Auto merge of #113271 - matthiaskrgr:rollup-2ik4vaj, r=matthiaskrgr

Rollup of 3 pull requests

Successful merges:

 - #113253 (Fixed documentation of from<CString> for Rc<CStr>: Arc -> Rc)
 - #113258 (Migrate GUI colors test to original CSS color format)
 - #113259 (Suggest `x build library` for a custom toolchain that fails to load `core`)

r? `@ghost`
`@rustbot` modify labels: rollup

2 files changed, 13 insertions, 4 deletions

diff --git a/compiler/rustc_metadata/messages.ftl b/compiler/rustc_metadata/messages.ftl
index 13b3dac85d1..cc58d51befd 100644
--- a/compiler/rustc_metadata/messages.ftl
+++ b/compiler/rustc_metadata/messages.ftl
@@ -25,6 +25,9 @@ metadata_conflicting_alloc_error_handler =
 metadata_conflicting_global_alloc =
     the `#[global_allocator]` in {$other_crate_name} conflicts with global allocator in: {$crate_name}
 
+metadata_consider_adding_std =
+    consider adding the standard library to the sysroot with `x build library --target {$locator_triple}`
+
 metadata_consider_building_std =
     consider building the standard library from source with `cargo build -Zbuild-std`
 
diff --git a/compiler/rustc_metadata/src/errors.rs b/compiler/rustc_metadata/src/errors.rs
index fca06c0f47c..b6c82376f4e 100644
--- a/compiler/rustc_metadata/src/errors.rs
+++ b/compiler/rustc_metadata/src/errors.rs
@@ -646,12 +646,18 @@ impl IntoDiagnostic<'_> for CannotFindCrate {
             } else {
                 diag.note(fluent::metadata_target_no_std_support);
             }
-            // NOTE: this suggests using rustup, even though the user may not have it installed.
-            // That's because they could choose to install it; or this may give them a hint which
-            // target they need to install from their distro.
+
             if self.missing_core {
-                diag.help(fluent::metadata_consider_downloading_target);
+                if env!("CFG_RELEASE_CHANNEL") == "dev" {
+                    diag.help(fluent::metadata_consider_adding_std);
+                } else {
+                    // NOTE: this suggests using rustup, even though the user may not have it installed.
+                    // That's because they could choose to install it; or this may give them a hint which
+                    // target they need to install from their distro.
+                    diag.help(fluent::metadata_consider_downloading_target);
+                }
             }
+
             // Suggest using #![no_std]. #[no_core] is unstable and not really supported anyway.
             // NOTE: this is a dummy span if `extern crate std` was injected by the compiler.
             // If it's not a dummy, that means someone added `extern crate std` explicitly and