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Implicit return working for async proc #20933

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merged 5 commits into from
Dec 9, 2022
Merged

Implicit return working for async proc #20933

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8ddc4c2
Implicit return working for asyncdispatch proc
ire4ever1190 Nov 26, 2022
1019c41
Test case
ire4ever1190 Nov 26, 2022
ba373b8
Test that return value is actually used
ire4ever1190 Nov 26, 2022
e2cf88a
Merge branch 'devel' into implicit-async-return
ire4ever1190 Nov 27, 2022
0357797
Update tests/async/t11558.nim
Araq Nov 28, 2022
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13 changes: 11 additions & 2 deletions lib/pure/asyncmacro.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -214,9 +214,18 @@ proc asyncSingleProc(prc: NimNode): NimNode =
# don't do anything with forward bodies (empty)
if procBody.kind != nnkEmpty:
# fix #13899, defer should not escape its original scope
procBody = newStmtList(newTree(nnkBlockStmt, newEmptyNode(), procBody))
procBody.add(createFutureVarCompletions(futureVarIdents, nil))
let blockStmt = newStmtList(newTree(nnkBlockStmt, newEmptyNode(), procBody))
procBody = newStmtList()
let resultIdent = ident"result"
procBody.add quote do:
template setResult(x: `subRetType`) {.used.} =
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We've considered a similar thing in chronos so that nim-result can work better - status-im/nim-chronos#297 - perhaps we should coordinate the mechanism here - one thing that often comes up is symbol resolution issues - ie template lookup scope is confusing / broken and has a tendency to ruin unrelated code when used together with generics: status-im/nim-stew#161 - as a consequence, we've started using more "unique" names, also for "private" templates like this.

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From reading those PR's I think this is a different problem to whats in them. This doesn't effect how its returned but just means that code like this can now compile and work (Doesn't effect how normal return and result = works)

# Not exactly a good async example, but just needed something basic
proc foo(x: int): Future[string] {.async.} =
  if x mod 2 == 0:
    "even"
  else:
    "odd"

But see what you mean about needing unique names. Maybe could make it very explicit like asyncDispatchSetResult?

# If the proc has implicit return then this will get called
`resultIdent` = x
template setResult(x: untyped) {.used.} =
# If the proc doesn't have implicit return then this will get called
x
procBody.add newCall(ident"setResult", blockStmt)
procBody.add(createFutureVarCompletions(futureVarIdents, nil))
procBody.insert(0): quote do:
{.push warning[resultshadowed]: off.}
when `subRetType` isnot void:
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13 changes: 13 additions & 0 deletions tests/async/t11558.nim
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
discard """
output: "Hello\n9"
"""
import std/asyncdispatch

proc foo(): Future[string] {.async.} =
"Hello"

proc bar(): Future[int] {.async.} =
result = 9

echo waitFor foo()
echo waitFor bar()