fix(parser): print the trace once in @def trace mode (#344)

CHANGELOG.md

@@ -6,6 +6,12 @@ All notable changes to CTParser will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### 🐛 Bug Fixes
+
+- **Trace mode (`@def name … end true`) no longer prints the parsed model twice** ([#344](https://github.com/control-toolbox/CTParser.jl/issues/344)). When the `:exa` backend is active, `def_fun` parses the definition a second time to build the ExaModels artifact; that second pass was inheriting the `log` flag and re-emitting the whole trace. It now runs with `log=false`.
+
 ## [0.9.4-beta] - 2026-08-30
 
 ### ✅ Compatibility

src/onepass.jl

@@ -1550,7 +1550,9 @@ function def_fun(e; log=false)
     end
 
     if is_active_backend(:exa)
-        build_exa = def_exa(e; log=log)
+        # log=false: the :fun pass above already emitted the trace; a second one here
+        # would print the whole parsed model twice (#344)
+        build_exa = def_exa(e; log=false)
         code = concat(code, :($pref.build($p_ocp; build_examodel=($build_exa))))
     else
         code = concat(code, :($pref.build($p_ocp)))

test/test_onepass_fun.jl

@@ -124,6 +124,33 @@ function test_onepass_fun()
         end true
         @test initial_time(o) == 0
         @test final_time(o, [0, 2]) == 2
+
+        # trace mode prints the parsed model once, not once per active backend (#344)
+        was_exa = is_active_backend(:exa)
+        was_exa || activate_backend(:exa)
+        try
+            trace = mktemp() do path, io
+                redirect_stdout(io) do
+                    CTParser.def_fun(
+                        :(begin
+                            tf ∈ R, variable
+                            t ∈ [0, tf], time
+                            x = (q, v) ∈ R², state
+                            u ∈ R, control
+                            ẋ(t) == [v(t), u(t)]
+                            ∫(u(t)^2) → min
+                        end);
+                        log=true,
+                    )
+                end
+                flush(io)
+                read(path, String)
+            end
+            @test count("objective (Lagrange)", trace) == 1
+            @test count("state: x, dim: 2", trace) == 1
+        finally
+            was_exa || deactivate_backend(:exa)
+        end
     end
 
     # ---------------------------------------------------------------