Internals: Add `--fourstate` flag and FUTURE warning (#7279)

docs/guide/warnings.rst

@@ -856,6 +856,11 @@ List Of Warnings
    pass.
 
 
+.. option:: FUTURE
+
+   Warns that a feature is under development and not yet supported.
+
+
 .. option:: GENCLK
 
    Historical, never issued since version 5.000.

src/V3Error.h

@@ -107,6 +107,7 @@ public:
         ENUMVALUE,      // Error: enum type needs explicit cast
         EOFNEWLINE,     // End-of-file missing newline
         FUNCTIMECTL,    // Functions cannot have timing/delay/wait
+        FUTURE,         // Feature is under development and not yet supported
         GENCLK,         // Generated Clock. Historical, never issued.
         GENUNNAMED,     // Generate unnamed, without label
         HIERBLOCK,      // Ignored hierarchical block setting
@@ -223,7 +224,7 @@ public:
             "CDCRSTLOGIC", "CLKDATA", "CMPCONST", "COLONPLUS", "COMBDLY", "CONSTRAINTIGN",
             "CONTASSREG", "COVERIGN", "DECLFILENAME", "DEFOVERRIDE", "DEFPARAM", "DEPRECATED",
             "ENCAPSULATED", "ENDLABEL", "ENUMITEMWIDTH", "ENUMVALUE", "EOFNEWLINE", "FUNCTIMECTL",
-            "GENCLK", "GENUNNAMED", "HIERBLOCK", "HIERPARAM", "IFDEPTH", "IGNOREDRETURN",
+            "FUTURE", "GENCLK", "GENUNNAMED", "HIERBLOCK", "HIERPARAM", "IFDEPTH", "IGNOREDRETURN",
             "IMPERFECTSCH", "IMPLICIT", "IMPLICITSTATIC", "IMPORTSTAR", "IMPURE", "INCABSPATH",
             "INFINITELOOP", "INITIALDLY", "INSECURE", "INSIDETRUE", "LATCH", "LITENDIAN",
             "MINTYPMAXDLY", "MISINDENT", "MODDUP", "MODMISSING", "MULTIDRIVEN", "MULTITOP",

src/V3Options.cpp

@@ -1056,6 +1056,10 @@ void V3Options::notify() VL_MT_DISABLED {
                       "--main not usable with SystemC. Suggest see examples for sc_main().");
     }
 
+    if (fourstate()) {
+        cmdfl->v3warn(FUTURE, "--fourstate is not supported as is under development");
+    }
+
     if (coverage() && savable()) {
         cmdfl->v3error("Unsupported: --coverage and --savable not supported together");
     }
@@ -1436,6 +1440,7 @@ void V3Options::parseOptsList(FileLine* fl, const string& optdir, int argc,
         parseOptsFile(fl, parseFileArg(optdir, valp), false);
     }).notForRerun();
     DECL_OPTION("-flatten", OnOff, &m_flatten);
+    DECL_OPTION("-fourstate", OnOff, &m_fourstate).undocumented();
     DECL_OPTION("-future0", CbVal, [this](const char* valp) { addFuture0(valp); });
     DECL_OPTION("-future1", CbVal, [this](const char* valp) { addFuture1(valp); });
 

src/V3Options.h

@@ -254,6 +254,7 @@ private:
     bool m_emitAccessors = false;   // main switch: --emit-accessors
     bool m_exe = false;             // main switch: --exe
     bool m_flatten = false;         // main switch: --flatten
+    bool m_fourstate = false;       // main switch: --fourstate
     bool m_hierarchical = false;    // main switch: --hierarchical
     bool m_ignc = false;            // main switch: --ignc
     bool m_jsonOnly = false;        // main switch: --json-only
@@ -545,6 +546,7 @@ public:
     bool emitAccessors() const { return m_emitAccessors; }
     bool exe() const { return m_exe; }
     bool flatten() const { return m_flatten; }
+    bool fourstate() const { return m_fourstate; }
     bool gmake() const { return m_gmake; }
     bool makeJson() const { return m_makeJson; }
     bool threadsDpiPure() const { return m_threadsDpiPure; }

test_regress/t/t_fourstate_fourstate_unsup.out

@@ -0,0 +1,4 @@
+%Warning-FUTURE: --fourstate is not supported as is under development
+                 ... For warning description see https://verilator.org/warn/FUTURE?v=latest
+                 ... Use "/* verilator lint_off FUTURE */" and lint_on around source to disable this message.
+%Error: Exiting due to

test_regress/t/t_fourstate_fourstate_unsup.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# 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-FileCopyrightText: 2026 Wilson Snyder
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.lint(verilator_flags2=['--fourstate'], fails=True, expect_filename=test.golden_filename)
+
+test.passes()

test_regress/t/t_fourstate_fourstate_unsup.v

@@ -0,0 +1,21 @@
+// DESCRIPTION: Verilator: Verilog Test module for SystemVerilog
+//
+// Assignment compatibility test.
+//
+// This file ONLY is placed under the Creative Commons Public Domain
+// SPDX-FileCopyrightText: 2026 Antmicro
+// SPDX-License-Identifier: CC0-1.0
+
+module t;
+  logic a = 'z;
+  logic b;
+
+  assign b = ~a;
+
+  initial begin
+    #1;
+    if (b !== 1) $stop;
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule

test_regress/t/t_fourstate_no_fourstate.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# 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-FileCopyrightText: 2026 Wilson Snyder
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile(verilator_flags2=['--binary', '--no-fourstate'])
+
+test.execute()
+
+test.passes()

test_regress/t/t_fourstate_no_fourstate.v

@@ -0,0 +1,21 @@
+// DESCRIPTION: Verilator: Verilog Test module for SystemVerilog
+//
+// Assignment compatibility test.
+//
+// This file ONLY is placed under the Creative Commons Public Domain
+// SPDX-FileCopyrightText: 2026 Antmicro
+// SPDX-License-Identifier: CC0-1.0
+
+module t;
+  logic a = 'z;
+  logic b;
+
+  assign b = ~a;
+
+  initial begin
+    #1;
+    if (b !== 1) $stop;
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule