clang-cl: Add support for /permissive-

[thakis]

Summary

https://blogs.msdn.microsoft.com/vcblog/2016/11/16/permissive-switch/ makes it sound like this is similar to -pedantic, which we currently don't expose from clang-cl. So map it to that for now and see how that feels in practice.

Looks like cl.exe only has a flag for /permissive-, but no explicit flag for /permissive (the default).

[hans]

lgtm

[majnemer]

I don't think this is correct. GDR (of Microsoft) says the behavior is different: https://www.reddit.com/r/cpp/comments/5dh7j5/visual_c_introduces_permissive_for_conformance/da5fxjj/

[Trass3r]

Has this ever gotten anywhere?
I think the correct mapping would be something like -fno-ms-compatibility -fno-delayed-template-parsing, not sure about -fms-volatile -fms-extensions. Edit: Actually no, you need the extensions and disabling compat makes it disguise as gcc. So only the template parsing is left.

include/clang/Driver/CLCompatOptions.td

 def _SLASH_Oi : CLFlag<"Oi">, HelpText<"Enable use of builtin functions">,
   Alias<fbuiltin>;
 def _SLASH_Oi_ : CLFlag<"Oi-">, HelpText<"Disable use of builtin functions">,
   Alias<fno_builtin>;
 def _SLASH_Os : CLFlag<"Os">, HelpText<"Optimize for size">, Alias<O>,
   AliasArgs<["s"]>;
 def _SLASH_Ot : CLFlag<"Ot">, HelpText<"Optimize for speed">, Alias<O>,
   AliasArgs<["2"]>;
+def _SLASH_permissive_ : CLFlag<"permissive-">, Alias<pedantic>,
+  HelpText<"Diagnose use of nonstandard language extensions">;
 def _SLASH_QUESTION : CLFlag<"?">, Alias<help>,
   HelpText<"Display available options">;
 def _SLASH_Qvec : CLFlag<"Qvec">,
   HelpText<"Enable the loop vectorization passes">, Alias<fvectorize>;
 def _SLASH_Qvec_ : CLFlag<"Qvec-">,
   HelpText<"Disable the loop vectorization passes">, Alias<fno_vectorize>;
 def _SLASH_showIncludes : CLFlag<"showIncludes">,
   HelpText<"Print info about included files to stderr">,

test/Driver/cl-options.c

 // Oy_2: -momit-leaf-frame-pointer
 // Oy_2: -O2
 
 // RUN: %clang_cl /Zs -Werror /Oy -- %s 2>&1
 
 // RUN: %clang_cl --target=i686-pc-win32 -Werror /Oy- -### -- %s 2>&1 | FileCheck -check-prefix=Oy_ %s
 // Oy_: -mdisable-fp-elim
 
+// RUN: %clang_cl /permissive- --target=i686-pc-windows-msvc -### -- %s 2>&1 | FileCheck -check-prefix=permissive_ %s
+// permissive_: -pedantic
+
 // RUN: %clang_cl /Qvec -### -- %s 2>&1 | FileCheck -check-prefix=Qvec %s
 // Qvec: -vectorize-loops
 
 // RUN: %clang_cl /Qvec /Qvec- -### -- %s 2>&1 | FileCheck -check-prefix=Qvec_ %s
 // Qvec_-NOT: -vectorize-loops
 
 // RUN: %clang_cl /showIncludes -### -- %s 2>&1 | FileCheck -check-prefix=showIncludes %s
 // showIncludes: --show-includes