Add -Xcpp CLI option for C preprocessor flags (-P with ldmd2)

driver/cl_options.cpp

@@ -400,16 +400,18 @@ cl::list<std::string>
                    cl::value_desc("linkerflag"), cl::cat(linkingCategory),
                    cl::Prefix);
 
-cl::list<std::string>
-    ccSwitches("Xcc", cl::desc("Pass <ccflag> to GCC/Clang for linking"),
-               cl::value_desc("ccflag"), cl::cat(linkingCategory));
+cl::list<std::string> ccSwitches(
+    "Xcc", cl::value_desc("ccflag"), cl::cat(linkingCategory),
+    cl::desc("Pass <ccflag> to GCC/Clang for linking/preprocessing"));
 
-cl::opt<std::string>
-    moduleDeps("deps", cl::ValueOptional, cl::ZeroOrMore,
-               cl::value_desc("filename"),
-               cl::desc("Write module dependencies to <filename> (only imports). "
-                        "'-deps' alone prints module dependencies "
-                        "(imports/file/version/debug/lib)"));
+cl::list<std::string> cppSwitches("Xcpp", cl::value_desc("cppflag"),
+                                  cl::desc("Pass <cppflag> to C preprocessor"));
+
+cl::opt<std::string> moduleDeps(
+    "deps", cl::ValueOptional, cl::ZeroOrMore, cl::value_desc("filename"),
+    cl::desc("Write module dependencies to <filename> (only imports). "
+             "'-deps' alone prints module dependencies "
+             "(imports/file/version/debug/lib)"));
 
 cl::opt<std::string>
     makeDeps("makedeps", cl::ValueOptional, cl::ZeroOrMore,

driver/cl_options.h

@@ -75,6 +75,7 @@ extern cl::opt<std::string> makeDeps;
 extern cl::opt<std::string> cacheDir;
 extern cl::list<std::string> linkerSwitches;
 extern cl::list<std::string> ccSwitches;
+extern cl::list<std::string> cppSwitches;
 extern cl::list<std::string> includeModulePatterns;
 
 extern cl::opt<bool> m32bits;

driver/cpreprocessor.cpp

@@ -46,7 +46,9 @@ FileName runCPreprocessor(FileName csrcfile, const Loc &loc, bool &ifile,
   for (const auto &ccSwitch : opts::ccSwitches) {
     args.push_back(ccSwitch);
   }
-  // TODO: -Xcpp switches?
+  for (const auto &cppSwitch : opts::cppSwitches) {
+    args.push_back(cppSwitch);
+  }
 
   if (isMSVC) {
     args.push_back("/P");               // run preprocessor

driver/ldmd.cpp

@@ -234,7 +234,9 @@ Where:\n\
 #if 0
 "  -os=<os>          sets target operating system to <os>\n"
 #endif
-"  -preview=<name>   enable an upcoming language change identified by 'name'\n\
+"  -P=<preprocessorflag>\n\
+                    pass preprocessorflag to C preprocessor\n\
+  -preview=<name>   enable an upcoming language change identified by 'name'\n\
   -preview=[h|help|?]\n\
                     list all upcoming language changes\n\
   -profile          profile runtime performance of generated code\n"
@@ -707,7 +709,11 @@ void translateArgs(const llvm::SmallVectorImpl<const char *> &ldmdArgs,
         exit(EXIT_SUCCESS);
       }
       /* -L
-       * -defaultlib
+       */
+      else if (p[1] == 'P') {
+        ldcArgs.push_back(concat("-Xcpp=", p + 2 + (p[2] == '=' ? 1 : 0)));
+      }
+      /* -defaultlib
        * -debuglib
        * -deps
        * -main

tests/dmd/compilable/cppflags.c

@@ -1,5 +1,4 @@
 /* REQUIRED_ARGS: -P=-DABC=3
  */
-// DISABLED: LDC // FIXME
 
 _Static_assert(ABC == 3, "1");