[clang] [llvm] Enable fexec-charset option (PR #138895)

[Hubert Tong via llvm-commits]

================
@@ -0,0 +1,53 @@
+//===--- LiteralConverter.cpp - Translator for String Literals -----------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Lex/LiteralConverter.h"
+#include "clang/Basic/DiagnosticDriver.h"
+
+using namespace llvm;
+
+llvm::TextEncodingConverter *
+LiteralConverter::getConverter(ConversionAction Action) {
+  if (Action == ToSystemEncoding)
+    return ToSystemEncodingConverter;
+  else if (Action == ToExecEncoding)
+    return ToExecEncodingConverter;
+  else
+    return nullptr;
+}
+
+void LiteralConverter::setConvertersFromOptions(
+    const clang::LangOptions &Opts, const clang::TargetInfo &TInfo,
+    clang::DiagnosticsEngine &Diags) {
+  using namespace llvm;
+  InternalEncoding = "UTF-8";
+  SystemEncoding = TInfo.getTriple().getDefaultTextEncoding();
+  ExecEncoding =
+      Opts.ExecEncoding.empty() ? InternalEncoding : Opts.ExecEncoding;
+  // Create converter between internal and system encoding
+  if (InternalEncoding != SystemEncoding) {
+    ErrorOr<TextEncodingConverter> ErrorOrConverter =
+        llvm::TextEncodingConverter::create(InternalEncoding, SystemEncoding);
+    if (!ErrorOrConverter)
+      return;
+    ToSystemEncodingConverter =
+        new TextEncodingConverter(std::move(*ErrorOrConverter));
+  }
+
+  // Create converter between internal and exec encoding specified
+  // in fexec-charset option.
+  if (InternalEncoding == ExecEncoding)
+    return;
+  ErrorOr<TextEncodingConverter> ErrorOrConverter =
+      llvm::TextEncodingConverter::create(InternalEncoding, ExecEncoding);
+  if (!ErrorOrConverter)
+    Diags.Report(clang::diag::err_drv_invalid_value)
+        << "-fexec-charset" << ExecEncoding;
+  ToExecEncodingConverter =
+      new TextEncodingConverter(std::move(*ErrorOrConverter));
----------------
hubert-reinterpretcast wrote:

Last I checked, the `Diags.Report` call _does_ return to this function.
Also, this PR is missing tests for the `-cc1` diagnostics here.

```suggestion
  else
    ToExecEncodingConverter =
        new TextEncodingConverter(std::move(*ErrorOrConverter));
```

https://github.com/llvm/llvm-project/pull/138895