stacktraces can now show custom runtime msgs per frame (#13351)

* stacktraces can now show custom runtime msgs
* improve tests/stdlib/tstackframes.nim
* fix test for --gc:arc
* test --stacktraceMsgs:on and --stacktraceMsgs:off
* --stacktracemsgs:off by default

tests/assert/tassert_c.nim

@@ -36,4 +36,4 @@ try:
 except AssertionError:
   let e = getCurrentException()
   let trace = e.getStackTrace
-  echo tmatch(trace, expected)
+  if tmatch(trace, expected): echo true else: echo "wrong trace:\n" & trace

tests/stdlib/mstackframes.nim

@@ -0,0 +1,38 @@
+import std/stackframes
+
+
+
+# line 5
+var count = 0
+
+proc main1(n: int) =
+  setFrameMsg $("main1", n)
+  if n > 0:
+    main1(n-1)
+
+proc main2(n: int) =
+  count.inc
+  setFrameMsg $("main2", n, count)
+  proc bar() =
+    setFrameMsg $("bar ",)
+    if n < 3: raise newException(CatchableError, "on purpose")
+  bar()
+  main2(n-1)
+
+proc main() =
+  var z = 0
+  setFrameMsg "\n  z: " & $z, prefix = ""
+  # multiple calls inside a frame are possible
+  z.inc
+  setFrameMsg "\n  z: " & $z, prefix = ""
+  try:
+    main2(5)
+  except CatchableError:
+    main1(10) # goes deep and then unwinds; sanity check to ensure `setFrameMsg` from inside
+              # `main1` won't invalidate the stacktrace; if StackTraceEntry.frameMsg
+              # were a reference instead of a copy, this would fail.
+    let e = getCurrentException()
+    let trace = e.getStackTrace
+    echo trace
+
+main()

tests/stdlib/tstackframes.nim

@@ -0,0 +1,34 @@
+import std/[strformat,os,osproc]
+import "$nim/compiler/unittest_light" # works even if moved by megatest
+
+proc main(opt: string, expected: string) =
+  const nim = getCurrentCompilerExe()
+  const file = currentSourcePath().parentDir / "mstackframes.nim"
+  let cmd = fmt"{nim} c -r --excessiveStackTrace:off --stacktraceMsgs:{opt} --hints:off {file}"
+  let (output, exitCode) = execCmdEx(cmd)
+  assertEquals output, expected
+  doAssert exitCode == 0
+
+main("on"): """
+mstackframes.nim(38)     mstackframes
+mstackframes.nim(29)     main
+  z: 0
+  z: 1
+mstackframes.nim(20)     main2 ("main2", 5, 1)
+mstackframes.nim(20)     main2 ("main2", 4, 2)
+mstackframes.nim(20)     main2 ("main2", 3, 3)
+mstackframes.nim(19)     main2 ("main2", 2, 4)
+mstackframes.nim(18)     bar ("bar ",)
+
+"""
+
+main("off"): """
+mstackframes.nim(38)     mstackframes
+mstackframes.nim(29)     main
+mstackframes.nim(20)     main2
+mstackframes.nim(20)     main2
+mstackframes.nim(20)     main2
+mstackframes.nim(19)     main2
+mstackframes.nim(18)     bar
+
+"""