1 files changed, 8 insertions, 5 deletions
diff --git a/lib/std/syncio.nim b/lib/std/syncio.nim
index b664c3b60..c34a025af 100644
--- a/lib/std/syncio.nim
+++ b/lib/std/syncio.nim
@@ -320,7 +320,7 @@ elif defined(windows):
 const
   BufSize = 4000
 
-proc close*(f: File) {.tags: [], gcsafe.} =
+proc close*(f: File) {.tags: [], gcsafe, sideEffect.} =
   ## Closes the file.
   if not f.isNil:
     discard c_fclose(f)
@@ -419,7 +419,7 @@ proc readLine*(f: File, line: var string): bool {.tags: [ReadIOEffect],
     if f.isatty:
       const numberOfCharsToRead = 2048
       var numberOfCharsRead = 0'i32
-      var buffer = newWideCString("", numberOfCharsToRead)
+      var buffer = newWideCString(numberOfCharsToRead)
       if readConsole(getOsFileHandle(f), addr(buffer[0]),
         numberOfCharsToRead, addr(numberOfCharsRead), nil) == 0:
         var error = getLastError()
@@ -648,6 +648,9 @@ const
         ""
     else:
       ""
+  RawFormatOpen: array[FileMode, cstring] = [
+    # used for open by FileHandle, which calls `fdopen`
+    cstring("rb"), "wb", "w+b", "r+b", "ab"]
   FormatOpen: array[FileMode, cstring] = [
     cstring("rb" & NoInheritFlag), "wb" & NoInheritFlag, "w+b" & NoInheritFlag,
     "r+b" & NoInheritFlag, "ab" & NoInheritFlag
@@ -749,7 +752,7 @@ proc open*(f: var File, filehandle: FileHandle,
         filehandle) else: filehandle
     if not setInheritable(oshandle, false):
       return false
-  f = c_fdopen(filehandle, FormatOpen[mode])
+  f = c_fdopen(filehandle, RawFormatOpen[mode])
   result = f != nil
 
 proc open*(filename: string,
@@ -763,7 +766,7 @@ proc open*(filename: string,
   if not open(result, filename, mode, bufSize):
     raise newException(IOError, "cannot open: " & filename)
 
-proc setFilePos*(f: File, pos: int64, relativeTo: FileSeekPos = fspSet) {.benign.} =
+proc setFilePos*(f: File, pos: int64, relativeTo: FileSeekPos = fspSet) {.benign, sideEffect.} =
   ## Sets the position of the file pointer that is used for read/write
   ## operations. The file's first byte has the index zero.
   if c_fseek(f, pos, cint(relativeTo)) != 0:
@@ -871,7 +874,7 @@ proc writeFile*(filename: string, content: openArray[byte]) {.since: (1, 1).} =
   var f: File = nil
   if open(f, filename, fmWrite):
     try:
-      f.writeBuffer(unsafeAddr content[0], content.len)
+      discard f.writeBuffer(unsafeAddr content[0], content.len)
     finally:
       close(f)
   else: