clang-cl: Warn about /U flags that look like filenames (PR31662)

[hans]

Summary

Both on Mac and Windows, it's common to have a 'Users' directory in the root of the filesystem, so one might specify a filename as '/Users/me/myfile.c'. clang-cl (as well as MSVC's cl.exe) will interpret that as invoking '/U' option, which is probably not what the user wanted. Add a warning about this.

[amccarth]

include/clang/Basic/DiagnosticDriverKinds.td

252

For Windows, wouldn't it make more sense to suggest using valid paths (with backslashes instead of slashes)?

What about all the other characters paths can begin with? Shouldn't we also warn that /code/myproject will also be interpreted as /c rather than \code\myproject?

[hans]

include/clang/Basic/DiagnosticDriverKinds.td

252

I think it's better with a suggestion that works on both platforms.

I also think users run into this more often on non-Windows.

For /code/myproject we will not interpret it as the /c option since it has to be an exact match. /I, /D and others are problematic though.

I think it's hard to fix this in general, but /U is the one people keep running into, so I think targeting that with a warning makes sense.

[rnk]

lgtm

[compnerd]

Thanks for adding this, diagnosing what was going on here the first time around took a little bit of thinking.

include/clang/Basic/DiagnosticDriverKinds.td

 
 def err_test_module_file_extension_format : Error<
   "-ftest-module-file-extension argument '%0' is not of the required form "
   "'blockname:major:minor:hashed:user info'">;
 
 def warn_drv_invoking_fallback : Warning<"falling back to %0">,
   InGroup<Fallback>;
 
+def warn_slash_u_filename : Warning<"'/U%0' treated as the '/U' option">,
+  InGroup<DiagGroup<"slash-u-filename">>;
+def note_use_dashdash : Note<"Use '--' to treat subsequent arguments as filenames">;
+
 def err_drv_ropi_rwpi_incompatible_with_pic : Error<
   "embedded and GOT-based position independence are incompatible">;
 def err_drv_ropi_incompatible_with_cxx : Error<
   "ROPI is not compatible with c++">;
 
 def warn_target_unsupported_nan2008 : Warning<
   "ignoring '-mnan=2008' option because the '%0' architecture does not support it">,
   InGroup<UnsupportedNan>;

lib/Driver/Driver.cpp

if (A->getOption().getKind() == Option::InputClass) {
 
       // Follow gcc behavior and treat as linker input for invalid -x
       // options. Its not clear why we shouldn't just revert to unknown; but
       // this isn't very important, we might as well be bug compatible.
       if (!InputType) {
         Diag(clang::diag::err_drv_unknown_language) << A->getValue();
         InputType = types::TY_Object;
       }
+    } else if (A->getOption().getID() == options::OPT__SLASH_U) {
+      assert(A->getNumValues() == 1 && "The /U option has one value.");
+      StringRef Val = A->getValue(0);
+      if (Val.find_first_of("/\\") != StringRef::npos) {
+        // Warn about e.g. "/Users/me/myfile.c".
+        Diag(diag::warn_slash_u_filename) << Val;
+        Diag(diag::note_use_dashdash);
+      }
     }
   }
   if (CCCIsCPP() && Inputs.empty()) {
     // If called as standalone preprocessor, stdin is processed
     // if no other input is present.
     Arg *A = MakeInputArg(Args, *Opts, "-");
     Inputs.push_back(std::make_pair(types::TY_C, A));
   }

test/Driver/cl-options.c

 // RUN:     /ZW:nostdlib \
 // RUN:     -- %s 2>&1
 
 // We support -Xclang for forwarding options to cc1.
 // RUN: %clang_cl -Xclang hellocc1 -### -- %s 2>&1 | FileCheck -check-prefix=Xclang %s
 // Xclang: "-cc1"
 // Xclang: "hellocc1"
 
+// Files under /Users are often confused with the /U flag. (This could happen
+// for other flags too, but this is the one people run into.)
+// RUN: %clang_cl /c /Users/me/myfile.c -### 2>&1 | FileCheck -check-prefix=SlashU %s
+// SlashU: warning: '/Users/me/myfile.c' treated as the '/U' option
+// SlashU: note: Use '--' to treat subsequent arguments as filenames
+
 // RTTI is on by default. /GR- controls -fno-rtti-data.
 // RUN: %clang_cl /c /GR- -### -- %s 2>&1 | FileCheck -check-prefix=NoRTTI %s
 // NoRTTI: "-fno-rtti-data"
 // NoRTTI-NOT: "-fno-rtti"
 // RUN: %clang_cl /c /GR -### -- %s 2>&1 | FileCheck -check-prefix=RTTI %s
 // RTTI-NOT: "-fno-rtti-data"
 // RTTI-NOT: "-fno-rtti"