From 5891e3612478da77788b1aaeeaf0d5d6460f4146 Mon Sep 17 00:00:00 2001
From: Gaurav Chaudhary <chaudharygaurav2004@gmail.com>
Date: Sat, 8 Aug 2026 17:28:22 +0530
Subject: [PATCH] wasm2c: reject contradictory imports instead of aborting
 Preflight ComputeUniqueImports() before codegen and return Result::Error when
 the same module/field name is imported with different external kinds, instead
 of hitting UNIMPLEMENTED/abort on valid-but-unlinkable modules. Fixes #2751

Signed-off-by: Gaurav Chaudhary <chaudharygaurav2004@gmail.com>
---
 src/c-writer.cc                       | 18 +++++++++++++-----
 test/wasm2c/contradictory-imports.txt |  9 +++++++++
 2 files changed, 22 insertions(+), 5 deletions(-)
 create mode 100644 test/wasm2c/contradictory-imports.txt

diff --git a/src/c-writer.cc b/src/c-writer.cc
index 74252fb59..425b8226f 100644
--- a/src/c-writer.cc
+++ b/src/c-writer.cc
@@ -378,7 +378,7 @@ class CWriter {
   void Write(const FuncTypeExpr&);
   void WriteTagDecls();
   void WriteTags();
-  void ComputeUniqueImports();
+  Result ComputeUniqueImports();
   void BeginInstance();
   void WriteImports();
   void WriteTailCallWeakImports();
@@ -1794,7 +1794,7 @@ void CWriter::WriteTags() {
   }
 }
 
-void CWriter::ComputeUniqueImports() {
+Result CWriter::ComputeUniqueImports() {
   using modname_name_pair = std::pair<std::string, std::string>;
   std::map<modname_name_pair, const Import*> import_map;
   for (const Import* import : module_->imports) {
@@ -1805,7 +1805,13 @@ void CWriter::ComputeUniqueImports() {
         modname_name_pair(import->module_name, import->field_name), import);
     if (!iterator_and_insertion_bool.second) {
       if (iterator_and_insertion_bool.first->second->kind() != import->kind()) {
-        UNIMPLEMENTED("contradictory import declaration");
+        fprintf(stderr,
+                "error: contradictory import declaration: \"%s\".\"%s\" is "
+                "imported as both a %s and a %s\n",
+                import->module_name.c_str(), import->field_name.c_str(),
+                GetKindName(iterator_and_insertion_bool.first->second->kind()),
+                GetKindName(import->kind()));
+        return Result::Error;
       } else {
         fprintf(stderr, "warning: duplicate import declaration \"%s\" \"%s\"\n",
                 import->module_name.c_str(), import->field_name.c_str());
@@ -1822,6 +1828,7 @@ void CWriter::ComputeUniqueImports() {
   for (const auto& node : import_map) {
     unique_imports_.push_back(node.second);
   }
+  return Result::Ok;
 }
 
 void CWriter::BeginInstance() {
@@ -1830,8 +1837,6 @@ void CWriter::BeginInstance() {
     return;
   }
 
-  ComputeUniqueImports();
-
   // define names of per-instance imports
   for (const Import* import : module_->imports) {
     DefineImportName(import, import->module_name, import->field_name);
@@ -6177,6 +6182,9 @@ void CWriter::WriteCSource() {
 Result CWriter::WriteModule(const Module& module) {
   WABT_USE(options_);
   module_ = &module;
+
+  CHECK_RESULT(ComputeUniqueImports());
+
   WriteCHeader();
   WriteCSource();
   return result_;
diff --git a/test/wasm2c/contradictory-imports.txt b/test/wasm2c/contradictory-imports.txt
new file mode 100644
index 000000000..3fd520fa0
--- /dev/null
+++ b/test/wasm2c/contradictory-imports.txt
@@ -0,0 +1,9 @@
+;;; RUN: %(wat2wasm)s %(in_file)s -o %(temp_file)s.wasm
+;;; RUN: %(wasm2c)s %(temp_file)s.wasm -o %(temp_file)s.c
+;;; ERROR: 1
+(module
+  (import "e" "x" (func))
+  (import "e" "x" (global i32)))
+(;; STDERR ;;;
+error: contradictory import declaration: "e"."x" is imported as both a func and a global
+;;; STDERR ;;)