From a8612da85b9c9fc985341d95de1cfe8ed535913b Mon Sep 17 00:00:00 2001
From: Alex Cameron <asc@tetsuo.sh>
Date: Sat, 24 Oct 2026 23:50:37 +1100
Subject: [PATCH] fix(translate): reject redefinition of a word with a
 diagnostic

Fixes #118
---
 lib/Translation/ForthToMLIR/ForthToMLIR.cpp          | 9 ++++++++-
 lib/Translation/ForthToMLIR/ForthToMLIR.h            | 3 +--
 test/Translation/Forth/word-redefinition-error.forth | 9 +++++++++
 3 files changed, 18 insertions(+), 3 deletions(-)
 create mode 100644 test/Translation/Forth/word-redefinition-error.forth

diff --git a/lib/Translation/ForthToMLIR/ForthToMLIR.cpp b/lib/Translation/ForthToMLIR/ForthToMLIR.cpp
index aa9f726..6e94a40 100644
--- a/lib/Translation/ForthToMLIR/ForthToMLIR.cpp
+++ b/lib/Translation/ForthToMLIR/ForthToMLIR.cpp
@@ -1405,6 +1405,13 @@ LogicalResult ForthParser::parseWordDefinition() {
     return emitError("kernel name '" + kernelName + "' conflicts with word " +
                      currentToken.text);
   }
+  llvm::SMLoc nameLoc = currentToken.location;
+  if (auto previous = wordDefs.find(wordName); previous != wordDefs.end()) {
+    (void)emitError("word '" + wordName + "' is already defined");
+    sourceMgr.PrintMessage(previous->second, llvm::SourceMgr::DK_Note,
+                           "previous definition is here");
+    return failure();
+  }
   consume(); // consume word name
 
   // Create function: !forth.stack -> !forth.stack
@@ -1435,7 +1442,7 @@ LogicalResult ForthParser::parseWordDefinition() {
   builder.create<func::ReturnOp>(loc, resultStack);
 
   // Register the word
-  wordDefs.insert(wordName);
+  wordDefs[wordName] = nameLoc;
 
   consume(); // consume ';'
   return success();
diff --git a/lib/Translation/ForthToMLIR/ForthToMLIR.h b/lib/Translation/ForthToMLIR/ForthToMLIR.h
index 04317f6..53ee87c 100644
--- a/lib/Translation/ForthToMLIR/ForthToMLIR.h
+++ b/lib/Translation/ForthToMLIR/ForthToMLIR.h
@@ -12,7 +12,6 @@
 #include "llvm/ADT/StringMap.h"
 #include "llvm/Support/SourceMgr.h"
 #include <string>
-#include <unordered_set>
 #include <vector>
 
 namespace mlir {
@@ -98,7 +97,7 @@ class ForthParser {
   OpBuilder builder;
   ForthLexer lexer;
   Token currentToken;
-  std::unordered_set<std::string> wordDefs;
+  llvm::StringMap<llvm::SMLoc> wordDefs;
   std::vector<ParamDecl> paramDecls;
   std::vector<SharedDecl> sharedDecls;
   llvm::StringMap<Value> paramValues;
diff --git a/test/Translation/Forth/word-redefinition-error.forth b/test/Translation/Forth/word-redefinition-error.forth
new file mode 100644
index 0000000..71cbaeb
--- /dev/null
+++ b/test/Translation/Forth/word-redefinition-error.forth
@@ -0,0 +1,9 @@
+\ RUN: %not %warpforth-translate --forth-to-mlir %s 2>&1 | %FileCheck %s
+\ CHECK: :[[@LINE+6]]:3: error: word 'FOO' is already defined
+\ CHECK: :[[@LINE+4]]:3: note: previous definition is here
+\ CHECK-NOT: redefinition of symbol
+\! kernel k
+\! param a i64[1]
+: foo 1 ;
+: foo 2 ;
+foo a !