From 3553c9c4da1f1f642b46c2c776d26e324e32f783 Mon Sep 17 00:00:00 2001
From: Rangi <sylvie.oukaour+rangi42@gmail.com>
Date: Tue, 18 Nov 2025 16:40:24 -0500
Subject: [PATCH] Fix RGBLINK evaluation of undefined RPN symbols

This was the only RPN case to not assign a deliberate value
in all possible branches.

Fixes #1858
---
 src/link/patch.cpp           | 1 +
 test/link/rpn-bad-sym-id.asm | 3 +++
 test/link/rpn-bad-sym-id.out | 5 +++++
 3 files changed, 9 insertions(+)
 create mode 100644 test/link/rpn-bad-sym-id.asm
 create mode 100644 test/link/rpn-bad-sym-id.out

diff --git a/src/link/patch.cpp b/src/link/patch.cpp
index 7d1b9ed6..36c839ca 100644
--- a/src/link/patch.cpp
+++ b/src/link/patch.cpp
@@ -437,6 +437,7 @@ static int32_t computeRPNExpr(Patch const &patch, std::vector<Symbol> const &fil
 			} else if (Symbol const *symbol = getSymbol(fileSymbols, value); !symbol) {
 				errorAt(patch, "Undefined symbol `%s`", fileSymbols[value].name.c_str());
 				sym_TraceLocalAliasedSymbols(fileSymbols[value].name);
+				value = 0;
 				isError = true;
 			} else if (std::holds_alternative<Label>(symbol->data)) {
 				Label const &label = std::get<Label>(symbol->data);
diff --git a/test/link/rpn-bad-sym-id.asm b/test/link/rpn-bad-sym-id.asm
new file mode 100644
index 00000000..28f1fd9d
--- /dev/null
+++ b/test/link/rpn-bad-sym-id.asm
@@ -0,0 +1,3 @@
+SECTION "bad", ROM0
+ld a, FOO * 256
+ld a, BAR * 256
diff --git a/test/link/rpn-bad-sym-id.out b/test/link/rpn-bad-sym-id.out
new file mode 100644
index 00000000..c12836f6
--- /dev/null
+++ b/test/link/rpn-bad-sym-id.out
@@ -0,0 +1,5 @@
+error: Undefined symbol `BAR`
+    at rpn-bad-sym-id.asm(3)
+error: Undefined symbol `FOO`
+    at rpn-bad-sym-id.asm(2)
+Linking failed with 2 errors