results.? compatibity

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

Author: arnetheduck

chronos.nimble

@@ -8,7 +8,7 @@ license       = "MIT or Apache License 2.0"
 skipDirs      = @["tests"]
 
 requires "nim >= 1.2.0",
-         "stew",
+         "stew#assign-result",
          "bearssl",
          "httputils",
          "unittest2"

chronos/asyncmacro2.nim

@@ -156,6 +156,13 @@ proc asyncSingleProc(prc: NimNode): NimNode {.compileTime.} =
 
       procBody = prc.body.processBody(castFutureSym, baseType)
 
+      # Support `let x = ? await ...`
+      assignResultSym = ident "assignResult?"
+      assignResult = quote do:
+        when declared(Result):
+          template `assignResultSym`(v: Result) {.used.} =
+            complete(`castFutureSym`, v)
+
     # don't do anything with forward bodies (empty)
     if procBody.kind != nnkEmpty:
       let
@@ -185,7 +192,7 @@ proc asyncSingleProc(prc: NimNode): NimNode {.compileTime.} =
 
         completeDecl = completeWithNode(castFutureSym, baseType, procBodyBlck)
 
-        closureBody = newStmtList(resultDecl, completeDecl)
+        closureBody = newStmtList(assignResult, resultDecl, completeDecl)
 
         internalFutureParameter = nnkIdentDefs.newTree(
           internalFutureSym, newIdentNode("FutureBase"), newEmptyNode())

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
@@ -226,3 +240,18 @@ suite "Closure iterator's exception transformation issues":
 
     waitFor(x())
 
+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