Add translation-time snprintf generation

Author: lucic71

cpp2rust/converter/models/converter_refcount.cpp

@@ -1048,12 +1048,50 @@ void ConverterRefCount::ConvertPrintf(clang::CallExpr *expr) {
   StrCat(')');
 }
 
+void ConverterRefCount::ConvertSnprintf(clang::CallExpr *expr) {
+  std::string format;
+  if (auto *str = clang::dyn_cast<clang::StringLiteral>(
+          expr->getArg(2)->IgnoreImplicit())) {
+    format = GetEscapedStringLiteral(str);
+  } else {
+    llvm::errs() << "Unknown snprintf format: ";
+    expr->getArg(2)->dump();
+    llvm::errs() << '\n';
+    exit(1);
+  }
+  auto types = printf2fmt(format);
+
+  StrCat("({ let __s = format!(", format);
+  unsigned j = 0;
+  for (unsigned i = 3, e = expr->getNumArgs(); i < e; ++i) {
+    StrCat(token::kComma);
+    Convert(expr->getArg(i));
+    if (types[j]) {
+      StrCat(keyword::kAs, types[j]);
+    }
+    ++j;
+  }
+  StrCat("); let __b = __s.as_bytes(); let __size = (");
+  Convert(expr->getArg(1));
+  StrCat(") as usize; if __size > 0 {",
+         "let __n = ::std::cmp::min(__b.len(), __size - 1); (");
+  Convert(expr->getArg(0));
+  StrCat(").with_slice_mut(__n + 1, |__dst| {",
+         "__dst[..__n].copy_from_slice(&__b[..__n]); __dst[__n] = 0; }); }",
+         "__b.len() as i32 })");
+}
+
 bool ConverterRefCount::VisitCallExpr(clang::CallExpr *expr) {
   if (IsBuiltinVaStart(expr) || IsBuiltinVaEnd(expr) || IsBuiltinVaCopy(expr)) {
     ConvertVAArgCall(expr);
     return false;
   }
 
+  if (Mapper::ToString(expr->getCallee()).starts_with("int snprintf")) {
+    ConvertSnprintf(expr);
+    return false;
+  }
+
   if (expr->isCallToStdMove()) {
     if (IsUniquePtr(expr->getArg(0)->getType())) {
       StrCat(std::format("{}.take()", ConvertLValue(expr->getArg(0))));

cpp2rust/converter/models/converter_refcount.h

@@ -82,6 +82,8 @@ class ConverterRefCount final : public Converter {
 
   void ConvertPrintf(clang::CallExpr *expr) override;
 
+  void ConvertSnprintf(clang::CallExpr *expr);
+
   void EmitFnPtrCall(clang::Expr *callee) override;
 
   void