Fix recursive default assignment for subarrays (#4589) (#7202)

docs/CONTRIBUTORS

@@ -134,6 +134,7 @@ Jose Loyola
 Josep Sans
 Joseph Nwabueze
 Josh Redford
+Julian Carrier
 Julian Daube
 Julie Schwartz
 Julien Margetts

src/V3Const.cpp

@@ -2667,12 +2667,27 @@ class ConstVisitor final : public VNVisitor {
         iterateChildren(nodep);
         if (const AstInitArray* const initp = VN_CAST(nodep->lhsp(), InitArray)) {
             if (!(m_doExpensive || m_params)) return false;
-            // At present only support 1D unpacked arrays
-            const auto initOfConst = [](const AstNode* const nodep) -> bool {  //
-                return VN_IS(nodep, Const) || VN_IS(nodep, InitItem);
+            const auto isConstInit = [](const AstNode* const exprp,
+                                        const auto& isConstInitRecurse) -> bool {
+                if (VN_IS(exprp, Const)) return true;
+                if (const AstInitItem* const itemp = VN_CAST(exprp, InitItem)) {
+                    return isConstInitRecurse(itemp->valuep(), isConstInitRecurse);
+                }
+                if (const AstInitArray* const arrayp = VN_CAST(exprp, InitArray)) {
+                    const auto itemIsConstInit = [&isConstInitRecurse](const AstNode* const itemp)
+                        -> bool {
+                        return isConstInitRecurse(itemp, isConstInitRecurse);
+                    };
+                    if (arrayp->initsp() && !arrayp->initsp()->forall(itemIsConstInit)) return false;
+                    if (arrayp->defaultp()
+                        && !isConstInitRecurse(arrayp->defaultp(), isConstInitRecurse)) {
+                        return false;
+                    }
+                    return true;
+                }
+                return false;
             };
-            if (initp->initsp() && !initp->initsp()->forall(initOfConst)) return false;
-            if (initp->defaultp() && !initp->defaultp()->forall(initOfConst)) return false;
+            if (!isConstInit(initp, isConstInit)) return false;
         } else if (!VN_IS(nodep->lhsp(), Const)) {
             return false;
         }

src/V3Width.cpp

@@ -5282,6 +5282,34 @@ class WidthVisitor final : public VNVisitor {
         return newp;
     }
 
+    AstPatMember* defaultPatp_patternArray(AstPatMember* defaultp, AstNodeDType* elemDTypep) {
+        AstNodeExpr* const valuep = defaultp->lhssp()->cloneTree(false);
+        AstNodeDType* const elemDTypeSkipRefp = elemDTypep->skipRefp();
+
+        if (!VN_IS(elemDTypeSkipRefp, UnpackArrayDType)) {
+            VL_DO_DANGLING(pushDeletep(valuep), valuep);
+            return defaultp->cloneTree(false);
+        }
+        if (VN_IS(valuep, Pattern)) {
+            VL_DO_DANGLING(pushDeletep(valuep), valuep);
+            return defaultp->cloneTree(false);
+        }
+        if (!valuep->dtypep()) userIterate(valuep, WidthVP{SELF, BOTH}.p());
+        if (valuep->dtypep()
+            && AstNode::computeCastable(valuep->dtypep()->skipRefp(), elemDTypeSkipRefp, nullptr)
+                   .isAssignable()) {
+            VL_DO_DANGLING(pushDeletep(valuep), valuep);
+            return defaultp->cloneTree(false);
+        }
+
+        AstPatMember* const nestedDefaultp
+            = new AstPatMember{defaultp->fileline(), valuep, nullptr, nullptr};
+        nestedDefaultp->isDefault(true);
+        AstPattern* const recursivePatternp
+            = new AstPattern{defaultp->fileline(), nestedDefaultp};
+        return new AstPatMember{defaultp->fileline(), recursivePatternp, nullptr, nullptr};
+    }
+
     void patternArray(AstPattern* nodep, AstNodeArrayDType* arrayDtp, AstPatMember* defaultp) {
         const VNumRange range = arrayDtp->declRange();
         PatVecMap patmap = patVectorMap(nodep, range);
@@ -5296,7 +5324,7 @@ class WidthVisitor final : public VNVisitor {
             const auto it = patmap.find(ent);
             if (it == patmap.end()) {
                 if (defaultp) {
-                    newpatp = defaultp->cloneTree(false);
+                    newpatp = defaultPatp_patternArray(defaultp, arrayDtp->subDTypep());
                     patp = newpatp;
                 } else if (!(VN_IS(arrayDtp, UnpackArrayDType) && !allConstant && isConcat)) {
                     // If arrayDtp is an unpacked array and item is not constant,

test_regress/t/t_array_pattern_default_recursive.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()
+
+test.execute()
+
+test.passes()

test_regress/t/t_array_pattern_default_recursive.v

@@ -0,0 +1,38 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain.
+// SPDX-FileCopyrightText: 2026 Wilson Snyder
+// SPDX-License-Identifier: CC0-1.0
+
+module t;
+
+  int arr_default_scalar[4][4];
+  int row[4];
+  int arr_default_array[2][4];
+  int arr_mixed_default[2][3];
+
+  initial begin
+    arr_default_scalar = '{default: 0};
+    foreach (arr_default_scalar[i, j]) begin
+      if (arr_default_scalar[i][j] != 0) $stop;
+    end
+
+    row = '{1, 2, 3, 4};
+    arr_default_array = '{default: row};
+    foreach (arr_default_array[i, j]) begin
+      if (arr_default_array[i][j] != row[j]) $stop;
+    end
+
+    arr_mixed_default = '{0: '{0: 1, default: 3}, default: '{default: 2}};
+    if (arr_mixed_default[0][0] != 1) $stop;
+    if (arr_mixed_default[0][1] != 3) $stop;
+    if (arr_mixed_default[0][2] != 3) $stop;
+    if (arr_mixed_default[1][0] != 2) $stop;
+    if (arr_mixed_default[1][1] != 2) $stop;
+    if (arr_mixed_default[1][2] != 2) $stop;
+
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+
+endmodule

test_regress/t/t_assert_elab_p.out

@@ -1,4 +1,4 @@
--Info: t/t_assert_elab_p.v:14:5: %m test.sv:25: 4=4 2=2 STAGE_IDS='{'h1, 'h1, 'h1, 'h1}
+-Info: t/t_assert_elab_p.v:14:5: %m test.sv:25: 4=4 2=2 STAGE_IDS='{'{'h1, 'h1}, '{'h1, 'h1}, '{'h1, 'h1}, '{'h1, 'h1}}
                                : ... note: In instance 't.pipe'
    14 |     $info("%m %s:%0d: 4=%0d 2=%0d STAGE_IDS=%p", "test.sv", 25, 4, 2, STAGE_IDS);
       |     ^~~~~