Add trace() API even when Verilated without --trace (#4462).

Changes

@@ -13,6 +13,7 @@ Verilator 5.017 devel
 
 **Minor:**
 
+* Add trace() API even when Verilated without --trace (#4462). [phelter]
 * Support randc (#4349).
 * Support resizing function call inout arguments (#4467).
 

src/V3EmitCModel.cpp

@@ -197,15 +197,13 @@ class EmitCModel final : public EmitCFunc {
         puts("/// Returns time at next time slot. Aborts if !eventsPending()\n");
         puts("uint64_t nextTimeSlot();\n");
 
-        if (v3Global.opt.trace()) {
-            puts("/// Trace signals in the model; called by application code\n");
-            puts("void trace(" + v3Global.opt.traceClassBase()
-                 + "C* tfp, int levels, int options = 0);\n");
-            if (optSystemC()) {
-                puts("/// SC tracing; avoid overloaded virtual function lint warning\n");
-                puts("void trace(sc_trace_file* tfp) const override { "
-                     "::sc_core::sc_module::trace(tfp); }\n");
-            }
+        puts("/// Trace signals in the model; called by application code\n");
+        puts("void trace(" + v3Global.opt.traceClassBase()
+             + "C* tfp, int levels, int options = 0);\n");
+        if (v3Global.opt.trace() && optSystemC()) {
+            puts("/// SC tracing; avoid overloaded virtual function lint warning\n");
+            puts("void trace(sc_trace_file* tfp) const override { "
+                 "::sc_core::sc_module::trace(tfp); }\n");
         }
 
         if (!optSystemC()) {
@@ -591,6 +589,15 @@ class EmitCModel final : public EmitCFunc {
 
         puts("}\n");
     }
+    void emitTraceOffMethods(AstNodeModule* modp) {
+        putSectionDelimiter("Trace configuration");
+        // ::trace
+        puts("\nVL_ATTR_COLD void " + topClassName() + "::trace(");
+        puts(v3Global.opt.traceClassBase() + "C* tfp, int levels, int options) {\n");
+        puts(/**/ "vl_fatal(__FILE__, __LINE__, __FILE__,\"'" + topClassName()
+             + +"::trace()' called on model that was Verilated without --trace option\");\n");
+        puts("}\n");
+    }
 
     void emitSerializationFunctions() {
         putSectionDelimiter("Model serialization");
@@ -635,8 +642,11 @@ class EmitCModel final : public EmitCFunc {
         emitDestructorImplementation();
         emitStandardMethods1(modp);
         emitStandardMethods2(modp);
-        if (v3Global.opt.trace()) { emitTraceMethods(modp); }
-        if (v3Global.opt.savable()) { emitSerializationFunctions(); }
+        if (v3Global.opt.trace())
+            emitTraceMethods(modp);
+        else
+            emitTraceOffMethods(modp);
+        if (v3Global.opt.savable()) emitSerializationFunctions();
 
         VL_DO_CLEAR(delete m_ofp, m_ofp = nullptr);
     }

test_regress/t/t_trace_noflag_bad.out

@@ -0,0 +1,2 @@
+%Error: Vt_trace_noflag_bad.cpp:106: 'Vt_trace_noflag_bad::trace()' called on model that was Verilated without --trace option
+Aborting...

test_regress/t/t_trace_noflag_bad.pl

@@ -0,0 +1,27 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+scenarios(vlt => 1);
+
+compile(
+    # We need to list verilated_vcd_c.cpp because without --trace Verilator
+    # won't build it itself automatically.
+    verilator_flags2 => ["--cc --exe $Self->{t_dir}/$Self->{name}_c.cpp verilated_vcd_c.cpp"],
+    make_top_shell => 0,
+    make_main => 0,
+    );
+
+execute(
+    fails => 1,
+    expect_filename => $Self->{golden_filename},
+    );
+
+ok(1);
+1;

test_regress/t/t_trace_noflag_bad.v

@@ -0,0 +1,14 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2020 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+module t(/*AUTOARG*/);
+   int i;
+   initial begin
+      i = 10;
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+endmodule

test_regress/t/t_trace_noflag_bad_c.cpp

@@ -0,0 +1,24 @@
+// -*- mode: C++; c-file-style: "cc-mode" -*-
+//
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2010 by Yu-Sheng Lin.
+// SPDX-License-Identifier: CC0-1.0
+
+#include <verilated.h>
+#include <verilated_vcd_c.h>
+
+#include "Vt_trace_noflag_bad.h"
+
+int main(int argc, char** argv) {
+    std::unique_ptr<VerilatedContext> contextp{new VerilatedContext};
+    contextp->traceEverOn(true);
+    std::unique_ptr<VerilatedVcdC> tfp{new VerilatedVcdC};
+    const std::unique_ptr<VM_PREFIX> topp{new VM_PREFIX{contextp.get()}};
+    topp->trace(tfp.get(), 99);  // Error!
+    tfp->open(VL_STRINGIFY(TEST_OBJ_DIR) "/dump.vcd");  // Error! shall put to the next line!
+    tfp->dump(0);
+    tfp->close();
+    return 0;
+}