old superseded fix for #10343 D20200623T225224

compiler/cgen.nim

@@ -1374,11 +1374,13 @@ proc genMainProc(m: BModule) =
       "}$N$N"
 
     NimMainProc =
+      # "void wrapNimMain(void (*fun_ptr)());$N" &
       "N_CDECL(void, NimMain)(void) {$N" &
         "\tvoid (*volatile inner)(void);$N" &
         "$4" &
         "\tinner = NimMainInner;$N" &
         "$2" &
+        # "\twrapNimMain(*inner);$N" &
         "\t(*inner)();$N" &
       "}$N$N"
 

lib/system.nim

@@ -54,7 +54,6 @@ type
 
 include "system/basic_types"
 
-
 proc compileOption*(option: string): bool {.
   magic: "CompileOption", noSideEffect.}
   ## Can be used to determine an `on|off` compile-time option. Example:
@@ -3026,7 +3025,6 @@ when defined(genode):
         # Perform application initialization
         # and return to thread entrypoint.
 
-
 import system/widestrs
 export widestrs
 

lib/system/ansi_c.nim

@@ -158,5 +158,6 @@ proc rawWrite*(f: CFilePtr, s: cstring) {.compilerproc, nonReloadable, inline.}
   # we cannot throw an exception here!
   discard c_fwrite(s, 1, cast[csize_t](s.len), f)
   discard c_fflush(f)
+  # todo: same treatment as D20190117T013551 in case `c_fwrite` fails
 
 {.pop.}

lib/system/excpt.nim

@@ -569,10 +569,12 @@ when defined(cpp) and appType != "lib" and not gotoBasedExceptions and
   proc setTerminate(handler: proc() {.noconv.})
     {.importc: "std::set_terminate", header: "<exception>".}
 
+
   setTerminate proc() {.noconv.} =
     # Remove ourself as a handler, reinstalling the default handler.
     setTerminate(nil)
 
+
     var msg = "Unknown error in unexpected exception handler"
     try:
       {.emit: "#if !defined(_MSC_VER) || (_MSC_VER >= 1923)".}
@@ -594,8 +596,8 @@ when defined(cpp) and appType != "lib" and not gotoBasedExceptions and
       # stderr not available by default, use the LOG session
       echo msg
     else:
-      writeToStdErr msg & "\n"
-
+      proc writeToStdErrRobust(msg: string) {.importc.}
+      writeToStdErrRobust msg & "\n"
     quit 1
 
 when not defined(noSignalHandler) and not defined(useNimRtl):

lib/system/io.nim

@@ -850,3 +850,65 @@ iterator lines*(f: File): TaintedString {.tags: [ReadIOEffect].} =
   ##       result.lines += 1
   var res = TaintedString(newStringOfCap(80))
   while f.readLine(res): yield res
+
+when defined(cpp):
+  {.emit:"""
+NIM_EXTERNC int fd_is_valid(int fd) {
+ return fcntl(fd, F_GETFD) != -1 || errno != EBADF;
+}
+""".}
+
+# NIM_EXP
+when false:
+# proc wrapNimMain(fun: proc(){.cdecl.}) {.exportc.} =
+ proc wrapNimMain(fun: proc(){.cdecl.}) {.exportc, compilerproc.} =
+# proc wrapNimMain(fun: proc(){.cdecl.}) {.compilerproc.} =
+  ## used to catch un-caught exceptions instead of falling through
+  ## `std::terminate`, for example allows to fix #10343
+  # Seems simpler than `std::set_terminate` alternatives.
+  fun()
+  when defined(cpp):
+    proc fd_is_valid(fd:cint): cint {.cdecl, importc.}
+    try:
+      fun()
+    except Exception as e:
+      let file = when defined(genode):
+        # stderr not available by default, use the LOG session
+        stdout
+      else: stderr
+
+      # using `c_feof(file)` doesn't work
+      let fd = c_fileno(file)
+      if fd_is_valid(fd) != 0.cint:
+        let ex = getCurrentException()
+        let trace = ex.getStackTrace()
+        let msg = trace & "Error: unhandled exception: " & ex.msg &
+          " [" & $ex.name & "]\n"
+        file.write msg
+        # stderr.write "uncaught exception:" & e.msg
+      else:
+        # note(D20190117T013551):
+        # write to a logfile ($pid.log) if `--logerrorDir:mydir` is passed
+        discard
+      quit(1)
+  else:
+    fun()
+
+when not defined(nimscript):
+  {.emit:"""
+    NIM_EXTERNC bool fileDescriptorIsValid(int fd) {
+     return fcntl(fd, F_GETFD) != -1 || errno != EBADF;
+    }
+    """.}
+
+  proc fileDescriptorIsValid(fd:cint): bool {.cdecl, importc.}
+
+  proc writeToStdErrRobust(msg: string) {.exportc.} =
+    # using `c_feof(stderr)` doesn't give usable answer
+    let fd = c_fileno(stderr)
+    if fileDescriptorIsValid(fd):
+      stderr.write msg
+    else:
+      # note(D20190117T013551):
+      # write to a logfile ($pid.log) if `--logerrorDir:mydir` is passed
+      discard

tests/exception/t9657.nim

@@ -1,11 +1,15 @@
 discard """
   action: run
   exitcode: 1
-  target: "c"
+  targets: "c cpp"
   disabled: "openbsd"
   disabled: "netbsd"
 """
-# todo: remove `target: "c"` workaround once #10343 is properly fixed
+
 close stdmsg
-const m = "exception!"
-discard writeBuffer(stdmsg, cstring(m), m.len)
+writeLine stdmsg, "exception!"
+
+when false:
+  # was there a 2nd issue/subtelty here?
+  const m = "exception!"
+  discard writeBuffer(stdmsg, cstring(m), m.len)