Revert "[lld/mac] Port typo correction for undefined symbols from ELF port"

This caused crashes/assert failures for some Chromium developers, see comment
on the code review.

> Ports:
> - core feature: https://reviews.llvm.org/D67039
> - case mismatch: https://reviews.llvm.org/D70506
> - extern "C" suggestions: https://reviews.llvm.org/D69592,
>   https://reviews.llvm.org/D69650
>
> Does not port https://reviews.llvm.org/D71735 since I believe that that doesn't
> apply to lld/Mach-O.
>
> Differential Revision: https://reviews.llvm.org/D135038

This reverts commit 8c45e80.

Author: zmodem

lld/MachO/SymbolTable.cpp

@@ -392,138 +392,8 @@ void macho::reportPendingDuplicateSymbols() {
   }
 }
 
-// Check whether the definition name def is a mangled function name that matches
-// the reference name ref.
-static bool canSuggestExternCForCXX(StringRef ref, StringRef def) {
-  llvm::ItaniumPartialDemangler d;
-  std::string name = def.str();
-  if (d.partialDemangle(name.c_str()))
-    return false;
-  char *buf = d.getFunctionName(nullptr, nullptr);
-  if (!buf)
-    return false;
-  bool ret = ref == buf;
-  free(buf);
-  return ret;
-}
-
-// Suggest an alternative spelling of an "undefined symbol" diagnostic. Returns
-// the suggested symbol, which is either in the symbol table, or in the same
-// file of sym.
-static const Symbol *getAlternativeSpelling(const Undefined &sym,
-                                            std::string &pre_hint,
-                                            std::string &post_hint) {
-  DenseMap<StringRef, const Symbol *> map;
-  if (sym.getFile() && sym.getFile()->kind() == InputFile::ObjKind) {
-    // Build a map of local defined symbols.
-    for (const Symbol *s : sym.getFile()->symbols)
-      if (auto *defined = dyn_cast<Defined>(s))
-        if (!defined->isExternal())
-          map.try_emplace(s->getName(), s);
-  }
-
-  auto suggest = [&](StringRef newName) -> const Symbol * {
-    // If defined locally.
-    if (const Symbol *s = map.lookup(newName))
-      return s;
-
-    // If in the symbol table and not undefined.
-    if (const Symbol *s = symtab->find(newName))
-      if (dyn_cast<Undefined>(s) == nullptr)
-        return s;
-
-    return nullptr;
-  };
-
-  // This loop enumerates all strings of Levenshtein distance 1 as typo
-  // correction candidates and suggests the one that exists as a non-undefined
-  // symbol.
-  StringRef name = sym.getName();
-  for (size_t i = 0, e = name.size(); i != e + 1; ++i) {
-    // Insert a character before name[i].
-    std::string newName = (name.substr(0, i) + "0" + name.substr(i)).str();
-    for (char c = '0'; c <= 'z'; ++c) {
-      newName[i] = c;
-      if (const Symbol *s = suggest(newName))
-        return s;
-    }
-    if (i == e)
-      break;
-
-    // Substitute name[i].
-    newName = std::string(name);
-    for (char c = '0'; c <= 'z'; ++c) {
-      newName[i] = c;
-      if (const Symbol *s = suggest(newName))
-        return s;
-    }
-
-    // Transpose name[i] and name[i+1]. This is of edit distance 2 but it is
-    // common.
-    if (i + 1 < e) {
-      newName[i] = name[i + 1];
-      newName[i + 1] = name[i];
-      if (const Symbol *s = suggest(newName))
-        return s;
-    }
-
-    // Delete name[i].
-    newName = (name.substr(0, i) + name.substr(i + 1)).str();
-    if (const Symbol *s = suggest(newName))
-      return s;
-  }
-
-  // Case mismatch, e.g. Foo vs FOO.
-  for (auto &it : map)
-    if (name.equals_insensitive(it.first))
-      return it.second;
-  for (Symbol *sym : symtab->getSymbols())
-    if (dyn_cast<Undefined>(sym) == nullptr &&
-        name.equals_insensitive(sym->getName()))
-      return sym;
-
-  // The reference may be a mangled name while the definition is not. Suggest a
-  // missing extern "C".
-  if (name.startswith("__Z")) {
-    std::string buf = name.str();
-    llvm::ItaniumPartialDemangler d;
-    if (!d.partialDemangle(buf.c_str()))
-      if (char *buf = d.getFunctionName(nullptr, nullptr)) {
-        const Symbol *s = suggest((Twine("_") + buf).str());
-        free(buf);
-        if (s) {
-          pre_hint = ": extern \"C\" ";
-          return s;
-        }
-      }
-  } else {
-    StringRef name_without_underscore = name;
-    name_without_underscore.consume_front("_");
-    const Symbol *s = nullptr;
-    for (auto &it : map)
-      if (canSuggestExternCForCXX(name_without_underscore, it.first)) {
-        s = it.second;
-        break;
-      }
-    if (!s)
-      for (Symbol *sym : symtab->getSymbols())
-        if (canSuggestExternCForCXX(name_without_underscore, sym->getName())) {
-          s = sym;
-          break;
-        }
-    if (s) {
-      pre_hint = " to declare ";
-      post_hint = " as extern \"C\"?";
-      return s;
-    }
-  }
-
-  return nullptr;
-}
-
 static void reportUndefinedSymbol(const Undefined &sym,
-                                  const UndefinedDiag &locations,
-                                  bool correctSpelling) {
+                                  const UndefinedDiag &locations) {
   std::string message = "undefined symbol";
   if (config->archMultiple)
     message += (" for arch " + getArchitectureName(config->arch())).str();
@@ -556,17 +426,6 @@ static void reportUndefinedSymbol(const Undefined &sym,
         ("\n>>> referenced " + Twine(totalReferences - i) + " more times")
             .str();
 
-  if (correctSpelling) {
-    std::string pre_hint = ": ", post_hint;
-    if (const Symbol *corrected =
-            getAlternativeSpelling(sym, pre_hint, post_hint)) {
-      message +=
-          "\n>>> did you mean" + pre_hint + toString(*corrected) + post_hint;
-      if (corrected->getFile())
-        message += "\n>>> defined in: " + toString(corrected->getFile());
-    }
-  }
-
   if (config->undefinedSymbolTreatment == UndefinedSymbolTreatment::error)
     error(message);
   else if (config->undefinedSymbolTreatment ==
@@ -577,9 +436,8 @@ static void reportUndefinedSymbol(const Undefined &sym,
 }
 
 void macho::reportPendingUndefinedSymbols() {
-  // Enable spell corrector for the first 2 diagnostics.
-  for (const auto &[i, undef] : llvm::enumerate(undefs))
-    reportUndefinedSymbol(*undef.first, undef.second, i < 2);
+  for (const auto &undef : undefs)
+    reportUndefinedSymbol(*undef.first, undef.second);
 
   // This function is called multiple times during execution. Clear the printed
   // diagnostics to avoid printing the same things again the next time.