Fix the crash when formatting unsupported encodings

[owenpan]

Summary

See PR33946.

[owenpan]

Moved "UTF-32 (LE)" to before "UTF-16 (LE)" in llvm::StringSwitch so that the former BOM wouldn't be misnamed as the latter.

[sammccall]

clang/tools/clang-format/ClangFormat.cpp

273

Seems unlikely we'll ever see any of these other than UTF{16,32}.
I'd suggest dropping them, but up to you.

276

SCSU?

[sammccall]

You might want to add a test for one of these?

[owenpan]

I copied the code from clang/lib/Basic/SourceManager.cpp. See D61628.

I will update this patch to correct the typo in SCSU or remove it along with the other rare BOMs. How do you add test cases for this kind of fixes that emit error messages?

[owenpan]

Fixed the typo for SCSU.

[owenpan]

clang/tools/clang-format/ClangFormat.cpp

273

I will keep the rare BOM cases to keep it in sync with D61628.

clang/tools/clang-format/ClangFormat.cpp

ErrorOr<std::unique_ptr<MemoryBuffer>> CodeOrErr =
                               MemoryBuffer::getFileOrSTDIN(FileName);
   if (std::error_code EC = CodeOrErr.getError()) {
     errs() << EC.message() << "\n";
     return true;
   }
   std::unique_ptr<llvm::MemoryBuffer> Code = std::move(CodeOrErr.get());
   if (Code->getBufferSize() == 0)
     return false; // Empty files are formatted correctly.
+
+  // Check to see if the buffer has a UTF Byte Order Mark (BOM).
+  // We only support UTF-8 with and without a BOM right now.  See
+  // http://en.wikipedia.org/wiki/Byte_order_mark for more information.
+  StringRef BufStr = Code->getBuffer();
+  const char *InvalidBOM = llvm::StringSwitch<const char *>(BufStr)
+    .StartsWith("\xFE\xFF", "UTF-16 (BE)")
+    .StartsWith("\xFF\xFE", "UTF-16 (LE)")
+    .StartsWith(llvm::StringLiteral::withInnerNUL("\x00\x00\xFE\xFF"),
+                                                  "UTF-32 (BE)")
+    .StartsWith(llvm::StringLiteral::withInnerNUL("\xFF\xFE\x00\x00"),
+                                                  "UTF-32 (LE)")
+    .StartsWith("\x2B\x2F\x76", "UTF-7")
+    .StartsWith("\xF7\x64\x4C", "UTF-1")
+    .StartsWith("\xDD\x73\x66\x73", "UTF-EBCDIC")
+    .StartsWith("\x0E\xFE\xFF", "SDSU")
+    .StartsWith("\xFB\xEE\x28", "BOCU-1")
+    .StartsWith("\x84\x31\x95\x33", "GB-18030")
+    .Default(nullptr);
+
+  if (InvalidBOM) {
+    errs() << "error: encoding with unsupported byte order mark \""
+           << InvalidBOM << "\" detected";
+    if (FileName != "-")
+      errs() << " in file '" << FileName << "'";
+    errs() << ".\n";
+    return true;
+  }
+
   std::vector<tooling::Range> Ranges;
   if (fillRanges(Code.get(), Ranges))
     return true;
   StringRef AssumedFileName = (FileName == "-") ? AssumeFileName : FileName;
 
   llvm::Expected<FormatStyle> FormatStyle =
       getStyle(Style, AssumedFileName, FallbackStyle, Code->getBuffer());
   if (!FormatStyle) {