Add RUSTC_EMIT option to pass on --emit to crates during bootstrap

src/bootstrap/CHANGELOG.md

@@ -26,6 +26,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   from the default rust toolchain. [#78513](https://github.com/rust-lang/rust/pull/78513)
 - Add options for enabling overflow checks, one for std (`overflow-checks-std`) and one for everything else (`overflow-checks`). Both default to false.
 - Add llvm option `enable-warnings` to have control on llvm compilation warnings. Default to false.
+- Add a `RUSTC_EMIT` environment variable which passes on `--emit` to `rustc`. [#108365](https://github.com/rust-lang/rust/pull/108365)
 
 
 ## [Version 2] - 2020-09-25

src/bootstrap/bin/rustc.rs

@@ -18,6 +18,7 @@
 include!("../dylib_util.rs");
 
 use std::env;
+use std::ffi::OsStr;
 use std::path::PathBuf;
 use std::process::{Child, Command};
 use std::str::FromStr;
@@ -70,6 +71,46 @@ fn main() {
                 cmd.arg("-Ztime-passes");
             }
         }
+
+        if let Some(crate_targets) = env::var_os("RUSTC_EMIT") {
+            let formats: Vec<&str> = crate_targets
+                .to_str()
+                .unwrap()
+                .split(';')
+                .filter_map(|target| {
+                    let mut iter = target.split('=');
+                    let krate = iter.next().unwrap();
+                    let formats = iter.next().unwrap();
+                    assert!(iter.next().is_none(), "Invalid format for RUSTC_EMIT");
+                    (krate.trim() == crate_name || krate.trim() == "*").then_some(formats)
+                })
+                .flat_map(|formats| formats.split(',').map(|format| format.trim()))
+                .collect();
+
+            if !formats.is_empty() {
+                let dir = PathBuf::from(
+                    env::var_os("RUSTC_EMIT_DIR").expect("RUSTC_EMIT_DIR was not set"),
+                );
+                std::fs::create_dir_all(&dir).expect("unable to create dump directory");
+
+                for format in formats {
+                    let ext = match format {
+                        "llvm-ir" => "ll",
+                        "llvm-bc" => "bc",
+                        "asm" => {
+                            if target.map_or(false, |target| target.starts_with("x86")) {
+                                cmd.arg("-Cllvm-args=-x86-asm-syntax=intel");
+                            }
+                            "s"
+                        }
+                        _ => format,
+                    };
+                    let mut arg = OsStr::new(&format!("--emit={format}=")).to_owned();
+                    arg.push(dir.join(format!("{crate_name}.{ext}")).as_os_str());
+                    cmd.arg(arg);
+                }
+            }
+        }
     }
 
     // Print backtrace in case of ICE

src/bootstrap/builder.rs

@@ -1183,6 +1183,11 @@ impl<'a> Builder<'a> {
         let mut cargo = self.bare_cargo(compiler, mode, target, cmd);
         let out_dir = self.stage_out(compiler, mode);
 
+        cargo.env(
+            "RUSTC_EMIT_DIR",
+            self.out.join(target.triple).join("emit").join(out_dir.file_name().unwrap()),
+        );
+
         // Codegen backends are not yet tracked by -Zbinary-dep-depinfo,
         // so we need to explicitly clear out if they've been updated.
         for backend in self.codegen_backends(compiler) {