From 941ecee692045f90a9c35c95fed5902ecc8cdb6c Mon Sep 17 00:00:00 2001
From: Vern Paxson <vern@corelight.com>
Date: Sat, 27 Sep 2025 22:23:57 -0700
Subject: [PATCH] fixes for re-declaring type identifiers in inconsistent ways
 - addresses GH-2686

---
 src/Var.cc                                    | 29 +++++++++++++++++++
 .../out                                       |  2 ++
 .../out                                       |  2 ++
 .../redeclaration-redefinition-errors.zeek    |  8 +++++
 4 files changed, 41 insertions(+)
 create mode 100644 testing/btest/Baseline/language.redeclaration-redefinition-errors-12/out
 create mode 100644 testing/btest/Baseline/language.redeclaration-redefinition-errors-13/out

diff --git a/src/Var.cc b/src/Var.cc
index f719a4f2ec..b83aef545b 100644
--- a/src/Var.cc
+++ b/src/Var.cc
@@ -348,6 +348,35 @@ extern ExprPtr add_and_assign_local(IDPtr id, ExprPtr init, ValPtr val) {
 }
 
 void add_type(ID* id, TypePtr t, std::unique_ptr<std::vector<AttrPtr>> attr) {
+    if ( const auto& old_t = id->GetType() ) {
+        // The identifier already has a type associated with it. This can
+        // be okay if (1) it's already been marked as a Type identifier,
+        // (2) the previous type is a stub, or an equivalent enum.
+        if ( ! id->IsType() ) {
+            reporter->Error("Identifier %s has already been declared and is not a type", id->Name());
+            return;
+        }
+
+        if ( old_t->Tag() == t->Tag() && ((old_t->Tag() == TYPE_RECORD && old_t->AsRecordType()->NumFields() == 0) ||
+                                          (t->Tag() == TYPE_ENUM && same_type(t, old_t))) )
+            // It has a consistent tag and is either redeclaring a stub
+            // record (used in init-bare.zeek) or an equivalent enum
+            // (which can appear due to specifiers in BiFs, for example).
+            ;
+
+        else {
+            std::string loc;
+            auto li = id->GetLocationInfo();
+            auto fn = li->FileName();
+            int ln = li->FirstLine();
+            if ( fn && fn[0] != '\0' )
+                loc = " at " + std::string(fn) + ":" + std::to_string(ln);
+
+            reporter->Error("Type %s has already been declared%s", id->Name(), loc.c_str());
+            return;
+        }
+    }
+
     std::string new_type_name = id->Name();
     std::string old_type_name = t->GetName();
 
diff --git a/testing/btest/Baseline/language.redeclaration-redefinition-errors-12/out b/testing/btest/Baseline/language.redeclaration-redefinition-errors-12/out
new file mode 100644
index 0000000000..e45adfd2bf
--- /dev/null
+++ b/testing/btest/Baseline/language.redeclaration-redefinition-errors-12/out
@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/redeclaration-redefinition-errors.zeek, line 2: Identifier f has already been declared and is not a type
diff --git a/testing/btest/Baseline/language.redeclaration-redefinition-errors-13/out b/testing/btest/Baseline/language.redeclaration-redefinition-errors-13/out
new file mode 100644
index 0000000000..2bf4d1f641
--- /dev/null
+++ b/testing/btest/Baseline/language.redeclaration-redefinition-errors-13/out
@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/redeclaration-redefinition-errors.zeek, line 2: Type f has already been declared at <...>/redeclaration-redefinition-errors.zeek:1
diff --git a/testing/btest/language/redeclaration-redefinition-errors.zeek b/testing/btest/language/redeclaration-redefinition-errors.zeek
index 5c44f2b9d6..0efb0d7341 100644
--- a/testing/btest/language/redeclaration-redefinition-errors.zeek
+++ b/testing/btest/language/redeclaration-redefinition-errors.zeek
@@ -59,3 +59,11 @@ global f: function();
 global f = function() { };
 global f: hook();
 global f: event();
+
+# @TEST-START-NEXT
+global f = function() { };
+type f: bool;
+
+# @TEST-START-NEXT
+type f: record {};
+type f: bool;