Merge branch 'master' into topic/grossag/msvs

12 files changed, 250 insertions, 140 deletions

diff --git a/src/CHANGES.txt b/src/CHANGES.txt
index ad42104..2b3e627 100755
--- a/src/CHANGES.txt
+++ b/src/CHANGES.txt
@@ -9,8 +9,9 @@
 
 RELEASE  VERSION/DATE TO BE FILLED IN LATER
 
-  From Adam Gross:
-    - Upgrade and improve Visual Studio solution/project generation code
+  From Joseph Brill:
+    - Code to supply correct version-specifier argument to vswhere for
+      VS version selection.
 
   From Peter Diener:
     - Additional fix to issue #3135 - Also handle 'pure' and 'elemental' type bound procedures
@@ -44,14 +45,30 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
     - Fix Issue #3350 - mslink failing when too many objects.  This is resolved by adding TEMPFILEARGJOIN variable
       which specifies what character to join all the argements output into the tempfile. The default remains a space
       when mslink, msvc, or mslib tools are loaded they change the TEMPFILEARGJOIN to be a line separator (\r\n on win32)
+    - Fix performance degradation for MD5-timestamp decider.  NOTE: This changes the Decider() function arguments.
+      From:
+          def my_decider(dependency, target, prev_ni):
+      To:
+          def my_decider(dependency, target, prev_ni, repo_node):
+      Where repo_node is the repository (or other) node to use to check if the node is out of date instead of dependency.
+
+  From Adam Gross:
+    - Upgrade and improve Visual Studio solution/project generation code
+
 
   From Michael Hartmann:
     - Fix handling of Visual Studio Compilers to properly reject any unknown HOST_PLATFORM or TARGET_PLATFORM
 
+  From Bert Huijben:
+    - Added support for Visual Studio 2019 toolset.
+
   From Mathew Robinson:
     - Update cache debug output to include cache hit rate.
     - No longer unintentionally hide exceptions in Action.py
 
+  From Leonard de Ruijter:
+    - Add logic to derive correct version argument to vswhere
+
   From Lukas Schrangl:
     - Enable LaTeX scanner to find more than one include per line
 
@@ -82,6 +99,10 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
     - Fix more re patterns that contain \ but not specified as raw strings
       (affects scanners for D, LaTeX, swig)
 
+  From Mathew Robinson:
+    - Update cache debug output to include cache hit rate.
+    - No longer unintentionally hide exceptions in Action.py
+    - Allow builders and pseudo-builders to inherit from OverrideEnvironments
 
 RELEASE 3.0.5 - Mon, 26 Mar 2019 15:04:42 -0700
 
diff --git a/src/RELEASE.txt b/src/RELEASE.txt
index efa35eb..9e4e314 100755
--- a/src/RELEASE.txt
+++ b/src/RELEASE.txt
@@ -41,6 +41,14 @@
 
   CHANGED/ENHANCED EXISTING FUNCTIONALITY
 
+      - Fix performance degradation for MD5-timestamp decider.  NOTE: This changes the Decider() function arguments.
+      From:
+          def my_decider(dependency, target, prev_ni):
+      To:
+          def my_decider(dependency, target, prev_ni, repo_node):
+      Where repo_node is the repository (or other) node to use to check if the node is out of date instead of dependency.
+
+
     - Enhanced --debug=explain output. Now the separate components of the dependency list are split up
       as follows:
 
@@ -54,6 +62,14 @@
            ->Implicit
            Old:/usr/bin/python	New:/usr/bin/python
 
+
+    - Changed: Pseudo-builders now inherit OverrideEnvironments. For
+      example when calling a pseudo-builder from another
+      pseudo-builder the override variables passed to the first
+      pseudo-builder call had to be explicitly passed on to the
+      internal pseudo-builder call. Now the second pseudo-builder call
+      will automatically inherit these override values.
+
   FIXES
 
     - List fixes of outright bugs
diff --git a/src/engine/SCons/Action.py b/src/engine/SCons/Action.py
index 3ec8a4c..c6fc575 100644
--- a/src/engine/SCons/Action.py
+++ b/src/engine/SCons/Action.py
@@ -534,7 +534,7 @@ class ActionBase(object):
         result = self.get_presig(target, source, env)
 
         if not isinstance(result,(bytes, bytearray)):
-            result = bytearray("",'utf-8').join([ SCons.Util.to_bytes(r) for r in result ])
+            result = bytearray(result, 'utf-8')
         else:
             # Make a copy and put in bytearray, without this the contents returned by get_presig
             # can be changed by the logic below, appending with each call and causing very
diff --git a/src/engine/SCons/Environment.py b/src/engine/SCons/Environment.py
index 7f9a76c..8d06af7 100644
--- a/src/engine/SCons/Environment.py
+++ b/src/engine/SCons/Environment.py
@@ -864,18 +864,21 @@ class SubstitutionEnvironment(object):
         return self
 
 
-def default_decide_source(dependency, target, prev_ni):
+def default_decide_source(dependency, target, prev_ni, repo_node=None):
     f = SCons.Defaults.DefaultEnvironment().decide_source
-    return f(dependency, target, prev_ni)
+    return f(dependency, target, prev_ni, repo_node)
 
-def default_decide_target(dependency, target, prev_ni):
+
+def default_decide_target(dependency, target, prev_ni, repo_node=None):
     f = SCons.Defaults.DefaultEnvironment().decide_target
-    return f(dependency, target, prev_ni)
+    return f(dependency, target, prev_ni, repo_node)
+
 
 def default_copy_from_cache(src, dst):
     f = SCons.Defaults.DefaultEnvironment().copy_from_cache
     return f(src, dst)
 
+
 class Base(SubstitutionEnvironment):
     """Base class for "real" construction Environments.  These are the
     primary objects used to communicate dependency and construction
@@ -1434,30 +1437,30 @@ class Base(SubstitutionEnvironment):
             _warn_copy_deprecated = False
         return self.Clone(*args, **kw)
 
-    def _changed_build(self, dependency, target, prev_ni):
-        if dependency.changed_state(target, prev_ni):
+    def _changed_build(self, dependency, target, prev_ni, repo_node=None):
+        if dependency.changed_state(target, prev_ni, repo_node):
             return 1
-        return self.decide_source(dependency, target, prev_ni)
+        return self.decide_source(dependency, target, prev_ni, repo_node)
 
-    def _changed_content(self, dependency, target, prev_ni):
-        return dependency.changed_content(target, prev_ni)
+    def _changed_content(self, dependency, target, prev_ni, repo_node=None):
+        return dependency.changed_content(target, prev_ni, repo_node)
 
-    def _changed_source(self, dependency, target, prev_ni):
+    def _changed_source(self, dependency, target, prev_ni, repo_node=None):
         target_env = dependency.get_build_env()
         type = target_env.get_tgt_sig_type()
         if type == 'source':
-            return target_env.decide_source(dependency, target, prev_ni)
+            return target_env.decide_source(dependency, target, prev_ni, repo_node)
         else:
-            return target_env.decide_target(dependency, target, prev_ni)
+            return target_env.decide_target(dependency, target, prev_ni, repo_node)
 
-    def _changed_timestamp_then_content(self, dependency, target, prev_ni):
-        return dependency.changed_timestamp_then_content(target, prev_ni)
+    def _changed_timestamp_then_content(self, dependency, target, prev_ni, repo_node=None):
+        return dependency.changed_timestamp_then_content(target, prev_ni, repo_node)
 
-    def _changed_timestamp_newer(self, dependency, target, prev_ni):
-        return dependency.changed_timestamp_newer(target, prev_ni)
+    def _changed_timestamp_newer(self, dependency, target, prev_ni, repo_node=None):
+        return dependency.changed_timestamp_newer(target, prev_ni, repo_node)
 
-    def _changed_timestamp_match(self, dependency, target, prev_ni):
-        return dependency.changed_timestamp_match(target, prev_ni)
+    def _changed_timestamp_match(self, dependency, target, prev_ni, repo_node=None):
+        return dependency.changed_timestamp_match(target, prev_ni, repo_node)
 
     def _copy_from_cache(self, src, dst):
         return self.fs.copy(src, dst)
@@ -2305,7 +2308,20 @@ class OverrideEnvironment(Base):
 
     # Methods that make this class act like a proxy.
     def __getattr__(self, name):
-        return getattr(self.__dict__['__subject'], name)
+        attr = getattr(self.__dict__['__subject'], name)
+        # Here we check if attr is one of the Wrapper classes. For
+        # example when a pseudo-builder is being called from an
+        # OverrideEnvironment.
+        #
+        # These wrappers when they're constructed capture the
+        # Environment they are being constructed with and so will not
+        # have access to overrided values. So we rebuild them with the
+        # OverrideEnvironment so they have access to overrided values.
+        if isinstance(attr, (MethodWrapper, BuilderWrapper)):
+            return attr.clone(self)
+        else:
+            return attr
+        
     def __setattr__(self, name, value):
         setattr(self.__dict__['__subject'], name, value)
 
diff --git a/src/engine/SCons/Environment.xml b/src/engine/SCons/Environment.xml
index 0982c31..1b0a04c 100644
--- a/src/engine/SCons/Environment.xml
+++ b/src/engine/SCons/Environment.xml
@@ -1213,6 +1213,17 @@ size, or content signature.
 </para>
 </listitem>
 </varlistentry>
+    <varlistentry>
+<term><parameter>repo_node</parameter></term>
+<listitem>
+<para>
+Use this node instead of the one specified by
+<varname>dependency</varname>
+    to determine if the dependency has changed.
+</para>
+</listitem>
+</varlistentry>
+
 </variablelist>
 </para>
 
@@ -1249,7 +1260,7 @@ Example:
 </para>
 
 <example_commands>
-def my_decider(dependency, target, prev_ni):
+def my_decider(dependency, target, prev_ni, repo_node=None):
     return not os.path.exists(str(target))
 
 env.Decider(my_decider)
diff --git a/src/engine/SCons/EnvironmentTests.py b/src/engine/SCons/EnvironmentTests.py
index 1a75a90..834cfd1 100644
--- a/src/engine/SCons/EnvironmentTests.py
+++ b/src/engine/SCons/EnvironmentTests.py
@@ -3587,6 +3587,10 @@ class OverrideEnvironmentTestCase(unittest.TestCase,TestEnvironmentFixture):
     def setUp(self):
         env = Environment()
         env._dict = {'XXX' : 'x', 'YYY' : 'y'}
+        def verify_value(env, key, value, *args, **kwargs):
+            """Verifies that key is value on the env this is called with."""
+            assert env[key] == value
+        env.AddMethod(verify_value)
         env2 = OverrideEnvironment(env, {'XXX' : 'x2'})
         env3 = OverrideEnvironment(env2, {'XXX' : 'x3', 'YYY' : 'y3', 'ZZZ' : 'z3'})
         self.envs = [ env, env2, env3 ]
@@ -3777,6 +3781,13 @@ class OverrideEnvironmentTestCase(unittest.TestCase,TestEnvironmentFixture):
     #    """Test the OverrideEnvironment WhereIs() method"""
     #    pass
 
+    def test_PseudoBuilderInherits(self):
+        """Test that pseudo-builders inherit the overrided values."""
+        env, env2, env3 = self.envs
+        env.verify_value('XXX', 'x')
+        env2.verify_value('XXX', 'x2')
+        env3.verify_value('XXX', 'x3')
+
     def test_Dir(self):
         """Test the OverrideEnvironment Dir() method"""
         env, env2, env3 = self.envs
diff --git a/src/engine/SCons/Node/FS.py b/src/engine/SCons/Node/FS.py
index 91d349d..33105fb 100644
--- a/src/engine/SCons/Node/FS.py
+++ b/src/engine/SCons/Node/FS.py
@@ -57,7 +57,6 @@ import SCons.Util
 import SCons.Warnings
 
 from SCons.Debug import Trace
-from . import DeciderNeedsNode
 
 print_duplicate = 0
 
@@ -2261,7 +2260,7 @@ class RootDir(Dir):
     this directory.
     """
 
-    __slots__ = ['_lookupDict']
+    __slots__ = ('_lookupDict', )
 
     def __init__(self, drive, fs):
         if SCons.Debug.track_instances: logInstanceCreation(self, 'Node.FS.RootDir')
@@ -2467,7 +2466,7 @@ class FileNodeInfo(SCons.Node.NodeInfoBase):
         """
         state = getattr(self, '__dict__', {}).copy()
         for obj in type(self).mro():
-            for name in getattr(obj,'__slots__',()):
+            for name in getattr(obj, '__slots__', ()):
                 if hasattr(self, name):
                     state[name] = getattr(self, name)
 
@@ -2511,7 +2510,7 @@ class FileBuildInfo(SCons.Node.BuildInfoBase):
                     or count of any of these could yield writing wrong csig, and then false positive
                     rebuilds
     """
-    __slots__ = ('dependency_map')
+    __slots__ = ['dependency_map', ]
     current_version_id = 2
 
     def __setattr__(self, key, value):
@@ -3283,14 +3282,14 @@ class File(Base):
             self._memo['changed'] = has_changed
         return has_changed
 
-    def changed_content(self, target, prev_ni):
+    def changed_content(self, target, prev_ni, repo_node=None):
         cur_csig = self.get_csig()
         try:
             return cur_csig != prev_ni.csig
         except AttributeError:
             return 1
 
-    def changed_state(self, target, prev_ni):
+    def changed_state(self, target, prev_ni, repo_node=None):
         return self.state != SCons.Node.up_to_date
 
 
@@ -3317,13 +3316,26 @@ class File(Base):
             len(binfo.bimplicitsigs)) == 0:
             return {}
 
-
-        # store this info so we can avoid regenerating it.
-        binfo.dependency_map = { str(child):signature for child, signature in zip(chain(binfo.bsources, binfo.bdepends, binfo.bimplicit),
+        binfo.dependency_map = { child:signature for child, signature in zip(chain(binfo.bsources, binfo.bdepends, binfo.bimplicit),
                                      chain(binfo.bsourcesigs, binfo.bdependsigs, binfo.bimplicitsigs))}
 
         return binfo.dependency_map
 
+    # @profile
+    def _add_strings_to_dependency_map(self, dmap):
+        """
+        In the case comparing node objects isn't sufficient, we'll add the strings for the nodes to the dependency map
+        :return:
+        """
+
+        first_string = str(next(iter(dmap)))
+
+        # print("DMAP:%s"%id(dmap))
+        if first_string not in dmap:
+                string_dict = {str(child): signature for child, signature in dmap.items()}
+                dmap.update(string_dict)
+        return dmap
+
     def _get_previous_signatures(self, dmap):
         """
         Return a list of corresponding csigs from previous
@@ -3342,37 +3354,62 @@ class File(Base):
         if len(dmap) == 0:
             if MD5_TIMESTAMP_DEBUG: print("Nothing dmap shortcutting")
             return None
+        elif MD5_TIMESTAMP_DEBUG: print("len(dmap):%d"%len(dmap))
+
 
-        if MD5_TIMESTAMP_DEBUG: print("len(dmap):%d"%len(dmap))
-        # First try the simple name for node
-        c_str = str(self)
-        if MD5_TIMESTAMP_DEBUG: print("Checking   :%s"%c_str)
-        df = dmap.get(c_str, None)
+        # First try retrieving via Node
+        if MD5_TIMESTAMP_DEBUG: print("Checking if self is in  map:%s id:%s type:%s"%(str(self), id(self), type(self)))
+        df = dmap.get(self, False)
         if df:
             return df
 
+        # Now check if self's repository file is in map.
+        rf = self.rfile()
+        if MD5_TIMESTAMP_DEBUG: print("Checking if self.rfile  is in  map:%s id:%s type:%s"%(str(rf), id(rf), type(rf)))
+        rfm = dmap.get(rf, False)
+        if rfm:
+            return rfm
+
+        # get default string for node and then also string swapping os.altsep for os.sep (/ for \)
+        c_strs = [str(self)]
+
         if os.altsep:
-            c_str = c_str.replace(os.sep, os.altsep)
-            df = dmap.get(c_str, None)
-            if MD5_TIMESTAMP_DEBUG: print("-->%s"%df)
+            c_strs.append(c_strs[0].replace(os.sep, os.altsep))
+
+        # In some cases the dependency_maps' keys are already strings check.
+        # Check if either string is now in dmap.
+        for s in c_strs:
+            if MD5_TIMESTAMP_DEBUG: print("Checking if str(self) is in map  :%s" % s)
+            df = dmap.get(s, False)
             if df:
                 return df
 
+        # Strings don't exist in map, add them and try again
+        # If there are no strings in this dmap, then add them.
+        # This may not be necessary, we could walk the nodes in the dmap and check each string
+        # rather than adding ALL the strings to dmap. In theory that would be n/2 vs 2n str() calls on node
+        # if not dmap.has_strings:
+        dmap = self._add_strings_to_dependency_map(dmap)
+
+        # In some cases the dependency_maps' keys are already strings check.
+        # Check if either string is now in dmap.
+        for s in c_strs:
+            if MD5_TIMESTAMP_DEBUG: print("Checking if str(self) is in map (now with strings)  :%s" % s)
+            df = dmap.get(s, False)
+            if df:
+                return df
+
+        # Lastly use nodes get_path() to generate string and see if that's in dmap
         if not df:
             try:
                 # this should yield a path which matches what's in the sconsign
                 c_str = self.get_path()
-                df = dmap.get(c_str, None)
-                if MD5_TIMESTAMP_DEBUG: print("-->%s"%df)
-                if df:
-                    return df
-
                 if os.altsep:
                     c_str = c_str.replace(os.sep, os.altsep)
-                    df = dmap.get(c_str, None)
-                    if MD5_TIMESTAMP_DEBUG: print("-->%s"%df)
-                    if df:
-                        return df
+
+                if MD5_TIMESTAMP_DEBUG: print("Checking if self.get_path is in map (now with strings)  :%s" % s)
+
+                df = dmap.get(c_str, None)
 
             except AttributeError as e:
                 raise FileBuildInfoFileToCsigMappingError("No mapping from file name to content signature for :%s"%c_str)
@@ -3392,16 +3429,12 @@ class File(Base):
             self - dependency
             target - target
             prev_ni - The NodeInfo object loaded from previous builds .sconsign
-            node - Node instance.  This is the only changed* function which requires
-                   node to function. So if we detect that it's not passed.
-                   we throw DeciderNeedsNode, and caller should handle this and pass node.
+            node - Node instance.  Check this node for file existence/timestamp
+                   if specified.
 
         Returns:
             Boolean - Indicates if node(File) has changed.
         """
-        if node is None:
-            # We need required node argument to get BuildInfo to function
-            raise DeciderNeedsNode(self.changed_timestamp_then_content)
 
         # Now get sconsign name -> csig map and then get proper prev_ni if possible
         bi = node.get_stored_info().binfo
@@ -3433,7 +3466,6 @@ class File(Base):
                 print("Mismatch self.changed_timestamp_match(%s, prev_ni) old:%s new:%s"%(str(target), old, new))
                 new_prev_ni = self._get_previous_signatures(dependency_map)
 
-
         if not new:
             try:
                 # NOTE: We're modifying the current node's csig in a query.
@@ -3443,13 +3475,13 @@ class File(Base):
             return False
         return self.changed_content(target, new_prev_ni)
 
-    def changed_timestamp_newer(self, target, prev_ni):
+    def changed_timestamp_newer(self, target, prev_ni, repo_node=None):
         try:
             return self.get_timestamp() > target.get_timestamp()
         except AttributeError:
             return 1
 
-    def changed_timestamp_match(self, target, prev_ni):
+    def changed_timestamp_match(self, target, prev_ni, repo_node=None):
         """
         Return True if the timestamps don't match or if there is no previous timestamp
         :param target:
@@ -3462,14 +3494,18 @@ class File(Base):
             return 1
 
     def is_up_to_date(self):
+        """Check for whether the Node is current
+           In all cases self is the target we're checking to see if it's up to date
+        """
+
         T = 0
         if T: Trace('is_up_to_date(%s):' % self)
         if not self.exists():
             if T: Trace(' not self.exists():')
-            # The file doesn't exist locally...
+            # The file (always a target) doesn't exist locally...
             r = self.rfile()
             if r != self:
-                # ...but there is one in a Repository...
+                # ...but there is one (always a target) in a Repository...
                 if not self.changed(r):
                     if T: Trace(' changed(%s):' % r)
                     # ...and it's even up-to-date...
diff --git a/src/engine/SCons/Node/__init__.py b/src/engine/SCons/Node/__init__.py
index aeb7092..3073d59 100644
--- a/src/engine/SCons/Node/__init__.py
+++ b/src/engine/SCons/Node/__init__.py
@@ -253,25 +253,10 @@ _target_from_source_map = {0 : target_from_source_none,
 # used by it.
 #
 
-
-class DeciderNeedsNode(Exception):
-    """
-    Indicate that the decider needs the node as well as the target and the dependency.
-    Normally the node and the target are the same, but in the case of repository
-    They may be different. Also the NodeInfo is retrieved from the node
-    """
-    def __init__(self, call_this_decider):
-        """
-        :param call_this_decider: to return the decider to call directly since deciders
-               are called through several levels of indirection
-        """
-        self.decider = call_this_decider
-
-
 #
 # First, the single decider functions
 #
-def changed_since_last_build_node(node, target, prev_ni):
+def changed_since_last_build_node(node, target, prev_ni, repo_node=None):
     """
 
     Must be overridden in a specific subclass to return True if this
@@ -292,7 +277,7 @@ def changed_since_last_build_node(node, target, prev_ni):
     raise NotImplementedError
 
 
-def changed_since_last_build_alias(node, target, prev_ni):
+def changed_since_last_build_alias(node, target, prev_ni, repo_node=None):
     cur_csig = node.get_csig()
     try:
         return cur_csig != prev_ni.csig
@@ -300,24 +285,24 @@ def changed_since_last_build_alias(node, target, prev_ni):
         return 1
 
 
-def changed_since_last_build_entry(node, target, prev_ni):
+def changed_since_last_build_entry(node, target, prev_ni, repo_node=None):
     node.disambiguate()
-    return _decider_map[node.changed_since_last_build](node, target, prev_ni)
+    return _decider_map[node.changed_since_last_build](node, target, prev_ni, repo_node)
 
 
-def changed_since_last_build_state_changed(node, target, prev_ni):
+def changed_since_last_build_state_changed(node, target, prev_ni, repo_node=None):
     return node.state != SCons.Node.up_to_date
 
 
-def decide_source(node, target, prev_ni):
-    return target.get_build_env().decide_source(node, target, prev_ni)
+def decide_source(node, target, prev_ni, repo_node=None):
+    return target.get_build_env().decide_source(node, target, prev_ni, repo_node)
 
 
-def decide_target(node, target, prev_ni):
-    return target.get_build_env().decide_target(node, target, prev_ni)
+def decide_target(node, target, prev_ni, repo_node=None):
+    return target.get_build_env().decide_target(node, target, prev_ni, repo_node)
 
 
-def changed_since_last_build_python(node, target, prev_ni):
+def changed_since_last_build_python(node, target, prev_ni, repo_node=None):
     cur_csig = node.get_csig()
     try:
         return cur_csig != prev_ni.csig
@@ -1505,17 +1490,11 @@ class Node(object, with_metaclass(NoSlotsPyPy)):
             result = True
 
         for child, prev_ni in zip(children, then):
-            try:
-                if _decider_map[child.changed_since_last_build](child, self, prev_ni):
-                    if t: Trace(': %s changed' % child)
-                    result = True
-            except DeciderNeedsNode as e:
-                if e.decider(self, prev_ni, node=node):
-                    if t: Trace(': %s changed' % child)
-                    result = True
+            if _decider_map[child.changed_since_last_build](child, self, prev_ni, node):
+                if t: Trace(': %s changed' % child)
+                result = True
 
         if self.has_builder():
-            import SCons.Util
             contents = self.get_executor().get_contents()
             newsig = SCons.Util.MD5signature(contents)
             if bi.bactsig != newsig:
diff --git a/src/engine/SCons/SConf.py b/src/engine/SCons/SConf.py
index 59afb40..71729c9 100644
--- a/src/engine/SCons/SConf.py
+++ b/src/engine/SCons/SConf.py
@@ -56,7 +56,6 @@ import SCons.Warnings
 import SCons.Conftest
 
 from SCons.Debug import Trace
-from SCons.Node import DeciderNeedsNode
 
 # Turn off the Conftest error logging
 SCons.Conftest.LogInputFiles = 0
@@ -407,12 +406,10 @@ class SConfBase(object):
             # that the correct .sconsign info will get calculated
             # and keep the build state consistent.
             def force_build(dependency, target, prev_ni,
-                            env_decider=env.decide_source,
-                            node=None):
+                            repo_node=None,
+                            env_decider=env.decide_source):
                 try:
-                    env_decider(dependency, target, prev_ni)
-                except DeciderNeedsNode as e:
-                    e.decider(target, prev_ni, node=target)
+                    env_decider(dependency, target, prev_ni, repo_node)
                 except Exception as e:
                     raise e
                 return True
diff --git a/src/engine/SCons/Tool/MSCommon/vc.py b/src/engine/SCons/Tool/MSCommon/vc.py
index d2a5573..0e4ef15 100644
--- a/src/engine/SCons/Tool/MSCommon/vc.py
+++ b/src/engine/SCons/Tool/MSCommon/vc.py
@@ -189,11 +189,19 @@ def get_host_target(env):
 
 # If you update this, update SupportedVSList in Tool/MSCommon/vs.py, and the
 # MSVC_VERSION documentation in Tool/msvc.xml.
-_VCVER = ["14.1", "14.0", "14.0Exp", "12.0", "12.0Exp", "11.0", "11.0Exp", "10.0", "10.0Exp", "9.0", "9.0Exp","8.0", "8.0Exp","7.1", "7.0", "6.0"]
+_VCVER = ["14.2", "14.1", "14.0", "14.0Exp", "12.0", "12.0Exp", "11.0", "11.0Exp", "10.0", "10.0Exp", "9.0", "9.0Exp","8.0", "8.0Exp","7.1", "7.0", "6.0"]
+
+# if using vswhere, a further mapping is needed
+_VCVER_TO_VSWHERE_VER = {
+    '14.2' : '[16.0, 17.0)',
+    '14.1' : '[15.0, 16.0)',
+}
 
 _VCVER_TO_PRODUCT_DIR = {
+    '14.2' : [
+        (SCons.Util.HKEY_LOCAL_MACHINE, r'')], # VS 2019 doesn't set this key
     '14.1' : [
-        (SCons.Util.HKEY_LOCAL_MACHINE, r'')], # Visual Studio 2017 doesn't set this registry key anymore
+        (SCons.Util.HKEY_LOCAL_MACHINE, r'')], # VS 2017 doesn't set this key
     '14.0' : [
         (SCons.Util.HKEY_LOCAL_MACHINE, r'Microsoft\VisualStudio\14.0\Setup\VC\ProductDir')],
     '14.0Exp' : [
@@ -254,42 +262,40 @@ def msvc_version_to_maj_min(msvc_version):
         raise ValueError("Unrecognized version %s (%s)" % (msvc_version,msvc_version_numeric))
 
 def is_host_target_supported(host_target, msvc_version):
-    """Check if the given (host, target) tuple is supported for given version.
-
-    Args:
-        host_target: tuple
-            tuple of (canonalized) host-targets, e.g. ("x86", "amd64")
-            for cross compilation from 32 bit Windows to 64 bits.
-        msvc_version: str
-            msvc version (major.minor, e.g. 10.0)
+    """Check if (host, target) pair is supported for a VC version.
 
-    Returns:
-        bool:
-
-    Note:
-        This only checks whether a given version *may* support the given (host,
+    :note: only checks whether a given version *may* support the given (host,
         target), not that the toolchain is actually present on the machine.
+    :param tuple host_target: canonalized host-targets pair, e.g.
+        ("x86", "amd64") for cross compilation from 32 bit Windows to 64 bits.
+    :param str msvc_version: Visual C++ version (major.minor), e.g. "10.0"
+    :returns: True or False
     """
     # We assume that any Visual Studio version supports x86 as a target
     if host_target[1] != "x86":
         maj, min = msvc_version_to_maj_min(msvc_version)
         if maj < 8:
             return False
-
     return True
 
 
 def find_vc_pdir_vswhere(msvc_version):
     """
-    Find the MSVC product directory using vswhere.exe.
+    Find the MSVC product directory using the vswhere program.
 
-    Run it asking for specified version and get MSVS  install location
-    :param msvc_version:
+    :param msvc_version: MSVC version to search for
     :return: MSVC install dir or None
+    :raises UnsupportedVersion: if the version is not known by this file
     """
 
+    try:
+        vswhere_version = _VCVER_TO_VSWHERE_VER[msvc_version]
+    except KeyError:
+        debug("Unknown version of MSVC: %s" % msvc_version)
+        raise UnsupportedVersion("Unknown version %s" % msvc_version)
+
     # For bug 3333 - support default location of vswhere for both 64 and 32 bit windows
-    # installs. 
+    # installs.
     for pf in ['Program Files (x86)', 'Program Files']:
         vswhere_path = os.path.join(
             'C:\\',
@@ -301,31 +307,36 @@ def find_vc_pdir_vswhere(msvc_version):
         if os.path.exists(vswhere_path):
             # If we found vswhere, then use it.
             break
+    else:
+        # No vswhere on system, no install info available
+        return None
 
-    vswhere_cmd = [vswhere_path, '-products', '*', '-version', msvc_version, '-property', 'installationPath']
-
-    if os.path.exists(vswhere_path):
-        #TODO PY27 cannot use Popen as context manager
-        # try putting it back to the old way for now
-        sp = subprocess.Popen(vswhere_cmd,
-                              stdout=subprocess.PIPE,
-                              stderr=subprocess.PIPE)
-        vsdir, err = sp.communicate()
-        if vsdir:
-            vsdir = vsdir.decode("mbcs").splitlines()
-            # vswhere could easily return multiple lines
-            # we could define a way to pick the one we prefer, but since
-            # this data is currently only used to make a check for existence,
-            # returning the first hit should be good enough for now.
-            vc_pdir = os.path.join(vsdir[0], 'VC')
-            return vc_pdir
+    vswhere_cmd = [vswhere_path,
+                   '-products', '*',
+                   '-version', vswhere_version,
+                   '-property', 'installationPath']
+
+    #TODO PY27 cannot use Popen as context manager
+    # try putting it back to the old way for now
+    sp = subprocess.Popen(vswhere_cmd,
+                          stdout=subprocess.PIPE,
+                          stderr=subprocess.PIPE)
+    vsdir, err = sp.communicate()
+    if vsdir:
+        vsdir = vsdir.decode("mbcs").splitlines()
+        # vswhere could easily return multiple lines
+        # we could define a way to pick the one we prefer, but since
+        # this data is currently only used to make a check for existence,
+        # returning the first hit should be good enough for now.
+        vc_pdir = os.path.join(vsdir[0], 'VC')
+        return vc_pdir
     else:
         # No vswhere on system, no install info available
         return None
 
 
 def find_vc_pdir(msvc_version):
-    """Find the product directory for the given version.
+    """Find the MSVC product directory for the given version.
 
     Tries to look up the path using a registry key from the table
     _VCVER_TO_PRODUCT_DIR; if there is no key, calls find_vc_pdir_wshere
@@ -462,7 +473,7 @@ def _check_cl_exists_in_vc_dir(env, vc_dir, msvc_version):
     host_platform = _ARCH_TO_CANONICAL[host_platform]
     target_platform = _ARCH_TO_CANONICAL[target_platform]
 
-    debug('_check_cl_exists_in_vc_dir(): host platform %s, target platform %s' % (host_platform, target_platform))
+    debug('_check_cl_exists_in_vc_dir(): host platform %s, target platform %s for version %s' % (host_platform, target_platform, msvc_version))
 
     ver_num = float(get_msvc_version_numeric(msvc_version))
 
@@ -510,7 +521,7 @@ def _check_cl_exists_in_vc_dir(env, vc_dir, msvc_version):
             # older versions of visual studio only had x86 binaries,
             # so if the host platform is amd64, we need to check cross
             # compile options (x86 binary compiles some other target on a 64 bit os)
-        
+
             # Set default value to be -1 as "" which is the value for x86/x86 yields true when tested
             # if not host_trgt_dir
             host_trgt_dir = _HOST_TARGET_TO_CL_DIR.get(('x86', target_platform), None)
diff --git a/src/engine/SCons/Tool/MSCommon/vs.py b/src/engine/SCons/Tool/MSCommon/vs.py
index 598b5e6..dfca48d 100644
--- a/src/engine/SCons/Tool/MSCommon/vs.py
+++ b/src/engine/SCons/Tool/MSCommon/vs.py
@@ -198,6 +198,17 @@ class VisualStudio(object):
 # Tool/MSCommon/vc.py, and the MSVC_VERSION documentation in Tool/msvc.xml.
 
 SupportedVSList = [
+    # Visual Studio 2019
+    VisualStudio('14.2',
+                 vc_version='14.2',
+                 sdk_version='10.0A',
+                 hkeys=[],
+                 common_tools_var='VS160COMNTOOLS',
+                 executable_path=r'Common7\IDE\devenv.com',
+                 batch_file_path=r'VC\Auxiliary\Build\vsvars32.bat',
+                 supported_arch=['x86', 'amd64', "arm"],
+                 ),
+
     # Visual Studio 2017
     VisualStudio('14.1',
                  vc_version='14.1',
diff --git a/src/engine/SCons/Tool/msvc.xml b/src/engine/SCons/Tool/msvc.xml
index dacdcba..ff65364 100644
--- a/src/engine/SCons/Tool/msvc.xml
+++ b/src/engine/SCons/Tool/msvc.xml
@@ -353,6 +353,7 @@ constructor; setting it later has no effect.
 
 <para>
 Valid values for Windows are
+<literal>14.2</literal>,
 <literal>14.1</literal>,
 <literal>14.0</literal>,
 <literal>14.0Exp</literal>,