Fix assemble_text_with_context link errors in CMake builds

Split assemble_text_with_context implementation between two files:
- source/text.cpp: Implementation for CMake builds (SPIRV_RUST_TARGET_ENV)
  using internal AssembleTextWithDiagnostics API
- context_bridge.cc: Implementation for standalone Rust builds (Bazel)
  using public spvTextToBinaryWithOptions C API

This avoids circular link dependencies in CMake builds where the Rust FFI
library is built before the C++ SPIRV-Tools library.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: LegNeato

rust/spirv-tools-ffi/src/context_bridge.cc

@@ -83,6 +83,10 @@ void dispatch_context_message(std::uintptr_t context_ptr, std::uint32_t level,
 #endif
 }
 
+// In CMake builds with SPIRV_RUST_TARGET_ENV, this function is provided by
+// source/text.cpp using internal APIs. In standalone Rust builds (Bazel),
+// we provide it here using the public C API.
+#ifndef SPIRV_RUST_TARGET_ENV
 AssembleResult assemble_text_with_context(std::size_t context_ptr,
                                           rust::Slice<const std::uint8_t> text,
                                           std::uint32_t options) {
@@ -113,6 +117,7 @@ AssembleResult assemble_text_with_context(std::size_t context_ptr,
 
   return result;
 }
+#endif
 
 ValidateResult validate_binary_with_options(
     std::uint32_t env, rust::Slice<const std::uint32_t> words,

source/text.cpp

@@ -1071,6 +1071,43 @@ spv_result_t spvTextToBinaryWithOptions(const spv_const_context context,
                                      sanitized_options, pBinary, pDiagnostic);
 }
 
+// FFI bridge for Rust assembler integration. In CMake builds with SPIRV_RUST_TARGET_ENV,
+// we provide this function here using internal C++ APIs. In standalone Rust builds (Bazel),
+// context_bridge.cc provides this using the public C API.
+#if defined(SPIRV_RUST_TARGET_ENV)
+namespace spvtools::ffi {
+AssembleResult assemble_text_with_context(std::size_t context_ptr,
+                                          rust::Slice<const std::uint8_t> text,
+                                          std::uint32_t options) {
+  AssembleResult result{false, ::rust::Vec<std::uint32_t>()};
+  auto* context = reinterpret_cast<spv_context>(context_ptr);
+  if (context == nullptr) {
+    return result;
+  }
+
+  spv_binary binary = nullptr;
+  spv_diagnostic diagnostic = nullptr;
+  const char* text_ptr = reinterpret_cast<const char*>(text.data());
+  const spv_result_t status = AssembleTextWithDiagnostics(
+      context, text_ptr, text.size(), options, &binary, &diagnostic);
+  if (diagnostic) {
+    spvDiagnosticDestroy(diagnostic);
+  }
+
+  if (status == SPV_SUCCESS && binary != nullptr) {
+    result.success = true;
+    result.binary.reserve(binary->wordCount);
+    for (size_t i = 0; i < binary->wordCount; ++i) {
+      result.binary.push_back(binary->code[i]);
+    }
+    spvBinaryDestroy(binary);
+  }
+
+  return result;
+}
+}  // namespace spvtools::ffi
+#endif
+
 void spvTextDestroy(spv_text text) {
   if (text) {
     if (text->str) delete[] text->str;