Trace tags for dumping the decision tree in org-mode format (#2871)

This would add tracing options to print the decision tree in [org-mode](https://orgmode.org/) format which can be viewed with emacs or [vim-orgmode](https://github.com/jceb/vim-orgmode). 

In the raw format, the number of asterisks denote the decision level of a decision, and within a propagation node, the number of spaces denote the level. Most viewers render the asterisks as indented bullets.

There are some options for controlling verbosity:
`dtview` - prints the decisions (basic option)
`dtview::command` - also prints smt-lib commands as they're issued
`dtview::conflict` - also prints conflicts
`dtview::prop` - also prints propagations 

Example usage:
`cvc4 -t dtview -t dtview::command -t dtview::conflict -t dtview::prop <example smt2 file> &> example-trace.org`

The resulting file when opened with an org-mode viewer has collapsible nodes, where "..." marks a node with children.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/smt/command.cpp b/src/smt/command.cpp
index 76ce1bda9..d8301283f 100644
--- a/src/smt/command.cpp
+++ b/src/smt/command.cpp
@@ -265,6 +265,8 @@ void EchoCommand::invoke(SmtEngine* smtEngine)
 void EchoCommand::invoke(SmtEngine* smtEngine, std::ostream& out)
 {
   out << d_output << std::endl;
+  Trace("dtview::command") << "* ~COMMAND: echo |" << d_output << "|~"
+                           << std::endl;
   d_commandStatus = CommandSuccess::instance();
   printResult(out,
               smtEngine->getOption("command-verbosity:" + getCommandName())
@@ -393,6 +395,8 @@ CheckSatCommand::CheckSatCommand(const Expr& expr) : d_expr(expr) {}
 Expr CheckSatCommand::getExpr() const { return d_expr; }
 void CheckSatCommand::invoke(SmtEngine* smtEngine)
 {
+  Trace("dtview::command") << "* ~COMMAND: " << getCommandName() << "~"
+                           << std::endl;
   try
   {
     d_result = smtEngine->checkSat(d_expr);
@@ -413,6 +417,7 @@ void CheckSatCommand::printResult(std::ostream& out, uint32_t verbosity) const
   }
   else
   {
+    Trace("dtview::command") << "* RESULT: " << d_result << std::endl;
     out << d_result << endl;
   }
 }
@@ -453,6 +458,8 @@ const std::vector<Expr>& CheckSatAssumingCommand::getTerms() const
 
 void CheckSatAssumingCommand::invoke(SmtEngine* smtEngine)
 {
+  Trace("dtview::command") << "* ~COMMAND: (check-sat-assuming ( " << d_terms
+                           << " )~" << std::endl;
   try
   {
     d_result = smtEngine->checkSat(d_terms);
@@ -466,6 +473,7 @@ void CheckSatAssumingCommand::invoke(SmtEngine* smtEngine)
 
 Result CheckSatAssumingCommand::getResult() const
 {
+  Trace("dtview::command") << "* ~RESULT: " << d_result << "~" << std::endl;
   return d_result;
 }