gnu: clang@7, clang@8: Do not refer to /lib on foreign distros.

Partly fixes <https://issues.guix.gnu.org/51088>.

* gnu/packages/patches/clang-7.0-libc-search-path.patch: Update.
* gnu/packages/patches/clang-8.0-libc-search-path.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/llvm.scm (clang-8): Use it.

gnu/local.mk

@@ -932,6 +932,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/clang-3.8-libc-search-path.patch		\
   %D%/packages/patches/clang-6.0-libc-search-path.patch		\
   %D%/packages/patches/clang-7.0-libc-search-path.patch		\
+  %D%/packages/patches/clang-8.0-libc-search-path.patch		\
   %D%/packages/patches/clang-9.0-libc-search-path.patch		\
   %D%/packages/patches/clang-10.0-libc-search-path.patch	\
   %D%/packages/patches/clang-11.0-libc-search-path.patch	\

gnu/packages/llvm.scm

@@ -681,7 +681,7 @@ of programming tools as well as libraries with equivalent functionality.")
 (define-public clang-8
   (clang-from-llvm llvm-8 clang-runtime-8
                    "0svk1f70hvpwrjp6x5i9kqwrqwxnmcrw5s7f4cxyd100mdd12k08"
-                   #:patches '("clang-7.0-libc-search-path.patch")))
+                   #:patches '("clang-8.0-libc-search-path.patch")))
 
 (define-public clang-toolchain-8
   (make-clang-toolchain clang-8))

gnu/packages/patches/clang-7.0-libc-search-path.patch

@@ -4,8 +4,39 @@ but unfortunately, that doesn't work for us.
 This patch makes it easy to insert libc's $libdir so that Clang passes the
 correct absolute file name of crt1.o etc. to 'ld'.  It also disables all
 the distro-specific stuff and removes the hard-coded FHS directory names
-to make sure Clang also works on non-GuixSD systems.
+to make sure Clang also works on foreign distros.
 
+diff --git a/lib/Driver/Distro.cpp b/lib/Driver/Distro.cpp
+index 2c4d44f..0493b0a 100644
+--- a/lib/Driver/Distro.cpp
++++ b/lib/Driver/Distro.cpp
+@@ -18,6 +18,10 @@ using namespace clang::driver;
+ using namespace clang;
+ 
+ static Distro::DistroType DetectDistro(vfs::FileSystem &VFS) {
++  // The compiler should always behave the same, even when used via Guix on a
++  // foreign distro.
++  return Distro::UnknownDistro;
++
+   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> File =
+       VFS.getBufferForFile("/etc/lsb-release");
+   if (File) {
+diff --git a/lib/Driver/ToolChains/Cuda.cpp b/lib/Driver/ToolChains/Cuda.cpp
+index 7fb4ae4..cb21344 100644
+--- a/lib/Driver/ToolChains/Cuda.cpp
++++ b/lib/Driver/ToolChains/Cuda.cpp
+@@ -66,6 +66,9 @@ CudaInstallationDetector::CudaInstallationDetector(
+     const Driver &D, const llvm::Triple &HostTriple,
+     const llvm::opt::ArgList &Args)
+     : D(D) {
++  // Don't look for CUDA in /usr.
++  return;
++
+   struct Candidate {
+     std::string Path;
+     bool StrictChecking;
+diff --git a/lib/Driver/ToolChains/Linux.cpp b/lib/Driver/ToolChains/Linux.cpp
+index f8f3623..36dc722 100644
 --- a/lib/Driver/ToolChains/Linux.cpp
 +++ b/lib/Driver/ToolChains/Linux.cpp
 @@ -225,7 +225,9 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
@@ -27,56 +58,37 @@ to make sure Clang also works on non-GuixSD systems.
  
    // The selection of paths to try here is designed to match the patterns which
    // the GCC driver itself uses, as this is part of the GCC-compatible driver.
-@@ -342,7 +345,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+@@ -348,6 +351,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
-     // the cross. Note that GCC does include some of these directories in some
-     // configurations but this seems somewhere between questionable and simply
-     // a bug.
--    if (StringRef(LibPath).startswith(SysRoot)) {
-+    if (0) {
-       addPathIfExists(D, LibPath + "/" + MultiarchTriple, Paths);
-       addPathIfExists(D, LibPath + "/../" + OSLibDir, Paths);
      }
-@@ -361,6 +364,8 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
-   addPathIfExists(D, SysRoot + "/lib/" + MultiarchTriple, Paths);
-   addPathIfExists(D, SysRoot + "/lib/../" + OSLibDir, Paths);
- 
-+  // This requires the commented distro tweaks above.
-+#if 0
-   if (IsAndroid) {
-     // Android sysroots contain a library directory for each supported OS
-     // version as well as some unversioned libraries in the usual multiarch
-@@ -389,10 +394,14 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
-     addPathIfExists(D, SysRoot + "/" + OSLibDir + "/" + ABIName, Paths);
-     addPathIfExists(D, SysRoot + "/usr/" + OSLibDir + "/" + ABIName, Paths);
    }
-+#endif
  
++#if 0
+   // Similar to the logic for GCC above, if we currently running Clang inside
+   // of the requested system root, add its parent library paths to
+   // those searched.
+@@ -393,6 +397,8 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
    // Try walking via the GCC triple path in case of biarch or multiarch GCC
    // installations with strange symlinks.
    if (GCCInstallation.isValid()) {
 +    // The following code would end up adding things like
 +    // "/usr/lib/x86_64-unknown-linux-gnu/../../lib64" to the search path.
-+#if 0
      addPathIfExists(D,
                      SysRoot + "/usr/lib/" + GCCInstallation.getTriple().str() +
                          "/../../" + OSLibDir,
-@@ -405,6 +414,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+@@ -428,9 +434,14 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
-                              BiarchSibling.gccSuffix(),
+   // directory ('Dir' below) or the ResourceDir.
-                       Paths);
-     }
-+#endif
- 
-     // See comments above on the multilib variant for details of why this is
-     // included even from outside the sysroot.
-@@ -429,8 +439,9 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
    if (StringRef(D.Dir).startswith(SysRoot))
      addPathIfExists(D, D.Dir + "/../lib", Paths);
- 
++#endif
--  addPathIfExists(D, SysRoot + "/lib", Paths);
++
--  addPathIfExists(D, SysRoot + "/usr/lib", Paths);
 +  // Add libc's lib/ directory to the search path, so that crt1.o, crti.o,
 +  // and friends can be found.
 +  addPathIfExists(D, "@GLIBC_LIBDIR@", Paths);
+ 
+-  addPathIfExists(D, SysRoot + "/lib", Paths);
+-  addPathIfExists(D, SysRoot + "/usr/lib", Paths);
++  // Add GCC's lib/ directory so libstdc++.so can be found.
++  addPathIfExists(D, GCCInstallation.getParentLibPath(), Paths);
  }
  
  bool Linux::HasNativeLLVMSupport() const { return true; }

gnu/packages/patches/clang-8.0-libc-search-path.patch

@@ -0,0 +1,94 @@
+Clang attempts to guess file names based on the OS and distro (yes!),
+but unfortunately, that doesn't work for us.
+
+This patch makes it easy to insert libc's $libdir so that Clang passes the
+correct absolute file name of crt1.o etc. to 'ld'.  It also disables all
+the distro-specific stuff and removes the hard-coded FHS directory names
+to make sure Clang also works on foreign distros.
+
+diff --git a/lib/Driver/Distro.cpp b/lib/Driver/Distro.cpp
+index 396d0bee..90e06613 100644
+--- a/lib/Driver/Distro.cpp
++++ b/lib/Driver/Distro.cpp
+@@ -19,6 +19,10 @@ using namespace clang::driver;
+ using namespace clang;
+ 
+ static Distro::DistroType DetectDistro(llvm::vfs::FileSystem &VFS) {
++  // The compiler should always behave the same, even when used via Guix on a
++  // foreign distro.
++  return Distro::UnknownDistro;
++
+   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> File =
+       VFS.getBufferForFile("/etc/lsb-release");
+   if (File) {
+diff --git a/lib/Driver/ToolChains/Cuda.cpp b/lib/Driver/ToolChains/Cuda.cpp
+index 57b8d434..57339f1a 100644
+--- a/lib/Driver/ToolChains/Cuda.cpp
++++ b/lib/Driver/ToolChains/Cuda.cpp
+@@ -68,6 +68,9 @@ CudaInstallationDetector::CudaInstallationDetector(
+     const Driver &D, const llvm::Triple &HostTriple,
+     const llvm::opt::ArgList &Args)
+     : D(D) {
++  // Don't look for CUDA in /usr.
++  return;
++
+   struct Candidate {
+     std::string Path;
+     bool StrictChecking;
+diff --git a/lib/Driver/ToolChains/Linux.cpp b/lib/Driver/ToolChains/Linux.cpp
+index 65ab9b2d..5ed28e0a 100644
+--- a/lib/Driver/ToolChains/Linux.cpp
++++ b/lib/Driver/ToolChains/Linux.cpp
+@@ -233,7 +233,9 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+   PPaths.push_back(Twine(GCCInstallation.getParentLibPath() + "/../" +
+                          GCCInstallation.getTriple().str() + "/bin")
+                        .str());
+-
++  // Comment out the distro-specific tweaks so that they don't bite when
++  // using Guix on a foreign distro.
++#if 0
+   Distro Distro(D.getVFS());
+ 
+   if (Distro.IsAlpineLinux() || Triple.isAndroid()) {
+@@ -304,6 +306,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+ 
+   if (IsAndroid || Distro.IsOpenSUSE())
+     ExtraOpts.push_back("--enable-new-dtags");
++#endif
+ 
+   // The selection of paths to try here is designed to match the patterns which
+   // the GCC driver itself uses, as this is part of the GCC-compatible driver.
+@@ -366,6 +369,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+     }
+   }
+ 
++#if 0
+   // Similar to the logic for GCC above, if we currently running Clang inside
+   // of the requested system root, add its parent library paths to
+   // those searched.
+@@ -411,6 +415,8 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+   // Try walking via the GCC triple path in case of biarch or multiarch GCC
+   // installations with strange symlinks.
+   if (GCCInstallation.isValid()) {
++    // The following code would end up adding things like
++    // "/usr/lib/x86_64-unknown-linux-gnu/../../lib64" to the search path.
+     addPathIfExists(D,
+                     SysRoot + "/usr/lib/" + GCCInstallation.getTriple().str() +
+                         "/../../" + OSLibDir,
+@@ -446,9 +452,14 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+   // directory ('Dir' below) or the ResourceDir.
+   if (StringRef(D.Dir).startswith(SysRoot))
+     addPathIfExists(D, D.Dir + "/../lib", Paths);
++#endif
++
++  // Add libc's lib/ directory to the search path, so that crt1.o, crti.o,
++  // and friends can be found.
++  addPathIfExists(D, "@GLIBC_LIBDIR@", Paths);
+ 
+-  addPathIfExists(D, SysRoot + "/lib", Paths);
+-  addPathIfExists(D, SysRoot + "/usr/lib", Paths);
++  // Add GCC's lib/ directory so libstdc++.so can be found.
++  addPathIfExists(D, GCCInstallation.getParentLibPath(), Paths);
+ }
+ 
+ ToolChain::CXXStdlibType Linux::GetDefaultCXXStdlibType() const {