drnim: tiny progress (#13882)

* drnim: tiny progress
* refactoring complete
* drnim: prove .ensures annotations
* Moved code around to avoid code duplication
* drnim: first implementation of the 'old' property
* drnim: be precise about the assignment statement
* first implementation of --assumeUnique
* progress on forall/exists handling

compiler/trees.nim

@@ -169,3 +169,24 @@ proc flattenStmts*(n: PNode): PNode =
 proc extractRange*(k: TNodeKind, n: PNode, a, b: int): PNode =
   result = newNodeI(k, n.info, b-a+1)
   for i in 0..b-a: result[i] = n[i+a]
+
+proc isTrue*(n: PNode): bool =
+  n.kind == nkSym and n.sym.kind == skEnumField and n.sym.position != 0 or
+    n.kind == nkIntLit and n.intVal != 0
+
+proc getRoot*(n: PNode): PSym =
+  ## ``getRoot`` takes a *path* ``n``. A path is an lvalue expression
+  ## like ``obj.x[i].y``. The *root* of a path is the symbol that can be
+  ## determined as the owner; ``obj`` in the example.
+  case n.kind
+  of nkSym:
+    if n.sym.kind in {skVar, skResult, skTemp, skLet, skForVar, skParam}:
+      result = n.sym
+  of nkDotExpr, nkBracketExpr, nkHiddenDeref, nkDerefExpr,
+      nkObjUpConv, nkObjDownConv, nkCheckedFieldExpr:
+    result = getRoot(n[0])
+  of nkHiddenStdConv, nkHiddenSubConv, nkConv:
+    result = getRoot(n[1])
+  of nkCallKinds:
+    if getMagic(n) == mSlice: result = getRoot(n[1])
+  else: discard