[Clang] Emit a warning for ambiguous joined '-o' arguments

The offloading toolchain makes heavy use of options beginning with
`--o`. This is problematic when combined with the joined `-o` flag. In
the following situation, the user will not get the expected output and
will not notice as the expected output will still be written.
```
clang++ -x cuda foo.cu -offload-arch=sm_80 -o foo
```

This patch introduces a warning that checks for joined `-o` arguments
that would also be a valid driver argument if an additional `-` were
added. I believe this situation is uncommon enough to warrant a warning,
and can be trivially fixed by the end user by using the more common
separate form instead.

Reviewed By: tra, MaskRay

Differential Revision: https://reviews.llvm.org/D135389

1 files changed, 13 insertions, 0 deletions

diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 21dc180..e612afd 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -327,6 +327,19 @@ InputArgList Driver::ParseArgStrings(ArrayRef<const char *> ArgStrings,
                      DiagnosticsEngine::Warning;
   }
 
+  for (const Arg *A : Args.filtered(options::OPT_o)) {
+    if (ArgStrings[A->getIndex()] == A->getSpelling())
+      continue;
+
+    // Warn on joined arguments that are similar to a long argument.
+    std::string ArgString = ArgStrings[A->getIndex()];
+    std::string Nearest;
+    if (getOpts().findNearest("-" + ArgString, Nearest, IncludedFlagsBitmask,
+                              ExcludedFlagsBitmask) == 0)
+      Diags.Report(diag::warn_drv_potentially_misspelled_joined_argument)
+          << A->getAsString(Args) << Nearest;
+  }
+
   return Args;
 }