[clang driver] Move default module cache from system temporary directory

1) Shared writable directories like /tmp are a security problem.
2) Systems provide dedicated cache directories these days anyway.
3) This also refines LLVM's cache_directory() on Darwin platforms to use
   the Darwin per-user cache directory.

Reviewers: compnerd, aprantl, jakehehrlich, espindola, respindola, ilya-biryukov, pcc, sammccall

Reviewed By: compnerd, sammccall

Subscribers: hiraditya, llvm-commits, cfe-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D82362

1 files changed, 16 insertions, 41 deletions

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 8903641..1fd638f 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -721,38 +721,6 @@ static void addDashXForInput(const ArgList &Args, const InputInfo &Input,
   }
 }
 
-static void appendUserToPath(SmallVectorImpl<char> &Result) {
-#ifdef LLVM_ON_UNIX
-  const char *Username = getenv("LOGNAME");
-#else
-  const char *Username = getenv("USERNAME");
-#endif
-  if (Username) {
-    // Validate that LoginName can be used in a path, and get its length.
-    size_t Len = 0;
-    for (const char *P = Username; *P; ++P, ++Len) {
-      if (!clang::isAlphanumeric(*P) && *P != '_') {
-        Username = nullptr;
-        break;
-      }
-    }
-
-    if (Username && Len > 0) {
-      Result.append(Username, Username + Len);
-      return;
-    }
-  }
-
-// Fallback to user id.
-#ifdef LLVM_ON_UNIX
-  std::string UID = llvm::utostr(getuid());
-#else
-  // FIXME: Windows seems to have an 'SID' that might work.
-  std::string UID = "9999";
-#endif
-  Result.append(UID.begin(), UID.end());
-}
-
 static void addPGOAndCoverageFlags(const ToolChain &TC, Compilation &C,
                                    const Driver &D, const InputInfo &Output,
                                    const ArgList &Args,
@@ -3201,11 +3169,13 @@ static void RenderBuiltinOptions(const ToolChain &TC, const llvm::Triple &T,
     CmdArgs.push_back("-fno-math-builtin");
 }
 
-void Driver::getDefaultModuleCachePath(SmallVectorImpl<char> &Result) {
-  llvm::sys::path::system_temp_directory(/*erasedOnReboot=*/false, Result);
-  llvm::sys::path::append(Result, "org.llvm.clang.");
-  appendUserToPath(Result);
-  llvm::sys::path::append(Result, "ModuleCache");
+bool Driver::getDefaultModuleCachePath(SmallVectorImpl<char> &Result) {
+  if (llvm::sys::path::cache_directory(Result)) {
+    llvm::sys::path::append(Result, "clang");
+    llvm::sys::path::append(Result, "ModuleCache");
+    return true;
+  }
+  return false;
 }
 
 static void RenderModulesOptions(Compilation &C, const Driver &D,
@@ -3262,6 +3232,7 @@ static void RenderModulesOptions(Compilation &C, const Driver &D,
     if (Arg *A = Args.getLastArg(options::OPT_fmodules_cache_path))
       Path = A->getValue();
 
+    bool HasPath = true;
     if (C.isForDiagnostics()) {
       // When generating crash reports, we want to emit the modules along with
       // the reproduction sources, so we ignore any provided module path.
@@ -3270,12 +3241,16 @@ static void RenderModulesOptions(Compilation &C, const Driver &D,
       llvm::sys::path::append(Path, "modules");
     } else if (Path.empty()) {
       // No module path was provided: use the default.
-      Driver::getDefaultModuleCachePath(Path);
+      HasPath = Driver::getDefaultModuleCachePath(Path);
     }
 
-    const char Arg[] = "-fmodules-cache-path=";
-    Path.insert(Path.begin(), Arg, Arg + strlen(Arg));
-    CmdArgs.push_back(Args.MakeArgString(Path));
+    // `HasPath` will only be false if getDefaultModuleCachePath() fails.
+    // That being said, that failure is unlikely and not caching is harmless.
+    if (HasPath) {
+      const char Arg[] = "-fmodules-cache-path=";
+      Path.insert(Path.begin(), Arg, Arg + strlen(Arg));
+      CmdArgs.push_back(Args.MakeArgString(Path));
+    }
   }
 
   if (HaveModules) {