From 8f18f0cf225245eb7fc380957e4f06d65e46e44c Mon Sep 17 00:00:00 2001
From: Wilson Snyder <wsnyder@wsnyder.org>
Date: Tue, 28 Apr 2026 17:59:18 -0400
Subject: [PATCH] Fix internal error instead of missing prototype error
 (#7485). [Alex Solomatnikov]

Fixes #7485.
---
 Changes                                    |  1 +
 src/V3LinkDot.cpp                          |  1 +
 src/V3SymTable.h                           | 11 ++++++++++-
 test_regress/t/t_class_extern_mis2_bad.out |  5 +++++
 test_regress/t/t_class_extern_mis2_bad.py  | 16 ++++++++++++++++
 test_regress/t/t_class_extern_mis2_bad.v   | 21 +++++++++++++++++++++
 6 files changed, 54 insertions(+), 1 deletion(-)
 create mode 100644 test_regress/t/t_class_extern_mis2_bad.out
 create mode 100755 test_regress/t/t_class_extern_mis2_bad.py
 create mode 100644 test_regress/t/t_class_extern_mis2_bad.v

diff --git a/Changes b/Changes
index 6ad820bff..6f3f2c62c 100644
--- a/Changes
+++ b/Changes
@@ -17,6 +17,7 @@ Verilator 5.049 devel
 * Fix inlining static initializer in V3Gate (#5381) (#7503). [Andrew Nolte] [Geza Lore, Testorrent USA, Inc.]
 * Fix generic interface port forwarded to a nested instance (#7454) (#7457). [Yilou Wang]
 * Fix internal error on multi-cycle SVA under default clocking (#7472) (#7506). [Yilou Wang]
+* Fix internal error instead of missing prototype error (#7485). [Alex Solomatnikov]
 * Fix mailbox#(packed_struct) type mismatch with parameterized class (#7494) (#7495). [Nikolai Kumar]
 * Fix std::randomize internal error on static member of different class (#7498) (#7499). [Alex Solomatnikov]
 * Fix virtual interface method call inlining and IMPURE suppression (#7505). [Nikolay Puzanov]
diff --git a/src/V3LinkDot.cpp b/src/V3LinkDot.cpp
index 758352a7f..66b9abcc6 100644
--- a/src/V3LinkDot.cpp
+++ b/src/V3LinkDot.cpp
@@ -193,6 +193,7 @@ public:
     void dumpSelf(const string& nameComment, bool force = false) {
         if (debug() >= 6 || dumpLevel() >= 6 || force) {
             const string filename = v3Global.debugFilename(nameComment) + ".txt";
+            UINFO(4, "Dumping " << filename);
             const std::unique_ptr<std::ofstream> logp{V3File::new_ofstream(filename)};
             if (logp->fail()) v3fatal("Can't write file: " << filename);
             std::ostream& os = *logp;
diff --git a/src/V3SymTable.h b/src/V3SymTable.h
index dbb5b383d..f3cb1bfb1 100644
--- a/src/V3SymTable.h
+++ b/src/V3SymTable.h
@@ -207,9 +207,18 @@ public:
     void importFromClass(VSymGraph* graphp, const VSymEnt* srcp) {
         // Import tokens from source symbol table into this symbol table
         // Used for classes in early parsing only to handle "extends"
+
+        // If an "extern foo" exists, then we can't import "foo" from the base class.
+        // But ok for "extern foo" and "foo" to both come from base (so must check before insert)
+        std::unordered_set<std::string> haveExterns;
         for (IdNameMap::const_iterator it = srcp->m_idNameMap.begin();
              it != srcp->m_idNameMap.end(); ++it) {
-            importOneSymbol(graphp, it->first, it->second, false);
+            if (m_idNameMap.count("extern " + it->first)) haveExterns.emplace(it->first);
+        }
+        for (IdNameMap::const_iterator it = srcp->m_idNameMap.begin();
+             it != srcp->m_idNameMap.end(); ++it) {
+            if (!haveExterns.count(it->first))
+                importOneSymbol(graphp, it->first, it->second, false);
         }
     }
     void importFromPackage(VSymGraph* graphp, const VSymEnt* srcp, const string& id_or_star) {
diff --git a/test_regress/t/t_class_extern_mis2_bad.out b/test_regress/t/t_class_extern_mis2_bad.out
new file mode 100644
index 000000000..2382ded8b
--- /dev/null
+++ b/test_regress/t/t_class_extern_mis2_bad.out
@@ -0,0 +1,5 @@
+%Error-PROTOTYPEMIS: t/t_class_extern_mis2_bad.v:15:21: Definition not found for extern prototype 'new'
+   15 |     extern function new();   
+      |                     ^~~
+                     ... For error description see https://verilator.org/warn/PROTOTYPEMIS?v=latest
+%Error: Exiting due to
diff --git a/test_regress/t/t_class_extern_mis2_bad.py b/test_regress/t/t_class_extern_mis2_bad.py
new file mode 100755
index 000000000..38cf36b43
--- /dev/null
+++ b/test_regress/t/t_class_extern_mis2_bad.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('linter')
+
+test.lint(fails=True, expect_filename=test.golden_filename)
+
+test.passes()
diff --git a/test_regress/t/t_class_extern_mis2_bad.v b/test_regress/t/t_class_extern_mis2_bad.v
new file mode 100644
index 000000000..a7985be14
--- /dev/null
+++ b/test_regress/t/t_class_extern_mis2_bad.v
@@ -0,0 +1,21 @@
+// 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
+
+package s_core_env_pkg;
+  virtual class x_scoreboard;
+    extern function void has_ext_ok();
+  endclass
+  function void x_scoreboard::has_ext_ok();
+  endfunction
+
+  class cls_misses_new_1 extends x_scoreboard;
+    extern function new();  // <--- BAD
+  endclass
+
+endpackage
+
+module t;
+endmodule