better nativestacktrace support; refs #15284; backport [1.2] (#15384)

* nimStackTraceOverride: enable stack traces in exceptions

This is a two-step stack trace collection scheme, because re-raised
exceptions will collect multiple stack traces but use them rarely, when
printing info about an uncaught exception, so it makes sense to only do
the cheap stack unwinding all the time and the relatively expensive
debugging information collection on-demand.

`asyncfutures` implements its own `$` proc for printing
`seq[StackTraceEntry]`, so we have to add the debugging info there, just
like we do for the private `$` proc in `system/excpt`.

* cleaned up PR #15284

Co-authored-by: Ștefan Talpalaru <stefantalpalaru@yahoo.com>

lib/system/excpt.nim

@@ -11,6 +11,7 @@
 # use the heap (and nor exceptions) do not include the GC or memory allocator.
 
 import std/private/miscdollars
+import stacktraces
 
 var
   errorMessageWriter*: (proc(msg: string) {.tags: [WriteIOEffect], benign,
@@ -137,20 +138,6 @@ const
   hasSomeStackTrace = NimStackTrace or defined(nimStackTraceOverride) or
     (defined(nativeStackTrace) and nativeStackTraceSupported)
 
-when defined(nimStackTraceOverride):
-  type StackTraceOverrideProc* = proc (): string {.nimcall, noinline, benign, raises: [], tags: [].}
-    ## Procedure type for overriding the default stack trace.
-
-  var stackTraceOverrideGetTraceback: StackTraceOverrideProc = proc(): string {.noinline.} =
-    result = "Stack trace override procedure not registered.\n"
-
-  proc registerStackTraceOverride*(overrideProc: StackTraceOverrideProc) =
-    ## Override the default stack trace inside rawWriteStackTrace() with your
-    ## own procedure.
-    stackTraceOverrideGetTraceback = overrideProc
-
-  proc auxWriteStackTraceWithOverride(s: var string) =
-    add(s, stackTraceOverrideGetTraceback())
 
 when defined(nativeStacktrace) and nativeStackTraceSupported:
   type
@@ -168,13 +155,13 @@ when defined(nativeStacktrace) and nativeStackTraceSupported:
 
   when not hasThreadSupport:
     var
-      tempAddresses: array[0..127, pointer] # should not be alloc'd on stack
+      tempAddresses: array[maxStackTraceLines, pointer] # should not be alloc'd on stack
       tempDlInfo: TDl_info
 
   proc auxWriteStackTraceWithBacktrace(s: var string) =
     when hasThreadSupport:
       var
-        tempAddresses: array[0..127, pointer] # but better than a threadvar
+        tempAddresses: array[maxStackTraceLines, pointer] # but better than a threadvar
         tempDlInfo: TDl_info
     # This is allowed to be expensive since it only happens during crashes
     # (but this way you don't need manual stack tracing)
@@ -202,11 +189,7 @@ when defined(nativeStacktrace) and nativeStackTraceSupported:
 
 when hasSomeStackTrace and not hasThreadSupport:
   var
-    tempFrames: array[0..127, PFrame] # should not be alloc'd on stack
-
-const
-  reraisedFromBegin = -10
-  reraisedFromEnd = -100
+    tempFrames: array[maxStackTraceLines, PFrame] # should not be alloc'd on stack
 
 template reraisedFrom(z): untyped =
   StackTraceEntry(procname: nil, line: z, filename: nil)
@@ -253,7 +236,12 @@ template addFrameEntry(s: var string, f: StackTraceEntry|PFrame) =
       for i in first..<f.frameMsgLen: add(s, frameMsgBuf[i])
   add(s, "\n")
 
-proc `$`(s: seq[StackTraceEntry]): string =
+proc `$`(stackTraceEntries: seq[StackTraceEntry]): string =
+  when defined(nimStackTraceOverride):
+    let s = addDebuggingInfo(stackTraceEntries)
+  else:
+    let s = stackTraceEntries
+
   result = newStringOfCap(2000)
   for i in 0 .. s.len-1:
     if s[i].line == reraisedFromBegin: result.add "[[reraised from:\n"
@@ -265,7 +253,7 @@ when hasSomeStackTrace:
   proc auxWriteStackTrace(f: PFrame, s: var string) =
     when hasThreadSupport:
       var
-        tempFrames: array[0..127, PFrame] # but better than a threadvar
+        tempFrames: array[maxStackTraceLines, PFrame] # but better than a threadvar
     const
       firstCalls = 32
     var
@@ -324,7 +312,9 @@ when hasSomeStackTrace:
       add(s, "No stack traceback available\n")
 
   proc rawWriteStackTrace(s: var seq[StackTraceEntry]) =
-    when NimStackTrace:
+    when defined(nimStackTraceOverride):
+      auxWriteStackTraceWithOverride(s)
+    elif NimStackTrace:
       auxWriteStackTrace(framePtr, s)
     else:
       s = @[]
@@ -468,7 +458,12 @@ proc raiseExceptionEx(e: sink(ref Exception), ename, procname, filename: cstring
   if e.name.isNil: e.name = ename
   when hasSomeStackTrace:
     when defined(nimStackTraceOverride):
-      e.trace = @[]
+      if e.trace.len == 0:
+        rawWriteStackTrace(e.trace)
+      else:
+        e.trace.add reraisedFrom(reraisedFromBegin)
+        auxWriteStackTraceWithOverride(e.trace)
+        e.trace.add reraisedFrom(reraisedFromEnd)
     elif NimStackTrace:
       if e.trace.len == 0:
         rawWriteStackTrace(e.trace)