[clang][driver] Add -fplugin-arg- to pass arguments to plugins

From GCC's manpage:
-fplugin-arg-name-key=value
   Define an argument called key with a value of value for the
   plugin called name.

Since we don't have a key-value pair similar to gcc's plugin_argument
struct, simply accept key=value here anyway and pass it along as-is to
plugins.

This translates to the already existing '-plugin-arg-pluginname arg'
that clang cc1 accepts.

There is an ambiguity here because in clang, both the plugin name
as well as the option name can contain dashes, so when e.g. passing

 -fplugin-arg-foo-bar-foo

it is not clear whether the plugin is foo-bar and the option is foo,
or the plugin is foo and the option is bar-foo. GCC solves this by
interpreting all dashes as part of the option name. So dashes can't be
part of the plugin name in this case.

Differential Revision: https://reviews.llvm.org/D113250

clang/docs/ClangPlugins.rst

@@ -125,6 +125,28 @@ Running the plugin
 ==================
 
 
+Using the compiler driver
+--------------------------
+
+The Clang driver accepts the `-fplugin` option to load a plugin.
+Clang plugins can receive arguments from the compiler driver command
+line via the `fplugin-arg-<plugin name>-<argument>` option. Using this
+method, the plugin name cannot contain dashes itself, but the argument
+passed to the plugin can.
+
+
+.. code-block:: console
+
+  $ export BD=/path/to/build/directory
+  $ make -C $BD CallSuperAttr
+  $ clang++ -fplugin=$BD/lib/CallSuperAttr.so \
+            -fplugin-arg-call_super_plugin-help \
+            test.cpp
+
+If your plugin name contains dashes, either rename the plugin or used the
+cc1 command line options listed below.
+
+
 Using the cc1 command line
 --------------------------
 

clang/docs/ReleaseNotes.rst

@@ -62,7 +62,8 @@ Non-comprehensive list of changes in this release
 New Compiler Flags
 ------------------
 
-- ...
+- Clang plugin arguments can now be passed through the compiler driver via
+  ``-fplugin-arg-pluginname-arg``, similar to GCC's ``-fplugin-arg``.
 
 Deprecated Compiler Flags
 -------------------------

clang/examples/CallSuperAttribute/CallSuperAttrInfo.cpp

@@ -145,6 +145,8 @@ public:
 
   bool ParseArgs(const CompilerInstance &CI,
                  const std::vector<std::string> &args) override {
+    if (!args.empty() && args[0] == "help")
+      llvm::errs() << "Help for the CallSuperAttr plugin goes here\n";
     return true;
   }
 

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -189,6 +189,12 @@ def err_drv_invalid_mtp : Error<
   "invalid thread pointer reading mode '%0'">;
 def err_drv_missing_arg_mtp : Error<
   "missing argument to '%0'">;
+def warn_drv_missing_plugin_name : Warning<
+  "missing plugin name in %0">,
+  InGroup<InvalidCommandLineArgument>;
+def warn_drv_missing_plugin_arg : Warning<
+  "missing plugin argument for plugin %0 in %1">,
+  InGroup<InvalidCommandLineArgument>;
 def err_drv_invalid_libcxx_deployment : Error<
   "invalid deployment target for -stdlib=libc++ (requires %0 or later)">;
 def err_drv_invalid_argument_to_option : Error<

clang/include/clang/Driver/Options.td

@@ -2504,6 +2504,9 @@ defm rwpi : BoolFOption<"rwpi",
   NegFlag<SetFalse>>;
 def fplugin_EQ : Joined<["-"], "fplugin=">, Group<f_Group>, Flags<[NoXarchOption]>, MetaVarName<"<dsopath>">,
   HelpText<"Load the named plugin (dynamic shared object)">;
+def fplugin_arg : Joined<["-"], "fplugin-arg-">,
+  MetaVarName<"<name>-<arg>">,
+  HelpText<"Pass <arg> to plugin <name>">;
 def fpass_plugin_EQ : Joined<["-"], "fpass-plugin=">,
   Group<f_Group>, Flags<[CC1Option]>, MetaVarName<"<dsopath>">,
   HelpText<"Load pass plugin from a dynamic shared object file (only with new pass manager).">,

clang/lib/Driver/ToolChains/Clang.cpp

@@ -6659,6 +6659,35 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     A->claim();
   }
 
+  // Turn -fplugin-arg-pluginname-key=value into
+  // -plugin-arg-pluginname key=value
+  // GCC has an actual plugin_argument struct with key/value pairs that it
+  // passes to its plugins, but we don't, so just pass it on as-is.
+  //
+  // The syntax for -fplugin-arg- is ambiguous if both plugin name and
+  // argument key are allowed to contain dashes. GCC therefore only
+  // allows dashes in the key. We do the same.
+  for (const Arg *A : Args.filtered(options::OPT_fplugin_arg)) {
+    auto ArgValue = StringRef(A->getValue());
+    auto FirstDashIndex = ArgValue.find('-');
+    StringRef PluginName = ArgValue.substr(0, FirstDashIndex);
+    StringRef Arg = ArgValue.substr(FirstDashIndex + 1);
+
+    A->claim();
+    if (FirstDashIndex == StringRef::npos || Arg.empty()) {
+      if (PluginName.empty()) {
+        D.Diag(diag::warn_drv_missing_plugin_name) << A->getAsString(Args);
+      } else {
+        D.Diag(diag::warn_drv_missing_plugin_arg)
+            << PluginName << A->getAsString(Args);
+      }
+      continue;
+    }
+
+    CmdArgs.push_back(Args.MakeArgString(Twine("-plugin-arg-") + PluginName));
+    CmdArgs.push_back(Args.MakeArgString(Arg));
+  }
+
   // Forward -fpass-plugin=name.so to -cc1.
   for (const Arg *A : Args.filtered(options::OPT_fpass_plugin_EQ)) {
     CmdArgs.push_back(

clang/test/Driver/plugin-driver-args.cpp

@@ -0,0 +1,22 @@
+/// Test passing args to plugins via the clang driver and -fplugin-arg
+// RUN: %clang -fplugin=%llvmshlibdir/CallSuperAttr%pluginext -fplugin-arg-call_super_plugin-help -fsyntax-only -### %s 2>&1 | FileCheck %s
+
+// CHECK: "-load"
+// CHECK-SAME: CallSuperAttr
+// CHECK-SAME: "-plugin-arg-call_super_plugin"
+// CHECK-SAME: "help"
+
+/// Check that dashed-args get forwarded like this to the plugin.
+/// Dashes cannot be part of the plugin name here
+// RUN: %clang -fplugin=%llvmshlibdir/CallSuperAttr%pluginext -fplugin-arg-call_super_plugin-help-long -fsyntax-only %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-CMD
+// CHECK-CMD: "-plugin-arg-call_super_plugin" "help-long"
+
+/// Error handling for -fplugin-arg-
+// RUN: %clang -fplugin=%llvmshlibdir/CallSuperAttr%pluginext -fplugin-arg- -fsyntax-only %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-NO-PLUGIN-NAME
+// CHECK-NO-PLUGIN-NAME: missing plugin name in -fplugin-arg-
+
+// RUN: %clang -fplugin=%llvmshlibdir/CallSuperAttr%pluginext -fplugin-arg-testname -fsyntax-only %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-NO-PLUGIN-ARG1
+// CHECK-NO-PLUGIN-ARG1: missing plugin argument for plugin testname in -fplugin-arg-testname
+
+// RUN: %clang -fplugin=%llvmshlibdir/CallSuperAttr%pluginext -fplugin-arg-testname- -fsyntax-only %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-NO-PLUGIN-ARG2
+// CHECK-NO-PLUGIN-ARG2: missing plugin argument for plugin testname in -fplugin-arg-testname-

clang/test/Frontend/plugin-call-super.cpp

@@ -1,5 +1,5 @@
-// RUN: %clang -fplugin=%llvmshlibdir/CallSuperAttr%pluginext -fsyntax-only -Xclang -verify=callsuper %s
-// RUN: %clang -fplugin=%llvmshlibdir/CallSuperAttr%pluginext -DBAD_CALLSUPER -fsyntax-only -Xclang -verify=badcallsuper %s
+// RUN: %clang_cc1 -load %llvmshlibdir/CallSuperAttr%pluginext -fsyntax-only -verify=callsuper %s
+// RUN: %clang_cc1 -load %llvmshlibdir/CallSuperAttr%pluginext -DBAD_CALLSUPER -fsyntax-only -verify=badcallsuper %s
 // REQUIRES: plugins, examples
 
 // callsuper-no-diagnostics