From a883424d0d7e5212040ef30df5fa00818e1a2c0e Mon Sep 17 00:00:00 2001
From: Dominik Picheta <dominikpicheta@gmail.com>
Date: Sun, 9 Apr 2017 11:49:50 +0200
Subject: [PATCH] Implements else branch for JSON unmarshalling of object
 variants.

---
 lib/pure/json.nim           | 87 +++++++++++++++++++++++++++++--------
 tests/stdlib/tjsonmacro.nim | 38 +++++++++++++++-
 2 files changed, 106 insertions(+), 19 deletions(-)

diff --git a/lib/pure/json.nim b/lib/pure/json.nim
index 752501465f..356f15fa53 100644
--- a/lib/pure/json.nim
+++ b/lib/pure/json.nim
@@ -1303,8 +1303,14 @@ template verifyJsonKind(node: JsonNode, kinds: set[JsonNodeKind],
     raise newException(JsonKindError, msg)
 
 proc getEnum(node: JsonNode, ast: string, T: typedesc): T =
-  verifyJsonKind(node, {JString}, ast)
-  return parseEnum[T](node.getStr())
+  when T is SomeInteger:
+    # TODO: I shouldn't need this proc.
+    proc convert[T](x: BiggestInt): T = T(x)
+    verifyJsonKind(node, {JInt}, ast)
+    return convert[T](node.getNum())
+  else:
+    verifyJsonKind(node, {JString}, ast)
+    return parseEnum[T](node.getStr())
 
 proc toIdentNode(typeNode: NimNode): NimNode =
   ## Converts a Sym type node (returned by getType et al.) into an
@@ -1322,26 +1328,32 @@ proc toIdentNode(typeNode: NimNode): NimNode =
   else:
     assert false, "Cannot convert typeNode to an ident node: " & $typeNode.kind
 
-proc createIfStmtForOf(ofBranch, jsonNode, kindType,
-                       value: NimNode): NimNode {.compileTime.} =
-  ## Transforms a case of branch into an if statement to be placed as the
-  ## ExprColonExpr body expr.
-  expectKind(ofBranch, nnkOfBranch)
-
+proc createGetEnumCall(jsonNode, kindType: NimNode): NimNode =
   # -> getEnum(`jsonNode`, `kindType`)
   let getEnumSym = bindSym("getEnum")
   let astStrLit = toStrLit(jsonNode)
   let getEnumCall = newCall(getEnumSym, jsonNode, astStrLit, kindType)
+  return getEnumCall
 
-  var cond = newEmptyNode()
+proc createOfBranchCond(ofBranch, getEnumCall: NimNode): NimNode =
+  var cond = newIdentNode("false")
   for ofCond in ofBranch:
     if ofCond.kind == nnkRecList:
       break
 
-    if cond.kind == nnkEmpty:
-      cond = infix(getEnumCall, "==", ofCond)
-    else:
-      cond = infix(cond, "or", infix(getEnumCall, "==", ofCond))
+    let comparison = infix(getEnumCall, "==", ofCond)
+    cond = infix(cond, "or", comparison)
+
+  return cond
+
+proc createIfStmtForOf(ofBranch, jsonNode, kindType,
+                       value: NimNode): NimNode {.compileTime.} =
+  ## Transforms a case ``of`` branch into an if statement to be placed as the
+  ## ExprColonExpr body expr.
+  expectKind(ofBranch, nnkOfBranch)
+
+  let getEnumCall = createGetEnumCall(jsonNode, kindType)
+  let cond = createOfBranchCond(ofBranch, getEnumCall)
 
   return newIfStmt(
     (cond, value)
@@ -1378,6 +1390,43 @@ proc processOfBranch(ofBranch, jsonNode, kindType,
       let ifStmt = createIfStmtForOf(ofBranch, kindJsonNode, kindType, objField[1])
       exprColonExpr.add(ifStmt)
 
+proc processElseBranch(recCaseNode, elseBranch, jsonNode, kindType,
+                       kindJsonNode: NimNode): seq[NimNode] {.compileTime.} =
+  ## Processes each field inside of a variant object's ``else`` branch.
+  ##
+  ## ..code-block::plain
+  ##   Else
+  ##     RecList
+  ##       Sym "other"
+  result = @[]
+  # TODO: Remove duplication between processOfBranch
+  let getEnumCall = createGetEnumCall(kindJsonNode, kindType)
+
+  # We need to build up a list of conditions from each ``of`` branch so that
+  # we can then negate it to get ``else``.
+  var cond = newIdentNode("false")
+  for i in 1 .. <len(recCaseNode):
+    if recCaseNode[i].kind == nnkElse:
+      break
+
+    cond = infix(cond, "or", createOfBranchCond(recCaseNode[i], getEnumCall))
+
+  # Negate the condition.
+  cond = prefix(cond, "not")
+
+  for branchField in elseBranch[^1]:
+    let objFields = processObjField(branchField, jsonNode)
+
+    for objField in objFields:
+      let exprColonExpr = newNimNode(nnkExprColonExpr)
+      result.add(exprColonExpr)
+      # Add the name of the field.
+      exprColonExpr.add(toIdentNode(objField[0]))
+
+      # Add the value of the field.
+      let ifStmt = newIfStmt((cond, objField[1]))
+      exprColonExpr.add(ifStmt)
+
 proc processObjField(field, jsonNode: NimNode): seq[NimNode] =
   ## Process a field from a ``RecList``.
   ##
@@ -1418,9 +1467,13 @@ proc processObjField(field, jsonNode: NimNode): seq[NimNode] =
 
     # Iterate through each `of` branch.
     for i in 1 .. <field.len:
-      expectKind(field[i], nnkOfBranch)
-
-      result.add processOfBranch(field[i], jsonNode, kindType, kindJsonNode)
+      case field[i].kind
+      of nnkOfBranch:
+        result.add processOfBranch(field[i], jsonNode, kindType, kindJsonNode)
+      of nnkElse:
+        result.add processElseBranch(field, field[i], jsonNode, kindType, kindJsonNode)
+      else:
+        assert false, "Expected OfBranch or Else node kinds, got: " & $field[i].kind
   else:
     assert false, "Unable to process object field: " & $field.kind
 
@@ -1593,7 +1646,7 @@ proc postProcess(node: NimNode): NimNode =
 
   # Create the type.
   # -> var res = Object()
-  var resIdent = newIdentNode("res")
+  var resIdent = genSym(nskVar, "res")
   # TODO: Placing `node[0]` inside quote is buggy
   var resType = toIdentNode(node[0])
 
diff --git a/tests/stdlib/tjsonmacro.nim b/tests/stdlib/tjsonmacro.nim
index f0f0e6b567..b5d73240eb 100644
--- a/tests/stdlib/tjsonmacro.nim
+++ b/tests/stdlib/tjsonmacro.nim
@@ -55,8 +55,42 @@ when isMainModule:
   doAssert y.test3
   doAssert y.testNil.isNil
 
-  # TODO: Test for custom object variants (without an enum).
-  # TODO: Test for object variant with an else branch.
+  # Test for custom object variants (without an enum) and with an else branch.
+  block:
+    type
+      TestVariant = object
+        name: string
+        case age: uint8
+        of 2:
+          preSchool: string
+        of 8:
+          primarySchool: string
+        else:
+          other: int
+
+    var node = %{
+      "name": %"Nim",
+      "age": %8,
+      "primarySchool": %"Sandtown"
+    }
+
+    var result = to(node, TestVariant)
+    doAssert result.age == 8
+    doAssert result.name == "Nim"
+    doAssert result.primarySchool == "Sandtown"
+
+    node = %{
+      "name": %"⚔️Foo☢️",
+      "age": %25,
+      "other": %98
+    }
+
+    result = to(node, TestVariant)
+    doAssert result.name == node["name"].getStr()
+    doAssert result.age == node["age"].getNum().uint8
+    doAssert result.other == node["other"].getNum()
+
+  # TODO: Test object variant with set in of branch.
 
   # Tests that verify the error messages for invalid data.
   block: