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

@@ -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.
@@ -131,6 +132,13 @@ proc asyncSingleProc(prc: NimNode): NimNode {.compileTime.} =
         cast[`internalFutureType`](`internalFutureSym`)
       procBody = prc.body.processBody(castFutureSym, baseTypeIsVoid)
 
+      # Support `let x = ? await ...`
+      assignResultSym = ident "assignResult?"
+      assignResult = quote do:
+        when declared(Result):
+          template `assignResultSym`(v: Result) =
+            `castFutureSym`.complete(v)
+
     # don't do anything with forward bodies (empty)
     if procBody.kind != nnkEmpty:
       # fix #13899, `defer` should not escape its original scope
@@ -143,11 +151,12 @@ proc asyncSingleProc(prc: NimNode): NimNode {.compileTime.} =
           template result: auto {.used.} =
             {.fatal: "You should not reference the `result` variable inside" &
                     " a void async proc".}
+
         # -> complete(chronosInternalRetFuture)
         let complete =
           newCall(newIdentNode("complete"), castFutureSym)
 
-        newStmtList(resultTemplate, procBodyBlck, complete)
+        newStmtList(resultTemplate, assignResult, procBodyBlck, complete)
       else:
         # -> iterator nameIter(chronosInternalRetFuture: Future[T]): FutureBase {.closure.} =
         # ->   {.push warning[resultshadowed]: off.}
@@ -170,6 +179,8 @@ proc asyncSingleProc(prc: NimNode): NimNode {.compileTime.} =
           newNimNode(nnkPragma).add(
             newIdentNode("pop")),
 
+          assignResult,
+
           procBodyBlck,
 
           # -> complete(chronosInternalRetFuture, 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
@@ -156,3 +170,18 @@ 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