trace: Add JSON output format

Add a new `--trace-format=` flag, to enable the new JSON trace
output format. This new format is easier to parse by machines
than the existing format. This new format also removes the
ambiguity of the whitespace in the "old" format (e.g. is that
whitespace part of a file path, or does it seperate arguments)

1 files changed, 73 insertions, 0 deletions

diff --git a/Source/cmake.cxx b/Source/cmake.cxx
index fdb3687..b1300c9 100644
--- a/Source/cmake.cxx
+++ b/Source/cmake.cxx
@@ -755,6 +755,15 @@ void cmake::SetArgs(const std::vector<std::string>& args)
       std::cout << "Running with expanded trace output on.\n";
       this->SetTrace(true);
       this->SetTraceExpand(true);
+    } else if (arg.find("--trace-format=", 0) == 0) {
+      this->SetTrace(true);
+      const auto traceFormat =
+        StringToTraceFormat(arg.substr(strlen("--trace-format=")));
+      if (traceFormat == TraceFormat::TRACE_UNDEFINED) {
+        cmSystemTools::Error("Invalid format specified for --trace-format");
+        return;
+      }
+      this->SetTraceFormat(traceFormat);
     } else if (arg.find("--trace-source=", 0) == 0) {
       std::string file = arg.substr(strlen("--trace-source="));
       cmSystemTools::ConvertToUnixSlashes(file);
@@ -895,6 +904,23 @@ cmake::LogLevel cmake::StringToLogLevel(const std::string& levelStr)
   return (it != levels.cend()) ? it->second : LogLevel::LOG_UNDEFINED;
 }
 
+cmake::TraceFormat cmake::StringToTraceFormat(const std::string& traceStr)
+{
+  using TracePair = std::pair<std::string, TraceFormat>;
+  static const std::vector<TracePair> levels = {
+    { "human", TraceFormat::TRACE_HUMAN },
+    { "json-v1", TraceFormat::TRACE_JSON_V1 },
+  };
+
+  const auto traceStrLowCase = cmSystemTools::LowerCase(traceStr);
+
+  const auto it = std::find_if(levels.cbegin(), levels.cend(),
+                               [&traceStrLowCase](const TracePair& p) {
+                                 return p.first == traceStrLowCase;
+                               });
+  return (it != levels.cend()) ? it->second : TraceFormat::TRACE_UNDEFINED;
+}
+
 void cmake::SetTraceFile(const std::string& file)
 {
   this->TraceFile.close();
@@ -909,6 +935,48 @@ void cmake::SetTraceFile(const std::string& file)
   std::cout << "Trace will be written to " << file << "\n";
 }
 
+void cmake::PrintTraceFormatVersion()
+{
+  if (!this->GetTrace()) {
+    return;
+  }
+
+  std::string msg;
+
+  switch (this->GetTraceFormat()) {
+    case TraceFormat::TRACE_JSON_V1: {
+#ifndef CMAKE_BOOTSTRAP
+      Json::Value val;
+      Json::Value version;
+      Json::StreamWriterBuilder builder;
+      builder["indentation"] = "";
+      version["major"] = 1;
+      version["minor"] = 0;
+      val["version"] = version;
+      msg = Json::writeString(builder, val);
+#endif
+      break;
+    }
+    case TraceFormat::TRACE_HUMAN:
+      msg = "";
+      break;
+    case TraceFormat::TRACE_UNDEFINED:
+      msg = "INTERNAL ERROR: Trace format is TRACE_UNDEFINED";
+      break;
+  }
+
+  if (msg.empty()) {
+    return;
+  }
+
+  auto& f = this->GetTraceFile();
+  if (f) {
+    f << msg << '\n';
+  } else {
+    cmSystemTools::Message(msg);
+  }
+}
+
 void cmake::SetDirectoriesFromFile(const std::string& arg)
 {
   // Check if the argument refers to a CMakeCache.txt or
@@ -1701,6 +1769,11 @@ int cmake::Run(const std::vector<std::string>& args, bool noconfigure)
     return -1;
   }
 
+  // Log the trace format version to the desired output
+  if (this->GetTrace()) {
+    this->PrintTraceFormatVersion();
+  }
+
   // If we are given a stamp list file check if it is really out of date.
   if (!this->CheckStampList.empty() &&
       cmakeCheckStampList(this->CheckStampList)) {