[clang-cl] Add support for CL and _CL_ environment variables

[majnemer]

Summary

cl uses 'CL' and '_CL_' to prepend and append command line options to
the given argument vector. There is an additional quirk whereby '#' is
transformed into '='.

[rnk]

lgtm

tools/driver/driver.cpp

464–466

How about adjusting all the options in place and then inserting them all at once to avoid the N^2 complexity?

[hans]

Out of curiosity, did you run in to something that relies on this in the wild?

tools/driver/driver.cpp

452

Maybe don't take the parameter as a const char* if the constness needs to be dropped for the adjusting to take place? The const_cast could just be moved to where you make the call below.

[rnk]

tools/driver/driver.cpp

451

I'd also rather factor this out of driver main, since it's really not important to most readers.

452

I think TokenizeCommandLine builds you a list of const strings, unfortunately. We could avoid the cast if we hooked into the tokenization or StringSaver, but it didn't seem worth it.

test/Driver/cl-options.c

 // Z7_gdwarf: "-gdwarf-4"
 
 // RUN: %clang_cl -fmsc-version=1800 -TP -### -- %s 2>&1 | FileCheck -check-prefix=CXX11 %s
 // CXX11: -std=c++11
 
 // RUN: %clang_cl -fmsc-version=1900 -TP -### -- %s 2>&1 | FileCheck -check-prefix=CXX14 %s
 // CXX14: -std=c++14
 
+// RUN: env CL="/Gy" %clang_cl -### -- %s 2>&1 | FileCheck -check-prefix=ENV-CL %s
+// ENV-CL: "-ffunction-sections"
+
+// RUN: env CL="/Gy" _CL_="/Gy- -- %s" %clang_cl -### 2>&1 | FileCheck -check-prefix=ENV-_CL_ %s
+// ENV-_CL_-NOT: "-ffunction-sections"
+
 // Accept "core" clang options.
 // (/Zs is for syntax-only, -Werror makes it fail hard on unknown options)
 // RUN: %clang_cl \
 // RUN:     --driver-mode=cl \
 // RUN:     -fcolor-diagnostics \
 // RUN:     -fno-color-diagnostics \
 // RUN:     -fdiagnostics-color \
 // RUN:     -fno-diagnostics-color \

tools/driver/driver.cpp

for (int i = 1, size = argv.size(); i < size; ++i) {
     if (argv[i] == nullptr)
       continue;
     if (StringRef(argv[i]) == "-no-canonical-prefixes") {
       CanonicalPrefixes = false;
       break;
     }
   }
 
+  // Handle CL and _CL_ which permits additional command line options to be
+  // prepended or appended.
+  if (Tokenizer == &llvm::cl::TokenizeWindowsCommandLine) {
+    // The first instance of '#' should be replaced with '='.
+    auto AdjustOpt = [] (const char *Opt) {
+      if (char *NumberSignPtr = const_cast<char *>(::strchr(Opt, '#')))
+        *NumberSignPtr = '=';
+      return Opt;
+    };
+
+    // Arguments in "CL" are prepended.
+    llvm::Optional<std::string> OptCL = llvm::sys::Process::GetEnv("CL");
+    if (OptCL.hasValue()) {
+      SmallVector<const char *, 8> PrependedOpts;
+      llvm::cl::TokenizeWindowsCommandLine(OptCL.getValue(), Saver,
+                                           PrependedOpts);
+      // Insert right after the program name to prepend to the argument list.
+      for (const char *PrependedOpt : PrependedOpts)
+        argv.insert(argv.begin() + 1, AdjustOpt(PrependedOpt));
+    }
+    // Arguments in "CL" are appended.
+    llvm::Optional<std::string> Opt_CL_ = llvm::sys::Process::GetEnv("_CL_");
+    if (Opt_CL_.hasValue()) {
+      SmallVector<const char *, 8> AppendedOpts;
+      llvm::cl::TokenizeWindowsCommandLine(Opt_CL_.getValue(), Saver,
+                                           AppendedOpts);
+      // Insert at the end of the argument list to append.
+      for (const char *AppendedOpt : AppendedOpts)
+        argv.push_back(AdjustOpt(AppendedOpt));
+    }
+  }
+
   std::set<std::string> SavedStrings;
   // Handle CCC_OVERRIDE_OPTIONS, used for editing a command line behind the
   // scenes.
   if (const char *OverrideStr = ::getenv("CCC_OVERRIDE_OPTIONS")) {
     // FIXME: Driver shouldn't take extra initial argument.
     ApplyQAOverride(argv, OverrideStr, SavedStrings);
   }