lld-link: Add a flag /lldignoreenv that makes lld-link ignore env vars.

[thakis]

Summary

This is useful for enforcing that builds are independent of the
environment; it can be used when all system library paths are added
via /libpath: already. It's similar ot cl.exe's /X flag.

Since it should also affect %LINK% (the other caller of
Process::GetEnv in lld/COFF), the early-option-parsing needs
to move around a bit. The options are:

• Add a manual loop over the argv ArrayRef and look for "/lldignoreenv". This repeats the name of the flag in both Options.td and in DriverUtils.cpp.

• Add yet another table.ParseArgs() call just for /lldignoreenv before adding %LINK%.

• Use the existing early ParseArgs() that's there for --rsp-quoting and use it for /lldignoreenv for %LINK% as well. This means --rsp-quoting and /lldignoreenv can't be passed via %LINK%.

I went with the third approach.

[ruiu]

LGTM

lld/COFF/Driver.h

 
 class COFFOptTable : public llvm::opt::OptTable {
 public:
   COFFOptTable();
 };
 
 class ArgParser {
 public:
-  // Concatenate LINK environment variable and given arguments and parse them.
-  llvm::opt::InputArgList parseLINK(std::vector<const char *> args);
+  // Parses command line options.
+  llvm::opt::InputArgList parse(llvm::ArrayRef<const char *> args);
 
   // Tokenizes a given string and then parses as command line options.
   llvm::opt::InputArgList parse(StringRef s) { return parse(tokenize(s)); }
 
   // Tokenizes a given string and then parses as command line options in
   // .drectve section. /EXPORT options are returned in second element
   // to be processed in fastpath.
   std::pair<llvm::opt::InputArgList, std::vector<StringRef>>
   parseDirectives(StringRef s);
 
 private:
-  // Parses command line options.
-  llvm::opt::InputArgList parse(llvm::ArrayRef<const char *> args);
+  // Concatenate LINK environment variable.
+  void addLINK(SmallVector<const char *, 256> &argv);
 
   std::vector<const char *> tokenize(StringRef s);
 
   COFFOptTable table;
 };
 
 class LinkerDriver {
 public:

lld/COFF/Driver.cpp

   if (argsArr.size() > 1 && StringRef(argsArr[1]).equals_lower("/lib")) {
     if (llvm::libDriverMain(argsArr.slice(1)) != 0)
       fatal("lib failed");
     return;
   }
 
   // Parse command line options.
   ArgParser parser;
-  opt::InputArgList args = parser.parseLINK(argsArr);
+  opt::InputArgList args = parser.parse(argsArr);
 
   // Parse and evaluate -mllvm options.
   std::vector<const char *> v;
   v.push_back("lld-link (LLVM option parsing)");
   for (auto *arg : args.filtered(OPT_mllvm))
     v.push_back(arg->getValue());
   cl::ParseCommandLineOptions(v.size(), v.data());
 

     else
       fatal("no input files");
   }
 
   // Construct search path list.
   searchPaths.push_back("");
   for (auto *arg : args.filtered(OPT_libpath))
     searchPaths.push_back(arg->getValue());
-  addLibSearchPaths();
+  if (!args.hasArg(OPT_lldignoreenv))
+    addLibSearchPaths();
 
   // Handle /ignore
   for (auto *arg : args.filtered(OPT_ignore)) {
     SmallVector<StringRef, 8> vec;
     StringRef(arg->getValue()).split(vec, ',');
     for (StringRef s : vec) {
       if (s == "4037")
         config->warnMissingOrderSymbol = false;

lld/COFF/DriverUtils.cpp

 // Parses a given list of options.
 opt::InputArgList ArgParser::parse(ArrayRef<const char *> argv) {
   // Make InputArgList from string vectors.
   unsigned missingIndex;
   unsigned missingCount;
 
   // We need to get the quoting style for response files before parsing all
   // options so we parse here before and ignore all the options but
-  // --rsp-quoting.
+  // --rsp-quoting and /lldignoreenv.
+  // (This means --rsp-quoting can't be added through %LINK%.)
   opt::InputArgList args = table.ParseArgs(argv, missingIndex, missingCount);
 
-  // Expand response files (arguments in the form of @<filename>)
-  // and then parse the argument again.
+
+  // Expand response files (arguments in the form of @<filename>) and insert
+  // flags from %LINK% and %_LINK_%, and then parse the argument again.
   SmallVector<const char *, 256> expandedArgv(argv.data(),
                                               argv.data() + argv.size());
+  if (!args.hasArg(OPT_lldignoreenv))
+    addLINK(expandedArgv);
   cl::ExpandResponseFiles(saver, getQuotingStyle(args), expandedArgv);
   args = table.ParseArgs(makeArrayRef(expandedArgv).drop_front(), missingIndex,
                          missingCount);
 
   // Print the real command line if response files are expanded.
   if (args.hasArg(OPT_verbose) && argv.size() != expandedArgv.size()) {
     std::string msg = "Command line:";
     for (const char *s : expandedArgv)
ArgParser::parseDirectives(StringRef s) {
   for (auto *arg : args.filtered(OPT_UNKNOWN))
     warn("ignoring unknown argument: " + arg->getAsString(args));
   return {std::move(args), std::move(exports)};
 }
 
 // link.exe has an interesting feature. If LINK or _LINK_ environment
 // variables exist, their contents are handled as command line strings.
 // So you can pass extra arguments using them.
-opt::InputArgList ArgParser::parseLINK(std::vector<const char *> argv) {
+void ArgParser::addLINK(SmallVector<const char *, 256> &argv) {
   // Concatenate LINK env and command line arguments, and then parse them.
   if (Optional<std::string> s = Process::GetEnv("LINK")) {
     std::vector<const char *> v = tokenize(*s);
     argv.insert(std::next(argv.begin()), v.begin(), v.end());
   }
   if (Optional<std::string> s = Process::GetEnv("_LINK_")) {
     std::vector<const char *> v = tokenize(*s);
     argv.insert(std::next(argv.begin()), v.begin(), v.end());
   }
-  return parse(argv);
 }
 
 std::vector<const char *> ArgParser::tokenize(StringRef s) {
   SmallVector<const char *, 16> tokens;
   cl::TokenizeWindowsCommandLine(s, saver, tokens);
   return std::vector<const char *>(tokens.begin(), tokens.end());
 }
 
 void printHelp(const char *argv0) {
   COFFOptTable().PrintHelp(outs(),
                            (std::string(argv0) + " [options] file...").c_str(),
                            "LLVM Linker", false);
 }
 
 } // namespace coff
 } // namespace lld

lld/COFF/Options.td

 def guard   : P<"guard", "Control flow guard">;
 def heap    : P<"heap", "Size of the heap">;
 def ignore : P<"ignore", "Specify warning codes to ignore">;
 def implib  : P<"implib", "Import library name">;
 def lib : F<"lib">,
     HelpText<"Act like lib.exe; must be first argument if present">;
 def libpath : P<"libpath", "Additional library search path">;
 def linkrepro : P<"linkrepro", "Dump linker invocation and input files for debugging">;
+def lldignoreenv : F<"lldignoreenv">,
+    HelpText<"Ignore environment variables like %LIB%">;
 def lldltocache : P<"lldltocache", "Path to ThinLTO cached object file directory">;
 def lldltocachepolicy : P<"lldltocachepolicy", "Pruning policy for the ThinLTO cache">;
 def lldsavetemps : F<"lldsavetemps">,
     HelpText<"Save temporary files instead of deleting them">;
 def machine : P<"machine", "Specify target platform">;
 def merge   : P<"merge", "Combine sections">;
 def mllvm   : P<"mllvm", "Options to pass to LLVM">;
 def nodefaultlib : P<"nodefaultlib", "Remove a default library">;

lld/docs/ReleaseNotes.rst

 ELF Improvements
 ----------------
 
 * ...
 
 COFF Improvements
 -----------------
 
+* The new `/lldignoreenv` flag makes lld-link ignore environment variables
+  like `%LIB%`.
 * ...
 
 MinGW Improvements
 ------------------
 
 * ...
 
 MachO Improvements

lld/test/COFF/libpath.test

 
 # RUN: lld-link /out:%t.exe /entry:main /verbose \
 # RUN:   %t/a/std64.lib /subsystem:console %p/Inputs/hello64.obj \
 # RUN:   /libpath:%t/b /verbose > %t.log 2>&1
 # RUN: FileCheck -check-prefix=CHECK3 %s < %t.log
 
 CHECK3:     Reading {{.*}}a/std64.lib
 CHECK3-NOT: Reading {{.*}}b/std64.lib
+
+# RUN: env LIB=%t/a lld-link /out:%t.exe /entry:main /verbose \
+# RUN:   std64.lib /subsystem:console %p/Inputs/hello64.obj \
+# RUN:   2> %t.log
+# RUN: FileCheck -check-prefix=CHECK4 %s < %t.log
+
+CHECK4: a{{[/\\]}}std64.lib
+
+# This should fail because /lldignoreenv should make lld-link
+# ignore the LIB env var.
+# RUN: env LIB=%t/a not lld-link /out:%t.exe /entry:main /verbose \
+# RUN:   std64.lib /subsystem:console %p/Inputs/hello64.obj \
+# RUN:   /lldignoreenv

lld/test/COFF/linkenv.test

 # RUN: env LINK=-help lld-link | FileCheck %s
 # RUN: env _LINK_=-help lld-link | FileCheck %s
 
 CHECK: OVERVIEW: LLVM Linker
+
+# RUN: env LINK=-help not lld-link /lldignoreenv 2>&1 | \
+# RUN:     FileCheck --check-prefix=ERR %s
+
+ERR: error: no input files