[core] Add default relative paths to the command line variables

Add 2 default entries to the command line variables:
- `nodeCacheFolder`, which contains the location of the cache folder
- `nodeSourceCodeFolder`, which contains the location of the file
describing the node

meshroom/core/attribute.py

@@ -362,7 +362,14 @@ class Attribute(BaseObject):
         Return the value. If it is a string, expressions will be evaluated.
         '''
         if isinstance(self.value, str):
-            return Template(self.value).safe_substitute(os.environ)
+            substituted = Template(self.value).safe_substitute(os.environ)
+            try:
+                varResolved = substituted.format(**self.node._cmdVars)
+                return varResolved
+            except (KeyError, IndexError):
+                # Catch KeyErrors and IndexErros to be able to open files created prior to the support of
+                # relative variables (when self.node._cmdVars was not used to evaluate expressions in the attribute)
+                return substituted
         return self.value
 
     def getValueStr(self, withQuotes=True):

meshroom/core/node.py

@@ -758,6 +758,8 @@ class BaseNode(BaseObject):
 
         """ Generate command variables using input attributes and resolved output attributes names and values. """
         self._cmdVars["uid"] = self._uid
+        self._cmdVars["nodeCacheFolder"] = self.internalFolder
+        self._cmdVars["nodeSourceCodeFolder"] = self.sourceCodeFolder
 
         # Evaluate input params
         for name, attr in self._attributes.objects.items():
@@ -1022,8 +1024,10 @@ class BaseNode(BaseObject):
 
         # Update command variables / output attributes
         self._cmdVars = {
-            'cache': cacheDir or self.graph.cacheDir,
-            'nodeType': self.nodeType,
+            "cache": cacheDir or self.graph.cacheDir,
+            "nodeType": self.nodeType,
+            "nodeCacheFolder": self._internalFolder,
+            "nodeSourceCodeFolder": self.sourceCodeFolder
         }
         self._computeUid()
         self._buildCmdVars()
@@ -1445,7 +1449,7 @@ class Node(BaseNode):
 
         self.packageName = self.nodeDesc.packageName
         self.packageVersion = self.nodeDesc.packageVersion
-        self._internalFolder = self.nodeDesc.internalFolder
+        self._internalFolder = "{cache}/{nodeType}/{uid}"
         self._sourceCodeFolder = self.nodeDesc.sourceCodeFolder
 
         for attrDesc in self.nodeDesc.inputs: