Merge branch 'devel' of github.com:nim-lang/Nim into devel

lib/pure/asyncfutures.nim

@@ -1,4 +1,4 @@
-import os, tables, strutils, times, heapqueue, options, deques
+import os, tables, strutils, times, heapqueue, options, deques, cstrutils
 
 # TODO: This shouldn't need to be included, but should ideally be exported.
 type
@@ -217,17 +217,78 @@ proc `callback=`*[T](future: Future[T],
   ## If future has already completed then ``cb`` will be called immediately.
   future.callback = proc () = cb(future)
 
-proc injectStacktrace[T](future: Future[T]) =
-  # TODO: Come up with something better.
-  when not defined(release):
-    var msg = ""
-    msg.add("\n  " & future.fromProc & "'s lead up to read of failed Future:")
+proc getHint(entry: StackTraceEntry): string =
+  ## We try to provide some hints about stack trace entries that the user
+  ## may not be familiar with, in particular calls inside the stdlib.
+  result = ""
+  if entry.procname == "processPendingCallbacks":
+    if cmpIgnoreStyle(entry.filename, "asyncdispatch.nim") == 0:
+      return "Executes pending callbacks"
+  elif entry.procname == "poll":
+    if cmpIgnoreStyle(entry.filename, "asyncdispatch.nim") == 0:
+      return "Processes asynchronous completion events"
 
-    if not future.errorStackTrace.isNil and future.errorStackTrace != "":
-      msg.add("\n" & indent(future.errorStackTrace.strip(), 4))
-    else:
-      msg.add("\n    Empty or nil stack trace.")
-    future.error.msg.add(msg)
+  if entry.procname.endsWith("_continue"):
+    if cmpIgnoreStyle(entry.filename, "asyncmacro.nim") == 0:
+      return "Resumes an async procedure"
+
+proc `$`*(entries: seq[StackTraceEntry]): string =
+  result = ""
+  # Find longest filename & line number combo for alignment purposes.
+  var longestLeft = 0
+  for entry in entries:
+    if entry.procName.isNil: continue
+
+    let left = $entry.filename & $entry.line
+    if left.len > longestLeft:
+      longestLeft = left.len
+
+  var indent = 2
+  # Format the entries.
+  for entry in entries:
+    if entry.procName.isNil:
+      if entry.line == -10:
+        result.add(spaces(indent) & "#[\n")
+        indent.inc(2)
+      else:
+        indent.dec(2)
+        result.add(spaces(indent)& "]#\n")
+      continue
+
+    let left = "$#($#)" % [$entry.filename, $entry.line]
+    result.add((spaces(indent) & "$#$# $#\n") % [
+      left,
+      spaces(longestLeft - left.len + 2),
+      $entry.procName
+    ])
+    let hint = getHint(entry)
+    if hint.len > 0:
+      result.add(spaces(indent+2) & "## " & hint & "\n")
+
+proc injectStacktrace[T](future: Future[T]) =
+  when not defined(release):
+    const header = "\nAsync traceback:\n"
+
+    var exceptionMsg = future.error.msg
+    if header in exceptionMsg:
+      # This is messy: extract the original exception message from the msg
+      # containing the async traceback.
+      let start = exceptionMsg.find(header)
+      exceptionMsg = exceptionMsg[0..<start]
+
+
+    var newMsg = exceptionMsg & header
+
+    let entries = getStackTraceEntries(future.error)
+    newMsg.add($entries)
+
+    newMsg.add("Exception message: " & exceptionMsg & "\n")
+    newMsg.add("Exception type:")
+
+    # # For debugging purposes
+    # for entry in getStackTraceEntries(future.error):
+    #   newMsg.add "\n" & $entry
+    future.error.msg = newMsg
 
 proc read*[T](future: Future[T] | FutureVar[T]): T =
   ## Retrieves the value of ``future``. Future must be finished otherwise

lib/pure/asyncmacro.nim

@@ -25,10 +25,10 @@ proc skipStmtList(node: NimNode): NimNode {.compileTime.} =
     result = node[0]
 
 template createCb(retFutureSym, iteratorNameSym,
-                  name, futureVarCompletions: untyped) =
+                  strName, identName, futureVarCompletions: untyped) =
   var nameIterVar = iteratorNameSym
   #{.push stackTrace: off.}
-  proc cb0 {.closure.} =
+  proc identName {.closure.} =
     try:
       if not nameIterVar.finished:
         var next = nameIterVar()
@@ -36,11 +36,11 @@ template createCb(retFutureSym, iteratorNameSym,
           if not retFutureSym.finished:
             let msg = "Async procedure ($1) yielded `nil`, are you await'ing a " &
                     "`nil` Future?"
-            raise newException(AssertionError, msg % name)
+            raise newException(AssertionError, msg % strName)
         else:
           {.gcsafe.}:
             {.push hint[ConvFromXtoItselfNotNeeded]: off.}
-            next.callback = (proc() {.closure, gcsafe.})(cb0)
+            next.callback = (proc() {.closure, gcsafe.})(identName)
             {.pop.}
     except:
       futureVarCompletions
@@ -52,7 +52,7 @@ template createCb(retFutureSym, iteratorNameSym,
       else:
         retFutureSym.fail(getCurrentException())
 
-  cb0()
+  identName()
   #{.pop.}
 proc generateExceptionCheck(futSym,
     tryStmt, rootReceiver, fromNode: NimNode): NimNode {.compileTime.} =
@@ -389,9 +389,12 @@ proc asyncSingleProc(prc: NimNode): NimNode {.compileTime.} =
     outerProcBody.add(closureIterator)
 
     # -> createCb(retFuture)
-    #var cbName = newIdentNode("cb")
+    # NOTE: The "_continue" suffix is checked for in asyncfutures.nim to produce
+    # friendlier stack traces:
+    var cbName = genSym(nskProc, prcName & "_continue")
     var procCb = getAst createCb(retFutureSym, iteratorNameSym,
                          newStrLitNode(prcName),
+                         cbName,
                          createFutureVarCompletions(futureVarIdents, nil))
     outerProcBody.add procCb