clang: Add support for relative linker paths with -fuse-ld

[keith]

Summary

This adds support for resolving linker executable paths relatively
instead of requiring them to be names, or absolute paths. This is useful
if you're vendoring an in-tree linker, and do not want to potentially
invalidate shared remote caches by using local absolute paths in command
lines.

[MaskRay]

clang/test/Driver/fuse-ld.c

7

This changes the working directory. It may be better moving cd tests to the bottom.

[keith]

Update tests

[keith]

Thanks I moved them to the bottom and I believe I fixed them on windows!

[keith]

The new test failure appears unrelated to my changes

[keith]

Fix test on windows

[keith]

https://reviews.llvm.org/D83015

clang/lib/Driver/ToolChain.cpp

if (Triple.isOSDarwin())
       LinkerName.append("ld64.");
     else
       LinkerName.append("ld.");
     LinkerName.append(UseLinker);
 
     std::string LinkerPath(GetProgramPath(LinkerName.c_str()));
     if (llvm::sys::fs::can_execute(LinkerPath))
       return LinkerPath;
+
+    const Arg *WorkingDir = Args.getLastArg(options::OPT_working_directory);
+    SmallString<128> ResolvedPath(UseLinker);
+    if (WorkingDir) {
+      sys::fs::make_absolute(WorkingDir->getValue(), ResolvedPath);
+      if (llvm::sys::fs::can_execute(ResolvedPath))
+        return std::string(ResolvedPath);
+    }
+
+    if (!sys::fs::make_absolute(ResolvedPath) &&
+        llvm::sys::fs::can_execute(ResolvedPath))
+      return std::string(ResolvedPath);
   }
 
   if (A)
     getDriver().Diag(diag::err_drv_invalid_linker_name) << A->getAsString(Args);
 
   return GetProgramPath(getDefaultLinker());
 }
 

clang/test/Driver/fuse-ld.c

 // RUN: %clang %s -### \
 // RUN:     -fuse-ld=/usr/local/bin/or1k-linux-ld 2>&1 \
 // RUN:     -target x86_64-unknown-linux \
 // RUN:   | FileCheck %s --check-prefix=CHECK-ABSOLUTE-LD
 // CHECK-ABSOLUTE-LD: /usr/local/bin/or1k-linux-ld
 
-
 // RUN: %clang %s -### \
 // RUN:     -target x86_64-unknown-freebsd 2>&1 \
 // RUN:   | FileCheck %s --check-prefix=CHECK-FREEBSD-LD
 // CHECK-FREEBSD-LD: ld
 
 // RUN: %clang %s -### -fuse-ld=bfd \
 // RUN:     --sysroot=%S/Inputs/basic_freebsd_tree \
 // RUN:     -target x86_64-unknown-freebsd \
 // RUN:     -B%S/Inputs/basic_freebsd_tree/usr/bin 2>&1 \

 // CHECK-WINDOWS-MSVC-LLD-LINK-SAME: "-out:{{.*}}"
 
 // RUN: %clang %s -### -fuse-ld=bfd \
 // RUN:     -target i686-unknown-windows-msvc \
 // RUN:     -B %S/Inputs/Windows/usr/bin 2>&1 \
 // RUN:   | FileCheck %s --check-prefix CHECK-WINDOWS-MSVC-BFD
 // CHECK-WINDOWS-MSVC-BFD: "{{.*}}ld.bfd"
 // CHECK-WINDOWS-MSVC-BFD-SAME: "-o"
+
+// RUN: %clang %s -### \
+// RUN:     -target x86_64-unknown-linux \
+// RUN:     -working-directory "%S/Inputs" \
+// RUN:     -fuse-ld=fuse_ld_windows/ld.foo.exe 2>&1 \
+// RUN:   | FileCheck %s --check-prefix=CHECK-RELATIVE-WORKDIR-LD
+// CHECK-RELATIVE-WORKDIR-LD-NOT: error: invalid linker name
+// CHECK-RELATIVE-WORKDIR-LD: test{{/|\\+}}Driver{{/|\\+}}Inputs/fuse_ld_windows/ld.foo.exe
+
+// RUN: cd "%S" && %clang %s -### \
+// RUN:     -target x86_64-unknown-linux \
+// RUN:     -fuse-ld=Inputs/fuse_ld_windows/ld.foo.exe 2>&1 \
+// RUN:   | FileCheck %s --check-prefix=CHECK-RELATIVE-LD
+// CHECK-RELATIVE-LD-NOT: error: invalid linker name
+// CHECK-RELATIVE-LD: test{{/|\\+}}Driver{{/|\\+}}Inputs/fuse_ld_windows/ld.foo.exe