[clangd] Improve serialization error messages. NFC

Author: sam-mccall

Diff for: clang-tools-extra/clangd/RIFF.cpp

@@ -8,25 +8,29 @@
 
 #include "RIFF.h"
 #include "llvm/Support/Endian.h"
+#include "llvm/Support/Error.h"
 
 namespace clang {
 namespace clangd {
 namespace riff {
 
-static llvm::Error makeError(const char *Msg) {
-  return llvm::createStringError(llvm::inconvertibleErrorCode(), Msg);
+static llvm::Error makeError(const llvm::Twine &Msg) {
+  return llvm::make_error<llvm::StringError>(Msg,
+                                             llvm::inconvertibleErrorCode());
 }
 
 llvm::Expected<Chunk> readChunk(llvm::StringRef &Stream) {
   if (Stream.size() < 8)
-    return makeError("incomplete chunk header");
+    return makeError("incomplete chunk header: " + llvm::Twine(Stream.size()) +
+                     " bytes available");
   Chunk C;
   std::copy(Stream.begin(), Stream.begin() + 4, C.ID.begin());
   Stream = Stream.drop_front(4);
   uint32_t Len = llvm::support::endian::read32le(Stream.take_front(4).begin());
   Stream = Stream.drop_front(4);
   if (Stream.size() < Len)
-    return makeError("truncated chunk");
+    return makeError("truncated chunk: want " + llvm::Twine(Len) + ", got " +
+                     llvm::Twine(Stream.size()));
   C.Data = Stream.take_front(Len);
   Stream = Stream.drop_front(Len);
   if (Len % 2 & !Stream.empty()) { // Skip padding byte.
@@ -53,7 +57,7 @@ llvm::Expected<File> readFile(llvm::StringRef Stream) {
   if (!RIFF)
     return RIFF.takeError();
   if (RIFF->ID != fourCC("RIFF"))
-    return makeError("not a RIFF container");
+    return makeError("not a RIFF container: root is " + fourCCStr(RIFF->ID));
   if (RIFF->Data.size() < 4)
     return makeError("RIFF chunk too short");
   File F;

Diff for: clang-tools-extra/clangd/RIFF.h

@@ -44,6 +44,9 @@ using FourCC = std::array<char, 4>;
 inline constexpr FourCC fourCC(const char (&Literal)[5]) {
   return FourCC{{Literal[0], Literal[1], Literal[2], Literal[3]}};
 }
+inline constexpr llvm::StringRef fourCCStr(const FourCC &Data) {
+  return llvm::StringRef(&Data[0], Data.size());
+}
 // A chunk is a section in a RIFF container.
 struct Chunk {
   FourCC ID;

Diff for: clang-tools-extra/clangd/index/Serialization.cpp

@@ -426,20 +426,25 @@ llvm::Expected<IndexFileIn> readRIFF(llvm::StringRef Data) {
   if (!RIFF)
     return RIFF.takeError();
   if (RIFF->Type != riff::fourCC("CdIx"))
-    return makeError("wrong RIFF type");
+    return makeError("wrong RIFF filetype: " + riff::fourCCStr(RIFF->Type));
   llvm::StringMap<llvm::StringRef> Chunks;
   for (const auto &Chunk : RIFF->Chunks)
     Chunks.try_emplace(llvm::StringRef(Chunk.ID.data(), Chunk.ID.size()),
                        Chunk.Data);
 
-  for (llvm::StringRef RequiredChunk : {"meta", "stri"})
+  if (!Chunks.count("meta"))
+    return makeError("missing meta chunk");
+  Reader Meta(Chunks.lookup("meta"));
+  auto SeenVersion = Meta.consume32();
+  if (SeenVersion != Version)
+    return makeError("wrong version: want " + llvm::Twine(Version) + ", got " +
+                     llvm::Twine(SeenVersion));
+
+  // meta chunk is checked above, as we prefer the "version mismatch" error.
+  for (llvm::StringRef RequiredChunk : {"stri"})
     if (!Chunks.count(RequiredChunk))
       return makeError("missing required chunk " + RequiredChunk);
 
-  Reader Meta(Chunks.lookup("meta"));
-  if (Meta.consume32() != Version)
-    return makeError("wrong version");
-
   auto Strings = readStringTable(Chunks.lookup("stri"));
   if (!Strings)
     return Strings.takeError();
@@ -665,7 +670,7 @@ std::unique_ptr<SymbolIndex> loadIndex(llvm::StringRef SymbolFilename,
   trace::Span OverallTracer("LoadIndex");
   auto Buffer = llvm::MemoryBuffer::getFile(SymbolFilename);
   if (!Buffer) {
-    elog("Can't open {0}", SymbolFilename);
+    elog("Can't open {0}: {1}", SymbolFilename, Buffer.getError().message());
     return nullptr;
   }
 
@@ -682,7 +687,7 @@ std::unique_ptr<SymbolIndex> loadIndex(llvm::StringRef SymbolFilename,
       if (I->Relations)
         Relations = std::move(*I->Relations);
     } else {
-      elog("Bad Index: {0}", I.takeError());
+      elog("Bad index file: {0}", I.takeError());
       return nullptr;
     }
   }