3 files changed, 49 insertions, 2 deletions

diff --git a/src/libutil/logging.cc b/src/libutil/logging.cc
index 832aee783..cbbf64395 100644
--- a/src/libutil/logging.cc
+++ b/src/libutil/logging.cc
@@ -184,6 +184,33 @@ struct JSONLogger : Logger {
         json["action"] = "msg";
         json["level"] = ei.level;
         json["msg"] = oss.str();
+        json["raw_msg"] = ei.hint->str();
+
+        if (ei.errPos.has_value() && (*ei.errPos)) {
+            json["line"] = ei.errPos->line;
+            json["column"] = ei.errPos->column;
+            json["file"] = ei.errPos->file;
+        } else {
+            json["line"] = nullptr;
+            json["column"] = nullptr;
+            json["file"] = nullptr;
+        }
+
+        if (loggerSettings.showTrace.get() && !ei.traces.empty()) {
+            nlohmann::json traces = nlohmann::json::array();
+            for (auto iter = ei.traces.rbegin(); iter != ei.traces.rend(); ++iter) {
+                nlohmann::json stackFrame;
+                stackFrame["raw_msg"] = iter->hint.str();
+                if (iter->pos.has_value() && (*iter->pos)) {
+                    stackFrame["line"] = iter->pos->line;
+                    stackFrame["column"] = iter->pos->column;
+                    stackFrame["file"] = iter->pos->file;
+                }
+                traces.push_back(stackFrame);
+            }
+
+            json["trace"] = traces;
+        }
 
         write(json);
     }
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index 69ae0874a..a6f1c42e9 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -23,7 +23,8 @@ struct Sink
 };
 
 
-/* A buffered abstract sink. */
+/* A buffered abstract sink. Warning: a BufferedSink should not be
+   used from multiple threads concurrently. */
 struct BufferedSink : virtual Sink
 {
     size_t bufSize, bufPos;
@@ -66,7 +67,8 @@ struct Source
 };
 
 
-/* A buffered abstract source. */
+/* A buffered abstract source. Warning: a BufferedSource should not be
+   used from multiple threads concurrently. */
 struct BufferedSource : Source
 {
     size_t bufSize, bufPosIn, bufPosOut;
diff --git a/src/libutil/tests/logging.cc b/src/libutil/tests/logging.cc
index ad588055f..7e53f17c6 100644
--- a/src/libutil/tests/logging.cc
+++ b/src/libutil/tests/logging.cc
@@ -34,6 +34,24 @@ namespace nix {
         }
     }
 
+    TEST(logEI, jsonOutput) {
+        SymbolTable testTable;
+        auto problem_file = testTable.create("random.nix");
+        testing::internal::CaptureStderr();
+
+        makeJSONLogger(*logger)->logEI({
+                .name = "error name",
+                .description = "error without any code lines.",
+                .hint = hintfmt("this hint has %1% templated %2%!!",
+                    "yellow",
+                    "values"),
+                .errPos = Pos(foFile, problem_file, 02, 13)
+            });
+
+        auto str = testing::internal::GetCapturedStderr();
+        ASSERT_STREQ(str.c_str(), "\x1B[31;1merror:\x1B[0m\x1B[34;1m --- SysError --- error-unit-test\x1B[0m\nopening file '\x1B[33;1mrandom.nix\x1B[0m': \x1B[33;1mNo such file or directory\x1B[0m\n@nix {\"action\":\"msg\",\"column\":13,\"file\":\"random.nix\",\"level\":0,\"line\":2,\"msg\":\"\\u001b[31;1merror:\\u001b[0m\\u001b[34;1m --- error name --- error-unit-test\\u001b[0m\\n\\u001b[34;1mat: \\u001b[33;1m(2:13)\\u001b[34;1m in file: \\u001b[0mrandom.nix\\n\\nerror without any code lines.\\n\\nthis hint has \\u001b[33;1myellow\\u001b[0m templated \\u001b[33;1mvalues\\u001b[0m!!\",\"raw_msg\":\"this hint has \\u001b[33;1myellow\\u001b[0m templated \\u001b[33;1mvalues\\u001b[0m!!\"}\n");
+    }
+
     TEST(logEI, appendingHintsToPreviousError) {
 
         MakeError(TestError, Error);