]> git.lizzy.rs Git - rust.git/blob - src/bootstrap/tool.rs
Support configurable deny-warnings for all in-tree crates.
[rust.git] / src / bootstrap / tool.rs
1 use std::collections::HashSet;
2 use std::env;
3 use std::fs;
4 use std::path::PathBuf;
5 use std::process::{exit, Command};
6
7 use build_helper::t;
8
9 use crate::builder::{Builder, Cargo as CargoCommand, RunConfig, ShouldRun, Step};
10 use crate::cache::Interned;
11 use crate::channel;
12 use crate::channel::GitInfo;
13 use crate::compile;
14 use crate::toolstate::ToolState;
15 use crate::util::{add_dylib_path, exe, CiEnv};
16 use crate::Compiler;
17 use crate::Mode;
18
19 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
20 pub enum SourceType {
21     InTree,
22     Submodule,
23 }
24
25 #[derive(Debug, Clone, Hash, PartialEq, Eq)]
26 struct ToolBuild {
27     compiler: Compiler,
28     target: Interned<String>,
29     tool: &'static str,
30     path: &'static str,
31     mode: Mode,
32     is_optional_tool: bool,
33     source_type: SourceType,
34     extra_features: Vec<String>,
35 }
36
37 impl Step for ToolBuild {
38     type Output = Option<PathBuf>;
39
40     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
41         run.never()
42     }
43
44     /// Builds a tool in `src/tools`
45     ///
46     /// This will build the specified tool with the specified `host` compiler in
47     /// `stage` into the normal cargo output directory.
48     fn run(self, builder: &Builder<'_>) -> Option<PathBuf> {
49         let compiler = self.compiler;
50         let target = self.target;
51         let tool = self.tool;
52         let path = self.path;
53         let is_optional_tool = self.is_optional_tool;
54
55         match self.mode {
56             Mode::ToolRustc => builder.ensure(compile::Rustc { compiler, target }),
57             Mode::ToolStd => builder.ensure(compile::Std { compiler, target }),
58             Mode::ToolBootstrap => {} // uses downloaded stage0 compiler libs
59             _ => panic!("unexpected Mode for tool build"),
60         }
61
62         let cargo = prepare_tool_cargo(
63             builder,
64             compiler,
65             self.mode,
66             target,
67             "build",
68             path,
69             self.source_type,
70             &self.extra_features,
71         );
72
73         builder.info(&format!("Building stage{} tool {} ({})", compiler.stage, tool, target));
74         let mut duplicates = Vec::new();
75         let is_expected = compile::stream_cargo(builder, cargo, vec![], &mut |msg| {
76             // Only care about big things like the RLS/Cargo for now
77             match tool {
78                 "rls" | "cargo" | "clippy-driver" | "miri" | "rustfmt" => {}
79
80                 _ => return,
81             }
82             let (id, features, filenames) = match msg {
83                 compile::CargoMessage::CompilerArtifact {
84                     package_id,
85                     features,
86                     filenames,
87                     target: _,
88                 } => (package_id, features, filenames),
89                 _ => return,
90             };
91             let features = features.iter().map(|s| s.to_string()).collect::<Vec<_>>();
92
93             for path in filenames {
94                 let val = (tool, PathBuf::from(&*path), features.clone());
95                 // we're only interested in deduplicating rlibs for now
96                 if val.1.extension().and_then(|s| s.to_str()) != Some("rlib") {
97                     continue;
98                 }
99
100                 // Don't worry about compiles that turn out to be host
101                 // dependencies or build scripts. To skip these we look for
102                 // anything that goes in `.../release/deps` but *doesn't* go in
103                 // `$target/release/deps`. This ensure that outputs in
104                 // `$target/release` are still considered candidates for
105                 // deduplication.
106                 if let Some(parent) = val.1.parent() {
107                     if parent.ends_with("release/deps") {
108                         let maybe_target = parent
109                             .parent()
110                             .and_then(|p| p.parent())
111                             .and_then(|p| p.file_name())
112                             .and_then(|p| p.to_str())
113                             .unwrap();
114                         if maybe_target != &*target {
115                             continue;
116                         }
117                     }
118                 }
119
120                 // Record that we've built an artifact for `id`, and if one was
121                 // already listed then we need to see if we reused the same
122                 // artifact or produced a duplicate.
123                 let mut artifacts = builder.tool_artifacts.borrow_mut();
124                 let prev_artifacts = artifacts.entry(target).or_default();
125                 let prev = match prev_artifacts.get(&*id) {
126                     Some(prev) => prev,
127                     None => {
128                         prev_artifacts.insert(id.to_string(), val);
129                         continue;
130                     }
131                 };
132                 if prev.1 == val.1 {
133                     return; // same path, same artifact
134                 }
135
136                 // If the paths are different and one of them *isn't* inside of
137                 // `release/deps`, then it means it's probably in
138                 // `$target/release`, or it's some final artifact like
139                 // `libcargo.rlib`. In these situations Cargo probably just
140                 // copied it up from `$target/release/deps/libcargo-xxxx.rlib`,
141                 // so if the features are equal we can just skip it.
142                 let prev_no_hash = prev.1.parent().unwrap().ends_with("release/deps");
143                 let val_no_hash = val.1.parent().unwrap().ends_with("release/deps");
144                 if prev.2 == val.2 || !prev_no_hash || !val_no_hash {
145                     return;
146                 }
147
148                 // ... and otherwise this looks like we duplicated some sort of
149                 // compilation, so record it to generate an error later.
150                 duplicates.push((id.to_string(), val, prev.clone()));
151             }
152         });
153
154         if is_expected && !duplicates.is_empty() {
155             println!(
156                 "duplicate artifacts found when compiling a tool, this \
157                       typically means that something was recompiled because \
158                       a transitive dependency has different features activated \
159                       than in a previous build:\n"
160             );
161             println!(
162                 "the following dependencies are duplicated although they \
163                       have the same features enabled:"
164             );
165             for (id, cur, prev) in duplicates.drain_filter(|(_, cur, prev)| cur.2 == prev.2) {
166                 println!("  {}", id);
167                 // same features
168                 println!("    `{}` ({:?})\n    `{}` ({:?})", cur.0, cur.1, prev.0, prev.1);
169             }
170             println!("the following dependencies have different features:");
171             for (id, cur, prev) in duplicates {
172                 println!("  {}", id);
173                 let cur_features: HashSet<_> = cur.2.into_iter().collect();
174                 let prev_features: HashSet<_> = prev.2.into_iter().collect();
175                 println!(
176                     "    `{}` additionally enabled features {:?} at {:?}",
177                     cur.0,
178                     &cur_features - &prev_features,
179                     cur.1
180                 );
181                 println!(
182                     "    `{}` additionally enabled features {:?} at {:?}",
183                     prev.0,
184                     &prev_features - &cur_features,
185                     prev.1
186                 );
187             }
188             println!();
189             println!(
190                 "to fix this you will probably want to edit the local \
191                       src/tools/rustc-workspace-hack/Cargo.toml crate, as \
192                       that will update the dependency graph to ensure that \
193                       these crates all share the same feature set"
194             );
195             panic!("tools should not compile multiple copies of the same crate");
196         }
197
198         builder.save_toolstate(
199             tool,
200             if is_expected { ToolState::TestFail } else { ToolState::BuildFail },
201         );
202
203         if !is_expected {
204             if !is_optional_tool {
205                 exit(1);
206             } else {
207                 None
208             }
209         } else {
210             let cargo_out =
211                 builder.cargo_out(compiler, self.mode, target).join(exe(tool, &compiler.host));
212             let bin = builder.tools_dir(compiler).join(exe(tool, &compiler.host));
213             builder.copy(&cargo_out, &bin);
214             Some(bin)
215         }
216     }
217 }
218
219 pub fn prepare_tool_cargo(
220     builder: &Builder<'_>,
221     compiler: Compiler,
222     mode: Mode,
223     target: Interned<String>,
224     command: &'static str,
225     path: &'static str,
226     source_type: SourceType,
227     extra_features: &[String],
228 ) -> CargoCommand {
229     let mut cargo = builder.cargo(compiler, mode, source_type, target, command);
230     let dir = builder.src.join(path);
231     cargo.arg("--manifest-path").arg(dir.join("Cargo.toml"));
232
233     let mut features = extra_features.to_vec();
234     if builder.build.config.cargo_native_static {
235         if path.ends_with("cargo")
236             || path.ends_with("rls")
237             || path.ends_with("clippy")
238             || path.ends_with("miri")
239             || path.ends_with("rustbook")
240             || path.ends_with("rustfmt")
241         {
242             cargo.env("LIBZ_SYS_STATIC", "1");
243             features.push("rustc-workspace-hack/all-static".to_string());
244         }
245     }
246
247     // if tools are using lzma we want to force the build script to build its
248     // own copy
249     cargo.env("LZMA_API_STATIC", "1");
250
251     // CFG_RELEASE is needed by rustfmt (and possibly other tools) which
252     // import rustc-ap-rustc_attr which requires this to be set for the
253     // `#[cfg(version(...))]` attribute.
254     cargo.env("CFG_RELEASE", builder.rust_release());
255     cargo.env("CFG_RELEASE_CHANNEL", &builder.config.channel);
256     cargo.env("CFG_VERSION", builder.rust_version());
257     cargo.env("CFG_RELEASE_NUM", channel::CFG_RELEASE_NUM);
258
259     let info = GitInfo::new(builder.config.ignore_git, &dir);
260     if let Some(sha) = info.sha() {
261         cargo.env("CFG_COMMIT_HASH", sha);
262     }
263     if let Some(sha_short) = info.sha_short() {
264         cargo.env("CFG_SHORT_COMMIT_HASH", sha_short);
265     }
266     if let Some(date) = info.commit_date() {
267         cargo.env("CFG_COMMIT_DATE", date);
268     }
269     if !features.is_empty() {
270         cargo.arg("--features").arg(&features.join(", "));
271     }
272     cargo
273 }
274
275 fn rustbook_features() -> Vec<String> {
276     let mut features = Vec::new();
277
278     // Due to CI budged and risk of spurious failures we want to limit jobs running this check.
279     // At same time local builds should run it regardless of the platform.
280     // `CiEnv::None` means it's local build and `CHECK_LINKS` is defined in x86_64-gnu-tools to
281     // explicitly enable it on single job
282     if CiEnv::current() == CiEnv::None || env::var("CHECK_LINKS").is_ok() {
283         features.push("linkcheck".to_string());
284     }
285
286     features
287 }
288
289 macro_rules! bootstrap_tool {
290     ($(
291         $name:ident, $path:expr, $tool_name:expr
292         $(,is_external_tool = $external:expr)*
293         $(,is_unstable_tool = $unstable:expr)*
294         $(,features = $features:expr)*
295         ;
296     )+) => {
297         #[derive(Copy, PartialEq, Eq, Clone)]
298         pub enum Tool {
299             $(
300                 $name,
301             )+
302         }
303
304         impl<'a> Builder<'a> {
305             pub fn tool_exe(&self, tool: Tool) -> PathBuf {
306                 match tool {
307                     $(Tool::$name =>
308                         self.ensure($name {
309                             compiler: self.compiler(0, self.config.build),
310                             target: self.config.build,
311                         }),
312                     )+
313                 }
314             }
315         }
316
317         $(
318             #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
319         pub struct $name {
320             pub compiler: Compiler,
321             pub target: Interned<String>,
322         }
323
324         impl Step for $name {
325             type Output = PathBuf;
326
327             fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
328                 run.path($path)
329             }
330
331             fn make_run(run: RunConfig<'_>) {
332                 run.builder.ensure($name {
333                     // snapshot compiler
334                     compiler: run.builder.compiler(0, run.builder.config.build),
335                     target: run.target,
336                 });
337             }
338
339             fn run(self, builder: &Builder<'_>) -> PathBuf {
340                 builder.ensure(ToolBuild {
341                     compiler: self.compiler,
342                     target: self.target,
343                     tool: $tool_name,
344                     mode: if false $(|| $unstable)* {
345                         // use in-tree libraries for unstable features
346                         Mode::ToolStd
347                     } else {
348                         Mode::ToolBootstrap
349                     },
350                     path: $path,
351                     is_optional_tool: false,
352                     source_type: if false $(|| $external)* {
353                         SourceType::Submodule
354                     } else {
355                         SourceType::InTree
356                     },
357                     extra_features: {
358                         // FIXME(#60643): avoid this lint by using `_`
359                         let mut _tmp = Vec::new();
360                         $(_tmp.extend($features);)*
361                         _tmp
362                     },
363                 }).expect("expected to build -- essential tool")
364             }
365         }
366         )+
367     }
368 }
369
370 bootstrap_tool!(
371     Rustbook, "src/tools/rustbook", "rustbook", features = rustbook_features();
372     UnstableBookGen, "src/tools/unstable-book-gen", "unstable-book-gen";
373     Tidy, "src/tools/tidy", "tidy";
374     Linkchecker, "src/tools/linkchecker", "linkchecker";
375     CargoTest, "src/tools/cargotest", "cargotest";
376     Compiletest, "src/tools/compiletest", "compiletest", is_unstable_tool = true;
377     BuildManifest, "src/tools/build-manifest", "build-manifest";
378     RemoteTestClient, "src/tools/remote-test-client", "remote-test-client";
379     RustInstaller, "src/tools/rust-installer", "fabricate", is_external_tool = true;
380     RustdocTheme, "src/tools/rustdoc-themes", "rustdoc-themes";
381     ExpandYamlAnchors, "src/tools/expand-yaml-anchors", "expand-yaml-anchors";
382 );
383
384 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
385 pub struct ErrorIndex {
386     pub compiler: Compiler,
387 }
388
389 impl ErrorIndex {
390     pub fn command(builder: &Builder<'_>, compiler: Compiler) -> Command {
391         let mut cmd = Command::new(builder.ensure(ErrorIndex { compiler }));
392         add_dylib_path(
393             vec![PathBuf::from(&builder.sysroot_libdir(compiler, compiler.host))],
394             &mut cmd,
395         );
396         cmd
397     }
398 }
399
400 impl Step for ErrorIndex {
401     type Output = PathBuf;
402
403     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
404         run.path("src/tools/error_index_generator")
405     }
406
407     fn make_run(run: RunConfig<'_>) {
408         // Compile the error-index in the same stage as rustdoc to avoid
409         // recompiling rustdoc twice if we can.
410         let stage = if run.builder.top_stage >= 2 { run.builder.top_stage } else { 0 };
411         run.builder
412             .ensure(ErrorIndex { compiler: run.builder.compiler(stage, run.builder.config.build) });
413     }
414
415     fn run(self, builder: &Builder<'_>) -> PathBuf {
416         builder
417             .ensure(ToolBuild {
418                 compiler: self.compiler,
419                 target: self.compiler.host,
420                 tool: "error_index_generator",
421                 mode: Mode::ToolRustc,
422                 path: "src/tools/error_index_generator",
423                 is_optional_tool: false,
424                 source_type: SourceType::InTree,
425                 extra_features: Vec::new(),
426             })
427             .expect("expected to build -- essential tool")
428     }
429 }
430
431 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
432 pub struct RemoteTestServer {
433     pub compiler: Compiler,
434     pub target: Interned<String>,
435 }
436
437 impl Step for RemoteTestServer {
438     type Output = PathBuf;
439
440     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
441         run.path("src/tools/remote-test-server")
442     }
443
444     fn make_run(run: RunConfig<'_>) {
445         run.builder.ensure(RemoteTestServer {
446             compiler: run.builder.compiler(run.builder.top_stage, run.builder.config.build),
447             target: run.target,
448         });
449     }
450
451     fn run(self, builder: &Builder<'_>) -> PathBuf {
452         builder
453             .ensure(ToolBuild {
454                 compiler: self.compiler,
455                 target: self.target,
456                 tool: "remote-test-server",
457                 mode: Mode::ToolStd,
458                 path: "src/tools/remote-test-server",
459                 is_optional_tool: false,
460                 source_type: SourceType::InTree,
461                 extra_features: Vec::new(),
462             })
463             .expect("expected to build -- essential tool")
464     }
465 }
466
467 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
468 pub struct Rustdoc {
469     /// This should only ever be 0 or 2.
470     /// We sometimes want to reference the "bootstrap" rustdoc, which is why this option is here.
471     pub compiler: Compiler,
472 }
473
474 impl Step for Rustdoc {
475     type Output = PathBuf;
476     const DEFAULT: bool = true;
477     const ONLY_HOSTS: bool = true;
478
479     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
480         run.path("src/tools/rustdoc").path("src/librustdoc")
481     }
482
483     fn make_run(run: RunConfig<'_>) {
484         run.builder
485             .ensure(Rustdoc { compiler: run.builder.compiler(run.builder.top_stage, run.host) });
486     }
487
488     fn run(self, builder: &Builder<'_>) -> PathBuf {
489         let target_compiler = self.compiler;
490         if target_compiler.stage == 0 {
491             if !target_compiler.is_snapshot(builder) {
492                 panic!("rustdoc in stage 0 must be snapshot rustdoc");
493             }
494             return builder.initial_rustc.with_file_name(exe("rustdoc", &target_compiler.host));
495         }
496         let target = target_compiler.host;
497         // Similar to `compile::Assemble`, build with the previous stage's compiler. Otherwise
498         // we'd have stageN/bin/rustc and stageN/bin/rustdoc be effectively different stage
499         // compilers, which isn't what we want. Rustdoc should be linked in the same way as the
500         // rustc compiler it's paired with, so it must be built with the previous stage compiler.
501         let build_compiler = builder.compiler(target_compiler.stage - 1, builder.config.build);
502
503         // The presence of `target_compiler` ensures that the necessary libraries (codegen backends,
504         // compiler libraries, ...) are built. Rustdoc does not require the presence of any
505         // libraries within sysroot_libdir (i.e., rustlib), though doctests may want it (since
506         // they'll be linked to those libraries). As such, don't explicitly `ensure` any additional
507         // libraries here. The intuition here is that If we've built a compiler, we should be able
508         // to build rustdoc.
509
510         let cargo = prepare_tool_cargo(
511             builder,
512             build_compiler,
513             Mode::ToolRustc,
514             target,
515             "build",
516             "src/tools/rustdoc",
517             SourceType::InTree,
518             &[],
519         );
520
521         builder.info(&format!(
522             "Building rustdoc for stage{} ({})",
523             target_compiler.stage, target_compiler.host
524         ));
525         builder.run(&mut cargo.into());
526
527         // Cargo adds a number of paths to the dylib search path on windows, which results in
528         // the wrong rustdoc being executed. To avoid the conflicting rustdocs, we name the "tool"
529         // rustdoc a different name.
530         let tool_rustdoc = builder
531             .cargo_out(build_compiler, Mode::ToolRustc, target)
532             .join(exe("rustdoc_tool_binary", &target_compiler.host));
533
534         // don't create a stage0-sysroot/bin directory.
535         if target_compiler.stage > 0 {
536             let sysroot = builder.sysroot(target_compiler);
537             let bindir = sysroot.join("bin");
538             t!(fs::create_dir_all(&bindir));
539             let bin_rustdoc = bindir.join(exe("rustdoc", &*target_compiler.host));
540             let _ = fs::remove_file(&bin_rustdoc);
541             builder.copy(&tool_rustdoc, &bin_rustdoc);
542             bin_rustdoc
543         } else {
544             tool_rustdoc
545         }
546     }
547 }
548
549 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
550 pub struct Cargo {
551     pub compiler: Compiler,
552     pub target: Interned<String>,
553 }
554
555 impl Step for Cargo {
556     type Output = PathBuf;
557     const DEFAULT: bool = true;
558     const ONLY_HOSTS: bool = true;
559
560     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
561         let builder = run.builder;
562         run.path("src/tools/cargo").default_condition(builder.config.extended)
563     }
564
565     fn make_run(run: RunConfig<'_>) {
566         run.builder.ensure(Cargo {
567             compiler: run.builder.compiler(run.builder.top_stage, run.builder.config.build),
568             target: run.target,
569         });
570     }
571
572     fn run(self, builder: &Builder<'_>) -> PathBuf {
573         builder
574             .ensure(ToolBuild {
575                 compiler: self.compiler,
576                 target: self.target,
577                 tool: "cargo",
578                 mode: Mode::ToolRustc,
579                 path: "src/tools/cargo",
580                 is_optional_tool: false,
581                 source_type: SourceType::Submodule,
582                 extra_features: Vec::new(),
583             })
584             .expect("expected to build -- essential tool")
585     }
586 }
587
588 macro_rules! tool_extended {
589     (($sel:ident, $builder:ident),
590        $($name:ident,
591        $toolstate:ident,
592        $path:expr,
593        $tool_name:expr,
594        stable = $stable:expr,
595        $(in_tree = $in_tree:expr,)*
596        $extra_deps:block;)+) => {
597         $(
598             #[derive(Debug, Clone, Hash, PartialEq, Eq)]
599         pub struct $name {
600             pub compiler: Compiler,
601             pub target: Interned<String>,
602             pub extra_features: Vec<String>,
603         }
604
605         impl Step for $name {
606             type Output = Option<PathBuf>;
607             const DEFAULT: bool = true; // Overwritten below
608             const ONLY_HOSTS: bool = true;
609
610             fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
611                 let builder = run.builder;
612                 run.path($path).default_condition(
613                     builder.config.extended
614                         && builder.config.tools.as_ref().map_or(
615                             // By default, on nightly/dev enable all tools, else only
616                             // build stable tools.
617                             $stable || builder.build.unstable_features(),
618                             // If `tools` is set, search list for this tool.
619                             |tools| {
620                                 tools.iter().any(|tool| match tool.as_ref() {
621                                     "clippy" => $tool_name == "clippy-driver",
622                                     x => $tool_name == x,
623                             })
624                         }),
625                 )
626             }
627
628             fn make_run(run: RunConfig<'_>) {
629                 run.builder.ensure($name {
630                     compiler: run.builder.compiler(run.builder.top_stage, run.builder.config.build),
631                     target: run.target,
632                     extra_features: Vec::new(),
633                 });
634             }
635
636             #[allow(unused_mut)]
637             fn run(mut $sel, $builder: &Builder<'_>) -> Option<PathBuf> {
638                 $extra_deps
639                 $builder.ensure(ToolBuild {
640                     compiler: $sel.compiler,
641                     target: $sel.target,
642                     tool: $tool_name,
643                     mode: Mode::ToolRustc,
644                     path: $path,
645                     extra_features: $sel.extra_features,
646                     is_optional_tool: true,
647                     source_type: if false $(|| $in_tree)* {
648                         SourceType::InTree
649                     } else {
650                         SourceType::Submodule
651                     },
652                 })
653             }
654         }
655         )+
656     }
657 }
658
659 // Note: tools need to be also added to `Builder::get_step_descriptions` in `build.rs`
660 // to make `./x.py build <tool>` work.
661 tool_extended!((self, builder),
662     Cargofmt, rustfmt, "src/tools/rustfmt", "cargo-fmt", stable=true, {};
663     CargoClippy, clippy, "src/tools/clippy", "cargo-clippy", stable=true, in_tree=true, {};
664     Clippy, clippy, "src/tools/clippy", "clippy-driver", stable=true, in_tree=true, {};
665     Miri, miri, "src/tools/miri", "miri", stable=false, {};
666     CargoMiri, miri, "src/tools/miri/cargo-miri", "cargo-miri", stable=false, {};
667     Rls, rls, "src/tools/rls", "rls", stable=true, {
668         builder.ensure(Clippy {
669             compiler: self.compiler,
670             target: self.target,
671             extra_features: Vec::new(),
672         });
673         self.extra_features.push("clippy".to_owned());
674     };
675     Rustfmt, rustfmt, "src/tools/rustfmt", "rustfmt", stable=true, {};
676 );
677
678 impl<'a> Builder<'a> {
679     /// Gets a `Command` which is ready to run `tool` in `stage` built for
680     /// `host`.
681     pub fn tool_cmd(&self, tool: Tool) -> Command {
682         let mut cmd = Command::new(self.tool_exe(tool));
683         let compiler = self.compiler(0, self.config.build);
684         let host = &compiler.host;
685         // Prepares the `cmd` provided to be able to run the `compiler` provided.
686         //
687         // Notably this munges the dynamic library lookup path to point to the
688         // right location to run `compiler`.
689         let mut lib_paths: Vec<PathBuf> = vec![
690             self.build.rustc_snapshot_libdir(),
691             self.cargo_out(compiler, Mode::ToolBootstrap, *host).join("deps"),
692         ];
693
694         // On MSVC a tool may invoke a C compiler (e.g., compiletest in run-make
695         // mode) and that C compiler may need some extra PATH modification. Do
696         // so here.
697         if compiler.host.contains("msvc") {
698             let curpaths = env::var_os("PATH").unwrap_or_default();
699             let curpaths = env::split_paths(&curpaths).collect::<Vec<_>>();
700             for &(ref k, ref v) in self.cc[&compiler.host].env() {
701                 if k != "PATH" {
702                     continue;
703                 }
704                 for path in env::split_paths(v) {
705                     if !curpaths.contains(&path) {
706                         lib_paths.push(path);
707                     }
708                 }
709             }
710         }
711
712         add_dylib_path(lib_paths, &mut cmd);
713         cmd
714     }
715 }