Merge pull request #4314 from abudden/2146-unbuffered-io

Added setStdIoUnbuffered for unbuffered stdio (fixes #2146).

lib/system.nim

@@ -2715,6 +2715,9 @@ when not defined(JS): #and not defined(nimscript):
       ##
       ## Default mode is readonly. Returns true iff the file could be reopened.
 
+    proc setStdIoUnbuffered*() {.tags: [], benign.}
+      ## Configures `stdin`, `stdout` and `stderr` to be unbuffered.
+
     proc close*(f: File) {.tags: [].}
       ## Closes the file.
 

lib/system/sysio.nim

@@ -369,4 +369,12 @@ proc writeFile(filename, content: string) =
   else:
     sysFatal(IOError, "cannot open: ", filename)
 
+proc setStdIoUnbuffered() =
+  when declared(stdout):
+    discard c_setvbuf(stdout, nil, IONBF, 0)
+  when declared(stderr):
+    discard c_setvbuf(stderr, nil, IONBF, 0)
+  when declared(stdin):
+    discard c_setvbuf(stdin, nil, IONBF, 0)
+
 {.pop.}

web/news/version_0_15_released.rst

@@ -16,6 +16,7 @@ Library Additions
 
 - Added ``readHeaderRow`` and ``rowEntry`` to ``parsecsv.nim`` to provide
   a lightweight alternative to python's ``csv.DictReader``.
+- Added ``setStdIoUnbuffered`` proc to ``system.nim`` to enable unbuffered I/O.
 
 Compiler Additions
 ------------------