[lldb] Avoid using any shell when calling xcrun.

[teemperor]

Summary

When we run xcrun we don't have any user input in our command so relying on the user's default
shell doesn't make a lot of sense. If the user has set the system shell to a something that isn't supported
yet (dash, ash) then we would run into the problem that we don't know how to escape our command string.

This patch just avoids using any shell at all as xcrun is always at the same path.

[teemperor]

FWIW, I'm open to preferring bash over zsh as the default shell. But as zsh is already the default on macOS we might as well start using it when possible.

[kastiglione]

Is there a utility for exec'ing a command without a shell? Seems this could also be solved by avoiding a shell altogether.

[aprantl]

lldb/source/Host/macosx/objcxx/HostInfoMacOSX.mm

385–386

I think this should always be /usr/bin/xcrun anyway, and then we can as @kastiglione suggested avoid using a shell altogether, right?

[teemperor]

• Addressing Adrian's comments (sorry for the delay)

[teemperor]

@kastiglione Good point, I dropped using any shell for the command.

[aprantl]

lldb/source/Host/macosx/objcxx/HostInfoMacOSX.mm

401

Can we increase this to something much larger? It's only supposed to guard against catastrophic failure and xcrun is known to take a surprising amount of time the first tie it's launched.

[JDevlieghere]

LGTM

[kastiglione]

nice

lldb/source/Host/macosx/objcxx/HostInfoMacOSX.mm

lldb_private::FileSpec HostInfoMacOSX::GetXcodeDeveloperDirectory() {
   return g_developer_directory;
 }
 
 static std::string GetXcodeSDK(XcodeSDK sdk) {
   XcodeSDK::Info info = sdk.Parse();
   std::string sdk_name = XcodeSDK::GetCanonicalName(info);
 
   auto xcrun = [](const std::string &sdk,
                   llvm::StringRef developer_dir = "") -> std::string {
-    std::string xcrun_cmd = "xcrun --show-sdk-path --sdk " + sdk;
-    if (!developer_dir.empty())
-      xcrun_cmd = "/usr/bin/env DEVELOPER_DIR=\"" + developer_dir.str() +
-                  "\" " + xcrun_cmd;
+    Args args;
+    if (!developer_dir.empty()) {
+      args.AppendArgument("/usr/bin/env");
+      args.AppendArgument("DEVELOPER_DIR=" + developer_dir.str());
+    }
+    args.AppendArgument("/usr/bin/xcrun");
+    args.AppendArgument("--show-sdk-path");
+    args.AppendArgument("--sdk");
+    args.AppendArgument(sdk);
 
     int status = 0;
     int signo = 0;
     std::string output_str;
     lldb_private::Status error =
-        Host::RunShellCommand(xcrun_cmd, FileSpec(), &status, &signo,
-                              &output_str, std::chrono::seconds(15));
+        Host::RunShellCommand(args, FileSpec(), &status, &signo, &output_str,
+                              std::chrono::seconds(15));
 
     // Check that xcrun return something useful.
     if (status != 0 || output_str.empty())
       return {};
 
     // Convert to a StringRef so we can manipulate the string without modifying
     // the underlying data.
     llvm::StringRef output(output_str);