Support pure constraint.

Changes

@@ -15,6 +15,7 @@ Verilator 5.031 devel
 
 * Support queue's assignment `push_back/push_front('{})` (#5585) (#5586). [Yilou Wang]
 * Support basic constrained random for multi-dimensional dynamic array and queue (#5591). [Yilou Wang]
+* Support `pure constraint`.
 * Add error on illegal enum base type (#3010). [Iztok Jeras]
 * Add error on `wait` with missing `.triggered` (#4457).
 * Add error when improperly storing to parameter (#5147). [Gökçe Aydos]

src/V3AstNodeOther.h

@@ -1026,7 +1026,8 @@ class AstConstraint final : public AstNode {
     // Constraint
     // @astgen op1 := itemsp : List[AstNode]
     string m_name;  // Name of constraint
-    bool m_isStatic = false;  // static constraint
+    bool m_isKwdPure = false;  // Pure constraint
+    bool m_isStatic = false;  // Static constraint
 public:
     AstConstraint(FileLine* fl, const string& name, AstNode* itemsp)
         : ASTGEN_SUPER_Constraint(fl)
@@ -1034,11 +1035,15 @@ public:
         this->addItemsp(itemsp);
     }
     ASTGEN_MEMBERS_AstConstraint;
+    void dump(std::ostream& str) const override;
+    void dumpJson(std::ostream& str) const override;
     string name() const override VL_MT_STABLE { return m_name; }  // * = Scope name
     bool isGateOptimizable() const override { return false; }
     bool isPredictOptimizable() const override { return false; }
     bool maybePointedTo() const override VL_MT_SAFE { return true; }
     bool same(const AstNode* /*samep*/) const override { return true; }
+    void isKwdPure(bool flag) { m_isKwdPure = flag; }
+    bool isKwdPure() const { return m_isKwdPure; }
     void isStatic(bool flag) { m_isStatic = flag; }
     bool isStatic() const { return m_isStatic; }
 };

src/V3AstNodes.cpp

@@ -366,7 +366,16 @@ void AstConsQueue::dumpJson(std::ostream& str) const {
     dumpJsonBoolFunc(str, rhsIsValue);
     dumpJsonGen(str);
 }
-
+void AstConstraint::dump(std::ostream& str) const {
+    this->AstNode::dump(str);
+    if (isKwdPure()) str << " [KWDPURE]";
+    if (isStatic()) str << " [STATIC]";
+}
+void AstConstraint::dumpJson(std::ostream& str) const {
+    dumpJsonBoolFunc(str, isKwdPure);
+    dumpJsonBoolFunc(str, isStatic);
+    dumpJsonGen(str);
+}
 AstConst* AstConst::parseParamLiteral(FileLine* fl, const string& literal) {
     bool success = false;
     if (literal[0] == '"') {

src/V3LinkDot.cpp

@@ -2334,13 +2334,13 @@ class LinkDotResolveVisitor final : public VNVisitor {
              ++it) {
             if (AstNode* interfaceSubp = it->second->nodep()) {
                 UINFO(8, indent() << "  SymFunc " << interfaceSubp << endl);
+                const string impOrExtends
+                    = baseClassp->isInterfaceClass() ? " implements " : " extends ";
                 if (VN_IS(interfaceSubp, NodeFTask)) {
                     const VSymEnt* const foundp = m_curSymp->findIdFlat(interfaceSubp->name());
                     const AstNodeFTask* const interfaceFuncp = VN_CAST(interfaceSubp, NodeFTask);
                     if (!interfaceFuncp || !interfaceFuncp->pureVirtual()) continue;
                     bool existsInChild = foundp && !foundp->imported();
-                    const string impOrExtends
-                        = baseClassp->isInterfaceClass() ? " implements " : " extends ";
                     if (!existsInChild && !implementsClassp->isInterfaceClass()) {
                         implementsClassp->v3error(
                             "Class " << implementsClassp->prettyNameQ() << impOrExtends
@@ -2368,6 +2368,25 @@ class LinkDotResolveVisitor final : public VNVisitor {
                     }
                     m_ifClassImpNames.emplace(interfaceSubp->name(), interfaceSubp);
                 }
+                if (VN_IS(interfaceSubp, Constraint)) {
+                    const VSymEnt* const foundp = m_curSymp->findIdFlat(interfaceSubp->name());
+                    const AstConstraint* const interfaceFuncp = VN_CAST(interfaceSubp, Constraint);
+                    if (!interfaceFuncp || !interfaceFuncp->isKwdPure()) continue;
+                    bool existsInChild = foundp && !foundp->imported();
+                    if (!existsInChild && !implementsClassp->isInterfaceClass()
+                        && !implementsClassp->isVirtual()) {
+                        implementsClassp->v3error(
+                            "Class " << implementsClassp->prettyNameQ() << impOrExtends
+                                     << baseClassp->prettyNameQ()
+                                     << " but is missing constraint implementation for "
+                                     << interfaceSubp->prettyNameQ()
+                                     << " (IEEE 1800-2023 18.5.2)\n"
+                                     << implementsClassp->warnContextPrimary() << '\n'
+                                     << interfaceSubp->warnOther()
+                                     << "... Location of interface class's pure constraint\n"
+                                     << interfaceSubp->warnContextSecondary());
+                    }
+                }
             }
         }
     }

src/V3WidthCommit.cpp

@@ -162,6 +162,18 @@ private:
         nodep->replaceWith(nodep->lhsp()->unlinkFrBack());
         VL_DO_DANGLING(pushDeletep(nodep), nodep);
     }
+    void visit(AstConstraint* nodep) override {
+        iterateChildren(nodep);
+        editDType(nodep);
+        {
+            const AstClass* const classp = VN_CAST(m_modp, Class);
+            if (nodep->isKwdPure()
+                && (!classp || (!classp->isInterfaceClass() && !classp->isVirtual()))) {
+                nodep->v3error("Illegal to have 'pure constraint' in non-abstract class"
+                               " (IEEE 1800-2023 18.5.2)");
+            }
+        }
+    }
     void visit(AstNodeDType* nodep) override {
         // Note some specific dtypes have unique visitors
         visitIterateNodeDType(nodep);

src/verilog.y

@@ -7391,8 +7391,7 @@ class_constraint<constraintp>:  // ==IEEE: class_constraint
                         { $$ = $4; $$->isStatic($1); SYMP->popScope($4);
                           BBUNSUP($1, "Unsupported: extern constraint"); }
         |       yPURE constraintStaticE yCONSTRAINT constraintIdNew ';'
-                        { $$ = $4; $$->isStatic($1); SYMP->popScope($4);
-                          BBUNSUP($1, "Unsupported: pure constraint"); }
+                        { $$ = $4; $$->isKwdPure($1); $$->isStatic($1); SYMP->popScope($4); }
         ;
 
 constraintIdNew<constraintp>:  // IEEE: id part of class_constraint

test_regress/t/t_constraint_pure.py

@@ -0,0 +1,21 @@
+#!/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('simulator')
+
+if not test.have_solver:
+    test.skip("No constraint solver installed")
+
+test.compile()
+
+test.execute()
+
+test.passes()

test_regress/t/t_constraint_pure.v

@@ -0,0 +1,26 @@
+// 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
+
+virtual class Base;
+    pure constraint raint;
+endclass
+
+class Cls extends Base;
+    rand int b2;
+    constraint raint { b2 == 5; }
+endclass
+
+virtual class Virt extends Base;
+   // No constraint needed
+endclass
+
+module t;
+   initial begin
+      Cls c = new;
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+endmodule

test_regress/t/t_constraint_pure_missing_bad.out

@@ -0,0 +1,7 @@
+%Error: t/t_constraint_pure_missing_bad.v:11:1: Class 'Cls' extends 'Base' but is missing constraint implementation for 'raint' (IEEE 1800-2023 18.5.2)
+   11 | class Cls extends Base;
+      | ^~~~~
+        t/t_constraint_pure_missing_bad.v:8:21: ... Location of interface class's pure constraint
+    8 |     pure constraint raint;
+      |                     ^~~~~
+%Error: Exiting due to

test_regress/t/t_constraint_pure_missing_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('vlt')
+
+test.lint(fails=True, expect_filename=test.golden_filename)
+
+test.passes()

test_regress/t/t_constraint_pure_missing_bad.v

@@ -0,0 +1,16 @@
+// 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
+
+virtual class Base;
+    pure constraint raint;
+endclass
+
+class Cls extends Base;
+   // Bad: Missing 'constraint raint'
+endclass
+
+module t;
+endmodule

test_regress/t/t_constraint_pure_nonabs_bad.out

@@ -0,0 +1,5 @@
+%Error: t/t_constraint_pure_nonabs_bad.v:8:21: Illegal to have 'pure constraint' in non-abstract class (IEEE 1800-2023 18.5.2)
+                                             : ... note: In instance 't'
+    8 |     pure constraint raintBad;   
+      |                     ^~~~~~~~
+%Error: Exiting due to

test_regress/t/t_constraint_pure_nonabs_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('vlt')
+
+test.lint(fails=True, expect_filename=test.golden_filename)
+
+test.passes()

test_regress/t/t_constraint_pure_nonabs_bad.v

@@ -0,0 +1,12 @@
+// 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
+
+class NonAsbstract;
+    pure constraint raintBad;  // Bad: Not in abstract class
+endclass
+
+module t;
+endmodule

test_regress/t/t_randomize_extern.out

@@ -1,10 +1,7 @@
-%Error-UNSUPPORTED: t/t_randomize_extern.v:8:4: Unsupported: pure constraint
-    8 |    pure constraint pur;
-      |    ^~~~
-                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
 %Error-UNSUPPORTED: t/t_randomize_extern.v:17:4: Unsupported: extern constraint
    17 |    extern constraint ex;
       |    ^~~~~~
+                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
 %Error-UNSUPPORTED: t/t_randomize_extern.v:21:1: Unsupported: extern constraint
    21 | constraint Packet::ex { header == 2; }
       | ^~~~~~~~~~