From c840ffb0ae8fe5cce69aba9b608e9e60af8668f9 Mon Sep 17 00:00:00 2001
From: Kamil Rakoczy <krakoczy@antmicro.com>
Date: Mon, 17 Feb 2025 13:47:41 +0100
Subject: [PATCH] Support nested classes (#4178) (#5778)

Signed-off-by: Kamil Rakoczy <krakoczy@antmicro.com>
---
 src/V3LinkDot.cpp                           | 43 +++++++++-
 src/V3WidthCommit.cpp                       | 10 ++-
 src/verilog.y                               |  3 +-
 test_regress/t/t_class_class.out            |  5 --
 test_regress/t/t_class_class.py             |  4 +-
 test_regress/t/t_class_class.v              |  3 +
 test_regress/t/t_class_compare.v            | 14 ++++
 test_regress/t/t_class_extends1.v           | 43 ++++++++++
 test_regress/t/t_class_extends2.v           | 46 +++++++++++
 test_regress/t/t_class_extends_param.v      | 35 ++++++++
 test_regress/t/t_class_extends_this.v       | 35 +++++++-
 test_regress/t/t_class_extends_this3.v      | 10 +++
 test_regress/t/t_class_extern.v             | 50 +++++++++++-
 test_regress/t/t_class_local.v              | 53 ++++++++++++
 test_regress/t/t_class_local_nested_bad.out |  9 +++
 test_regress/t/t_class_local_nested_bad.py  | 16 ++++
 test_regress/t/t_class_local_nested_bad.v   | 25 ++++++
 test_regress/t/t_class_module.v             | 11 +++
 test_regress/t/t_class_nested.py            | 18 +++++
 test_regress/t/t_class_nested.v             | 90 +++++++++++++++++++++
 test_regress/t/t_class_new.v                | 15 ++++
 test_regress/t/t_class_param.v              | 11 +++
 test_regress/t/t_class_param_rewrite.v      |  8 ++
 test_regress/t/t_class_static_member.v      |  8 +-
 test_regress/t/t_class_virtual.v            | 24 ++++++
 test_regress/t/t_implements_nested.py       | 16 ++++
 test_regress/t/t_implements_nested.v        | 16 ++++
 test_regress/t/t_implements_nested_bad.out  |  7 +-
 test_regress/t/t_implements_nested_bad.v    |  4 +-
 test_regress/t/t_semaphore_class_nested.py  | 16 ++++
 test_regress/t/t_semaphore_class_nested.v   | 39 +++++++++
 31 files changed, 664 insertions(+), 23 deletions(-)
 delete mode 100644 test_regress/t/t_class_class.out
 create mode 100644 test_regress/t/t_class_local_nested_bad.out
 create mode 100755 test_regress/t/t_class_local_nested_bad.py
 create mode 100644 test_regress/t/t_class_local_nested_bad.v
 create mode 100755 test_regress/t/t_class_nested.py
 create mode 100644 test_regress/t/t_class_nested.v
 create mode 100755 test_regress/t/t_implements_nested.py
 create mode 100644 test_regress/t/t_implements_nested.v
 create mode 100755 test_regress/t/t_semaphore_class_nested.py
 create mode 100644 test_regress/t/t_semaphore_class_nested.v

diff --git a/src/V3LinkDot.cpp b/src/V3LinkDot.cpp
index 9f77c8aad..b1b0b9223 100644
--- a/src/V3LinkDot.cpp
+++ b/src/V3LinkDot.cpp
@@ -1013,6 +1013,7 @@ class LinkDotFindVisitor final : public VNVisitor {
         VL_RESTORER(m_modBlockNum);
         VL_RESTORER(m_modWithNum);
         VL_RESTORER(m_modArgNum);
+        VL_RESTORER(m_explicitNew);
         {
             UINFO(4, "     Link Class: " << nodep << endl);
             VSymEnt* const upperSymp = m_curSymp;
@@ -1176,12 +1177,39 @@ class LinkDotFindVisitor final : public VNVisitor {
             }
             // Change to appropriate package if extern declaration (vs definition)
             if (nodep->classOrPackagep()) {
+                // class-in-class
+                AstDot* const dotp = VN_CAST(nodep->classOrPackagep(), Dot);
                 AstClassOrPackageRef* const cpackagerefp
                     = VN_CAST(nodep->classOrPackagep(), ClassOrPackageRef);
-                if (!cpackagerefp) {
-                    nodep->v3warn(E_UNSUPPORTED,
-                                  "Unsupported: extern function definition with class-in-class");
-                } else {
+                if (dotp) {
+                    AstClassOrPackageRef* const lhsp = VN_AS(dotp->lhsp(), ClassOrPackageRef);
+                    m_statep->resolveClassOrPackage(m_curSymp, lhsp, false,
+                                                    "External definition :: reference");
+                    AstClass* const lhsclassp = VN_CAST(lhsp->classOrPackageSkipp(), Class);
+                    if (!lhsclassp) {
+                        nodep->v3error("Extern declaration's scope is not a defined class");
+                    } else {
+                        m_curSymp = m_statep->getNodeSym(lhsclassp);
+                        upSymp = m_curSymp;
+                        AstClassOrPackageRef* const rhsp = VN_AS(dotp->rhsp(), ClassOrPackageRef);
+                        m_statep->resolveClassOrPackage(m_curSymp, rhsp, false,
+                                                        "External definition :: reference");
+                        AstClass* const rhsclassp = VN_CAST(rhsp->classOrPackageSkipp(), Class);
+                        if (!rhsclassp) {
+                            nodep->v3error("Extern declaration's scope is not a defined class");
+                        } else {
+                            m_curSymp = m_statep->getNodeSym(rhsclassp);
+                            upSymp = m_curSymp;
+                            if (!nodep->isExternDef()) {
+                                // Move it to proper spot under the target class
+                                nodep->unlinkFrBack();
+                                rhsclassp->addStmtsp(nodep);
+                                nodep->isExternDef(true);  // So we check there's a matching extern
+                                nodep->classOrPackagep()->unlinkFrBack()->deleteTree();
+                            }
+                        }
+                    }
+                } else if (cpackagerefp) {
                     if (!cpackagerefp->classOrPackageSkipp()) {
                         m_statep->resolveClassOrPackage(m_curSymp, cpackagerefp, false,
                                                         "External definition :: reference");
@@ -1200,6 +1228,8 @@ class LinkDotFindVisitor final : public VNVisitor {
                             nodep->classOrPackagep()->unlinkFrBack()->deleteTree();
                         }
                     }
+                } else {
+                    v3fatalSrc("Unhandled extern function definition package");
                 }
             }
             // Set the class as package for iteration
@@ -4007,6 +4037,11 @@ class LinkDotResolveVisitor final : public VNVisitor {
         LINKDOT_VISIT_START();
         UINFO(5, indent() << "visit " << nodep << endl);
         checkNoDot(nodep);
+        AstClass* const topclassp = VN_CAST(m_modp, Class);
+        if (nodep->isInterfaceClass() && topclassp && topclassp->isInterfaceClass()) {
+            nodep->v3error("Interface class shall not be nested within another interface class."
+                           " (IEEE 1800-2023 8.26)");
+        }
         VL_RESTORER(m_curSymp);
         VL_RESTORER(m_modSymp);
         VL_RESTORER(m_modp);
diff --git a/src/V3WidthCommit.cpp b/src/V3WidthCommit.cpp
index 5050fda8d..0318294e8 100644
--- a/src/V3WidthCommit.cpp
+++ b/src/V3WidthCommit.cpp
@@ -100,9 +100,15 @@ private:
         if (local || prot) {
             const auto refClassp = VN_CAST(m_modp, Class);
             const char* how = nullptr;
-            if (local && defClassp && refClassp != defClassp) {
+            // Inner nested classes can access `local` or `protected` members of their outer class
+            const auto nestedAccess = [refClassp](const AstClass*, const AstNode* memberp) {
+                return memberp == refClassp;
+            };
+            if (local && defClassp
+                && ((refClassp != defClassp) && !(defClassp->existsMember(nestedAccess)))) {
                 how = "'local'";
-            } else if (prot && defClassp && !AstClass::isClassExtendedFrom(refClassp, defClassp)) {
+            } else if (prot && defClassp && !AstClass::isClassExtendedFrom(refClassp, defClassp)
+                       && !(defClassp->existsMember(nestedAccess))) {
                 how = "'protected'";
             }
             if (how) {
diff --git a/src/verilog.y b/src/verilog.y
index 3d66945f0..c1e5a51c4 100644
--- a/src/verilog.y
+++ b/src/verilog.y
@@ -7354,8 +7354,7 @@ class_item<nodep>:                      // ==IEEE: class_item
         |       class_method                            { $$ = $1; }
         |       class_constraint                        { $$ = $1; }
         //
-        |       class_declaration
-                        { $$ = nullptr; BBUNSUP($1, "Unsupported: class within class"); }
+        |       class_declaration                       { $$ = $1; }
         |       timeunits_declaration                   { $$ = $1; }
         |       covergroup_declaration
                         { $$ = nullptr; BBCOVERIGN($1, "Ignoring unsupported: covergroup within class"); }
diff --git a/test_regress/t/t_class_class.out b/test_regress/t/t_class_class.out
deleted file mode 100644
index 2ec79ad39..000000000
--- a/test_regress/t/t_class_class.out
+++ /dev/null
@@ -1,5 +0,0 @@
-%Error-UNSUPPORTED: t/t_class_class.v:12:4: Unsupported: class within class
-   12 |    class SubCls;
-      |    ^~~~~
-                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
-%Error: Exiting due to
diff --git a/test_regress/t/t_class_class.py b/test_regress/t/t_class_class.py
index 710a094ab..d4f986441 100755
--- a/test_regress/t/t_class_class.py
+++ b/test_regress/t/t_class_class.py
@@ -11,6 +11,8 @@ import vltest_bootstrap
 
 test.scenarios('simulator')
 
-test.compile(fails=test.vlt_all, expect_filename=test.golden_filename)
+test.compile()
+
+test.execute()
 
 test.passes()
diff --git a/test_regress/t/t_class_class.v b/test_regress/t/t_class_class.v
index bf1ae7da4..14177f768 100644
--- a/test_regress/t/t_class_class.v
+++ b/test_regress/t/t_class_class.v
@@ -31,5 +31,8 @@ module t (/*AUTOARG*/);
       if (c.imemberb != 20) $stop;
       if (c.sc.smembera != 30) $stop;
       if (c.sc.smemberb != 40) $stop;
+
+      $write("*-* All Finished *-*\n");
+      $finish;
    end
 endmodule
diff --git a/test_regress/t/t_class_compare.v b/test_regress/t/t_class_compare.v
index bcbb1842a..b20d435cd 100644
--- a/test_regress/t/t_class_compare.v
+++ b/test_regress/t/t_class_compare.v
@@ -11,6 +11,9 @@
 `define check_ne(lhs, rhs) `check_comp(lhs, rhs, ==, 1'b0) `check_comp(lhs, rhs, !=, 1'b1)
 
 class Cls;
+   class InnerCls;
+      int j;
+   endclass
    int i;
 endclass
 
@@ -22,14 +25,25 @@ module t;
       Cls a = new;
       Cls b = new;
       ExtendCls ext = new;
+      Cls::InnerCls ia = new;
+      Cls::InnerCls ib = new;
+      ExtendCls::InnerCls iext = new;
       `check_ne(a, b)
       `check_ne(a, ext)
       `check_ne(ext, a)
+      `check_ne(ia, ib)
+      `check_ne(ia, iext)
+      `check_ne(iext, ia)
       a = b;
+      ia = ib;
       `check_eq(a, b)
+      `check_eq(ia, ib)
       a = ext;
+      ia = iext;
       `check_eq(a, ext)
       `check_eq(ext, a)
+      `check_eq(ia, iext)
+      `check_eq(iext, ia)
       $write("*-* All Finished *-*\n");
       $finish;
    end
diff --git a/test_regress/t/t_class_extends1.v b/test_regress/t/t_class_extends1.v
index c0f8ceeec..afe7878d9 100644
--- a/test_regress/t/t_class_extends1.v
+++ b/test_regress/t/t_class_extends1.v
@@ -5,21 +5,55 @@
 // SPDX-License-Identifier: CC0-1.0
 
 class Base0;
+   class BaseInnerOnly;
+     int inneronly;
+     function new();
+       inneronly = 10;
+       if (inneronly != 10) $stop;
+     endfunction
+   endclass
+
+   class BaseInnerOver;
+     int innerover;
+     function new();
+       innerover = 10;
+       if (innerover != 10) $stop;
+     endfunction
+   endclass
+
    int baseonly;
    int baseover;
+   BaseInnerOnly inneronly = new;
+   BaseInnerOver innerover = new;
 
    function void b_set_bo(int v); baseover = v; endfunction
    function int b_get_bo(); return baseover; endfunction
    function int get_bo(); return baseover; endfunction
+   function void b_set_io(int v); innerover.innerover = v; endfunction
+   function int b_get_io(); return innerover.innerover; endfunction
+   function int get_io(); return innerover.innerover; endfunction
 endclass
 
 class Ext extends Base0;
+   class BaseInnerOver;
+     int innerover;
+     function new();
+       innerover = 20;
+       if (innerover != 20) $stop;
+     endfunction
+   endclass
+
    int baseover;
    int extonly;
+   BaseInnerOnly inneronly = new;
+   BaseInnerOver innerover = new;
 
    function void e_set_bo(int v); baseover = v; endfunction
    function int e_get_bo(); return baseover; endfunction
    function int get_bo(); return baseover; endfunction
+   function void e_set_io(int v); innerover.innerover = v; endfunction
+   function int e_get_io(); return innerover.innerover; endfunction
+   function int get_io(); return innerover.innerover; endfunction
 endclass
 
 module t (/*AUTOARG*/);
@@ -29,15 +63,24 @@ module t (/*AUTOARG*/);
       c.baseonly = 10;
       c.baseover = 20;
       c.extonly = 30;
+      c.inneronly.inneronly = 40;
+      c.innerover.innerover = 50;
       if (c.baseonly != 10) $stop;
       if (c.baseover != 20) $stop;
       if (c.extonly != 30) $stop;
+      if (c.inneronly.inneronly != 40) $stop;
+      if (c.innerover.innerover != 50) $stop;
 
       c.b_set_bo(100);
       c.e_set_bo(200);
+      c.b_set_io(300);
+      c.e_set_io(400);
       if (c.b_get_bo() != 100) $stop;
       if (c.e_get_bo() != 200) $stop;
       if (c.get_bo() != 200) $stop;
+      if (c.b_get_io() != 300) $stop;
+      if (c.e_get_io() != 400) $stop;
+      if (c.get_io() != 400) $stop;
 
       $write("*-* All Finished *-*\n");
       $finish;
diff --git a/test_regress/t/t_class_extends2.v b/test_regress/t/t_class_extends2.v
index 8c30f0c6b..14d50907b 100644
--- a/test_regress/t/t_class_extends2.v
+++ b/test_regress/t/t_class_extends2.v
@@ -6,22 +6,59 @@
 
 package Pkg;
 class Base0;
+   class BaseInnerOnly;
+     int inneronly;
+     function new();
+       inneronly = 10;
+       if (inneronly != 10) $stop;
+     endfunction
+   endclass
+
+   class BaseInnerOver;
+     int innerover;
+     function new();
+       innerover = 10;
+       if (innerover != 10) $stop;
+     endfunction
+   endclass
+
    int baseonly;
    int baseover;
+   BaseInnerOnly inneronly = new;
+   BaseInnerOver innerover = new;
 
    function void b_set_bo(int v); baseover = v; endfunction
    function int b_get_bo(); return baseover; endfunction
    function int get_bo(); return baseover; endfunction
+   function void b_set_io(int v); innerover.innerover = v; endfunction
+   function int b_get_io(); return innerover.innerover; endfunction
+   function int get_io(); return innerover.innerover; endfunction
 endclass
 endpackage
 
+// We need to import Base0, as verilator currently doesn't support
+// multiple `::` references, but we would need to do that to reference
+// `BaseInnerOnly` class inside `Ext` class.
+import Pkg::Base0;
 class Ext extends Pkg::Base0;
+   class BaseInnerOver;
+     int innerover;
+     function new();
+       innerover = 20;
+       if (innerover != 20) $stop;
+     endfunction
+   endclass
    int baseover;
    int extonly;
+   BaseInnerOnly inneronly = new;
+   BaseInnerOver innerover = new;
 
    function void e_set_bo(int v); baseover = v; endfunction
    function int e_get_bo(); return baseover; endfunction
    function int get_bo(); return baseover; endfunction
+   function void e_set_io(int v); innerover.innerover = v; endfunction
+   function int e_get_io(); return innerover.innerover; endfunction
+   function int get_io(); return innerover.innerover; endfunction
 endclass
 
 module t (/*AUTOARG*/);
@@ -31,15 +68,24 @@ module t (/*AUTOARG*/);
       c.baseonly = 10;
       c.baseover = 20;
       c.extonly = 30;
+      c.inneronly.inneronly = 40;
+      c.innerover.innerover = 50;
       if (c.baseonly != 10) $stop;
       if (c.baseover != 20) $stop;
       if (c.extonly != 30) $stop;
+      if (c.inneronly.inneronly != 40) $stop;
+      if (c.innerover.innerover != 50) $stop;
 
       c.b_set_bo(100);
       c.e_set_bo(200);
+      c.b_set_io(300);
+      c.e_set_io(400);
       if (c.b_get_bo() != 100) $stop;
       if (c.e_get_bo() != 200) $stop;
       if (c.get_bo() != 200) $stop;
+      if (c.b_get_io() != 300) $stop;
+      if (c.e_get_io() != 400) $stop;
+      if (c.get_io() != 400) $stop;
 
       $write("*-* All Finished *-*\n");
       $finish;
diff --git a/test_regress/t/t_class_extends_param.v b/test_regress/t/t_class_extends_param.v
index f84fe1fa2..f8544aa80 100644
--- a/test_regress/t/t_class_extends_param.v
+++ b/test_regress/t/t_class_extends_param.v
@@ -8,26 +8,53 @@ module t (/*AUTOARG*/
    );
 
    class Foo;
+      class InnerFoo;
+        int y = 10;
+        function int get_y;
+           return y;
+         endfunction
+        function int get_30;
+           return 30;
+         endfunction
+      endclass
+
       int x = 1;
+      InnerFoo foo = new;
       function int get_x;
          return x;
       endfunction
       function int get_3;
          return 3;
       endfunction
+      function InnerFoo get_foo;
+        return foo;
+      endfunction
    endclass
 
    class Bar #(type T=Foo) extends T;
    endclass
 
    class Baz;
+      class InnerFoo;
+        int y = 20;
+        function int get_y;
+           return y;
+         endfunction
+        function int get_40;
+           return 40;
+         endfunction
+      endclass
       int x = 2;
+      InnerFoo foo = new;
       function int get_x;
          return x;
       endfunction
       function int get_4;
          return 4;
       endfunction
+      function InnerFoo get_foo;
+        return foo;
+      endfunction
    endclass
 
    class ExtendBar extends Bar#();
@@ -71,6 +98,9 @@ module t (/*AUTOARG*/
       function int get_x_of_item(int i);
          return q[i].x;
       endfunction
+      function int get_y_of_item(int i);
+        return q[i].get_foo().get_y();
+      endfunction
    endclass
 
    Bar #() bar_foo_i;
@@ -93,8 +123,12 @@ module t (/*AUTOARG*/
 
       if (bar_foo_i.get_x() != 1) $stop;
       if (bar_foo_i.get_3() != 3) $stop;
+      if (bar_foo_i.get_foo().get_y() != 10) $stop;
+      if (bar_foo_i.get_foo().get_30() != 30) $stop;
       if (bar_baz_i.get_x() != 2) $stop;
       if (bar_baz_i.get_4() != 4) $stop;
+      if (bar_baz_i.get_foo().get_y() != 20) $stop;
+      if (bar_baz_i.get_foo().get_40() != 40) $stop;
       if (extend_bar_i.get_x() != 1) $stop;
       if (extend_bar_i.get_6() != 6) $stop;
       if (extend_bar_i.get_x() != 1) $stop;
@@ -106,6 +140,7 @@ module t (/*AUTOARG*/
       if (extend_extend_bar_i.get_x() != 1) $stop;
       if (extend_extend_bar_i.get_12() != 12) $stop;
       if (extend_foo_dict_i.get_x_of_item(1) != 1) $stop;
+      if (extend_foo_dict_i.get_y_of_item(1) != 10) $stop;
 
       $write("*-* All Finished *-*\n");
       $finish;
diff --git a/test_regress/t/t_class_extends_this.v b/test_regress/t/t_class_extends_this.v
index fb185267d..00fd653b9 100644
--- a/test_regress/t/t_class_extends_this.v
+++ b/test_regress/t/t_class_extends_this.v
@@ -7,7 +7,20 @@
 typedef class Cls;
 
 class Base;
+   class BaseInner;
+      int value = 10;
+      function void test;
+         if (value != 10) $stop;
+         if (this.value != 10) $stop;
+         value = 20;
+         if (value != 20) $stop;
+         this.value = 30;
+         if (value != 30) $stop;
+      endfunction
+   endclass
+
    int value = 1;
+   BaseInner inner = new;
    function void test;
       if (value != 1) $stop;
       if (this.value != 1) $stop;
@@ -19,7 +32,25 @@ class Base;
 endclass
 
 class Cls extends Base;
+   class BaseInner extends Base::BaseInner;
+      int value = 100;
+      function void test;
+         if (value != 100) $stop;
+         if (this.value != 100) $stop;
+         if (super.value != 10) $stop;
+         super.test();
+         if (value != 100) $stop;
+         if (this.value != 100) $stop;
+         if (super.value != 30) $stop;
+         value = 200;
+         if (value != 200) $stop;
+         this.value = 300;
+         if (value != 300) $stop;
+      endfunction
+   endclass
+
    int value = 20;
+   BaseInner inner = new;
    function void test;
       if (value != 20) $stop;
       if (this.value != 20) $stop;
@@ -31,7 +62,9 @@ class Cls extends Base;
       super.value = 9;
       this.value = 29;
       if (super.value != 9) $stop;
-      if (value != 29) $stop;;
+      if (value != 29) $stop;
+
+      inner.test();
    endfunction
 endclass
 
diff --git a/test_regress/t/t_class_extends_this3.v b/test_regress/t/t_class_extends_this3.v
index 20a66e469..908276e58 100644
--- a/test_regress/t/t_class_extends_this3.v
+++ b/test_regress/t/t_class_extends_this3.v
@@ -7,15 +7,24 @@
 typedef class Cls;
 
 class Base;
+   class Inner;
+      int value = 10;
+      function void testBaseInner;
+         if (value != 10) $stop;
+      endfunction
+   endclass
    int value = 1;
+   Inner inner = new;
    function void testBase;
       if (value != 1) $stop;
+      if (inner.value != 10) $stop;
    endfunction
 endclass
 
 class Cls extends Base;
    function void testDerived;
       if (value != 1) $stop;
+      if (inner.value != 10) $stop;
    endfunction
 endclass
 
@@ -25,6 +34,7 @@ module t (/*AUTOARG*/);
       c = new;
       c.testBase();
       c.testDerived();
+      c.inner.testBaseInner();
       $write("*-* All Finished *-*\n");
       $finish;
    end
diff --git a/test_regress/t/t_class_extern.v b/test_regress/t/t_class_extern.v
index 0cddfdc3f..3afa91045 100644
--- a/test_regress/t/t_class_extern.v
+++ b/test_regress/t/t_class_extern.v
@@ -13,6 +13,16 @@ class Cls;
    extern task ext_t_np;
    extern task ext_t_p();
    extern task ext_t_i(int in);
+   class SubCls;
+      int value;
+      extern function int ext_f_np;
+      extern function int ext_f_p();
+      extern function int ext_f_i(int in);
+      extern static function int get_10();
+      extern task ext_t_np;
+      extern task ext_t_p();
+      extern task ext_t_i(int in);
+   endclass
 endclass
 
 function int Cls::ext_f_np;
@@ -42,15 +52,51 @@ task Cls::ext_t_i(int in);
    value = in;
 endtask
 
+function int Cls::SubCls::ext_f_np;
+   return 10;
+endfunction
+
+function int Cls::SubCls::ext_f_p();
+   return value;
+endfunction
+
+function int Cls::SubCls::ext_f_i(int in);
+   return in+10;
+endfunction
+
+function int Cls::SubCls::get_10();
+   return 10;
+endfunction
+
+task Cls::SubCls::ext_t_np();
+   $write("Cls::SubCls::ext_t_np\n");
+endtask
+task Cls::SubCls::ext_t_p();
+   $write("Cls::SubCls::ext_t_p\n");
+endtask
+task Cls::SubCls::ext_t_i(int in);
+   if (in != 20) $stop;
+   value = in;
+endtask
+
+
 module t (/*AUTOARG*/);
    initial begin
       Cls c = new;
+      Cls::SubCls subc = new;
       c.ext_t_i(2);
-      c.ext_t_np();
-      c.ext_t_p();
       if (c.ext_f_np() != 1) $stop;
       if (c.ext_f_p() != 2) $stop;
       if (c.ext_f_i(10) != 11) $stop;
       if (Cls::get_1() != 1) $stop;
+      subc.ext_t_i(20);
+      if (subc.ext_f_np() != 10) $stop;
+      if (subc.ext_f_p() != 20) $stop;
+      if (subc.ext_f_i(11) != 21) $stop;
+      if (Cls::SubCls::get_10() != 10) $stop;
+      subc.ext_t_np();
+      subc.ext_t_p();
+      c.ext_t_np();
+      c.ext_t_p();
    end
 endmodule
diff --git a/test_regress/t/t_class_local.v b/test_regress/t/t_class_local.v
index 0a5b6cf78..db9d9e975 100644
--- a/test_regress/t/t_class_local.v
+++ b/test_regress/t/t_class_local.v
@@ -31,6 +31,34 @@ class Cls;
       Cls::s_loc();  // Ok
       Cls::s_prot();  // Ok
    endtask
+   class InnerCls;
+      typedef enum {A = 10, B = 20, C = 30} en_t;
+
+      int m_pub = 1;
+      local int m_loc = 2;
+      protected int m_prot = B;
+      task f_pub; endtask
+      local task f_loc; endtask
+      protected task f_prot; endtask
+      static task s_pub; endtask
+      static local task s_loc; endtask
+      static protected task s_prot; endtask
+      task check;
+         Cls o;
+         if (m_pub != 1) $stop;
+         if (m_loc != 2) $stop;
+         if (m_prot != 20) $stop;
+         f_pub();  // Ok
+         f_loc();  // Ok
+         f_prot();  // Ok
+         s_pub();  // Ok
+         s_loc();  // Ok
+         s_prot();  // Ok
+         Cls::s_pub();  // Ok
+         Cls::s_loc();  // Ok
+         Cls::s_prot();  // Ok
+      endtask
+   endclass
 endclass
 
 class Ext extends Cls;
@@ -44,27 +72,52 @@ class Ext extends Cls;
       Cls::s_pub();  // Ok
       Cls::s_prot();  // Ok
    endtask
+   class ExtInner extends Cls::InnerCls;
+      task check;
+         if (m_pub != 1) $stop;
+         if (m_prot != 20) $stop;
+         f_pub();  // Ok
+         f_prot();  // Ok
+         s_pub();  // Ok
+         s_prot();  // Ok
+         Cls::InnerCls::s_pub();  // Ok
+         Cls::InnerCls::s_prot();  // Ok
+      endtask
+   endclass
 endclass
 
 module t (/*AUTOARG*/);
    const Cls mod_c = new;
+   const Cls::InnerCls imod_c = new;
 
    initial begin
       Cls c;
+      Cls::InnerCls i;
       Ext e;
+      Ext::ExtInner ei;
       if (c.A != 10) $stop;
+      if (i.A != 10) $stop;
       c = new;
+      i = new;
       e = new;
+      ei = new;
       if (c.m_pub != 1) $stop;
+      if (i.m_pub != 1) $stop;
       //
       if (mod_c.A != 10) $stop;
+      if (imod_c.A != 10) $stop;
       //
       c.check();
+      i.check();
       e.check();
+      ei.check();
       //
       Cls::s_pub();  // Ok
+      Cls::InnerCls::s_pub();  // Ok
       c.s_pub();  // Ok
+      i.s_pub();  // Ok
       e.s_pub();  // Ok
+      ei.s_pub();  // Ok
       //
       $write("*-* All Finished *-*\n");
       $finish;
diff --git a/test_regress/t/t_class_local_nested_bad.out b/test_regress/t/t_class_local_nested_bad.out
new file mode 100644
index 000000000..8f4b39314
--- /dev/null
+++ b/test_regress/t/t_class_local_nested_bad.out
@@ -0,0 +1,9 @@
+%Error-ENCAPSULATED: t/t_class_local_nested_bad.v:14:22: 'name' is hidden as 'local' within this context (IEEE 1800-2023 8.18)
+                                                       : ... note: In instance 't'
+   14 |         name = Node::name;
+      |                      ^~~~
+                     t/t_class_local_nested_bad.v:14:22: ... Location of definition
+    9 |         static local string name;
+      |                             ^~~~
+                     ... For error description see https://verilator.org/warn/ENCAPSULATED?v=latest
+%Error: Exiting due to
diff --git a/test_regress/t/t_class_local_nested_bad.py b/test_regress/t/t_class_local_nested_bad.py
new file mode 100755
index 000000000..710a094ab
--- /dev/null
+++ b/test_regress/t/t_class_local_nested_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('simulator')
+
+test.compile(fails=test.vlt_all, expect_filename=test.golden_filename)
+
+test.passes()
diff --git a/test_regress/t/t_class_local_nested_bad.v b/test_regress/t/t_class_local_nested_bad.v
new file mode 100644
index 000000000..f5e7b1155
--- /dev/null
+++ b/test_regress/t/t_class_local_nested_bad.v
@@ -0,0 +1,25 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Antmicro.
+// SPDX-License-Identifier: CC0-1.0
+
+class NodeList;
+    class Node;
+        static local string name;
+    endclass
+
+    string name;
+    function new();
+        name = Node::name;
+    endfunction
+endclass
+
+module t(/*AUTOARG*/);
+    initial begin
+        NodeList n = new;
+
+        $write("*-* All Finished *-*\n");
+        $finish;
+    end
+endmodule
diff --git a/test_regress/t/t_class_module.v b/test_regress/t/t_class_module.v
index 60f043d9c..483026de2 100644
--- a/test_regress/t/t_class_module.v
+++ b/test_regress/t/t_class_module.v
@@ -7,8 +7,13 @@
 module t (/*AUTOARG*/);
 
 class Cls;
+   class Inner;
+      int imemberinnera;
+      int imemberinnerb;
+   endclass
    int imembera;
    int imemberb;
+   Inner innermemberc;
 endclass : Cls
 
 class Dead;
@@ -18,10 +23,16 @@ endclass
       Cls c;
       if (c != null) $stop;
       c = new;
+      if (c.innermemberc != null) $stop;
+      c.innermemberc = new;
       c.imembera = 10;
       c.imemberb = 20;
+      c.innermemberc.imemberinnera = 30;
+      c.innermemberc.imemberinnerb = 40;
       if (c.imembera != 10) $stop;
       if (c.imemberb != 20) $stop;
+      if (c.innermemberc.imemberinnera != 30) $stop;
+      if (c.innermemberc.imemberinnerb != 40) $stop;
       $write("*-* All Finished *-*\n");
       $finish;
    end
diff --git a/test_regress/t/t_class_nested.py b/test_regress/t/t_class_nested.py
new file mode 100755
index 000000000..49d728ea8
--- /dev/null
+++ b/test_regress/t/t_class_nested.py
@@ -0,0 +1,18 @@
+#!/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')
+
+test.compile(verilator_flags2=["--exe --main"])
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_class_nested.v b/test_regress/t/t_class_nested.v
new file mode 100644
index 000000000..4a9e2e74d
--- /dev/null
+++ b/test_regress/t/t_class_nested.v
@@ -0,0 +1,90 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Antmicro.
+// SPDX-License-Identifier: CC0-1.0
+
+class NodeList;
+    class Node;
+        string name;
+        Node link;
+
+        function new();
+            name = "node";
+        endfunction
+    endclass
+
+    Node head;
+endclass
+
+class NodeTree;
+    class Node;
+        int id;
+        Node link;
+    endclass
+
+    Node root;
+endclass
+
+// Based on IEEE 1800-2017 section 8.23 Nested classes
+class Outer;
+    int outerProp;
+    local int outerLocalProp;
+    static int outerStaticProp;
+    static local int outerLocalStaticProp;
+
+    class Inner;
+        function void innerMethod(Outer h);
+            outerStaticProp = 1;
+            outerLocalStaticProp = 1;
+            h.outerProp = 1;
+            h.outerLocalProp = 1;
+        endfunction
+    endclass
+endclass
+
+
+module t(/*AUTOARG*/);
+    initial begin
+        NodeList n = new;
+        NodeList::Node n1 = new;
+        NodeList::Node n2 = new;
+        NodeTree tr = new;
+        NodeTree::Node t1 = new;
+        NodeTree::Node t2 = new;
+        Outer o = new;
+        Outer::Inner i = new;
+
+        i.innerMethod(o);
+
+        if(o.outerProp != 1) $stop;
+        if(Outer::outerStaticProp != 1) $stop;
+
+        if (n1.name != "node") $stop;
+
+        n1.name = "n1";
+        if (n1.name != "n1") $stop;
+
+        n2.name = "n2";
+        if (n2.name != "n2") $stop;
+
+        n.head = n1;
+        n1.link = n2;
+        if (n.head.name != "n1") $stop;
+        if (n.head.link.name != "n2") $stop;
+
+        t1.id = 1;
+        if (t1.id != 1) $stop;
+
+        t2.id = 2;
+        if (t2.id != 2) $stop;
+
+        tr.root = t1;
+        t1.link = t2;
+        if (tr.root.id != 1) $stop;
+        if (tr.root.link.id != 2) $stop;
+
+        $write("*-* All Finished *-*\n");
+        $finish;
+    end
+endmodule
diff --git a/test_regress/t/t_class_new.v b/test_regress/t/t_class_new.v
index 9d625c5a5..8f4ba17d5 100644
--- a/test_regress/t/t_class_new.v
+++ b/test_regress/t/t_class_new.v
@@ -11,6 +11,17 @@ class ClsNoArg;
       imembera = 5;
       if (other != 6) $stop;
    endfunction : new
+   class InnerNoArg;
+      const int imembera;
+      function new();
+         int other = other_func();
+         imembera = 5;
+         if (other != 6) $stop;
+      endfunction
+      function int other_func();
+         return 6;
+      endfunction
+   endclass
    function int other_func();
       return 6;
    endfunction
@@ -52,6 +63,7 @@ module t (/*AUTOARG*/);
       ClsArg   c2;
       Cls2Arg  c3;
       Cls2Arg  c4;
+      ClsNoArg::InnerNoArg c5 = new;
 
       c1 = new;
       if (c1.imembera != 5) $stop;
@@ -72,6 +84,9 @@ module t (/*AUTOARG*/);
       if (c4.imembera != 6) $stop;
       if (c4.imemberb != 9) $stop;
 
+      c5 = new;
+      if (c5.imembera != 5) $stop;
+
       $write("*-* All Finished *-*\n");
       $finish;
    end
diff --git a/test_regress/t/t_class_param.v b/test_regress/t/t_class_param.v
index f2510ed1d..62ed7508a 100644
--- a/test_regress/t/t_class_param.v
+++ b/test_regress/t/t_class_param.v
@@ -42,6 +42,9 @@ class Cls #(parameter PBASE = 12);
       return PBASE;
    endfunction
    typedef enum { E_PBASE = PBASE } enum_t;
+   class ClsInner;
+      bit [PBASE-1:0] member;
+   endclass
 endclass
 
 typedef Cls#(8) Cls8_t;
@@ -136,6 +139,8 @@ module t (/*AUTOARG*/);
    Cls c12;
    Cls #(.PBASE(4)) c4;
    Cls8_t c8;
+   Cls#()::ClsInner ci;
+   Cls#(8)::ClsInner ci8;
    Wrap #(.P(16)) w16;
    Wrap2 #(.P(32)) w32;
    SelfRefClassTypeParam src_logic;
@@ -155,6 +160,8 @@ module t (/*AUTOARG*/);
       c12 = new;
       c4 = new;
       c8 = new;
+      ci = new;
+      ci8 = new;
       w16 = new;
       w32 = new;
       src_int = new;
@@ -195,6 +202,10 @@ module t (/*AUTOARG*/);
       c4.member = 32'haaaaaaaa;
       c8.member = 32'haaaaaaaa;
       // verilator lint_on WIDTH
+      ci.member = 12'haaa;
+      ci8.member = 8'hff;
+      if (ci.member != 12'haaa) $stop;
+      if (ci8.member != 8'hff) $stop;
       if (c12.member != 12'haaa) $stop;
       if (c4.member != 4'ha) $stop;
       if (c12.get_member() != 12'haaa) $stop;
diff --git a/test_regress/t/t_class_param_rewrite.v b/test_regress/t/t_class_param_rewrite.v
index 17664ec71..b88019127 100644
--- a/test_regress/t/t_class_param_rewrite.v
+++ b/test_regress/t/t_class_param_rewrite.v
@@ -14,10 +14,18 @@ module test;
       if (enum_item.first().name() != "BAR_0")
         $stop;
     endfunction
+    class Inner1;
+      static function void print();
+        E enum_item;
+        if (enum_item.first().name() != "BAR_0")
+          $stop;
+      endfunction
+    endclass
   endclass
 
   initial begin
     baz#(bar_e)::print();
+    baz#(bar_e)::Inner1::print();
 
     $write("*-* All Finished *-*\n");
     $finish;
diff --git a/test_regress/t/t_class_static_member.v b/test_regress/t/t_class_static_member.v
index 1867b73b0..f6a0be448 100644
--- a/test_regress/t/t_class_static_member.v
+++ b/test_regress/t/t_class_static_member.v
@@ -8,6 +8,12 @@
 `define checkh(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got='h%x exp='h%x\n", `__FILE__,`__LINE__, (gotv), (expv)); `stop; end while(0);
 
 class Cls;
+   class InnerCls;
+      static function int f_inner_cs_st();
+         ++c_st; return c_st;
+      endfunction
+   endclass
+
    int c_no = 2;
    //automatic int c_au = 2;  // automatic not a legal keyword here
    static int c_st = 22;
@@ -22,7 +28,6 @@ class Cls;
    static function int f_cs_st ();
       ++c_st; return c_st;
    endfunction
-
 endclass
 
 module t (/*AUTOARG*/);
@@ -43,6 +48,7 @@ module t (/*AUTOARG*/);
       v = b.f_c_st(); `checkh(v, 26);
       //
       v = Cls::f_cs_st(); `checkh(v, 27);
+      v = Cls::InnerCls::f_inner_cs_st(); `checkh(v, 28);
 
       $write("*-* All Finished *-*\n");
       $finish;
diff --git a/test_regress/t/t_class_virtual.v b/test_regress/t/t_class_virtual.v
index 5b2e9511d..8c0b80920 100644
--- a/test_regress/t/t_class_virtual.v
+++ b/test_regress/t/t_class_virtual.v
@@ -8,18 +8,33 @@ virtual class VBase;
    virtual function int hello;
       return 1;
    endfunction
+   virtual class VNested;
+      virtual function int hello;
+         return 10;
+      endfunction
+   endclass
 endclass
 
 class VA extends VBase;
    virtual function int hello;
       return 2;
    endfunction
+   class VNested extends VBase::VNested;
+      virtual function int hello;
+         return 20;
+      endfunction
+   endclass
 endclass
 
 class VB extends VBase;
    virtual function int hello;
       return 3;
    endfunction
+   class VNested extends VBase::VNested;
+      virtual function int hello;
+         return 30;
+      endfunction
+   endclass
 endclass
 
 virtual class uvm_phase;
@@ -59,18 +74,27 @@ module t;
    initial begin
       VA va = new;
       VB vb = new;
+      VA::VNested vna = new;
+      VB::VNested vnb = new;
       VBase b;
+      VBase::VNested bn;
 
       uvm_build_phase ph;
       ExtendsCls ec;
 
       if (va.hello() != 2) $stop;
       if (vb.hello() != 3) $stop;
+      if (vna.hello() != 20) $stop;
+      if (vnb.hello() != 30) $stop;
 
       b = va;
+      bn = vna;
       if (b.hello() != 2) $stop;
+      if (bn.hello() != 20) $stop;
       b = vb;
+      bn = vnb;
       if (b.hello() != 3) $stop;
+      if (bn.hello() != 30) $stop;
 
       ph = new;
       if (ph.get1() != 1) $stop;
diff --git a/test_regress/t/t_implements_nested.py b/test_regress/t/t_implements_nested.py
new file mode 100755
index 000000000..c2d985114
--- /dev/null
+++ b/test_regress/t/t_implements_nested.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()
+
+test.passes()
diff --git a/test_regress/t/t_implements_nested.v b/test_regress/t/t_implements_nested.v
new file mode 100644
index 000000000..87fc8d603
--- /dev/null
+++ b/test_regress/t/t_implements_nested.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, 2025 Antmicro.
+// SPDX-License-Identifier: CC0-1.0
+
+class Cls;
+   // IEEE 2023 only disallows nested interface inside another interface, not
+   // class
+   interface class good_can_nest;
+   endclass
+endclass
+
+module t (/*AUTOARG*/);
+   Cls c;
+endmodule
diff --git a/test_regress/t/t_implements_nested_bad.out b/test_regress/t/t_implements_nested_bad.out
index 1121c001f..fab3573e0 100644
--- a/test_regress/t/t_implements_nested_bad.out
+++ b/test_regress/t/t_implements_nested_bad.out
@@ -1,5 +1,4 @@
-%Error-UNSUPPORTED: t/t_implements_nested_bad.v:8:14: Unsupported: class within class
-    8 |    interface class bad_cannot_nest;
-      |              ^~~~~
-                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+%Error: t/t_implements_nested_bad.v:9:17: Interface class shall not be nested within another interface class. (IEEE 1800-2023 8.26)
+    9 |       interface class bad_cannot_nest;
+      |                 ^~~~~
 %Error: Exiting due to
diff --git a/test_regress/t/t_implements_nested_bad.v b/test_regress/t/t_implements_nested_bad.v
index 119033fa3..be483fb27 100644
--- a/test_regress/t/t_implements_nested_bad.v
+++ b/test_regress/t/t_implements_nested_bad.v
@@ -5,7 +5,9 @@
 // SPDX-License-Identifier: CC0-1.0
 
 class Cls;
-   interface class bad_cannot_nest;
+   interface class inte;
+      interface class bad_cannot_nest;
+      endclass
    endclass
 endclass
 
diff --git a/test_regress/t/t_semaphore_class_nested.py b/test_regress/t/t_semaphore_class_nested.py
new file mode 100755
index 000000000..bbbcfc078
--- /dev/null
+++ b/test_regress/t/t_semaphore_class_nested.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('simulator')
+
+test.compile(verilator_flags2=["--binary --timing"])
+
+test.passes()
diff --git a/test_regress/t/t_semaphore_class_nested.v b/test_regress/t/t_semaphore_class_nested.v
new file mode 100644
index 000000000..c18f65b45
--- /dev/null
+++ b/test_regress/t/t_semaphore_class_nested.v
@@ -0,0 +1,39 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Antmicro.
+// SPDX-License-Identifier: CC0-1.0
+
+class semaphore_cls;
+   class InnerKeyClass;
+      int innerKeys;
+      function new(int keyCount = 0);
+         innerKeys = keyCount;
+      endfunction
+   endclass
+   // Test an implementation similar to what Verilator will do internally
+   InnerKeyClass m_keys;
+   function new(int keyCount = 0);
+      m_keys = new(keyCount);
+   endfunction
+   function void put(int keyCount = 1);
+      m_keys.innerKeys += keyCount;
+   endfunction
+   task get(int keyCount = 1);
+      wait (m_keys.innerKeys >= keyCount);
+      m_keys.innerKeys -= keyCount;
+   endtask
+   function int try_get(int keyCount = 1);
+      if (m_keys.innerKeys >= keyCount) begin
+         m_keys.innerKeys -= keyCount;
+         return 1;
+      end
+      else begin
+         return 0;
+      end
+   endfunction
+endclass
+
+`define SEMAPHORE_T semaphore_cls
+
+`include "t_semaphore.v"