[clang] Add a new flag -fexperimental-library to enable experimental library features

Based on the discussion at [1], this patch adds a Clang flag called
-fexperimental-library that controls whether experimental library
features are provided in libc++. In essence, it links against the
experimental static archive provided by libc++ and defines a feature
that can be picked up by libc++ to enable experimental features.

This ensures that users don't start depending on experimental
(and hence unstable) features unknowingly.

[1]: https://discourse.llvm.org/t/rfc-a-compiler-flag-to-enable-experimental-unstable-language-and-library-features

Differential Revision: https://reviews.llvm.org/D121141

15 files changed, 32 insertions, 7 deletions

diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 5130eb9..7a4319e 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -1013,6 +1013,8 @@ void ToolChain::AddCXXStdlibLibArgs(const ArgList &Args,
   switch (Type) {
   case ToolChain::CST_Libcxx:
     CmdArgs.push_back("-lc++");
+    if (Args.hasArg(options::OPT_fexperimental_library))
+      CmdArgs.push_back("-lc++experimental");
     break;
 
   case ToolChain::CST_Libstdcxx:
diff --git a/clang/lib/Driver/ToolChains/AIX.cpp b/clang/lib/Driver/ToolChains/AIX.cpp
index 878b84a..19054ae 100644
--- a/clang/lib/Driver/ToolChains/AIX.cpp
+++ b/clang/lib/Driver/ToolChains/AIX.cpp
@@ -275,6 +275,8 @@ void AIX::AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
     llvm::report_fatal_error("linking libstdc++ unimplemented on AIX");
   case ToolChain::CST_Libcxx:
     CmdArgs.push_back("-lc++");
+    if (Args.hasArg(options::OPT_fexperimental_library))
+      CmdArgs.push_back("-lc++experimental");
     CmdArgs.push_back("-lc++abi");
     return;
   }
diff --git a/clang/lib/Driver/ToolChains/BareMetal.cpp b/clang/lib/Driver/ToolChains/BareMetal.cpp
index cd07692..5f1638a 100644
--- a/clang/lib/Driver/ToolChains/BareMetal.cpp
+++ b/clang/lib/Driver/ToolChains/BareMetal.cpp
@@ -276,6 +276,8 @@ void BareMetal::AddCXXStdlibLibArgs(const ArgList &Args,
   switch (GetCXXStdlibType(Args)) {
   case ToolChain::CST_Libcxx:
     CmdArgs.push_back("-lc++");
+    if (Args.hasArg(options::OPT_fexperimental_library))
+      CmdArgs.push_back("-lc++experimental");
     CmdArgs.push_back("-lc++abi");
     break;
   case ToolChain::CST_Libstdcxx:
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 881ba3f..9a4b643 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5858,12 +5858,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back(A->getValue());
   }
 
-  if (Args.hasArg(options::OPT_funstable)) {
-    CmdArgs.push_back("-funstable");
-    if (!Args.hasArg(options::OPT_fno_coroutines_ts))
-      CmdArgs.push_back("-fcoroutines-ts");
-    CmdArgs.push_back("-fmodules-ts");
-  }
+  Args.AddLastArg(CmdArgs, options::OPT_fexperimental_library);
 
   if (Args.hasArg(options::OPT_fexperimental_new_constant_interpreter))
     CmdArgs.push_back("-fexperimental-new-constant-interpreter");
diff --git a/clang/lib/Driver/ToolChains/CloudABI.cpp b/clang/lib/Driver/ToolChains/CloudABI.cpp
index 501e3a3..9fd0529 100644
--- a/clang/lib/Driver/ToolChains/CloudABI.cpp
+++ b/clang/lib/Driver/ToolChains/CloudABI.cpp
@@ -117,6 +117,8 @@ void CloudABI::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
 void CloudABI::AddCXXStdlibLibArgs(const ArgList &Args,
                                    ArgStringList &CmdArgs) const {
   CmdArgs.push_back("-lc++");
+  if (Args.hasArg(options::OPT_fexperimental_library))
+    CmdArgs.push_back("-lc++experimental");
   CmdArgs.push_back("-lc++abi");
   CmdArgs.push_back("-lunwind");
 }
diff --git a/clang/lib/Driver/ToolChains/CrossWindows.cpp b/clang/lib/Driver/ToolChains/CrossWindows.cpp
index 2b043fb..681a682 100644
--- a/clang/lib/Driver/ToolChains/CrossWindows.cpp
+++ b/clang/lib/Driver/ToolChains/CrossWindows.cpp
@@ -273,8 +273,11 @@ AddClangCXXStdlibIncludeArgs(const llvm::opt::ArgList &DriverArgs,
 void CrossWindowsToolChain::
 AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                     llvm::opt::ArgStringList &CmdArgs) const {
-  if (GetCXXStdlibType(Args) == ToolChain::CST_Libcxx)
+  if (GetCXXStdlibType(Args) == ToolChain::CST_Libcxx) {
     CmdArgs.push_back("-lc++");
+    if (Args.hasArg(options::OPT_fexperimental_library))
+      CmdArgs.push_back("-lc++experimental");
+  }
 }
 
 clang::SanitizerMask CrossWindowsToolChain::getSupportedSanitizers() const {
diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
index c9e7737..71b0c5b 100644
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -2448,6 +2448,7 @@ void DarwinClang::AddClangCXXStdlibIncludeArgs(
     break;
   }
 }
+
 void DarwinClang::AddCXXStdlibLibArgs(const ArgList &Args,
                                       ArgStringList &CmdArgs) const {
   CXXStdlibType Type = GetCXXStdlibType(Args);
@@ -2455,6 +2456,8 @@ void DarwinClang::AddCXXStdlibLibArgs(const ArgList &Args,
   switch (Type) {
   case ToolChain::CST_Libcxx:
     CmdArgs.push_back("-lc++");
+    if (Args.hasArg(options::OPT_fexperimental_library))
+      CmdArgs.push_back("-lc++experimental");
     break;
 
   case ToolChain::CST_Libstdcxx:
diff --git a/clang/lib/Driver/ToolChains/FreeBSD.cpp b/clang/lib/Driver/ToolChains/FreeBSD.cpp
index 1476d11..fec80f8 100644
--- a/clang/lib/Driver/ToolChains/FreeBSD.cpp
+++ b/clang/lib/Driver/ToolChains/FreeBSD.cpp
@@ -430,6 +430,8 @@ void FreeBSD::AddCXXStdlibLibArgs(const ArgList &Args,
   switch (Type) {
   case ToolChain::CST_Libcxx:
     CmdArgs.push_back(Profiling ? "-lc++_p" : "-lc++");
+    if (Args.hasArg(options::OPT_fexperimental_library))
+      CmdArgs.push_back("-lc++experimental");
     break;
 
   case ToolChain::CST_Libstdcxx:
diff --git a/clang/lib/Driver/ToolChains/Fuchsia.cpp b/clang/lib/Driver/ToolChains/Fuchsia.cpp
index f96cfde..d63c69c 100644
--- a/clang/lib/Driver/ToolChains/Fuchsia.cpp
+++ b/clang/lib/Driver/ToolChains/Fuchsia.cpp
@@ -417,6 +417,8 @@ void Fuchsia::AddCXXStdlibLibArgs(const ArgList &Args,
   switch (GetCXXStdlibType(Args)) {
   case ToolChain::CST_Libcxx:
     CmdArgs.push_back("-lc++");
+    if (Args.hasArg(options::OPT_fexperimental_library))
+      CmdArgs.push_back("-lc++experimental");
     break;
 
   case ToolChain::CST_Libstdcxx:
diff --git a/clang/lib/Driver/ToolChains/Hexagon.cpp b/clang/lib/Driver/ToolChains/Hexagon.cpp
index ed07e71..0e47704 100644
--- a/clang/lib/Driver/ToolChains/Hexagon.cpp
+++ b/clang/lib/Driver/ToolChains/Hexagon.cpp
@@ -616,6 +616,8 @@ void HexagonToolChain::AddCXXStdlibLibArgs(const ArgList &Args,
     CmdArgs.push_back("-lc++");
     CmdArgs.push_back("-lc++abi");
     CmdArgs.push_back("-lunwind");
+    if (Args.hasArg(options::OPT_fexperimental_library))
+      CmdArgs.push_back("-lc++experimental");
     break;
 
   case ToolChain::CST_Libstdcxx:
diff --git a/clang/lib/Driver/ToolChains/MipsLinux.cpp b/clang/lib/Driver/ToolChains/MipsLinux.cpp
index 41b7b83..9c58583 100644
--- a/clang/lib/Driver/ToolChains/MipsLinux.cpp
+++ b/clang/lib/Driver/ToolChains/MipsLinux.cpp
@@ -112,6 +112,8 @@ void MipsLLVMToolChain::AddCXXStdlibLibArgs(const ArgList &Args,
          "Only -lc++ (aka libxx) is supported in this toolchain.");
 
   CmdArgs.push_back("-lc++");
+  if (Args.hasArg(options::OPT_fexperimental_library))
+    CmdArgs.push_back("-lc++experimental");
   CmdArgs.push_back("-lc++abi");
   CmdArgs.push_back("-lunwind");
 }
diff --git a/clang/lib/Driver/ToolChains/NaCl.cpp b/clang/lib/Driver/ToolChains/NaCl.cpp
index 753459c..3815173 100644
--- a/clang/lib/Driver/ToolChains/NaCl.cpp
+++ b/clang/lib/Driver/ToolChains/NaCl.cpp
@@ -308,6 +308,8 @@ void NaClToolChain::AddCXXStdlibLibArgs(const ArgList &Args,
   // if the value is libc++, and emits an error for other values.
   GetCXXStdlibType(Args);
   CmdArgs.push_back("-lc++");
+  if (Args.hasArg(options::OPT_fexperimental_library))
+    CmdArgs.push_back("-lc++experimental");
 }
 
 void NaClToolChain::addLibCxxIncludePaths(
diff --git a/clang/lib/Driver/ToolChains/OpenBSD.cpp b/clang/lib/Driver/ToolChains/OpenBSD.cpp
index cd50582..44cc9de 100644
--- a/clang/lib/Driver/ToolChains/OpenBSD.cpp
+++ b/clang/lib/Driver/ToolChains/OpenBSD.cpp
@@ -331,6 +331,8 @@ void OpenBSD::AddCXXStdlibLibArgs(const ArgList &Args,
   bool Profiling = Args.hasArg(options::OPT_pg);
 
   CmdArgs.push_back(Profiling ? "-lc++_p" : "-lc++");
+  if (Args.hasArg(options::OPT_fexperimental_library))
+    CmdArgs.push_back("-lc++experimental");
   CmdArgs.push_back(Profiling ? "-lc++abi_p" : "-lc++abi");
   CmdArgs.push_back(Profiling ? "-lpthread_p" : "-lpthread");
 }
diff --git a/clang/lib/Driver/ToolChains/VEToolchain.cpp b/clang/lib/Driver/ToolChains/VEToolchain.cpp
index 1e43796..9be2392 100644
--- a/clang/lib/Driver/ToolChains/VEToolchain.cpp
+++ b/clang/lib/Driver/ToolChains/VEToolchain.cpp
@@ -141,6 +141,8 @@ void VEToolChain::AddCXXStdlibLibArgs(const ArgList &Args,
   tools::addArchSpecificRPath(*this, Args, CmdArgs);
 
   CmdArgs.push_back("-lc++");
+  if (Args.hasArg(options::OPT_fexperimental_library))
+    CmdArgs.push_back("-lc++experimental");
   CmdArgs.push_back("-lc++abi");
   CmdArgs.push_back("-lunwind");
   // libc++ requires -lpthread under glibc environment
diff --git a/clang/lib/Driver/ToolChains/WebAssembly.cpp b/clang/lib/Driver/ToolChains/WebAssembly.cpp
index c5e4d56..b051bff 100644
--- a/clang/lib/Driver/ToolChains/WebAssembly.cpp
+++ b/clang/lib/Driver/ToolChains/WebAssembly.cpp
@@ -444,6 +444,8 @@ void WebAssembly::AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
   switch (GetCXXStdlibType(Args)) {
   case ToolChain::CST_Libcxx:
     CmdArgs.push_back("-lc++");
+    if (Args.hasArg(options::OPT_fexperimental_library))
+      CmdArgs.push_back("-lc++experimental");
     CmdArgs.push_back("-lc++abi");
     break;
   case ToolChain::CST_Libstdcxx: