Add error when improperly storing to parameter (#5147).

Changes

@@ -14,6 +14,7 @@ Verilator 5.031 devel
 **Minor:**
 
 * Add coverage point hierarchy to coverage reports (#5575) (#5576). [Andrew Nolte]
+* Add error when improperly storing to parameter (#5147). [Gökçe Aydos]
 * Fix can't locate scope error in interface task delayed assignment (#5462) (#5568). [Zhou Shen]
 * Fix BLKANDNBLK for for VARXREFs (#5569). [Todd Strader]
 * Fix VPI error instead of fatal for vpi_get_value() on large signals (#5571). [Todd Strader]

src/V3AstNodeOther.h

@@ -2069,7 +2069,7 @@ public:
     bool isTristate() const { return m_tristate; }
     bool isPrimaryIO() const VL_MT_SAFE { return m_primaryIO; }
     bool isPrimaryInish() const { return isPrimaryIO() && isNonOutput(); }
-    bool isIfaceRef() const { return (varType() == VVarType::IFACEREF); }
+    bool isIfaceRef() const { return varType() == VVarType::IFACEREF; }
     bool isIfaceParent() const { return m_isIfaceParent; }
     bool isInternal() const { return m_isInternal; }
     bool isSignal() const { return varType().isSignal(); }
@@ -2085,11 +2085,11 @@ public:
                 && !isSc() && !isPrimaryIO() && !isConst() && !isDouble() && !isString());
     }
     bool isClassMember() const { return varType() == VVarType::MEMBER; }
-    bool isStatementTemp() const { return (varType() == VVarType::STMTTEMP); }
-    bool isXTemp() const { return (varType() == VVarType::XTEMP); }
+    bool isStatementTemp() const { return varType() == VVarType::STMTTEMP; }
+    bool isXTemp() const { return varType() == VVarType::XTEMP; }
     bool isParam() const { return varType().isParam(); }
-    bool isGParam() const { return (varType() == VVarType::GPARAM); }
-    bool isGenVar() const { return (varType() == VVarType::GENVAR); }
+    bool isGParam() const { return varType() == VVarType::GPARAM; }
+    bool isGenVar() const { return varType() == VVarType::GENVAR; }
     bool isBitLogic() const {
         AstBasicDType* bdtypep = basicp();
         return bdtypep && bdtypep->isBitLogic();

src/V3LinkLValue.cpp

@@ -48,6 +48,13 @@ class LinkLValueVisitor final : public VNVisitor {
         if (m_setIfRand && !(nodep->varp() && nodep->varp()->isRand())) return;
         if (m_setRefLvalue != VAccess::NOCHANGE) nodep->access(m_setRefLvalue);
         if (nodep->varp() && nodep->access().isWriteOrRW()) {
+            if (nodep->varp()->isParam()) {
+                // All parameters that did get constified happened before now
+                // as V3LinkLValue runs after V3Param
+                nodep->v3error("Storing to parameter variable "
+                               << nodep->prettyNameQ()
+                               << " in a context that is determed only at runtime");
+            }
             if (m_setContinuously) {
                 nodep->varp()->isContinuously(true);
                 // Strength may only be specified in continuous assignment,

test_regress/t/t_param_store_bad.out

@@ -0,0 +1,4 @@
+%Error: t/t_param_store_bad.v:12:31: Storing to parameter variable 'S' in a context that is determed only at runtime
+   12 |       $value$plusargs("S=%s", S);   
+      |                               ^
+%Error: Exiting due to

test_regress/t/t_param_store_bad.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2024 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
+
+import vltest_bootstrap
+
+test.scenarios('linter')
+
+test.lint(fails=True, expect_filename=test.golden_filename)
+
+test.passes()

test_regress/t/t_param_store_bad.v

@@ -0,0 +1,18 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2024 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+module t #(
+           string S = "<unset>"
+           );
+
+   initial begin
+      $value$plusargs("S=%s", S);  // BAD assignment to S
+      #1;  // Original bug got compile time error only with this line
+      $display("S=%s", S);
+      $finish;
+   end
+
+endmodule