From 78b21907c6b25418107c1bd7e337c11d05c7798b Mon Sep 17 00:00:00 2001
From: Daniel Kroening <dkr@amazon.com>
Date: Tue, 3 Mar 2026 19:34:45 +0000
Subject: [PATCH] SystemVerilog: detect import conflicts

Per IEEE 1800-2017 section 26.3, this adds error detection for:
- Direct imports that conflict with local declarations
- Wildcard imports that are used in expressions and then redeclared

Wildcard imports that are not used remain 'potentially locally visible'
and can be shadowed by local declarations.
---
 regression/verilog/packages/import6.desc |  4 ++--
 regression/verilog/packages/import8.desc |  2 +-
 src/verilog/verilog_scope.cpp            | 18 ++++++++++++++++++
 src/verilog/verilog_scope.h              |  7 +------
 4 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/regression/verilog/packages/import6.desc b/regression/verilog/packages/import6.desc
index bcb0df282..cf9c2675d 100644
--- a/regression/verilog/packages/import6.desc
+++ b/regression/verilog/packages/import6.desc
@@ -1,7 +1,7 @@
-KNOWNBUG
+CORE
 import6.sv
 --bound 0
-^EXIT=2$
+^EXIT=6$
 ^SIGNAL=0$
 --
 --
diff --git a/regression/verilog/packages/import8.desc b/regression/verilog/packages/import8.desc
index 16e116fcb..0313a744c 100644
--- a/regression/verilog/packages/import8.desc
+++ b/regression/verilog/packages/import8.desc
@@ -1,7 +1,7 @@
 KNOWNBUG
 import8.sv
 --bound 0
-^EXIT=2$
+^EXIT=6$
 ^SIGNAL=0$
 --
 --
diff --git a/src/verilog/verilog_scope.cpp b/src/verilog/verilog_scope.cpp
index fc63e4429..11a4b5130 100644
--- a/src/verilog/verilog_scope.cpp
+++ b/src/verilog/verilog_scope.cpp
@@ -51,6 +51,16 @@ const verilog_scopet *verilog_scopest::lookup(irep_idt base_name) const
   return nullptr;
 }
 
+verilog_scopet &verilog_scopest::add_name(
+  irep_idt _base_name,
+  const std::string &separator,
+  scopet::kindt kind)
+{
+  auto result = current_scope().scope_map.emplace(
+    _base_name, scopet{_base_name, separator, &current_scope(), kind});
+  return result.first->second;
+}
+
 void verilog_scopet::print_rec(std::size_t indent, std::ostream &out) const
 {
   out << std::string(indent, ' ') << prefix << '\n';
@@ -96,6 +106,14 @@ void verilog_scopest::import(irep_idt package, irep_idt base_name)
   auto name_it = package_it->second.scope_map.find(base_name);
   if(name_it != package_it->second.scope_map.end())
   {
+    // Check if the identifier already exists in the current scope
+    auto existing = current_scope().scope_map.find(base_name);
+    if(existing != current_scope().scope_map.end())
+    {
+      throw typecheckt::errort().with_location(source_locationt())
+        << "identifier '" << base_name
+        << "' conflicts with earlier declaration";
+    }
     auto &scope = add_name(base_name, "", name_it->second.kind);
     scope.import = name_it->second.identifier();
   }
diff --git a/src/verilog/verilog_scope.h b/src/verilog/verilog_scope.h
index 076957a92..23ebf712e 100644
--- a/src/verilog/verilog_scope.h
+++ b/src/verilog/verilog_scope.h
@@ -100,12 +100,7 @@ class verilog_scopest
   scopet &add_name(
     irep_idt _base_name,
     const std::string &separator,
-    scopet::kindt kind)
-  {
-    auto result = current_scope().scope_map.emplace(
-      _base_name, scopet{_base_name, separator, &current_scope(), kind});
-    return result.first->second;
-  }
+    scopet::kindt kind);
 
   // Scope stack
   std::vector<scopet *> scope_stack = {&top_scope};