Provide the option to use libc++ even on all platforms

This is the default on platforms which use libc++ as the default C++ library but this option allows using libc++ on others as well.

Author: petrhosek

config.toml.example

@@ -90,6 +90,12 @@
 # with clang-cl, so this is special in that it only compiles LLVM with clang-cl
 #clang-cl = '/path/to/clang-cl.exe'
 
+# Use libc++ when building LLVM instead of libstdc++. This is the default on
+# platforms already use libc++ as the default C++ library, but this option
+# allows you to use libc++ even on platforms when it's not. You need to ensure
+# that your host compiler ships with libc++.
+#use-libcxx = true
+
 # =============================================================================
 # General build configuration options
 # =============================================================================

src/bootstrap/compile.rs

@@ -752,6 +752,9 @@ pub fn build_codegen_backend(builder: &Builder,
  if builder.config.llvm_link_shared {
  cargo.env("LLVM_LINK_SHARED", "1");
  }
+ if builder.config.llvm_use_libcxx {
+ cargo.env("LLVM_USE_LIBCXX", "1");
+ }
  }
  _ => panic!("unknown backend: {}", backend),
  }

src/bootstrap/config.rs

@@ -82,6 +82,8 @@ pub struct Config {
  pub lldb_enabled: bool,
  pub llvm_tools_enabled: bool,
 
+ pub llvm_use_libcxx: bool,
+
  // rust codegen options
  pub rust_optimize: bool,
  pub rust_codegen_units: Option<u32>,
@@ -252,6 +254,7 @@ struct Llvm {
  link_shared: Option<bool>,
  version_suffix: Option<String>,
  clang_cl: Option<String>,
+ use_libcxx: Option<bool>,
 }
 
 #[derive(Deserialize, Default, Clone)]
@@ -513,6 +516,7 @@ impl Config {
  config.llvm_link_jobs = llvm.link_jobs;
  config.llvm_version_suffix = llvm.version_suffix.clone();
  config.llvm_clang_cl = llvm.clang_cl.clone();
+ set(&mut config.llvm_use_libcxx, llvm.use_libcxx);
  }
 
  if let Some(ref rust) = toml.rust {

src/bootstrap/configure.py

@@ -62,6 +62,7 @@ def v(*args):
 o("lld", "rust.lld", "build lld")
 o("lldb", "rust.lldb", "build lldb")
 o("missing-tools", "dist.missing-tools", "allow failures when building tools")
+o("use-libcxx", "llvm.use_libcxx", "build LLVM with libc++")
 
 # Optimization and debugging options. These may be overridden by the release
 # channel, etc.

src/librustc_llvm/build.rs

@@ -232,6 +232,7 @@ fn main() {
  }
 
  let llvm_static_stdcpp = env::var_os("LLVM_STATIC_STDCPP");
+ let llvm_use_libcxx = env::var_os("LLVM_USE_LIBCXX");
 
  let stdcppname = if target.contains("openbsd") {
  // llvm-config on OpenBSD doesn't mention stdlib=libc++
@@ -241,6 +242,8 @@ fn main() {
  } else if target.contains("netbsd") && llvm_static_stdcpp.is_some() {
  // NetBSD uses a separate library when relocation is required
  "stdc++_pic"
+ } else if llvm_use_libcxx.is_some() {
+ "c++"
  } else {
  "stdc++"
  };