Handle uplifting in libstd dist step

src/bootstrap/src/core/build_steps/compile.rs

@@ -123,7 +123,9 @@ impl Std {
 }
 
 impl Step for Std {
-    type Output = ();
+    /// Build stamp of std, if it was indeed built or uplifted.
+    type Output = Option<BuildStamp>;
+
     const DEFAULT: bool = true;
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
@@ -160,7 +162,7 @@ impl Step for Std {
     /// This will build the standard library for a particular stage of the build
     /// using the `compiler` targeting the `target` architecture. The artifacts
     /// created will also be linked into the sysroot directory.
-    fn run(self, builder: &Builder<'_>) {
+    fn run(self, builder: &Builder<'_>) -> Self::Output {
         let target = self.target;
 
         // We already have std ready to be used for stage 0.
@@ -168,7 +170,7 @@ impl Step for Std {
             let compiler = self.build_compiler;
             builder.ensure(StdLink::from_std(self, compiler));
 
-            return;
+            return None;
         }
 
         let build_compiler = if builder.download_rustc() && self.force_recompile {
@@ -193,7 +195,7 @@ impl Step for Std {
                 &sysroot,
                 builder.config.ci_rust_std_contents(),
             );
-            return;
+            return None;
         }
 
         if builder.config.keep_stage.contains(&build_compiler.stage)
@@ -209,7 +211,7 @@ impl Step for Std {
             self.copy_extra_objects(builder, &build_compiler, target);
 
             builder.ensure(StdLink::from_std(self, build_compiler));
-            return;
+            return Some(build_stamp::libstd_stamp(builder, build_compiler, target));
         }
 
         let mut target_deps = builder.ensure(StartupObjects { compiler: build_compiler, target });
@@ -219,7 +221,7 @@ impl Step for Std {
 
         if Self::should_be_uplifted_from_stage_1(builder, build_compiler.stage, target) {
             let build_compiler_for_std_to_uplift = builder.compiler(1, builder.host_target);
-            builder.std(build_compiler_for_std_to_uplift, target);
+            let stage_1_stamp = builder.std(build_compiler_for_std_to_uplift, target);
 
             let msg = if build_compiler_for_std_to_uplift.host == target {
                 format!(
@@ -240,7 +242,7 @@ impl Step for Std {
             self.copy_extra_objects(builder, &build_compiler, target);
 
             builder.ensure(StdLink::from_std(self, build_compiler_for_std_to_uplift));
-            return;
+            return stage_1_stamp;
         }
 
         target_deps.extend(self.copy_extra_objects(builder, &build_compiler, target));
@@ -293,11 +295,13 @@ impl Step for Std {
             build_compiler,
             target,
         );
+
+        let stamp = build_stamp::libstd_stamp(builder, build_compiler, target);
         run_cargo(
             builder,
             cargo,
             vec![],
-            &build_stamp::libstd_stamp(builder, build_compiler, target),
+            &stamp,
             target_deps,
             self.is_for_mir_opt_tests, // is_check
             false,
@@ -307,6 +311,7 @@ impl Step for Std {
             self,
             builder.compiler(build_compiler.stage, builder.config.host_target),
         ));
+        Some(stamp)
     }
 
     fn metadata(&self) -> Option<StepMetadata> {

src/bootstrap/src/core/build_steps/dist.rs

@@ -791,12 +791,14 @@ impl Step for Std {
             return None;
         }
 
-        builder.std(build_compiler, target);
+        // It's possible that std was uplifted and thus built with a different build compiler
+        // So we need to read the stamp that was actually generated when std was built
+        let stamp =
+            builder.std(build_compiler, target).expect("Standard library has to be built for dist");
 
         let mut tarball = Tarball::new(builder, "rust-std", &target.triple);
         tarball.include_target_in_component_name(true);
 
-        let stamp = build_stamp::libstd_stamp(builder, build_compiler, target);
         verify_uefi_rlib_format(builder, target, &stamp);
         copy_target_libs(builder, target, tarball.image_dir(), &stamp);
 

src/bootstrap/src/core/builder/mod.rs

@@ -22,6 +22,7 @@ use crate::core::build_steps::{
 };
 use crate::core::config::flags::Subcommand;
 use crate::core::config::{DryRun, TargetSelection};
+use crate::utils::build_stamp::BuildStamp;
 use crate::utils::cache::Cache;
 use crate::utils::exec::{BootstrapCommand, ExecutionContext, command};
 use crate::utils::helpers::{self, LldThreads, add_dylib_path, exe, libdir, linker_args, t};
@@ -1412,6 +1413,8 @@ impl<'a> Builder<'a> {
     /// The standard library will be linked to the sysroot of the passed compiler.
     ///
     /// Prefer using this method rather than manually invoking `Std::new`.
+    ///
+    /// Returns an optional build stamp, if libstd was indeed built.
     #[cfg_attr(
         feature = "tracing",
         instrument(
@@ -1425,7 +1428,7 @@ impl<'a> Builder<'a> {
             ),
         ),
     )]
-    pub fn std(&self, compiler: Compiler, target: TargetSelection) {
+    pub fn std(&self, compiler: Compiler, target: TargetSelection) -> Option<BuildStamp> {
         // FIXME: make the `Std` step return some type-level "proof" that std was indeed built,
         // and then require passing that to all Cargo invocations that we do.
 
@@ -1444,10 +1447,11 @@ You have to build a stage1 compiler for `{}` first, and then use it to build a s
 
             // We still need to link the prebuilt standard library into the ephemeral stage0 sysroot
             self.ensure(StdLink::from_std(Std::new(compiler, target), compiler));
+            None
         } else {
             // This step both compiles the std and links it into the compiler's sysroot.
             // Yes, it's quite magical and side-effecty.. would be nice to refactor later.
-            self.ensure(Std::new(compiler, target));
+            self.ensure(Std::new(compiler, target))
         }
     }