Revert "[clang][Darwin] Try to guess the SDK root with xcrun when unspecified"

This reverts commit ecade80.
Breaks tests on macOS and tries to run xcrun on non-mac platforms,
see comments on https://reviews.llvm.org/D136315

Author: nico

clang/docs/UsersManual.rst

@@ -3824,20 +3824,6 @@ backend.
 Operating System Features and Limitations
 -----------------------------------------
 
-Apple
-^^^^^
-
-On Apple platforms, the standard headers and libraries are not provided by
-the base system and are instead part of the Xcode SDK application. The location
-of the SDK is determined any of the following ways:
-
-- If passed to Clang, the ``-isysroot`` option specifies the path to the SDK.
-
-- If the sysroot isn't provided, the ``SDKROOT`` environment variable is checked.
-  This variable is set by various Xcode tools.
-
-- Otherwise, Clang uses Xcode's ``xcrun`` tool to find the SDK.
-
 Windows
 ^^^^^^^
 

clang/lib/Driver/ToolChains/Darwin.cpp

@@ -18,22 +18,15 @@
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
-#include "llvm/ADT/ArrayRef.h"
-#include "llvm/ADT/Optional.h"
-#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/ProfileData/InstrProf.h"
-#include "llvm/Support/FileSystem.h"
-#include "llvm/Support/FileUtilities.h"
 #include "llvm/Support/Path.h"
-#include "llvm/Support/Program.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/TargetParser.h"
 #include "llvm/Support/Threading.h"
 #include "llvm/Support/VirtualFileSystem.h"
 #include <cstdlib> // ::getenv
-#include <memory>  // std::unique_ptr
 
 using namespace clang::driver;
 using namespace clang::driver::tools;
@@ -2085,89 +2078,21 @@ std::optional<DarwinSDKInfo> parseSDKSettings(llvm::vfs::FileSystem &VFS,
 void Darwin::AddDeploymentTarget(DerivedArgList &Args) const {
   const OptTable &Opts = getDriver().getOpts();
 
-  // On Apple platforms, standard headers and libraries are not provided with
-  // the base system (e.g. in /usr/{include,lib}). Instead, they are provided
-  // in various SDKs for the different Apple platforms. Clang needs to know
-  // where that SDK lives, and there are a couple ways this can be achieved:
-  //
-  // (1) If `-isysroot <path-to-SDK>` is passed explicitly, use that.
+  // Support allowing the SDKROOT environment variable used by xcrun and other
+  // Xcode tools to define the default sysroot, by making it the default for
+  // isysroot.
   if (const Arg *A = Args.getLastArg(options::OPT_isysroot)) {
     // Warn if the path does not exist.
     if (!getVFS().exists(A->getValue()))
       getDriver().Diag(clang::diag::warn_missing_sysroot) << A->getValue();
-  }
-
-  // (2) If the SDKROOT environment variable is defined and points to a valid
-  //     path, use that. $SDKROOT is set by `xcrun` and other Xcode tools, so
-  //     running `xcrun clang` will work by going through this path.
-  else if (char *env = ::getenv("SDKROOT")) {
-    // We only use this value as the default if it is an absolute path,
-    // exists, and it is not the root path.
-    if (llvm::sys::path::is_absolute(env) && getVFS().exists(env) &&
-        StringRef(env) != "/") {
-      Args.append(Args.MakeSeparateArg(
-          nullptr, Opts.getOption(options::OPT_isysroot), env));
-    }
-  }
-
-  // (3) Otherwise, we try to guess the path of the default SDK by running
-  //     `xcrun --show-sdk-path`. This won't always be correct, but if the
-  //      user wants to use the non-default SDK, they should specify it
-  //      explicitly with methods (1) or (2) above.
-  else {
-    llvm::SmallString<64> OutputFile;
-    llvm::sys::fs::createTemporaryFile("print-sdk-path", "" /* No Suffix */,
-                                       OutputFile);
-    llvm::FileRemover OutputRemover(OutputFile.c_str());
-    std::optional<llvm::StringRef> Redirects[] = {{""}, OutputFile.str(), {""}};
-
-    Optional<StringRef> SDKName = std::nullopt;
-    switch (getTriple().getOS()) {
-    case llvm::Triple::OSType::WatchOS:
-      if (getTriple().isSimulatorEnvironment())
-        SDKName = "watchsimulator";
-      else
-        SDKName = "watchos";
-      break;
-    case llvm::Triple::OSType::TvOS:
-      if (getTriple().isSimulatorEnvironment())
-        SDKName = "appletvsimulator";
-      else
-        SDKName = "appletvos";
-      break;
-    case llvm::Triple::OSType::IOS:
-      if (getTriple().isSimulatorEnvironment())
-        SDKName = "iphonesimulator";
-      else
-        SDKName = "iphoneos";
-      break;
-    case llvm::Triple::OSType::Darwin:
-    case llvm::Triple::OSType::MacOSX:
-      SDKName = "macosx";
-      break;
-    case llvm::Triple::OSType::DriverKit:
-      SDKName = "driverkit";
-      break;
-    default:
-      llvm_unreachable("unknown kind of Darwin platform");
-    }
-
-    if (SDKName) {
-      int Result = llvm::sys::ExecuteAndWait(
-          "/usr/bin/xcrun",
-          {"/usr/bin/xcrun", "--sdk", *SDKName, "--show-sdk-path"},
-          /* Inherit environment from parent process */ std::nullopt, Redirects,
-          /* SecondsToWait */ 0, /*MemoryLimit*/ 0);
-      if (Result == 0) {
-        llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> OutputBuf =
-            llvm::MemoryBuffer::getFile(OutputFile.c_str(), /* IsText */ true);
-        if (OutputBuf) {
-          llvm::StringRef SdkPath = (*OutputBuf)->getBuffer().trim();
-          if (getVFS().exists(SdkPath)) {
-            Args.append(Args.MakeSeparateArg(
-                nullptr, Opts.getOption(options::OPT_isysroot), SdkPath));
-          }
-        }
+  } else {
+    if (char *env = ::getenv("SDKROOT")) {
+      // We only use this value as the default if it is an absolute path,
+      // exists, and it is not the root path.
+      if (llvm::sys::path::is_absolute(env) && getVFS().exists(env) &&
+          StringRef(env) != "/") {
+        Args.append(Args.MakeSeparateArg(
+            nullptr, Opts.getOption(options::OPT_isysroot), env));
       }
     }
   }