src/bootstrap/bin/rustc.rs - third_party/rust - Git at Google

 //! Shim which is passed to Cargo as "rustc" when running the bootstrap.
 //!
 //! This shim will take care of some various tasks that our build process
 //! requires that Cargo can't quite do through normal configuration:
 //!
 //! 1. When compiling build scripts and build dependencies, we need a guaranteed
 //!    full standard library available. The only compiler which actually has
 //!    this is the snapshot, so we detect this situation and always compile with
 //!    the snapshot compiler.
 //! 2. We pass a bunch of `--cfg` and other flags based on what we're compiling
 //!    (and this slightly differs based on a whether we're using a snapshot or
 //!    not), so we do that all here.
 //!
 //! This may one day be replaced by RUSTFLAGS, but the dynamic nature of
 //! switching compilers for the bootstrap and for build scripts will probably
 //! never get replaced.

 // NO-RUSTC-WRAPPER
 #![deny(warnings, rust_2018_idioms, unused_lifetimes)]

 use std::env;
 use std::ffi::OsString;
 use std::io;
 use std::path::PathBuf;
 use std::process::Command;
 use std::str::FromStr;
 use std::time::Instant;

 fn main() {
     let mut args = env::args_os().skip(1).collect::<Vec<_>>();

     // Append metadata suffix for internal crates. See the corresponding entry
     // in bootstrap/lib.rs for details.
     if let Ok(s) = env::var("RUSTC_METADATA_SUFFIX") {
         for i in 1..args.len() {
             // Dirty code for borrowing issues
             let mut new = None;
             if let Some(current_as_str) = args[i].to_str() {
                 if (&*args[i - 1] == "-C" && current_as_str.starts_with("metadata")) ||
                     current_as_str.starts_with("-Cmetadata") {
                     new = Some(format!("{}-{}", current_as_str, s));
                 }
             }
             if let Some(new) = new { args[i] = new.into(); }
         }
     }

     // Detect whether or not we're a build script depending on whether --target
     // is passed (a bit janky...)
     let target = args.windows(2)
         .find(|w| &*w[0] == "--target")
         .and_then(|w| w[1].to_str());
     let version = args.iter().find(|w| &**w == "-vV");

     let verbose = match env::var("RUSTC_VERBOSE") {
         Ok(s) => usize::from_str(&s).expect("RUSTC_VERBOSE should be an integer"),
         Err(_) => 0,
     };

     // Use a different compiler for build scripts, since there may not yet be a
     // libstd for the real compiler to use. However, if Cargo is attempting to
     // determine the version of the compiler, the real compiler needs to be
     // used. Currently, these two states are differentiated based on whether
     // --target and -vV is/isn't passed.
     let (rustc, libdir) = if target.is_none() && version.is_none() {
         ("RUSTC_SNAPSHOT", "RUSTC_SNAPSHOT_LIBDIR")
     } else {
         ("RUSTC_REAL", "RUSTC_LIBDIR")
     };
     let stage = env::var("RUSTC_STAGE").expect("RUSTC_STAGE was not set");
     let sysroot = env::var_os("RUSTC_SYSROOT").expect("RUSTC_SYSROOT was not set");
     let on_fail = env::var_os("RUSTC_ON_FAIL").map(|of| Command::new(of));

     let rustc = env::var_os(rustc).unwrap_or_else(|| panic!("{:?} was not set", rustc));
     let libdir = env::var_os(libdir).unwrap_or_else(|| panic!("{:?} was not set", libdir));
     let mut dylib_path = bootstrap::util::dylib_path();
     dylib_path.insert(0, PathBuf::from(&libdir));

     let mut cmd = Command::new(rustc);
     cmd.args(&args)
         .env(bootstrap::util::dylib_path_var(),
              env::join_paths(&dylib_path).unwrap());

     // Get the name of the crate we're compiling, if any.
     let crate_name = args.windows(2)
         .find(|args| args[0] == "--crate-name")
         .and_then(|args| args[1].to_str());

     if let Some(crate_name) = crate_name {
         if let Some(target) = env::var_os("RUSTC_TIME") {
             if target == "all" ||
                 target.into_string().unwrap().split(",").any(|c| c.trim() == crate_name)
             {
                 cmd.arg("-Ztime");
             }
         }
     }

     // Non-zero stages must all be treated uniformly to avoid problems when attempting to uplift
     // compiler libraries and such from stage 1 to 2.
     //
     // FIXME: the fact that core here is excluded is due to core_arch from our stdarch submodule
     // being broken on the beta compiler with bootstrap passed, so this is a temporary workaround
     // (we've just snapped, so there are no cfg(bootstrap) related annotations in core).
     if stage == "0" {
         if crate_name != Some("core") {
             cmd.arg("--cfg").arg("bootstrap");
         } else {
             // NOTE(eddyb) see FIXME above, except now we need annotations again in core.
             cmd.arg("--cfg").arg("boostrap_stdarch_ignore_this");
         }
     }

     // Print backtrace in case of ICE
     if env::var("RUSTC_BACKTRACE_ON_ICE").is_ok() && env::var("RUST_BACKTRACE").is_err() {
         cmd.env("RUST_BACKTRACE", "1");
     }

     cmd.env("RUSTC_BREAK_ON_ICE", "1");

     if let Ok(debuginfo_level) = env::var("RUSTC_DEBUGINFO_LEVEL") {
         cmd.arg(format!("-Cdebuginfo={}", debuginfo_level));
     }

     if env::var_os("RUSTC_DENY_WARNINGS").is_some() &&
        env::var_os("RUSTC_EXTERNAL_TOOL").is_none() {
         // When extending this list, search for `NO-RUSTC-WRAPPER` and add the new lints
         // there as well, some code doesn't go through this `rustc` wrapper.
         cmd.arg("-Dwarnings");
         cmd.arg("-Drust_2018_idioms");
         cmd.arg("-Dunused_lifetimes");
         if use_internal_lints(crate_name) {
             cmd.arg("-Zunstable-options");
             cmd.arg("-Drustc::internal");
         }
     }

     if let Some(target) = target {
         // The stage0 compiler has a special sysroot distinct from what we
         // actually downloaded, so we just always pass the `--sysroot` option,
         // unless one is already set.
         if !args.iter().any(|arg| arg == "--sysroot") {
             cmd.arg("--sysroot").arg(&sysroot);
         }

         cmd.arg("-Zexternal-macro-backtrace");

         // Link crates to the proc macro crate for the target, but use a host proc macro crate
         // to actually run the macros
         if env::var_os("RUST_DUAL_PROC_MACROS").is_some() {
             cmd.arg("-Zdual-proc-macros");
         }

         // When we build Rust dylibs they're all intended for intermediate
         // usage, so make sure we pass the -Cprefer-dynamic flag instead of
         // linking all deps statically into the dylib.
         if env::var_os("RUSTC_NO_PREFER_DYNAMIC").is_none() {
             cmd.arg("-Cprefer-dynamic");
         }

         // Help the libc crate compile by assisting it in finding various
         // sysroot native libraries.
         if let Some(s) = env::var_os("MUSL_ROOT") {
             if target.contains("musl") {
                 let mut root = OsString::from("native=");
                 root.push(&s);
                 root.push("/lib");
                 cmd.arg("-L").arg(&root);
             }
         }
         if let Some(s) = env::var_os("WASI_ROOT") {
             let mut root = OsString::from("native=");
             root.push(&s);
             root.push("/lib/wasm32-wasi");
             cmd.arg("-L").arg(&root);
         }

         // Override linker if necessary.
         if let Ok(target_linker) = env::var("RUSTC_TARGET_LINKER") {
             cmd.arg(format!("-Clinker={}", target_linker));
         }

         // If we're compiling specifically the `panic_abort` crate then we pass
         // the `-C panic=abort` option. Note that we do not do this for any
         // other crate intentionally as this is the only crate for now that we
         // ship with panic=abort.
         //
         // This... is a bit of a hack how we detect this. Ideally this
         // information should be encoded in the crate I guess? Would likely
         // require an RFC amendment to RFC 1513, however.
         //
         // `compiler_builtins` are unconditionally compiled with panic=abort to
         // workaround undefined references to `rust_eh_unwind_resume` generated
         // otherwise, see issue https://github.com/rust-lang/rust/issues/43095.
         if crate_name == Some("panic_abort") ||
            crate_name == Some("compiler_builtins") && stage != "0" {
             cmd.arg("-C").arg("panic=abort");
         }

         // Set various options from config.toml to configure how we're building
         // code.
         let debug_assertions = match env::var("RUSTC_DEBUG_ASSERTIONS") {
             Ok(s) => if s == "true" { "y" } else { "n" },
             Err(..) => "n",
         };

         // The compiler builtins are pretty sensitive to symbols referenced in
         // libcore and such, so we never compile them with debug assertions.
         if crate_name == Some("compiler_builtins") {
             cmd.arg("-C").arg("debug-assertions=no");
         } else {
             cmd.arg("-C").arg(format!("debug-assertions={}", debug_assertions));
         }

         if let Ok(s) = env::var("RUSTC_CODEGEN_UNITS") {
             cmd.arg("-C").arg(format!("codegen-units={}", s));
         }

         // Emit save-analysis info.
         if env::var("RUSTC_SAVE_ANALYSIS") == Ok("api".to_string()) {
             cmd.arg("-Zsave-analysis");
             cmd.env("RUST_SAVE_ANALYSIS_CONFIG",
                     "{\"output_file\": null,\"full_docs\": false,\
                      \"pub_only\": true,\"reachable_only\": false,\
                      \"distro_crate\": true,\"signatures\": false,\"borrow_data\": false}");
         }

         // Dealing with rpath here is a little special, so let's go into some
         // detail. First off, `-rpath` is a linker option on Unix platforms
         // which adds to the runtime dynamic loader path when looking for
         // dynamic libraries. We use this by default on Unix platforms to ensure
         // that our nightlies behave the same on Windows, that is they work out
         // of the box. This can be disabled, of course, but basically that's why
         // we're gated on RUSTC_RPATH here.
         //
         // Ok, so the astute might be wondering "why isn't `-C rpath` used
         // here?" and that is indeed a good question to task. This codegen
         // option is the compiler's current interface to generating an rpath.
         // Unfortunately it doesn't quite suffice for us. The flag currently
         // takes no value as an argument, so the compiler calculates what it
         // should pass to the linker as `-rpath`. This unfortunately is based on
         // the **compile time** directory structure which when building with
         // Cargo will be very different than the runtime directory structure.
         //
         // All that's a really long winded way of saying that if we use
         // `-Crpath` then the executables generated have the wrong rpath of
         // something like `$ORIGIN/deps` when in fact the way we distribute
         // rustc requires the rpath to be `$ORIGIN/../lib`.
         //
         // So, all in all, to set up the correct rpath we pass the linker
         // argument manually via `-C link-args=-Wl,-rpath,...`. Plus isn't it
         // fun to pass a flag to a tool to pass a flag to pass a flag to a tool
         // to change a flag in a binary?
         if env::var("RUSTC_RPATH") == Ok("true".to_string()) {
             let rpath = if target.contains("apple") {

                 // Note that we need to take one extra step on macOS to also pass
                 // `-Wl,-instal_name,@rpath/...` to get things to work right. To
                 // do that we pass a weird flag to the compiler to get it to do
                 // so. Note that this is definitely a hack, and we should likely
                 // flesh out rpath support more fully in the future.
                 cmd.arg("-Z").arg("osx-rpath-install-name");
                 Some("-Wl,-rpath,@loader_path/../lib")
             } else if !target.contains("windows") &&
                       !target.contains("wasm32") &&
                       !target.contains("fuchsia") {
                 Some("-Wl,-rpath,$ORIGIN/../lib")
             } else {
                 None
             };
             if let Some(rpath) = rpath {
                 cmd.arg("-C").arg(format!("link-args={}", rpath));
             }
         }

         if let Ok(s) = env::var("RUSTC_CRT_STATIC") {
             if s == "true" {
                 cmd.arg("-C").arg("target-feature=+crt-static");
             }
             if s == "false" {
                 cmd.arg("-C").arg("target-feature=-crt-static");
             }
         }
     } else {
         // Override linker if necessary.
         if let Ok(host_linker) = env::var("RUSTC_HOST_LINKER") {
             cmd.arg(format!("-Clinker={}", host_linker));
         }

         if let Ok(s) = env::var("RUSTC_HOST_CRT_STATIC") {
             if s == "true" {
                 cmd.arg("-C").arg("target-feature=+crt-static");
             }
             if s == "false" {
                 cmd.arg("-C").arg("target-feature=-crt-static");
             }
         }
     }

     if let Ok(map) = env::var("RUSTC_DEBUGINFO_MAP") {
         cmd.arg("--remap-path-prefix").arg(&map);
     }

     // Force all crates compiled by this compiler to (a) be unstable and (b)
     // allow the `rustc_private` feature to link to other unstable crates
     // also in the sysroot. We also do this for host crates, since those
     // may be proc macros, in which case we might ship them.
     if env::var_os("RUSTC_FORCE_UNSTABLE").is_some() && (stage != "0" || target.is_some()) {
         cmd.arg("-Z").arg("force-unstable-if-unmarked");
     }

     if env::var_os("RUSTC_PARALLEL_COMPILER").is_some() {
         cmd.arg("--cfg").arg("parallel_compiler");
     }

     if verbose > 1 {
         eprintln!(
             "rustc command: {:?}={:?} {:?}",
             bootstrap::util::dylib_path_var(),
             env::join_paths(&dylib_path).unwrap(),
             cmd,
         );
         eprintln!("sysroot: {:?}", sysroot);
         eprintln!("libdir: {:?}", libdir);
     }

     if let Some(mut on_fail) = on_fail {
         let e = match cmd.status() {
             Ok(s) if s.success() => std::process::exit(0),
             e => e,
         };
         println!("\nDid not run successfully: {:?}\n{:?}\n-------------", e, cmd);
         exec_cmd(&mut on_fail).expect("could not run the backup command");
         std::process::exit(1);
     }

     if env::var_os("RUSTC_PRINT_STEP_TIMINGS").is_some() {
         if let Some(crate_name) = crate_name {
             let start = Instant::now();
             let status = cmd
                 .status()
                 .unwrap_or_else(|_| panic!("\n\n failed to run {:?}", cmd));
             let dur = start.elapsed();

             let is_test = args.iter().any(|a| a == "--test");
             eprintln!("[RUSTC-TIMING] {} test:{} {}.{:03}",
                       crate_name,
                       is_test,
                       dur.as_secs(),
                       dur.subsec_nanos() / 1_000_000);

             match status.code() {
                 Some(i) => std::process::exit(i),
                 None => {
                     eprintln!("rustc exited with {}", status);
                     std::process::exit(0xfe);
                 }
             }
         }
     }

     let code = exec_cmd(&mut cmd).unwrap_or_else(|_| panic!("\n\n failed to run {:?}", cmd));
     std::process::exit(code);
 }

 // Rustc crates for which internal lints are in effect.
 fn use_internal_lints(crate_name: Option<&str>) -> bool {
     crate_name.map_or(false, |crate_name| {
         crate_name.starts_with("rustc") || crate_name.starts_with("syntax") ||
         ["arena", "fmt_macros"].contains(&crate_name)
     })
 }

 #[cfg(unix)]
 fn exec_cmd(cmd: &mut Command) -> io::Result<i32> {
     use std::os::unix::process::CommandExt;
     Err(cmd.exec())
 }

 #[cfg(not(unix))]
 fn exec_cmd(cmd: &mut Command) -> io::Result<i32> {
     cmd.status().map(|status| status.code().unwrap())
 }
	//! Shim which is passed to Cargo as "rustc" when running the bootstrap.
	//!
	//! This shim will take care of some various tasks that our build process
	//! requires that Cargo can't quite do through normal configuration:
	//!
	//! 1. When compiling build scripts and build dependencies, we need a guaranteed
	//! full standard library available. The only compiler which actually has
	//! this is the snapshot, so we detect this situation and always compile with
	//! the snapshot compiler.
	//! 2. We pass a bunch of `--cfg` and other flags based on what we're compiling
	//! (and this slightly differs based on a whether we're using a snapshot or
	//! not), so we do that all here.
	//!
	//! This may one day be replaced by RUSTFLAGS, but the dynamic nature of
	//! switching compilers for the bootstrap and for build scripts will probably
	//! never get replaced.

	// NO-RUSTC-WRAPPER
	#![deny(warnings, rust_2018_idioms, unused_lifetimes)]

	use std::env;
	use std::ffi::OsString;
	use std::io;
	use std::path::PathBuf;
	use std::process::Command;
	use std::str::FromStr;
	use std::time::Instant;

	fn main() {
	let mut args = env::args_os().skip(1).collect::<Vec<_>>();

	// Append metadata suffix for internal crates. See the corresponding entry
	// in bootstrap/lib.rs for details.
	if let Ok(s) = env::var("RUSTC_METADATA_SUFFIX") {
	for i in 1..args.len() {
	// Dirty code for borrowing issues
	let mut new = None;
	if let Some(current_as_str) = args[i].to_str() {
	if (&*args[i - 1] == "-C" && current_as_str.starts_with("metadata")) \|\|
	current_as_str.starts_with("-Cmetadata") {
	new = Some(format!("{}-{}", current_as_str, s));
	}
	}
	if let Some(new) = new { args[i] = new.into(); }
	}
	}

	// Detect whether or not we're a build script depending on whether --target
	// is passed (a bit janky...)
	let target = args.windows(2)
	.find(\|w\| &*w[0] == "--target")
	.and_then(\|w\| w[1].to_str());
	let version = args.iter().find(\|w\| &**w == "-vV");

	let verbose = match env::var("RUSTC_VERBOSE") {
	Ok(s) => usize::from_str(&s).expect("RUSTC_VERBOSE should be an integer"),
	Err(_) => 0,
	};

	// Use a different compiler for build scripts, since there may not yet be a
	// libstd for the real compiler to use. However, if Cargo is attempting to
	// determine the version of the compiler, the real compiler needs to be
	// used. Currently, these two states are differentiated based on whether
	// --target and -vV is/isn't passed.
	let (rustc, libdir) = if target.is_none() && version.is_none() {
	("RUSTC_SNAPSHOT", "RUSTC_SNAPSHOT_LIBDIR")
	} else {
	("RUSTC_REAL", "RUSTC_LIBDIR")
	};
	let stage = env::var("RUSTC_STAGE").expect("RUSTC_STAGE was not set");
	let sysroot = env::var_os("RUSTC_SYSROOT").expect("RUSTC_SYSROOT was not set");
	let on_fail = env::var_os("RUSTC_ON_FAIL").map(\|of\| Command::new(of));

	let rustc = env::var_os(rustc).unwrap_or_else(\|\| panic!("{:?} was not set", rustc));
	let libdir = env::var_os(libdir).unwrap_or_else(\|\| panic!("{:?} was not set", libdir));
	let mut dylib_path = bootstrap::util::dylib_path();
	dylib_path.insert(0, PathBuf::from(&libdir));

	let mut cmd = Command::new(rustc);
	cmd.args(&args)
	.env(bootstrap::util::dylib_path_var(),
	env::join_paths(&dylib_path).unwrap());

	// Get the name of the crate we're compiling, if any.
	let crate_name = args.windows(2)
	.find(\|args\| args[0] == "--crate-name")
	.and_then(\|args\| args[1].to_str());

	if let Some(crate_name) = crate_name {
	if let Some(target) = env::var_os("RUSTC_TIME") {
	if target == "all" \|\|
	target.into_string().unwrap().split(",").any(\|c\| c.trim() == crate_name)
	{
	cmd.arg("-Ztime");
	}
	}
	}

	// Non-zero stages must all be treated uniformly to avoid problems when attempting to uplift
	// compiler libraries and such from stage 1 to 2.
	//
	// FIXME: the fact that core here is excluded is due to core_arch from our stdarch submodule
	// being broken on the beta compiler with bootstrap passed, so this is a temporary workaround
	// (we've just snapped, so there are no cfg(bootstrap) related annotations in core).
	if stage == "0" {
	if crate_name != Some("core") {
	cmd.arg("--cfg").arg("bootstrap");
	} else {
	// NOTE(eddyb) see FIXME above, except now we need annotations again in core.
	cmd.arg("--cfg").arg("boostrap_stdarch_ignore_this");
	}
	}

	// Print backtrace in case of ICE
	if env::var("RUSTC_BACKTRACE_ON_ICE").is_ok() && env::var("RUST_BACKTRACE").is_err() {
	cmd.env("RUST_BACKTRACE", "1");
	}

	cmd.env("RUSTC_BREAK_ON_ICE", "1");

	if let Ok(debuginfo_level) = env::var("RUSTC_DEBUGINFO_LEVEL") {
	cmd.arg(format!("-Cdebuginfo={}", debuginfo_level));
	}

	if env::var_os("RUSTC_DENY_WARNINGS").is_some() &&
	env::var_os("RUSTC_EXTERNAL_TOOL").is_none() {
	// When extending this list, search for `NO-RUSTC-WRAPPER` and add the new lints
	// there as well, some code doesn't go through this `rustc` wrapper.
	cmd.arg("-Dwarnings");
	cmd.arg("-Drust_2018_idioms");
	cmd.arg("-Dunused_lifetimes");
	if use_internal_lints(crate_name) {
	cmd.arg("-Zunstable-options");
	cmd.arg("-Drustc::internal");
	}
	}

	if let Some(target) = target {
	// The stage0 compiler has a special sysroot distinct from what we
	// actually downloaded, so we just always pass the `--sysroot` option,
	// unless one is already set.
	if !args.iter().any(\|arg\| arg == "--sysroot") {
	cmd.arg("--sysroot").arg(&sysroot);
	}

	cmd.arg("-Zexternal-macro-backtrace");

	// Link crates to the proc macro crate for the target, but use a host proc macro crate
	// to actually run the macros
	if env::var_os("RUST_DUAL_PROC_MACROS").is_some() {
	cmd.arg("-Zdual-proc-macros");
	}

	// When we build Rust dylibs they're all intended for intermediate
	// usage, so make sure we pass the -Cprefer-dynamic flag instead of
	// linking all deps statically into the dylib.
	if env::var_os("RUSTC_NO_PREFER_DYNAMIC").is_none() {
	cmd.arg("-Cprefer-dynamic");
	}

	// Help the libc crate compile by assisting it in finding various
	// sysroot native libraries.
	if let Some(s) = env::var_os("MUSL_ROOT") {
	if target.contains("musl") {
	let mut root = OsString::from("native=");
	root.push(&s);
	root.push("/lib");
	cmd.arg("-L").arg(&root);
	}
	}
	if let Some(s) = env::var_os("WASI_ROOT") {
	let mut root = OsString::from("native=");
	root.push(&s);
	root.push("/lib/wasm32-wasi");
	cmd.arg("-L").arg(&root);
	}

	// Override linker if necessary.
	if let Ok(target_linker) = env::var("RUSTC_TARGET_LINKER") {
	cmd.arg(format!("-Clinker={}", target_linker));
	}

	// If we're compiling specifically the `panic_abort` crate then we pass
	// the `-C panic=abort` option. Note that we do not do this for any
	// other crate intentionally as this is the only crate for now that we
	// ship with panic=abort.
	//
	// This... is a bit of a hack how we detect this. Ideally this
	// information should be encoded in the crate I guess? Would likely
	// require an RFC amendment to RFC 1513, however.
	//
	// `compiler_builtins` are unconditionally compiled with panic=abort to
	// workaround undefined references to `rust_eh_unwind_resume` generated
	// otherwise, see issue https://github.com/rust-lang/rust/issues/43095.
	if crate_name == Some("panic_abort") \|\|
	crate_name == Some("compiler_builtins") && stage != "0" {
	cmd.arg("-C").arg("panic=abort");
	}

	// Set various options from config.toml to configure how we're building
	// code.
	let debug_assertions = match env::var("RUSTC_DEBUG_ASSERTIONS") {
	Ok(s) => if s == "true" { "y" } else { "n" },
	Err(..) => "n",
	};

	// The compiler builtins are pretty sensitive to symbols referenced in
	// libcore and such, so we never compile them with debug assertions.
	if crate_name == Some("compiler_builtins") {
	cmd.arg("-C").arg("debug-assertions=no");
	} else {
	cmd.arg("-C").arg(format!("debug-assertions={}", debug_assertions));
	}

	if let Ok(s) = env::var("RUSTC_CODEGEN_UNITS") {
	cmd.arg("-C").arg(format!("codegen-units={}", s));
	}

	// Emit save-analysis info.
	if env::var("RUSTC_SAVE_ANALYSIS") == Ok("api".to_string()) {
	cmd.arg("-Zsave-analysis");
	cmd.env("RUST_SAVE_ANALYSIS_CONFIG",
	"{\"output_file\": null,\"full_docs\": false,\
	\"pub_only\": true,\"reachable_only\": false,\
	\"distro_crate\": true,\"signatures\": false,\"borrow_data\": false}");
	}

	// Dealing with rpath here is a little special, so let's go into some
	// detail. First off, `-rpath` is a linker option on Unix platforms
	// which adds to the runtime dynamic loader path when looking for
	// dynamic libraries. We use this by default on Unix platforms to ensure
	// that our nightlies behave the same on Windows, that is they work out
	// of the box. This can be disabled, of course, but basically that's why
	// we're gated on RUSTC_RPATH here.
	//
	// Ok, so the astute might be wondering "why isn't `-C rpath` used
	// here?" and that is indeed a good question to task. This codegen
	// option is the compiler's current interface to generating an rpath.
	// Unfortunately it doesn't quite suffice for us. The flag currently
	// takes no value as an argument, so the compiler calculates what it
	// should pass to the linker as `-rpath`. This unfortunately is based on
	// the compile time directory structure which when building with
	// Cargo will be very different than the runtime directory structure.
	//
	// All that's a really long winded way of saying that if we use
	// `-Crpath` then the executables generated have the wrong rpath of
	// something like `$ORIGIN/deps` when in fact the way we distribute
	// rustc requires the rpath to be `$ORIGIN/../lib`.
	//
	// So, all in all, to set up the correct rpath we pass the linker
	// argument manually via `-C link-args=-Wl,-rpath,...`. Plus isn't it
	// fun to pass a flag to a tool to pass a flag to pass a flag to a tool
	// to change a flag in a binary?
	if env::var("RUSTC_RPATH") == Ok("true".to_string()) {
	let rpath = if target.contains("apple") {

	// Note that we need to take one extra step on macOS to also pass
	// `-Wl,-instal_name,@rpath/...` to get things to work right. To
	// do that we pass a weird flag to the compiler to get it to do
	// so. Note that this is definitely a hack, and we should likely
	// flesh out rpath support more fully in the future.
	cmd.arg("-Z").arg("osx-rpath-install-name");
	Some("-Wl,-rpath,@loader_path/../lib")
	} else if !target.contains("windows") &&
	!target.contains("wasm32") &&
	!target.contains("fuchsia") {
	Some("-Wl,-rpath,$ORIGIN/../lib")
	} else {
	None
	};
	if let Some(rpath) = rpath {
	cmd.arg("-C").arg(format!("link-args={}", rpath));
	}
	}

	if let Ok(s) = env::var("RUSTC_CRT_STATIC") {
	if s == "true" {
	cmd.arg("-C").arg("target-feature=+crt-static");
	}
	if s == "false" {
	cmd.arg("-C").arg("target-feature=-crt-static");
	}
	}
	} else {
	// Override linker if necessary.
	if let Ok(host_linker) = env::var("RUSTC_HOST_LINKER") {
	cmd.arg(format!("-Clinker={}", host_linker));
	}

	if let Ok(s) = env::var("RUSTC_HOST_CRT_STATIC") {
	if s == "true" {
	cmd.arg("-C").arg("target-feature=+crt-static");
	}
	if s == "false" {
	cmd.arg("-C").arg("target-feature=-crt-static");
	}
	}
	}

	if let Ok(map) = env::var("RUSTC_DEBUGINFO_MAP") {
	cmd.arg("--remap-path-prefix").arg(&map);
	}

	// Force all crates compiled by this compiler to (a) be unstable and (b)
	// allow the `rustc_private` feature to link to other unstable crates
	// also in the sysroot. We also do this for host crates, since those
	// may be proc macros, in which case we might ship them.
	if env::var_os("RUSTC_FORCE_UNSTABLE").is_some() && (stage != "0" \|\| target.is_some()) {
	cmd.arg("-Z").arg("force-unstable-if-unmarked");
	}

	if env::var_os("RUSTC_PARALLEL_COMPILER").is_some() {
	cmd.arg("--cfg").arg("parallel_compiler");
	}

	if verbose > 1 {
	eprintln!(
	"rustc command: {:?}={:?} {:?}",
	bootstrap::util::dylib_path_var(),
	env::join_paths(&dylib_path).unwrap(),
	cmd,
	);
	eprintln!("sysroot: {:?}", sysroot);
	eprintln!("libdir: {:?}", libdir);
	}

	if let Some(mut on_fail) = on_fail {
	let e = match cmd.status() {
	Ok(s) if s.success() => std::process::exit(0),
	e => e,
	};
	println!("\nDid not run successfully: {:?}\n{:?}\n-------------", e, cmd);
	exec_cmd(&mut on_fail).expect("could not run the backup command");
	std::process::exit(1);
	}

	if env::var_os("RUSTC_PRINT_STEP_TIMINGS").is_some() {
	if let Some(crate_name) = crate_name {
	let start = Instant::now();
	let status = cmd
	.status()
	.unwrap_or_else(\|_\| panic!("\n\n failed to run {:?}", cmd));
	let dur = start.elapsed();

	let is_test = args.iter().any(\|a\| a == "--test");
	eprintln!("[RUSTC-TIMING] {} test:{} {}.{:03}",
	crate_name,
	is_test,
	dur.as_secs(),
	dur.subsec_nanos() / 1_000_000);

	match status.code() {
	Some(i) => std::process::exit(i),
	None => {
	eprintln!("rustc exited with {}", status);
	std::process::exit(0xfe);
	}
	}
	}
	}

	let code = exec_cmd(&mut cmd).unwrap_or_else(\|_\| panic!("\n\n failed to run {:?}", cmd));
	std::process::exit(code);
	}

	// Rustc crates for which internal lints are in effect.
	fn use_internal_lints(crate_name: Option<&str>) -> bool {
	crate_name.map_or(false, \|crate_name\| {
	crate_name.starts_with("rustc") \|\| crate_name.starts_with("syntax") \|\|
	["arena", "fmt_macros"].contains(&crate_name)
	})
	}

	#[cfg(unix)]
	fn exec_cmd(cmd: &mut Command) -> io::Result<i32> {
	use std::os::unix::process::CommandExt;
	Err(cmd.exec())
	}

	#[cfg(not(unix))]
	fn exec_cmd(cmd: &mut Command) -> io::Result<i32> {
	cmd.status().map(\|status\| status.code().unwrap())
	}