, binfo.bimplicitsigs))}
 
         return binfo.dependency_map
@@ -3456,7 +3459,7 @@
         try:
             dependency_map = bi.dependency_map
         except AttributeError as e:
-            dependency_map = self._build_dependency_map(bi)
+            dependency_map = self._build_dependency_map(bi, node)
             rebuilt = True
 
         if len(dependency_map) == 0: