Auto merge of #7421 - ehuss:build-std-sysroot, r=alexcrichton

Change build-std to use --sysroot

This transitions build-std to use `--sysroot` instead of `--extern`. This is necessary because existing crates have a certain expectation of how standard library crates are exposed. It was intended that explicit dependencies in `Cargo.toml` would solve this problem, but I didn't really consider this would be a backwards-incompatible change, so using `--sysroot` is probably the best way to go, even though it's not ideal.

Closes rust-lang/wg-cargo-std-aware#31
Closes rust-lang/wg-cargo-std-aware#40

Author: bors

crates/cargo-test-support/src/paths.rs

@@ -6,6 +6,7 @@ use std::env;
 use std::fs;
 use std::io::{self, ErrorKind};
 use std::path::{Path, PathBuf};
+use std::process::Command;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Mutex;
 
@@ -252,3 +253,14 @@ pub fn get_lib_extension(kind: &str) -> &str {
         _ => unreachable!(),
     }
 }
+
+/// Returns the sysroot as queried from rustc.
+pub fn sysroot() -> String {
+    let output = Command::new("rustc")
+        .arg("--print=sysroot")
+        .output()
+        .expect("rustc to run");
+    assert!(output.status.success());
+    let sysroot = String::from_utf8(output.stdout).unwrap();
+    sysroot.trim().to_string()
+}

src/cargo/core/compiler/compilation.rs

@@ -203,7 +203,13 @@ impl<'cfg> Compilation<'cfg> {
                 super::filter_dynamic_search_path(self.native_dirs.iter(), &self.root_output);
             search_path.push(self.deps_output.clone());
             search_path.push(self.root_output.clone());
-            search_path.push(self.target_dylib_path.clone());
+            // For build-std, we don't want to accidentally pull in any shared
+            // libs from the sysroot that ships with rustc. This may not be
+            // required (at least I cannot craft a situation where it
+            // matters), but is here to be safe.
+            if self.config.cli_unstable().build_std.is_none() {
+                search_path.push(self.target_dylib_path.clone());
+            }
             search_path
         };
 

src/cargo/core/compiler/context/mod.rs

@@ -18,6 +18,7 @@ use super::custom_build::{self, BuildDeps, BuildScriptOutputs, BuildScripts};
 use super::fingerprint::Fingerprint;
 use super::job_queue::JobQueue;
 use super::layout::Layout;
+use super::standard_lib;
 use super::unit_dependencies::{UnitDep, UnitGraph};
 use super::{BuildContext, Compilation, CompileMode, Executor, FileFlavor, Kind};
 
@@ -304,7 +305,11 @@ impl<'a, 'cfg> Context<'a, 'cfg> {
         };
         let host_layout = Layout::new(self.bcx.ws, None, dest)?;
         let target_layout = match self.bcx.build_config.requested_target.as_ref() {
-            Some(target) => Some(Layout::new(self.bcx.ws, Some(target), dest)?),
+            Some(target) => {
+                let layout = Layout::new(self.bcx.ws, Some(target), dest)?;
+                standard_lib::prepare_sysroot(&layout)?;
+                Some(layout)
+            }
             None => None,
         };
         self.primary_packages

src/cargo/core/compiler/job_queue.rs

@@ -17,6 +17,7 @@ use super::job::{
     Freshness::{self, Dirty, Fresh},
     Job,
 };
+use super::standard_lib;
 use super::timings::Timings;
 use super::{BuildContext, BuildPlan, CompileMode, Context, Unit};
 use crate::core::{PackageId, TargetKind};
@@ -607,7 +608,7 @@ impl<'a, 'cfg> JobQueue<'a, 'cfg> {
         id: u32,
         unit: &Unit<'a>,
         artifact: Artifact,
-        cx: &mut Context<'_, '_>,
+        cx: &mut Context<'a, '_>,
     ) -> CargoResult<()> {
         if unit.mode.is_run_custom_build() && cx.bcx.show_warnings(unit.pkg.package_id()) {
             self.emit_warnings(None, unit, cx)?;
@@ -617,6 +618,23 @@ impl<'a, 'cfg> JobQueue<'a, 'cfg> {
             Artifact::All => self.timings.unit_finished(id, unlocked),
             Artifact::Metadata => self.timings.unit_rmeta_finished(id, unlocked),
         }
+        if unit.is_std && unit.kind == super::Kind::Target && !cx.bcx.build_config.build_plan {
+            // This is a bit of an unusual place to copy files around, and
+            // ideally this would be somewhere like the Work closure
+            // (`link_targets`). The tricky issue is handling rmeta files for
+            // pipelining. Since those are emitted asynchronously, the code
+            // path (like `on_stderr_line`) does not have enough information
+            // to know where the sysroot is, and that it is an std unit. If
+            // possible, it might be nice to eventually move this to the
+            // worker thread, but may be tricky to have the paths available.
+            // Another possibility is to disable pipelining between std ->
+            // non-std. The pipelining opportunities are small, and are not a
+            // huge win (in a full build, only proc_macro overlaps for 2
+            // seconds out of a 90s build on my system). Care must also be
+            // taken to properly copy these artifacts for Fresh units.
+            let rmeta = artifact == Artifact::Metadata;
+            standard_lib::add_sysroot_artifact(cx, unit, rmeta)?;
+        }
         Ok(())
     }
 

src/cargo/core/compiler/layout.rs

@@ -12,6 +12,10 @@
 //!     .rustc-info.json
 //!
 //!     # All final artifacts are linked into this directory from `deps`.
+//!     # Note that named profiles will soon be included as separate directories
+//!     # here. They have a restricted format, similar to Rust identifiers, so
+//!     # Cargo-specific directories added in the future should use some prefix
+//!     # like `.` to avoid name collisions.
 //!     debug/  # or release/
 //!
 //!         # File used to lock the directory to prevent multiple cargo processes
@@ -46,6 +50,11 @@
 //!         # incremental is enabled.
 //!         incremental/
 //!
+//!         # The sysroot for -Zbuild-std builds. This only appears in
+//!         # target-triple directories (not host), and only if -Zbuild-std is
+//!         # enabled.
+//!         .sysroot/
+//!
 //!     # This is the location at which the output of all custom build
 //!     # commands are rooted.
 //!     build/
@@ -116,6 +125,10 @@ pub struct Layout {
     examples: PathBuf,
     /// The directory for rustdoc output: `$root/doc`
     doc: PathBuf,
+    /// The local sysroot for the build-std feature.
+    sysroot: Option<PathBuf>,
+    /// The "lib" directory within `sysroot`.
+    sysroot_libdir: Option<PathBuf>,
     /// The lockfile for a build (`.cargo-lock`). Will be unlocked when this
     /// struct is `drop`ped.
     _lock: FileLock,
@@ -139,18 +152,21 @@ impl Layout {
         // Flexible target specifications often point at json files, so interpret
         // the target triple as a Path and then just use the file stem as the
         // component for the directory name in that case.
-        if let Some(triple) = triple {
-            let triple = Path::new(triple);
-            if triple.extension().and_then(|s| s.to_str()) == Some("json") {
-                root.push(
-                    triple
-                        .file_stem()
+        let triple_path = if let Some(s) = triple {
+            let p = Path::new(s);
+            let tp = if p.extension().and_then(|s| s.to_str()) == Some("json") {
+                Path::new(
+                    p.file_stem()
                         .ok_or_else(|| failure::format_err!("invalid target"))?,
-                );
+                )
             } else {
-                root.push(triple);
-            }
-        }
+                p
+            };
+            root.push(tp);
+            Some(tp)
+        } else {
+            None
+        };
         let dest = root.join(dest);
         // If the root directory doesn't already exist go ahead and create it
         // here. Use this opportunity to exclude it from backups as well if the
@@ -167,6 +183,17 @@ impl Layout {
         let root = root.into_path_unlocked();
         let dest = dest.into_path_unlocked();
 
+        // Compute the sysroot path for the build-std feature.
+        let build_std = ws.config().cli_unstable().build_std.as_ref();
+        let (sysroot, sysroot_libdir) = if let Some(tp) = build_std.and(triple_path) {
+            // This uses a leading dot to avoid collision with named profiles.
+            let sysroot = dest.join(".sysroot");
+            let sysroot_libdir = sysroot.join("lib").join("rustlib").join(tp).join("lib");
+            (Some(sysroot), Some(sysroot_libdir))
+        } else {
+            (None, None)
+        };
+
         Ok(Layout {
             deps: dest.join("deps"),
             build: dest.join("build"),
@@ -176,6 +203,8 @@ impl Layout {
             doc: root.join("doc"),
             root,
             dest,
+            sysroot,
+            sysroot_libdir,
             _lock: lock,
         })
     }
@@ -223,6 +252,16 @@ impl Layout {
     pub fn build(&self) -> &Path {
         &self.build
     }
+    /// The local sysroot for the build-std feature.
+    ///
+    /// Returns None if build-std is not enabled or this is the Host layout.
+    pub fn sysroot(&self) -> Option<&Path> {
+        self.sysroot.as_ref().map(|p| p.as_ref())
+    }
+    /// The "lib" directory within `sysroot`.
+    pub fn sysroot_libdir(&self) -> Option<&Path> {
+        self.sysroot_libdir.as_ref().map(|p| p.as_ref())
+    }
 }
 
 #[cfg(not(target_os = "macos"))]

src/cargo/core/compiler/mod.rs

@@ -50,7 +50,7 @@ use crate::util::paths;
 use crate::util::{self, machine_message, ProcessBuilder};
 use crate::util::{internal, join_paths, profile};
 
-/// Indicates whether an object is for the host architcture or the target architecture.
+/// Indicates whether an object is for the host architecture or the target architecture.
 ///
 /// These will be the same unless cross-compiling.
 #[derive(PartialEq, Eq, Hash, Debug, Clone, Copy, PartialOrd, Ord, Serialize)]
@@ -915,6 +915,16 @@ fn build_base_args<'a, 'cfg>(
         let dir = cx.files().layout(unit.kind).incremental().as_os_str();
         opt(cmd, "-C", "incremental=", Some(dir));
     }
+
+    if unit.is_std {
+        // -Zforce-unstable-if-unmarked prevents the accidental use of
+        // unstable crates within the sysroot (such as "extern crate libc" or
+        // any non-public crate in the sysroot).
+        //
+        // RUSTC_BOOTSTRAP allows unstable features on stable.
+        cmd.arg("-Zforce-unstable-if-unmarked")
+            .env("RUSTC_BOOTSTRAP", "1");
+    }
     Ok(())
 }
 
@@ -968,7 +978,17 @@ fn build_deps_args<'a, 'cfg>(
 
     let mut unstable_opts = false;
 
+    if let Some(sysroot) = cx.files().layout(Kind::Target).sysroot() {
+        if unit.kind == Kind::Target {
+            cmd.arg("--sysroot").arg(sysroot);
+        }
+    }
+
     for dep in deps {
+        if !unit.is_std && dep.unit.is_std {
+            // Dependency to sysroot crate uses --sysroot.
+            continue;
+        }
         if dep.unit.mode.is_run_custom_build() {
             cmd.env("OUT_DIR", &cx.files().build_script_out_dir(&dep.unit));
         }

src/cargo/core/compiler/standard_lib.rs

@@ -1,11 +1,13 @@
 //! Code for building the standard library.
 
-use crate::core::compiler::{BuildContext, CompileMode, Kind, Unit};
+use super::layout::Layout;
+use crate::core::compiler::{BuildContext, CompileMode, Context, FileFlavor, Kind, Unit};
 use crate::core::profiles::UnitFor;
 use crate::core::resolver::ResolveOpts;
 use crate::core::{Dependency, PackageId, PackageSet, Resolve, SourceId, Workspace};
 use crate::ops::{self, Packages};
 use crate::util::errors::CargoResult;
+use crate::util::paths;
 use std::collections::{HashMap, HashSet};
 use std::env;
 use std::path::PathBuf;
@@ -141,9 +143,15 @@ pub fn generate_std_roots<'a>(
                 bcx.build_config.release,
             );
             let features = std_resolve.features_sorted(pkg.package_id());
-            Ok(bcx
-                .units
-                .intern(pkg, lib, profile, Kind::Target, mode, features))
+            Ok(bcx.units.intern(
+                pkg,
+                lib,
+                profile,
+                Kind::Target,
+                mode,
+                features,
+                /*is_std*/ true,
+            ))
         })
         .collect::<CargoResult<Vec<_>>>()
 }
@@ -173,3 +181,33 @@ fn detect_sysroot_src_path(ws: &Workspace<'_>) -> CargoResult<PathBuf> {
     }
     Ok(src_path)
 }
+
+/// Prepare the output directory for the local sysroot.
+pub fn prepare_sysroot(layout: &Layout) -> CargoResult<()> {
+    if let Some(libdir) = layout.sysroot_libdir() {
+        if libdir.exists() {
+            paths::remove_dir_all(libdir)?;
+        }
+        paths::create_dir_all(libdir)?;
+    }
+    Ok(())
+}
+
+/// Copy an artifact to the sysroot.
+pub fn add_sysroot_artifact<'a>(
+    cx: &Context<'a, '_>,
+    unit: &Unit<'a>,
+    rmeta: bool,
+) -> CargoResult<()> {
+    let outputs = cx.outputs(unit)?;
+    let outputs = outputs
+        .iter()
+        .filter(|output| output.flavor == FileFlavor::Linkable { rmeta })
+        .map(|output| &output.path);
+    for path in outputs {
+        let libdir = cx.files().layout(Kind::Target).sysroot_libdir().unwrap();
+        let dst = libdir.join(path.file_name().unwrap());
+        paths::link_or_copy(path, dst)?;
+    }
+    Ok(())
+}

src/cargo/core/compiler/unit.rs

@@ -51,6 +51,8 @@ pub struct UnitInner<'a> {
     /// The `cfg` features to enable for this unit.
     /// This must be sorted.
     pub features: Vec<&'a str>,
+    /// Whether this is a standard library unit.
+    pub is_std: bool,
 }
 
 impl UnitInner<'_> {
@@ -144,6 +146,7 @@ impl<'a> UnitInterner<'a> {
         kind: Kind,
         mode: CompileMode,
         features: Vec<&'a str>,
+        is_std: bool,
     ) -> Unit<'a> {
         let inner = self.intern_inner(&UnitInner {
             pkg,
@@ -152,6 +155,7 @@ impl<'a> UnitInterner<'a> {
             kind,
             mode,
             features,
+            is_std,
         });
         Unit { inner }
     }

src/cargo/core/compiler/unit_dependencies.rs

@@ -573,7 +573,7 @@ fn new_unit_dep_with_profile<'a>(
     let unit = state
         .bcx
         .units
-        .intern(pkg, target, profile, kind, mode, features);
+        .intern(pkg, target, profile, kind, mode, features, state.is_std);
     Ok(UnitDep {
         unit,
         unit_for,

src/cargo/ops/cargo_clean.rs

@@ -94,10 +94,9 @@ pub fn clean(ws: &Workspace<'_>, opts: &CleanOptions<'_>) -> CargoResult<()> {
                             )
                         };
                         let features = resolve.features_sorted(pkg.package_id());
-                        units.push(
-                            bcx.units
-                                .intern(pkg, target, profile, *kind, *mode, features),
-                        );
+                        units.push(bcx.units.intern(
+                            pkg, target, profile, *kind, *mode, features, /*is_std*/ false,
+                        ));
                     }
                 }
             }

src/cargo/ops/cargo_compile.rs

@@ -309,6 +309,11 @@ pub fn compile_ws<'a>(
     let (mut packages, resolve_with_overrides) = resolve;
 
     let std_resolve = if let Some(crates) = &config.cli_unstable().build_std {
+        if build_config.build_plan {
+            config
+                .shell()
+                .warn("-Zbuild-std does not currently fully support --build-plan")?;
+        }
         if build_config.requested_target.is_none() {
             // TODO: This should eventually be fixed. Unfortunately it is not
             // easy to get the host triple in BuildConfig. Consider changing
@@ -703,8 +708,15 @@ fn generate_targets<'a>(
             bcx.build_config.release,
         );
         let features = resolve.features_sorted(pkg.package_id());
-        bcx.units
-            .intern(pkg, target, profile, kind, target_mode, features)
+        bcx.units.intern(
+            pkg,
+            target,
+            profile,
+            kind,
+            target_mode,
+            features,
+            /*is_std*/ false,
+        )
     };
 
     // Create a list of proposed targets.