From 3e675f4c5085df8ae19392e6de2caef7cb336f27 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jakub=20Ber=C3=A1nek?= <berykubik@gmail.com>
Date: Wed, 9 Jul 2025 22:25:03 +0200
Subject: [PATCH] Fix `--skip-std-check-if-no-download-rustc`

Since https://github.com/rust-lang/rust/pull/143048, we now explicitly set the build compiler for `check::Std`, which caused it to be built before we checked `--skip-std-check-if-no-download-rustc`. So I moved the check earlier to `make_run`, which resolves it.

I also added a regression test for this. Sadly we can't really test for the positive case easily (when download-ci-rustc is enabled), but we can test the negative cases, where it is disabled.
---
 src/bootstrap/src/core/build_steps/check.rs | 14 ++++++------
 src/bootstrap/src/core/builder/tests.rs     | 24 +++++++++++++++++++++
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/src/bootstrap/src/core/build_steps/check.rs b/src/bootstrap/src/core/build_steps/check.rs
index 0497bae86a1c8..0cc4628310aba 100644
--- a/src/bootstrap/src/core/build_steps/check.rs
+++ b/src/bootstrap/src/core/build_steps/check.rs
@@ -47,6 +47,13 @@ impl Step for Std {
     }
 
     fn make_run(run: RunConfig<'_>) {
+        if !run.builder.download_rustc() && run.builder.config.skip_std_check_if_no_download_rustc {
+            eprintln!(
+                "WARNING: `--skip-std-check-if-no-download-rustc` flag was passed and `rust.download-rustc` is not available. Skipping."
+            );
+            return;
+        }
+
         let crates = std_crates_for_run_make(&run);
         run.builder.ensure(Std {
             build_compiler: prepare_compiler_for_check(run.builder, run.target, Mode::Std),
@@ -56,13 +63,6 @@ impl Step for Std {
     }
 
     fn run(self, builder: &Builder<'_>) {
-        if !builder.download_rustc() && builder.config.skip_std_check_if_no_download_rustc {
-            eprintln!(
-                "WARNING: `--skip-std-check-if-no-download-rustc` flag was passed and `rust.download-rustc` is not available. Skipping."
-            );
-            return;
-        }
-
         let build_compiler = self.build_compiler;
         let stage = build_compiler.stage;
         let target = self.target;
diff --git a/src/bootstrap/src/core/builder/tests.rs b/src/bootstrap/src/core/builder/tests.rs
index bbcb58fca14f3..75cc5e01ec90f 100644
--- a/src/bootstrap/src/core/builder/tests.rs
+++ b/src/bootstrap/src/core/builder/tests.rs
@@ -1439,6 +1439,30 @@ mod snapshot {
         ");
     }
 
+    /// Make sure that we don't check library when download-rustc is disabled
+    /// when `--skip-std-check-if-no-download-rustc` was passed.
+    #[test]
+    fn check_library_skip_without_download_rustc() {
+        let ctx = TestCtx::new();
+        let args = ["--set", "rust.download-rustc=false", "--skip-std-check-if-no-download-rustc"];
+        insta::assert_snapshot!(
+            ctx.config("check")
+                .paths(&["library"])
+                .args(&args)
+                .render_steps(), @"");
+
+        insta::assert_snapshot!(
+            ctx.config("check")
+                .paths(&["library", "compiler"])
+                .args(&args)
+                .render_steps(), @r"
+        [build] llvm <host>
+        [check] rustc 0 <host> -> rustc 1 <host>
+        [check] rustc 0 <host> -> cranelift 1 <host>
+        [check] rustc 0 <host> -> gcc 1 <host>
+        ");
+    }
+
     #[test]
     fn check_miri_no_explicit_stage() {
         let ctx = TestCtx::new();