[clang-cl] Always interpret the LIB env var as separated with semicolons

[mstorsjo]

Summary

When cross compiling with clang-cl, clang splits the INCLUDE env variable around semicolons (clang/lib/Driver/ToolChains/MSVC.cpp, MSVCToolChain::AddClangSystemIncludeArgs) and lld splits the LIB variable similarly (lld/COFF/Driver.cpp, LinkerDriver::addLibSearchPaths). Therefore, the consensus for cross compilation with clang-cl and lld-link seems to be to use semicolons, despite path lists normally being separated by colons on unix and EnvPathSeparator being set to that.

Therefore, handle the LIB variable similarly in Clang, when handling lib file arguments when driving linking via Clang.

This fixes commands like "clang-cl test.c -Fetest.exe kernel32.lib" in a cross compilation setting. Normally, most users call (lld-)link directly, but meson happens to use this command syntax for has_function() tests.

[rnk]

lgtm

clang/lib/Driver/Driver.cpp

bool Driver::DiagnoseInputExistence(const DerivedArgList &Args, StringRef Value,
   if (Value == "-")
     return true;
 
   if (getVFS().exists(Value))
     return true;
 
   if (IsCLMode()) {
     if (!llvm::sys::path::is_absolute(Twine(Value)) &&
-        llvm::sys::Process::FindInEnvPath("LIB", Value))
+        llvm::sys::Process::FindInEnvPath("LIB", Value, ';'))
       return true;
 
     if (Args.hasArg(options::OPT__SLASH_link) && Ty == types::TY_Object) {
       // Arguments to the /link flag might cause the linker to search for object
       // and library files in paths we don't know about. Don't error in such
       // cases.
       return true;
     }

clang/test/Driver/cl-inputs.c

 
 // RUN: %clang_cl /TP /TC /TP -### -- %s 2>&1 | FileCheck -check-prefix=WARN %s
 // WARN: warning: overriding '/TP' option with '/TC'
 // WARN: warning: overriding '/TC' option with '/TP'
 // WARN: note: The last /TC or /TP option takes precedence over earlier instances
 // WARN-NOT: note
 
 // MSYS2_ARG_CONV_EXCL tells MSYS2 to skip conversion of the specified argument.
-// RUN: env LIB=%S/Inputs/cl-libs MSYS2_ARG_CONV_EXCL="/TP;/c" %clang_cl /c /TP cl-test.lib -### 2>&1 | FileCheck -check-prefix=TPlib %s
+// Add a dummy "other" entry to the path as well, to check that it's split
+// around semicolons even on unix.
+// RUN: env LIB="other;%S/Inputs/cl-libs" MSYS2_ARG_CONV_EXCL="/TP;/c" %clang_cl /c /TP cl-test.lib -### 2>&1 | FileCheck -check-prefix=TPlib %s
 // TPlib: warning: cl-test.lib: 'linker' input unused
 // TPlib: warning: argument unused during compilation: '/TP'
 // TPlib-NOT: cl-test.lib
 
 // RUN: env LIB=%S/Inputs/cl-libs MSYS2_ARG_CONV_EXCL="/TC;/c" %clang_cl /c /TC cl-test.lib -### 2>&1 | FileCheck -check-prefix=TClib %s
 // TClib: warning: cl-test.lib: 'linker' input unused
 // TClib: warning: argument unused during compilation: '/TC'
 // TClib-NOT: cl-test.lib

llvm/include/llvm/Support/Process.h

 #ifndef LLVM_SUPPORT_PROCESS_H
 #define LLVM_SUPPORT_PROCESS_H
 
 #include "llvm/ADT/Optional.h"
 #include "llvm/Support/AllocatorBase.h"
 #include "llvm/Support/Chrono.h"
 #include "llvm/Support/DataTypes.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/Program.h"
 #include <system_error>
 
 namespace llvm {
 template <typename T> class ArrayRef;
 class StringRef;
 
 namespace sys {
 
public:
   /// This function searches for an existing file in the list of directories
   /// in a PATH like environment variable, and returns the first file found,
   /// according to the order of the entries in the PATH like environment
   /// variable.  If an ignore list is specified, then any folder which is in
   /// the PATH like environment variable but is also in IgnoreList is not
   /// considered.
   static Optional<std::string> FindInEnvPath(StringRef EnvName,
                                              StringRef FileName,
-                                             ArrayRef<std::string> IgnoreList);
+                                             ArrayRef<std::string> IgnoreList,
+                                             char Separator = EnvPathSeparator);
 
   static Optional<std::string> FindInEnvPath(StringRef EnvName,
-                                             StringRef FileName);
+                                             StringRef FileName,
+                                             char Separator = EnvPathSeparator);
 
   // This functions ensures that the standard file descriptors (input, output,
   // and error) are properly mapped to a file descriptor before we use any of
   // them.  This should only be called by standalone programs, library
   // components should not call this.
   static std::error_code FixupStandardFileDescriptors();
 
   // This function safely closes a file descriptor.  It is not safe to retry

llvm/lib/Support/Process.cpp

 using namespace llvm;
 using namespace sys;
 
 //===----------------------------------------------------------------------===//
 //=== WARNING: Implementation here must contain only TRULY operating system
 //===          independent code.
 //===----------------------------------------------------------------------===//
 
-Optional<std::string> Process::FindInEnvPath(StringRef EnvName,
-                                             StringRef FileName) {
-  return FindInEnvPath(EnvName, FileName, {});
+Optional<std::string>
+Process::FindInEnvPath(StringRef EnvName, StringRef FileName, char Separator) {
+  return FindInEnvPath(EnvName, FileName, {}, Separator);
 }
 
 Optional<std::string> Process::FindInEnvPath(StringRef EnvName,
                                              StringRef FileName,
-                                             ArrayRef<std::string> IgnoreList) {
+                                             ArrayRef<std::string> IgnoreList,
+                                             char Separator) {
   assert(!path::is_absolute(FileName));
   Optional<std::string> FoundPath;
   Optional<std::string> OptPath = Process::GetEnv(EnvName);
   if (!OptPath.hasValue())
     return FoundPath;
 
-  const char EnvPathSeparatorStr[] = {EnvPathSeparator, '\0'};
+  const char EnvPathSeparatorStr[] = {Separator, '\0'};
   SmallVector<StringRef, 8> Dirs;
   SplitString(OptPath.getValue(), Dirs, EnvPathSeparatorStr);
 
   for (StringRef Dir : Dirs) {
     if (Dir.empty())
       continue;
 
     if (any_of(IgnoreList, [&](StringRef S) { return fs::equivalent(S, Dir); }))