From 883de9b8d71b9cb984d8ff315b4dcc30e0ca9082 Mon Sep 17 00:00:00 2001
From: Vincent Ambo <mail@tazj.in>
Date: Thu, 20 Aug 2020 01:25:19 +0100
Subject: feat(tvix): Add a no-op stream buffer for discarding build logs

In some cases we don't have anywhere for the build logs to go. Until
we understand those cases fully and can get rid of them, this null
sink implementation can be used.

Change-Id: Ib93c43caf268e2c01c43d59737a829e8c43d223e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1792
Tested-by: BuildkiteCI
Reviewed-by: kanepyork <rikingcoding@gmail.com>
Reviewed-by: glittershark <grfn@gws.fyi>
---
 third_party/nix/src/libstore/store-api.cc | 13 +++++++++++++
 third_party/nix/src/libstore/store-api.hh |  6 ++++++
 2 files changed, 19 insertions(+)

diff --git a/third_party/nix/src/libstore/store-api.cc b/third_party/nix/src/libstore/store-api.cc
index fc33c7ce57..3ada63532c 100644
--- a/third_party/nix/src/libstore/store-api.cc
+++ b/third_party/nix/src/libstore/store-api.cc
@@ -1,6 +1,8 @@
 #include "libstore/store-api.hh"
 
 #include <future>
+#include <ostream>
+#include <streambuf>
 #include <utility>
 
 #include <absl/status/status.h>
@@ -23,6 +25,17 @@
 
 namespace nix {
 
+namespace {
+class NullStream : public std::streambuf {
+ public:
+  int overflow(int c) override { return c; }
+};
+
+static NullStream NULL_STREAM{};
+}  // namespace
+
+std::ostream DiscardLogsSink() { return std::ostream(&NULL_STREAM); }
+
 std::optional<BuildMode> BuildModeFrom(nix::proto::BuildMode mode) {
   switch (mode) {
     case nix::proto::BuildMode::Normal:
diff --git a/third_party/nix/src/libstore/store-api.hh b/third_party/nix/src/libstore/store-api.hh
index b1c0b50de3..39769dfb3c 100644
--- a/third_party/nix/src/libstore/store-api.hh
+++ b/third_party/nix/src/libstore/store-api.hh
@@ -19,6 +19,12 @@
 
 namespace nix {
 
+// Create a no-op stream buffer used to discard build output in cases
+// where we don't have a build log sink to thread through.
+//
+// TODO(tazjin): Get rid of this and do *something* with those logs.
+std::ostream DiscardLogsSink();
+
 MakeError(SubstError, Error);
 MakeError(BuildError, Error); /* denotes a permanent build failure */
 MakeError(InvalidPath, Error);
-- 
cgit 1.4.1