clean up the implementation of the new memfiles.resize

lib/pure/memfiles.nim

@@ -282,34 +282,34 @@ proc flush*(f: var MemFile; attempts: Natural = 3) =
       if lastErr != EBUSY.OSErrorCode:
         raiseOSError(lastErr, "error flushing mapping")
 
-proc resize*(f: var MemFile, newFileSize: int) =
-  ## resize and re-map the file underlying an ``allowRemap MemFile``.  NOTE:
-  ## this assumes the entire file is mapped read-write at offset zero.  Also,
-  ## the value of ``.mem`` will probably change.
-  when defined(windows):
-    discard #TODO This needs to be implemented.
-  else:
-    if f.handle == -1:
-      raise newException(IOError,
-                         "Cannot resize MemFile opened with allowRemap=false")
-    if ftruncate(f.handle, newFileSize) == -1:
-      raiseOSError(osLastError())
-    when defined(linux):                          #Maybe NetBSD, too?
-      #On Linux this can be over 100 times faster than a munmap,mmap cycle.
-      proc mremap(old: pointer; oldSize,newSize: csize; flags: cint): pointer {.
-        importc: "mremap", header: "<sys/mman.h>" .}
-      let newAddr = mremap(f.mem, csize(f.size), csize(newFileSize), cint(1))
-      if newAddr == cast[pointer](MAP_FAILED):
+when defined(posix) or defined(nimdoc):
+  proc resize*(f: var MemFile, newFileSize: int) {.raises: [IOError, OSError].} =
+    ## resize and re-map the file underlying an ``allowRemap MemFile``.
+    ## **Note**: this assumes the entire file is mapped read-write at offset zero.
+    ## Also, the value of ``.mem`` will probably change.
+    ## **Note**: This is not (yet) avaiable on Windows.
+    when defined(posix):
+      if f.handle == -1:
+        raise newException(IOError,
+                            "Cannot resize MemFile opened with allowRemap=false")
+      if ftruncate(f.handle, newFileSize) == -1:
         raiseOSError(osLastError())
-    else:
-      if munmap(f.mem, f.size) != 0:
-        raiseOSError(osLastError())
-      let newAddr = mmap(nil, newFileSize, PROT_READ or PROT_WRITE,
-                         MAP_SHARED or MAP_POPULATE, f.handle, 0)
-      if newAddr == cast[pointer](MAP_FAILED):
-        raiseOSError(osLastError())
-    f.mem = newAddr
-    f.size = newFileSize
+      when defined(linux):                          #Maybe NetBSD, too?
+        #On Linux this can be over 100 times faster than a munmap,mmap cycle.
+        proc mremap(old: pointer; oldSize,newSize: csize; flags: cint): pointer {.
+          importc: "mremap", header: "<sys/mman.h>" .}
+        let newAddr = mremap(f.mem, csize(f.size), csize(newFileSize), cint(1))
+        if newAddr == cast[pointer](MAP_FAILED):
+          raiseOSError(osLastError())
+      else:
+        if munmap(f.mem, f.size) != 0:
+          raiseOSError(osLastError())
+        let newAddr = mmap(nil, newFileSize, PROT_READ or PROT_WRITE,
+                            MAP_SHARED or MAP_POPULATE, f.handle, 0)
+        if newAddr == cast[pointer](MAP_FAILED):
+          raiseOSError(osLastError())
+      f.mem = newAddr
+      f.size = newFileSize
 
 proc close*(f: var MemFile) =
   ## closes the memory mapped file `f`. All changes are written back to the