Fix warning when assing size_t type value to uv_buf_t.len, convert type to ULONG on Windows.

src/nvim/event/rstream.c

@@ -95,7 +95,7 @@ static void alloc_cb(uv_handle_t *handle, size_t suggested, uv_buf_t *buf)
   // `uv_buf_t.len` happens to have different size on Windows.
   size_t write_count;
   buf->base = rbuffer_write_ptr(stream->buffer, &write_count);
-  buf->len = write_count;
+  buf->len = UV_BUF_LEN(write_count);
 }
 
 // Callback invoked by libuv after it copies the data into the buffer provided
@@ -146,7 +146,7 @@ static void fread_idle_cb(uv_idle_t *handle)
   // `uv_buf_t.len` happens to have different size on Windows.
   size_t write_count;
   stream->uvbuf.base = rbuffer_write_ptr(stream->buffer, &write_count);
-  stream->uvbuf.len = write_count;
+  stream->uvbuf.len = UV_BUF_LEN(write_count);
 
   // the offset argument to uv_fs_read is int64_t, could someone really try
   // to read more than 9 quintillion (9e18) bytes?

src/nvim/event/wstream.c

@@ -90,7 +90,7 @@ bool wstream_write(Stream *stream, WBuffer *buffer)
 
   uv_buf_t uvbuf;
   uvbuf.base = buffer->data;
-  uvbuf.len = buffer->size;
+  uvbuf.len = UV_BUF_LEN(buffer->size);
 
   if (uv_write(&data->uv_req, stream->uvstream, &uvbuf, 1, write_cb)) {
     xfree(data);

src/nvim/macros.h

@@ -188,4 +188,11 @@
 /// @return ((Type *)obj).
 #define STRUCT_CAST(Type, obj) ((Type *)(obj))
 
+// Type of uv_buf_t.len on Windows is ULONG, but others is size_t.
+#if defined(WIN32)
+# define UV_BUF_LEN(x)  (ULONG)(x)
+#else
+# define UV_BUF_LEN(x)  (x)
+#endif
+
 #endif  // NVIM_MACROS_H

src/nvim/tui/tui.c

@@ -1744,14 +1744,14 @@ static void flush_buf(UI *ui)
     // cursor is visible. Write a "cursor invisible" command before writing the
     // buffer.
     bufp->base = data->invis;
-    bufp->len = data->invislen;
+    bufp->len = UV_BUF_LEN(data->invislen);
     bufp++;
     data->is_invisible = true;
   }
 
   if (data->bufpos > 0) {
     bufp->base = data->buf;
-    bufp->len = data->bufpos;
+    bufp->len = UV_BUF_LEN(data->bufpos);
     bufp++;
   }
 
@@ -1759,7 +1759,7 @@ static void flush_buf(UI *ui)
     // not busy and the cursor is invisible. Write a "cursor normal" command
     // after writing the buffer.
     bufp->base = data->norm;
-    bufp->len = data->normlen;
+    bufp->len = UV_BUF_LEN(data->normlen);
     bufp++;
     data->is_invisible = data->busy;
   }

test/functional/fixtures/tty-test.c

@@ -94,7 +94,14 @@ static void read_cb(uv_stream_t *stream, ssize_t cnt, const uv_buf_t *buf)
   uv_tty_init(&write_loop, &out, fileno(stdout), 0);
 
   uv_write_t req;
-  uv_buf_t b = {.base = buf->base, .len = (size_t)cnt};
+  uv_buf_t b = {
+    .base = buf->base,
+#ifdef WIN32
+    .len = (ULONG)cnt
+#else
+    .len = (size_t)cnt
+#endif
+  };
   uv_write(&req, STRUCT_CAST(uv_stream_t, &out), &b, 1, NULL);
   uv_run(&write_loop, UV_RUN_DEFAULT);