Follow-up work for `download-rustc`

[jyn514]

These are all the features for download-rustc that didn't land in the initial MVP (#79540).

Required before this is made a default

• Download a separate beta compiler for stage0 and only use CI artifacts for stage1 onward. Right now, every time you rebase, stage0 tools (bootstrap, tidy, ...) will have to be recompiled. Additionally running x.py setup tools will compile rustbuild twice. Allow building rustdoc without first building rustc (MVP) #79540 (comment), Use the beta compiler for building bootstrap tools when download-rustc is set #82739
• Compile a new version of tracing so that rustdoc still gets debug logging (since CI artifacts always disable debug and trace logging). Always compile rustdoc with debug logging enabled when download-rustc is set #81932
• Right now only rustdoc is ever rebuilt. This is not ideal and should probably at least compile compiler tools (rustfmt, clippy, miri). Allow building rustdoc without first building rustc (MVP) #79540 (comment), Remove ENABLE_DOWNLOAD_RUSTC constant #82480
• Using git log --author=bors sometimes breaks. This should use git merge-base instead, or use some other workaround that doesn't break. Allow building rustdoc without first building rustc (MVP) #79540 (comment), Fix commit detected when using download-rustc #82740
• This breaks during release week (but only release week). Download a more recent LLVM version if src/version is modified #83350

Nice to have

• Add download-rustc = "if-unchanged" which rebuilds rustc instead of warning when compiler/ has been modified. Follow-up work for download-rustc #81930 (comment), Add download-rustc = "if-unchanged" #83368
• x.py check --stage 0 doesn't work. Follow-up work for download-rustc #81930 (comment), Use the beta compiler for building bootstrap tools when download-rustc is set #82739
• x.py check --stage 1 src/tools/rustdoc doesn't work. Follow-up work for download-rustc #81930 (comment), fixed in Fix x check --stage 1 when download-rustc is enabled #110121
• Add x.py setup tools to enable this conveniently (it doesn't make sense to use this for compiler developers). This shouldn't be added until people have used this feature for a little bit and it works reasonably well. Add x.py setup tools which enables download-rustc by default #83370
• Enable verification for the commit tarballs. This requires first signing nightly commits; right now the .sha256 URLs gave a 404. This seems fairly simple to fix but also not high priority.
• Give a better error message when rebasing an old branch (I think commits are kept at most 160 days?). Allow building rustdoc without first building rustc (MVP) #79540 (comment)
• It would be nice to support cross-compiling the standard library - fixed in Fix x test ui --target foo when download-rustc is enabled #110113
• Some tests fail when download-rustc is enabled: https://github.com/rust-lang/rust/issues?q=is%3Aissue+is%3Aopen+label%3AA-testsuite+label%3AA-download-rustc
• Combine download-rustc and download-ci-llvm into the same option. This needs quite a bit more design work. Allow building rustdoc without first building rustc (MVP) #79540 (comment), Unify download-* settings in config.toml #83369 This doesn't seem useful.

[jyn514]

Right now only rustdoc is ever rebuilt. This is not ideal and should probably at least compile compiler tools (rustfmt, clippy, miri). #79540 (comment)

While working on this, I found that the handling of ENABLE_DOWNLOAD_STAGE0 is broken: if a Step is called as part of ensure() instead of through maybe_run, it will still be built even if the constant is set to false. Not yet sure how to fix this.

Details

Note that this has local changes enabling the constant for clippy:

diff --git a/src/bootstrap/tool.rs b/src/bootstrap/tool.rs
index 5c874f69bd9..c82b78c1c71 100644
--- a/src/bootstrap/tool.rs
+++ b/src/bootstrap/tool.rs
@@ -564,6 +564,7 @@ pub struct Cargo {
 impl Step for Cargo {
     type Output = PathBuf;
     const DEFAULT: bool = true;
+    const ENABLE_DOWNLOAD_RUSTC: bool = true;
     const ONLY_HOSTS: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -647,6 +648,7 @@ pub struct $name {
         impl Step for $name {
             type Output = Option<PathBuf>;
             const DEFAULT: bool = true; // Overwritten below
+            const ENABLE_DOWNLOAD_RUSTC: bool = true;
             const ONLY_HOSTS: bool = true;
 
             fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {

$ x.py build -v src/tools/clippy
detected default triple x86_64-unknown-linux-gnu
Updating only changed submodules
Submodules updated in 0.01 seconds
using downloaded stage1 artifacts from CI (commit fe1bf8e05c39bdcc73fc09e246b7209444e389bc)
running: /home/joshua/rustc3/build/x86_64-unknown-linux-gnu/stage0/bin/cargo build --manifest-path /home/joshua/rustc3/src/bootstrap/Cargo.toml
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
running: /home/joshua/rustc3/build/bootstrap/debug/bootstrap build -v src/tools/clippy
finding compilers
CC_x86_64-unknown-linux-gnu = "cc"
CFLAGS_x86_64-unknown-linux-gnu = ["-ffunction-sections", "-fdata-sections", "-fPIC", "-m64"]
CXX_x86_64-unknown-linux-gnu = "c++"
CXXFLAGS_x86_64-unknown-linux-gnu = ["-ffunction-sections", "-fdata-sections", "-fPIC", "-m64"]
AR_x86_64-unknown-linux-gnu = "ar"
running sanity check
auto-detected local-rebuild 1.52.0-nightly
learning about cargo
> Assemble { target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
  > Assemble { target_compiler: Compiler { stage: 0, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
  < Assemble { target_compiler: Compiler { stage: 0, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
  > Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
  < Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
< Assemble { target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
> Clippy { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, extra_features: [] }
  > ToolBuild { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, tool: "clippy-driver", path: "src/tools/clippy", mode: ToolRustc, is_optional_tool: true, source_type: InTree, extra_features: [] }
    > Rustc { target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      > Std { target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        > StartupObjects { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        < StartupObjects { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        c Assemble { target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        > Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
          c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        < Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        c Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Assemble { target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        > StdLink { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
          c Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
          c Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        < StdLink { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
      < Std { target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      c Assemble { target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      c Assemble { target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      c Std { target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      c Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
      c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      > Llvm { target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
      < Llvm { target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
      c Assemble { target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      > RustcLink { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        c Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        c Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
      < RustcLink { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
    < Rustc { target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
    c Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
    c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
    c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
    c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
    c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
    c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
  < ToolBuild { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, tool: "clippy-driver", path: "src/tools/clippy", mode: ToolRustc, is_optional_tool: true, source_type: InTree, extra_features: [] }
< Clippy { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, extra_features: [] }
c Assemble { target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
> CargoClippy { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, extra_features: [] }
  > ToolBuild { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, tool: "cargo-clippy", path: "src/tools/clippy", mode: ToolRustc, is_optional_tool: true, source_type: InTree, extra_features: [] }
    c Rustc { target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
    c Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
    c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
    c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
    c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
    c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
    c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
  < ToolBuild { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, tool: "cargo-clippy", path: "src/tools/clippy", mode: ToolRustc, is_optional_tool: true, source_type: InTree, extra_features: [] }
< CargoClippy { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, extra_features: [] }
> Assemble { target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
  > Assemble { target_compiler: Compiler { stage: 0, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
  < Assemble { target_compiler: Compiler { stage: 0, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
  > Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
  < Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
< Assemble { target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
> Clippy { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, extra_features: [] }
  > ToolBuild { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, tool: "clippy-driver", path: "src/tools/clippy", mode: ToolRustc, is_optional_tool: true, source_type: InTree, extra_features: [] }
    > Rustc { target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
      > Std { target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None }, compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        > StartupObjects { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        < StartupObjects { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        c Assemble { target_compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        > Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
          c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        < Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        c Libdir { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Sysroot { compiler: Compiler { stage: 1, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
Building stage1 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
running: "/home/joshua/rustc3/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-Zbinary-dep-depinfo" "-j" "8" "--release" "--features" "panic-unwind backtrace compiler-builtins-c" "--manifest-path" "/home/joshua/rustc3/library/test/Cargo.toml" "--message-format" "json-render-diagnostics"
   Compiling core v0.0.0 (/home/joshua/rustc3/library/core)
^C  Building [======>                     ] 9/33: core                              
Build completed unsuccessfully in 0:00:01

[jyn514]

lol I also found that this completely ignores all test suites, making it pretty useless:

Not running bootstrap::test::RustdocUi because its artifacts have been downloaded from CI (`download-rustc` is set)

[camelid]

Required before this is made a default

I don't think this should be enabled by default until this is addressed as well so that it won't use the CI rustc if you've made local changes to rustc. Otherwise it would be really frustrating for people making changes to rustc and rustdoc (et al.).

[jyn514]

@camelid that's why it has a warning. Do you think it should force you to disable the option? That seems like it could be frustrating.

[jyn514]

I definitely don't think it should silently use the in-tree compiler if you make changes, it should always do what you specify in config.toml.

[camelid]

I was thinking that there could be a download-rustc = "if-no-local-changes" option or something like that, where it would only download rustc if compiler/ isn't dirty.