varpartitions: add support for if/try/case paths

This commit adds basic support for paths in conditional cases.
Conditionals are considered valid paths when all branches of
execution that does not terminate execution yields the same
path.

compiler/sem/varpartitions.nim

@@ -362,6 +362,40 @@ proc pathExpr(node: PNode; owner: PSym): PNode =
           break
       else:
         break
+    of nkElifExpr, nkElifBranch, nkElseExpr, nkElse, nkExceptBranch, nkOfBranch:
+      n = n.lastSon
+    of nkIfExpr, nkIfStmt, nkTryStmt, nkCaseStmt:
+      block samePathCheck:
+        let firstExpr =
+          case n.kind
+          of nkTryStmt:
+            n[0] # First element is try body
+          of nkCaseStmt:
+            n[1].lastSon # First branch is the second element
+          else:
+            n[0].lastSon
+        let firstValidPath = pathExpr(firstExpr, owner)
+        # The first expression should be a valid path
+        if firstValidPath == nil:
+          break samePathCheck
+
+        let remainderStart = if n.kind == nkCaseStmt: 2 else: 1
+        for idx in remainderStart ..< n.len:
+          # Only check branches with a type, as no types implies noreturn for
+          # expressions
+          if not n[idx].lastSon.typ.isEmptyType():
+            # If the first path is not a symbol, then we currently can't check
+            # if other paths points to the same resource, so bail.
+            if firstValidPath.kind != nkSym:
+              break samePathCheck
+
+            let path = pathExpr(n[idx], owner)
+            if path.kind != nkSym or path.sym.itemId != firstValidPath.sym.itemId:
+              break samePathCheck
+
+        result = firstValidPath
+
+      break
     else:
       break
   # borrowFromConstExpr(n) is correct here because we need 'node'