use initial rustc's std on stage 0

On stage 0, rather than compiling std utilize the one from the stage0 sysroot
as stage 0 should represent the snapshot version not the compiled one.

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

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

@@ -149,12 +149,17 @@ impl Step for Std {
         let target = self.target;
         let compiler = self.compiler;
 
+        // We already have std ready to be used for stage 0.
+        if compiler.stage == 0 {
+            builder.ensure(StdLink::from_std(self, compiler));
+
+            return;
+        }
+
         // When using `download-rustc`, we already have artifacts for the host available. Don't
         // recompile them.
-        if builder.download_rustc() && builder.config.is_host_target(target)
-            // NOTE: the beta compiler may generate different artifacts than the downloaded compiler, so
-            // its artifacts can't be reused.
-            && compiler.stage != 0
+        if builder.download_rustc()
+            && builder.config.is_host_target(target)
             && !self.force_recompile
         {
             let sysroot = builder.ensure(Sysroot { compiler, force_recompile: false });
@@ -753,23 +758,16 @@ impl Step for StdLink {
             (libdir, hostdir)
         };
 
-        add_to_sysroot(
-            builder,
-            &libdir,
-            &hostdir,
-            &build_stamp::libstd_stamp(builder, compiler, target),
-        );
+        let is_downloaded_beta_stage0 = builder
+            .build
+            .config
+            .initial_rustc
+            .starts_with(builder.out.join(compiler.host).join("stage0/bin"));
 
         // Special case for stage0, to make `rustup toolchain link` and `x dist --stage 0`
         // work for stage0-sysroot. We only do this if the stage0 compiler comes from beta,
         // and is not set to a custom path.
-        if compiler.stage == 0
-            && builder
-                .build
-                .config
-                .initial_rustc
-                .starts_with(builder.out.join(compiler.host).join("stage0/bin"))
-        {
+        if compiler.stage == 0 && is_downloaded_beta_stage0 {
             // Copy bin files from stage0/bin to stage0-sysroot/bin
             let sysroot = builder.out.join(compiler.host).join("stage0-sysroot");
 
@@ -779,21 +777,8 @@ impl Step for StdLink {
             t!(fs::create_dir_all(&sysroot_bin_dir));
             builder.cp_link_r(&stage0_bin_dir, &sysroot_bin_dir);
 
-            // Copy all files from stage0/lib to stage0-sysroot/lib
             let stage0_lib_dir = builder.out.join(host).join("stage0/lib");
-            if let Ok(files) = fs::read_dir(stage0_lib_dir) {
-                for file in files {
-                    let file = t!(file);
-                    let path = file.path();
-                    if path.is_file() {
-                        builder.copy_link(
-                            &path,
-                            &sysroot.join("lib").join(path.file_name().unwrap()),
-                            FileType::Regular,
-                        );
-                    }
-                }
-            }
+            builder.cp_link_r(&stage0_lib_dir, &sysroot.join("lib"));
 
             // Copy codegen-backends from stage0
             let sysroot_codegen_backends = builder.sysroot_codegen_backends(compiler);
@@ -807,6 +792,16 @@ impl Step for StdLink {
             if stage0_codegen_backends.exists() {
                 builder.cp_link_r(&stage0_codegen_backends, &sysroot_codegen_backends);
             }
+        } else if compiler.stage == 0 {
+            let sysroot = builder.out.join(compiler.host.triple).join("stage0-sysroot");
+            builder.cp_link_r(&builder.initial_sysroot.join("lib"), &sysroot.join("lib"));
+        } else {
+            add_to_sysroot(
+                builder,
+                &libdir,
+                &hostdir,
+                &build_stamp::libstd_stamp(builder, compiler, target),
+            );
         }
     }
 }