FEATURE: Use the AST Pretty Printer for TRACE and assert output.

examples/module_example/modules/host_module.ucg

@@ -1,4 +1,4 @@
-let host_mod = module{
+let host_mod = TRACE module{
     hostname="",
     mem=2048,
     cpu=2,

src/ast/printer/mod.rs

@@ -184,7 +184,7 @@ where
         Ok(())
     }
 
-    fn render_expr(&mut self, expr: &Expression) -> std::io::Result<()> {
+    pub fn render_expr(&mut self, expr: &Expression) -> std::io::Result<()> {
         match expr {
             Expression::Binary(_def) => {
                 let op = match _def.kind {
@@ -331,7 +331,7 @@ where
                     self.render_expr(e)?;
                     write!(self.w, ") ")?;
                 }
-                write!(self.w, "{{")?;
+                write!(self.w, "{{\n")?;
                 self.curr_indent += self.indent;
                 let indent = self.make_indent();
                 for stmt in _def.statements.iter() {
@@ -372,7 +372,7 @@ where
         Ok(())
     }
 
-    fn render_stmt(&mut self, stmt: &Statement) -> std::io::Result<()> {
+    pub fn render_stmt(&mut self, stmt: &Statement) -> std::io::Result<()> {
         // All statements start at the beginning of a line.
         match stmt {
             Statement::Let(def) => {

src/build/mod.rs

@@ -1654,11 +1654,17 @@ impl<'a> FileBuilder<'a> {
             // we are not in validate_mode so build_asserts are noops.
             return Ok(Rc::new(Val::Empty));
         }
+        let mut buffer: Vec<u8> = Vec::new();
+        {
+            let mut printer = crate::ast::printer::AstPrinter::new(2, &mut buffer);
+            let _ = printer.render_expr(expr);
+        }
+        let expr_pretty = String::from_utf8(buffer).unwrap();
         let ok = match self.eval_expr(expr, scope) {
             Ok(v) => v,
             Err(e) => {
                 // failure!
-                let msg = format!("CompileError: {}\n", e);
+                let msg = format!("CompileError: {}\nfor expression:\n{}\n", e, expr_pretty);
                 self.record_assert_result(&msg, false);
                 return Ok(Rc::new(Val::Empty));
             }
@@ -1965,9 +1971,16 @@ impl<'a> FileBuilder<'a> {
                 };
             }
             &Expression::Debug(ref def) => {
+                let mut buffer: Vec<u8> = Vec::new();
+                {
+                    let mut printer = crate::ast::printer::AstPrinter::new(2, &mut buffer);
+                    let _ = printer.render_expr(&def.expr);
+                }
+                let expr_pretty = String::from_utf8(buffer).unwrap();
+
                 let val = self.eval_expr(&def.expr, scope);
                 if let Ok(ref val) = val {
-                    eprintln!("TRACE: {} at {}", val, def.pos);
+                    eprintln!("TRACE: {} = {} at {}", expr_pretty, val, def.pos);
                 }
                 val
             }