[clang][Driver] Add gcc-toolset-12 and devtoolset-12 prefixes

[tbaeder]

Summary

This reverts commit 35aaf548237a4f213ba9d95de53b33c5ce1eadce and commit 9f97720268911abae2ad9d90e270358db234a1c1 and adds the prefix like we did before.

The issues with the approach are explained in https://github.com/llvm/llvm-project/issues/57843. If clang16 stops doing the gcc/devtoolset detection and relies on a config file instead, that's fine but for the time being (and for a backport to clang15), we need to fix this problem.

[MaskRay]

If clang16 stops doing the gcc/devtoolset detection and relies on a config file instead, that's fine but for the time being (and for a backport to clang15), we need to fix this problem.

I think this is fine. The test removal is fine if the future direction is to remove the Prefixes.push_back("/opt/rh/ code and rely on configuration files (https://github.com/llvm/llvm-project/issues/57843#issuecomment-1287299027).
If this is the agreed-upon direction, perhaps leave a TODO URI before Prefixes.push_back("/opt/rh/gcc-toolset-12/root/usr");

clang/lib/Driver/ToolChains/Gnu.cpp

if (TargetTriple.getOS() == llvm::Triple::Solaris) {
     }
     return;
   }
 
   // For Linux, if --sysroot is not specified, look for RHEL/CentOS devtoolsets
   // and gcc-toolsets.
   if (SysRoot.empty() && TargetTriple.getOS() == llvm::Triple::Linux &&
       D.getVFS().exists("/opt/rh")) {
-    // Find the directory in /opt/rh/ starting with gcc-toolset-* or
-    // devtoolset-* with the highest version number and add that
-    // one to our prefixes.
-    std::string ChosenToolsetDir;
-    unsigned ChosenToolsetVersion = 0;
-    std::error_code EC;
-    for (llvm::vfs::directory_iterator LI = D.getVFS().dir_begin("/opt/rh", EC),
-                                       LE;
-         !EC && LI != LE; LI = LI.increment(EC)) {
-      StringRef ToolsetDir = llvm::sys::path::filename(LI->path());
-      unsigned ToolsetVersion;
-      if ((!ToolsetDir.startswith("gcc-toolset-") &&
-           !ToolsetDir.startswith("devtoolset-")) ||
-          ToolsetDir.substr(ToolsetDir.rfind('-') + 1)
-              .getAsInteger(10, ToolsetVersion))
-        continue;
-
-      if (ToolsetVersion > ChosenToolsetVersion) {
-        ChosenToolsetVersion = ToolsetVersion;
-        ChosenToolsetDir = "/opt/rh/" + ToolsetDir.str();
-      }
-    }
-
-    if (ChosenToolsetVersion > 0)
-      Prefixes.push_back(ChosenToolsetDir + "/root/usr");
+    // TODO: We may want to remove this, since the functionality
+    //   can be achieved using config files.
+    Prefixes.push_back("/opt/rh/gcc-toolset-12/root/usr");
+    Prefixes.push_back("/opt/rh/gcc-toolset-11/root/usr");
+    Prefixes.push_back("/opt/rh/gcc-toolset-10/root/usr");
+    Prefixes.push_back("/opt/rh/devtoolset-12/root/usr");
+    Prefixes.push_back("/opt/rh/devtoolset-11/root/usr");
+    Prefixes.push_back("/opt/rh/devtoolset-10/root/usr");
+    Prefixes.push_back("/opt/rh/devtoolset-9/root/usr");
+    Prefixes.push_back("/opt/rh/devtoolset-8/root/usr");
+    Prefixes.push_back("/opt/rh/devtoolset-7/root/usr");
+    Prefixes.push_back("/opt/rh/devtoolset-6/root/usr");
+    Prefixes.push_back("/opt/rh/devtoolset-4/root/usr");
+    Prefixes.push_back("/opt/rh/devtoolset-3/root/usr");
+    Prefixes.push_back("/opt/rh/devtoolset-2/root/usr");
   }
 
   // Fall back to /usr which is used by most non-Solaris systems.
   Prefixes.push_back(concat(SysRoot, "/usr"));
 }
 
 /*static*/ void Generic_GCC::GCCInstallationDetector::CollectLibDirsAndTriples(
     const llvm::Triple &TargetTriple, const llvm::Triple &BiarchTriple,

clang/unittests/Driver/ToolChainTest.cpp

 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/TargetOptions.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/MC/TargetRegistry.h"
-#include "llvm/Support/Host.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Support/raw_ostream.h"
 #include "gtest/gtest.h"
 #include <memory>
 
 #include "SimpleDiagnosticConsumer.h"
 
void clear() override {
     Msgs.clear();
     Errors.clear();
     DiagnosticConsumer::clear();
   }
   std::vector<SmallString<32>> Msgs;
   std::vector<SmallString<32>> Errors;
 };
 
-TEST(ToolChainTest, Toolsets) {
-  // Ignore this test on Windows hosts.
-  llvm::Triple Host(llvm::sys::getProcessTriple());
-  if (Host.isOSWindows())
-    GTEST_SKIP();
-
-  IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts = new DiagnosticOptions();
-  IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
-
-  // Check (newer) GCC toolset installation.
-  {
-    IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> InMemoryFileSystem(
-        new llvm::vfs::InMemoryFileSystem);
-
-    // These should be ignored.
-    InMemoryFileSystem->addFile("/opt/rh/gcc-toolset-2", 0,
-                                llvm::MemoryBuffer::getMemBuffer("\n"));
-    InMemoryFileSystem->addFile("/opt/rh/gcc-toolset-", 0,
-                                llvm::MemoryBuffer::getMemBuffer("\n"));
-    InMemoryFileSystem->addFile("/opt/rh/gcc-toolset--", 0,
-                                llvm::MemoryBuffer::getMemBuffer("\n"));
-    InMemoryFileSystem->addFile("/opt/rh/gcc-toolset--1", 0,
-                                llvm::MemoryBuffer::getMemBuffer("\n"));
-
-    // File needed for GCC installation detection.
-    InMemoryFileSystem->addFile("/opt/rh/gcc-toolset-12/root/usr/lib/gcc/"
-                                "x86_64-redhat-linux/11/crtbegin.o",
-                                0, llvm::MemoryBuffer::getMemBuffer("\n"));
-
-    DiagnosticsEngine Diags(DiagID, &*DiagOpts, new SimpleDiagnosticConsumer);
-    Driver TheDriver("/bin/clang", "x86_64-redhat-linux", Diags,
-                     "clang LLVM compiler", InMemoryFileSystem);
-    std::unique_ptr<Compilation> C(
-        TheDriver.BuildCompilation({"clang", "--gcc-toolchain="}));
-    ASSERT_TRUE(C);
-    std::string S;
-    {
-      llvm::raw_string_ostream OS(S);
-      C->getDefaultToolChain().printVerboseInfo(OS);
-    }
-    EXPECT_EQ("Found candidate GCC installation: "
-              "/opt/rh/gcc-toolset-12/root/usr/lib/gcc/x86_64-redhat-linux/11\n"
-              "Selected GCC installation: "
-              "/opt/rh/gcc-toolset-12/root/usr/lib/gcc/x86_64-redhat-linux/11\n"
-              "Candidate multilib: .;@m64\n"
-              "Selected multilib: .;@m64\n",
-              S);
-  }
-
-  // And older devtoolset.
-  {
-    IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> InMemoryFileSystem(
-        new llvm::vfs::InMemoryFileSystem);
-
-    // These should be ignored.
-    InMemoryFileSystem->addFile("/opt/rh/devtoolset-2", 0,
-                                llvm::MemoryBuffer::getMemBuffer("\n"));
-    InMemoryFileSystem->addFile("/opt/rh/devtoolset-", 0,
-                                llvm::MemoryBuffer::getMemBuffer("\n"));
-    InMemoryFileSystem->addFile("/opt/rh/devtoolset--", 0,
-                                llvm::MemoryBuffer::getMemBuffer("\n"));
-    InMemoryFileSystem->addFile("/opt/rh/devtoolset--1", 0,
-                                llvm::MemoryBuffer::getMemBuffer("\n"));
-
-    // File needed for GCC installation detection.
-    InMemoryFileSystem->addFile("/opt/rh/devtoolset-12/root/usr/lib/gcc/"
-                                "x86_64-redhat-linux/11/crtbegin.o",
-                                0, llvm::MemoryBuffer::getMemBuffer("\n"));
-
-    DiagnosticsEngine Diags(DiagID, &*DiagOpts, new SimpleDiagnosticConsumer);
-    Driver TheDriver("/bin/clang", "x86_64-redhat-linux", Diags,
-                     "clang LLVM compiler", InMemoryFileSystem);
-    std::unique_ptr<Compilation> C(
-        TheDriver.BuildCompilation({"clang", "--gcc-toolchain="}));
-    ASSERT_TRUE(C);
-    std::string S;
-    {
-      llvm::raw_string_ostream OS(S);
-      C->getDefaultToolChain().printVerboseInfo(OS);
-    }
-    EXPECT_EQ("Found candidate GCC installation: "
-              "/opt/rh/devtoolset-12/root/usr/lib/gcc/x86_64-redhat-linux/11\n"
-              "Selected GCC installation: "
-              "/opt/rh/devtoolset-12/root/usr/lib/gcc/x86_64-redhat-linux/11\n"
-              "Candidate multilib: .;@m64\n"
-              "Selected multilib: .;@m64\n",
-              S);
-  }
-}
-
 TEST(ToolChainTest, ConfigFileSearch) {
   IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts = new DiagnosticOptions();
   IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
   struct TestDiagnosticConsumer : public DiagnosticConsumer {};
   DiagnosticsEngine Diags(DiagID, &*DiagOpts, new TestDiagnosticConsumer);
   IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> FS(
       new llvm::vfs::InMemoryFileSystem);