[clangd] Get rid of Lexer usage in CodeComplete

[sammccall]

clang-tools-extra/clangd/CodeComplete.cpp

593

what if beginLoc and endLoc are in different files?
(this is most of what Lexer deals with, I think)

I think you want TokenBuffer::expandedTokens(SourceRange), then spelledForExpanded, and then FileRange(...).text().

[kadircet]

clang-tools-extra/clangd/CodeComplete.cpp

593

right, thinking about it again, I suppose it is better to keep lexer here as there's syntax::FileRange doesn't support macroIDs.
We would need to handle it ourselves in here which wouldn't reduce technical debt at all.

clang-tools-extra/clangd/CodeComplete.cpp

 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/FrontendActions.h"
 #include "clang/Lex/ExternalPreprocessorSource.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Lex/PreprocessorOptions.h"
 #include "clang/Sema/CodeCompleteConsumer.h"
 #include "clang/Sema/DeclSpec.h"
 #include "clang/Sema/Sema.h"
+#include "clang/Tooling/Syntax/Tokens.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
if (!SemaSpecifier) {
     return {EnclosingAtFront, Opts.AllScopes};
   }
   // Case 3: sema saw and resolved a scope qualifier.
   if (SemaSpecifier && SemaSpecifier->isValid())
     return {Scopes.scopesForIndexQuery(), false};
 
   // Case 4: There was a qualifier, and Sema didn't resolve it.
   Scopes.AccessibleScopes.push_back(""); // Make sure global scope is included.
-  llvm::StringRef SpelledSpecifier = Lexer::getSourceText(
-      CharSourceRange::getCharRange(SemaSpecifier->getRange()),
-      CCSema.SourceMgr, clang::LangOptions());
+  llvm::StringRef SpelledSpecifier =
+      syntax::FileRange(CCSema.SourceMgr, SemaSpecifier->getBeginLoc(),
+                        SemaSpecifier->getEndLoc())
+          .text(CCSema.SourceMgr);
   if (SpelledSpecifier.consume_front("::"))
     Scopes.AccessibleScopes = {""};
   Scopes.UnresolvedQualifier = std::string(SpelledSpecifier);
   // Sema excludes the trailing "::".
   if (!Scopes.UnresolvedQualifier->empty())
     *Scopes.UnresolvedQualifier += "::";
 
   return {Scopes.scopesForIndexQuery(), false};