[lld] Add (ignored) /link flag to lld-link for compatibility with MSVC link.exe

[frankier]

Various build tools may produce command lines invoking clang-cl and lld-link which contain /link twice like so: e.g. clang-cl.exe sanitycheckcpp.cc /Fesanitycheckcpp.exe .... /link /link ...

If link.exe is used, it ignores the extra /link and just issues a warning, however lld-link tries to treat /link as a file name.

This PR adds a flag which is ignored in order to improve compatibility with link.exe

There's some extra context including an "in-the-wild" example and reproducer of the problem here: https://github.com/frankier/meson_clang_win_activation

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[llvmbot]

@llvm/pr-subscribers-lld-coff
@llvm/pr-subscribers-platform-windows

@llvm/pr-subscribers-lld

Author: Frankie Robertson (frankier)

Changes

Various build tools may produce command lines invoking clang-cl and lld-link which contain /link twice like so: e.g. clang-cl.exe sanitycheckcpp.cc /Fesanitycheckcpp.exe .... /link /link ...

If link.exe is used, it ignores the extra /link and just issues a warning, however lld-link tries to treat /link as a file name.

This PR adds a flag which is ignored in order to improve compatibility with link.exe

There's some extra context including an "in-the-wild" example and reproducer of the problem here: https://github.com/frankier/meson_clang_win_activation

---

Full diff: https://github.com/llvm/llvm-project/pull/168364.diff

3 Files Affected:

• (modified) lld/COFF/DriverUtils.cpp (+3)
• (modified) lld/COFF/Options.td (+1)
• (modified) lld/test/COFF/driver.test (+3)

diff --git a/lld/COFF/DriverUtils.cpp b/lld/COFF/DriverUtils.cpp
index 10a3934d53284..42c7f93381510 100644
--- a/lld/COFF/DriverUtils.cpp
+++ b/lld/COFF/DriverUtils.cpp
@@ -862,6 +862,9 @@ opt::InputArgList ArgParser::parse(ArrayRef<const char *> argv) {
                 << "', did you mean '" << nearest << "'";
   }
 
+  if (args.hasArg(OPT_link))
+    Warn(ctx) << "ignoring /link, did you pass it multiple times?";
+
   if (args.hasArg(OPT_lib))
     Warn(ctx) << "ignoring /lib since it's not the first argument";
 
diff --git a/lld/COFF/Options.td b/lld/COFF/Options.td
index d77478fc9c987..6c4c7f897513d 100644
--- a/lld/COFF/Options.td
+++ b/lld/COFF/Options.td
@@ -71,6 +71,7 @@ def noimplib : F<"noimplib">,
 def lib : F<"lib">,
     HelpText<"Act like lib.exe; must be first argument if present">;
 def libpath : P<"libpath", "Additional library search path">;
+def link : F<"link">, HelpText<"Ignored for compatibility">;
 def linkrepro : Joined<["/", "-", "/?", "-?"], "linkrepro:">,
     MetaVarName<"directory">,
     HelpText<"Write repro.tar containing inputs and command to reproduce link">;
diff --git a/lld/test/COFF/driver.test b/lld/test/COFF/driver.test
index 8f58ff44e83e3..1c265bff75df5 100644
--- a/lld/test/COFF/driver.test
+++ b/lld/test/COFF/driver.test
@@ -17,6 +17,9 @@ LIBHELP: OVERVIEW: LLVM Lib
 # RUN: env LLD_IN_TEST=1 not lld-link /WX /lib 2>&1 | FileCheck -check-prefix=LIBBAD %s
 LIBBAD: ignoring /lib since it's not the first argument
 
+# RUN: env LLD_IN_TEST=1 not lld-link /link 2>&1 | FileCheck -check-prefix=LINKBAD %s
+LINKBAD: ignoring /link, did you pass it multiple times?
+
 # RUN: yaml2obj %p/Inputs/hello32.yaml -o %t.obj
 # RUN: not lld-link /out:/ %t.obj 2>&1 | FileCheck -check-prefix=DIR %s
 DIR: cannot open output file

[aganea]

Is there any value for this message? We can silently ignore the flng and nothing bad will happen.

[frankier]

I did this to match link.exe which gives a warning.