results.? compatibity

This PR uses the facilities provided in
status-im/nim-stew#134 to support `?` in `async`
proc's.

Author: arnetheduck

chronos/asyncmacro2.nim

@@ -7,7 +7,8 @@
 #    distribution, for details about the copyright.
 #
 
-import std/[macros]
+import
+  std/[macros]
 
 proc skipUntilStmtList(node: NimNode): NimNode {.compileTime.} =
   # Skips a nest of StmtList's.
@@ -17,7 +18,6 @@ proc skipUntilStmtList(node: NimNode): NimNode {.compileTime.} =
 
 proc processBody(node, retFutureSym: NimNode,
                  subTypeIsVoid: bool): NimNode {.compileTime.} =
-  #echo(node.treeRepr)
   result = node
   case node.kind
   of nnkReturnStmt:
@@ -147,6 +147,12 @@ proc asyncSingleProc(prc: NimNode): NimNode {.compileTime.} =
       # fix #13899, `defer` should not escape its original scope
       procBody = newStmtList(newTree(nnkBlockStmt, newEmptyNode(), procBody))
 
+      # Support `let x = ? await ...`
+      let ar = ident "assignResult?"
+      procBody.insert 0, quote do:
+        template `ar`(v: Result) =
+          `internalFutureSym`.complete(v)
+
       if not subtypeIsVoid:
         procBody.insert(0, newNimNode(nnkPragma).add(newIdentNode("push"),
           newNimNode(nnkExprColonExpr).add(newNimNode(nnkBracketExpr).add(
@@ -328,5 +334,5 @@ macro async*(prc: untyped): untyped =
       result.add asyncSingleProc(oneProc)
   else:
     result = asyncSingleProc(prc)
-  when chronosDumpAsync:
+  when true or chronosDumpAsync:
     echo repr result

tests/testmacro.nim

@@ -94,6 +94,20 @@ proc testAwaitne(): Future[bool] {.async.} =
 
   return true
 
+proc resultOk(): Future[Result[int, string]] {.async.} =
+  return ok(42)
+
+proc resultErr(): Future[Result[int, string]] {.async.} =
+  return err("string")
+
+proc testResult: Future[Result[int, string]] {.async.} =
+  let
+    x = ? await resultOk()
+
+  if x == 42:
+    let _ = ? await resultErr()
+  return err("not this one")
+
 suite "Macro transformations test suite":
   test "`await` command test":
     check waitFor(testAwait()) == true
@@ -139,3 +153,19 @@ suite "Closure iterator's exception transformation issues":
         answer.inc(10)
     waitFor(a())
     check answer == 42
+
+suite "Result integration":
+  test "question mark":
+    # generics are tricky and buggy, test them more!
+    proc someFunc2[T](v: T): Future[Result[T, string]] {.async.} =
+      return ok(v)
+    proc someFunc[T](v: T): Future[Result[T, string]] {.async.} =
+      let tmp = ? await someFunc2(v)
+      return ok(tmp + 2)
+
+    proc caller(v: int): Future[Result[int, string]] {.async.} =
+      return ok(3 + ? await someFunc(v))
+
+    check waitFor(testResult()).error() == "string"
+
+    check waitFor(caller(42))[] == 42 + 2 + 3