--- a/clang-tools-extra/clangd/CompileCommands.h	Tue Jun 15 19:13:43 2021 +0900
+++ b/clang-tools-extra/clangd/CompileCommands.h	Tue Jun 15 19:15:29 2021 +0900
@@ -8,8 +8,11 @@
 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_COMPILECOMMANDS_H
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_COMPILECOMMANDS_H
 
+#include "support/Threading.h"
 #include "clang/Tooling/ArgumentsAdjusters.h"
 #include "clang/Tooling/CompilationDatabase.h"
+#include "llvm/ADT/StringMap.h"
+#include <deque>
 #include <string>
 #include <vector>
 
@@ -40,12 +43,64 @@
   static CommandMangler detect();
 
   void adjust(std::vector<std::string> &Cmd) const;
-  explicit operator clang::tooling::ArgumentsAdjuster();
+  explicit operator clang::tooling::ArgumentsAdjuster() &&;
 
 private:
   CommandMangler() = default;
+  Memoize<llvm::StringMap<std::string>> ResolvedDrivers;
+  Memoize<llvm::StringMap<std::string>> ResolvedDriversNoFollow;
 };
 
+// Removes args from a command-line in a semantically-aware way.
+//
+// Internally this builds a large (0.5MB) table of clang options on first use.
+// Both strip() and process() are fairly cheap after that.
+//
+// FIXME: this reimplements much of OptTable, it might be nice to expose more.
+// The table-building strategy may not make sense outside clangd.
+class ArgStripper {
+public:
+  ArgStripper() = default;
+  ArgStripper(ArgStripper &&) = default;
+  ArgStripper(const ArgStripper &) = delete;
+  ArgStripper &operator=(ArgStripper &&) = default;
+  ArgStripper &operator=(const ArgStripper &) = delete;
+
+  // Adds the arg to the set which should be removed.
+  //
+  // Recognized clang flags are stripped semantically. When "-I" is stripped:
+  //  - so is its value (either as -Ifoo or -I foo)
+  //  - aliases like --include-directory=foo are also stripped
+  //  - CL-style /Ifoo will be removed if the args indicate MS-compatible mode
+  // Compile args not recognized as flags are removed literally, except:
+  //  - strip("ABC*") will remove any arg with an ABC prefix.
+  //
+  // In either case, the -Xclang prefix will be dropped if present.
+  void strip(llvm::StringRef Arg);
+  // Remove the targets from a compile command, in-place.
+  void process(std::vector<std::string> &Args) const;
+
+private:
+  // Deletion rules, to be checked for each arg.
+  struct Rule {
+    llvm::StringRef Text;    // Rule applies only if arg begins with Text.
+    unsigned char Modes = 0; // Rule applies only in specified driver modes.
+    uint16_t Priority = 0;   // Lower is better.
+    uint16_t ExactArgs = 0;  // Num args consumed when Arg == Text.
+    uint16_t PrefixArgs = 0; // Num args consumed when Arg starts with Text.
+  };
+  static llvm::ArrayRef<Rule> rulesFor(llvm::StringRef Arg);
+  const Rule *matchingRule(llvm::StringRef Arg, unsigned Mode,
+                           unsigned &ArgCount) const;
+  llvm::SmallVector<Rule> Rules;
+  std::deque<std::string> Storage; // Store strings not found in option table.
+};
+
+// Renders an argv list, with arguments separated by spaces.
+// Where needed, arguments are "quoted" and escaped.
+std::string printArgv(llvm::ArrayRef<llvm::StringRef> Args);
+std::string printArgv(llvm::ArrayRef<std::string> Args);
+
 } // namespace clangd
 } // namespace clang