Add test and fix to regression in current 3.1.0 drop

2 files changed, 16 insertions, 10 deletions

diff --git a/src/CHANGES.txt b/src/CHANGES.txt
index 8a48bd4..4a8262c 100755
--- a/src/CHANGES.txt
+++ b/src/CHANGES.txt
@@ -10,6 +10,10 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
 
     - Remove obsoleted references to DeciderNeedsNode which could cause crash when using --debug=explain
 
+  From Jason Kenny
+
+    - Add Fix and test for regression in 3.1.0 when using Decider('MD5-timestamp') and --debug=explain
+
 
 RELEASE 3.1.0 - Mon, 20 Jul 2019 16:59:23 -0700
 
@@ -20,7 +24,7 @@ RELEASE 3.1.0 - Mon, 20 Jul 2019 16:59:23 -0700
   From William Deegan:
     - Enhanced --debug=explain output. Now the separate components of the dependency list are split up
       as follows:
-      
+
       scons: rebuilding `file3' because:
            the dependency order changed:
            ->Sources
@@ -91,7 +95,7 @@ RELEASE 3.1.0 - Mon, 20 Jul 2019 16:59:23 -0700
     - More fixes for newer Java versions (since 9): handle new jdk directory
       naming (jdk-X.Y instead of jdkX.Y) on Windows; handle two-digit major
       version. Docstrings improved.
-    - Fixups for pylint: exception types, redefined functions, 
+    - Fixups for pylint: exception types, redefined functions,
       globals, etc.  Some old code removed to resolve issues (hashlib is
       always present on modern Pythons; no longer need the code for
       2.5-and-earlier optparse). cmp is not a builtin function in Py3,
@@ -101,7 +105,7 @@ RELEASE 3.1.0 - Mon, 20 Jul 2019 16:59:23 -0700
     - Add a PY3-only function for setting up the cachedir that should be less
       prone to races. Add a hack to the PY2 version (from Issue #3351) to
       be less prone to a race in the check for old-style cache.
-    - Fix coding error in docbook tool only exercised when using python lxml 
+    - Fix coding error in docbook tool only exercised when using python lxml
     - Recognize two additional GNU compiler header directory options in
       ParseFlags: -iquote and -idirafter.
     - Fix more re patterns that contain \ but not specified as raw strings
@@ -148,7 +152,7 @@ From Daniel Moody:
 
   From Bernhard M. Wiedemann:
     - Do not store build host+user name if reproducible builds are wanted
-    
+
 
 RELEASE 3.0.4 - Mon, 20 Jan 2019 22:49:27 +0000
 
@@ -216,9 +220,9 @@ RELEASE 3.0.2 - Mon, 31 Dec 2018 16:00:12 -0700
     - Fix GH Issue #2580 - # in FRAMEWORKPATH doesn't get properly expanded. The # is left in the
       command line.
     - Fix issue #2980 with credit to Piotr Bartosik (and William Blevins).  This is an issue where using
-      TimeStamp-MD5 Decider and CacheDir can yield incorrect md5's being written into the .sconsign.  
-      The difference between Piotr Bartosik's patch and the current code is that the more complicated 
-      creation of file to csig map is only done when the count of children for the current node doesn't 
+      TimeStamp-MD5 Decider and CacheDir can yield incorrect md5's being written into the .sconsign.
+      The difference between Piotr Bartosik's patch and the current code is that the more complicated
+      creation of file to csig map is only done when the count of children for the current node doesn't
       match the previous count which is loaded from the sconsign.
     - Fix issue # 3106 MSVC if using MSVC_BATCH and target dir had a space would fail due to quirk in
       MSVC's handling of escaped targetdirs when batch compiling.
@@ -254,7 +258,7 @@ RELEASE 3.0.2 - Mon, 31 Dec 2018 16:00:12 -0700
     - Removed unused --warn options from the man page and source code.
 
   From Arda Fu
-    - Fix cpp scanner regex logic to treat ifndef for py3.5+. Previously it was 
+    - Fix cpp scanner regex logic to treat ifndef for py3.5+. Previously it was
       not properly differentiating between if, ifdef, and ifndef.
 
   From Philipp Maierhöfer
@@ -265,7 +269,7 @@ RELEASE 3.0.2 - Mon, 31 Dec 2018 16:00:12 -0700
   From Matthew Marinets:
     - Fixed an issue that caused the Java emitter to incorrectly parse arguments to constructors that
       implemented a class.
-      
+
   From Fredrik Medley:
     - Fix exception when printing of EnviromentError messages.
       Specifically, this fixes error reporting of the race condition when
@@ -386,7 +390,7 @@ RELEASE 3.0.2 - Mon, 31 Dec 2018 16:00:12 -0700
       filter type -> list in ipk
 
   From Bernhard M. Wiedemann:
-    - Update SCons' internal scons build logic to allow overriding build date 
+    - Update SCons' internal scons build logic to allow overriding build date
       with SOURCE_DATE_EPOCH for SCons itself.
     - Change the datestamps in SCons' docs and embedded in code use ISO 8601 format and UTC
 
diff --git a/src/engine/SCons/Node/FS.py b/src/engine/SCons/Node/FS.py
index 33105fb..6b0fe98 100644
--- a/src/engine/SCons/Node/FS.py
+++ b/src/engine/SCons/Node/FS.py
@@ -3436,6 +3436,8 @@ class File(Base):
             Boolean - Indicates if node(File) has changed.
         """
 
+        if node is None:
+            node = self
         # Now get sconsign name -> csig map and then get proper prev_ni if possible
         bi = node.get_stored_info().binfo
         rebuilt = False