require -Zunstable-options to use new link-self-contained values and

linker flavors

- only the stable values for `-Clink-self-contained` can be used on stable until we
have more feedback on the interface
- `-Zunstable-options` is required to use unstable linker flavors

compiler/rustc_session/src/config.rs

@@ -11,7 +11,7 @@
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stable_hasher::{StableOrd, ToStableHashKey};
 use rustc_target::abi::Align;
-use rustc_target::spec::{LinkerFlavorCli, PanicStrategy, SanitizerSet, SplitDebuginfo};
+use rustc_target::spec::{PanicStrategy, SanitizerSet, SplitDebuginfo};
 use rustc_target::spec::{Target, TargetTriple, TargetWarnings, TARGETS};
 
 use crate::parse::{CrateCheckConfig, CrateConfig};
@@ -308,6 +308,14 @@ pub fn on() -> Self {
         on
     }
 
+    /// To help checking CLI usage while some of the values are unstable: returns whether one of the
+    /// components was set individually. This would also require the `-Zunstable-options` flag, to
+    /// be allowed.
+    fn are_unstable_variants_set(&self) -> bool {
+        let any_component_set = !self.components.is_empty();
+        self.explicitly_set.is_none() && any_component_set
+    }
+
     /// Returns whether the self-contained linker component is enabled.
     pub fn linker(&self) -> bool {
         self.components.contains(LinkSelfContainedComponents::LINKER)
@@ -2648,16 +2656,28 @@ pub fn build_session_options(
         }
     }
 
-    if let Some(flavor) = cg.linker_flavor {
+    // For testing purposes, until we have more feedback about these options: ensure `-Z
-        if matches!(flavor, LinkerFlavorCli::BpfLinker | LinkerFlavorCli::PtxLinker)
+    // unstable-options` is required when using the unstable `-C link-self-contained` options, like
-            && !nightly_options::is_unstable_enabled(matches)
+    // `-C link-self-contained=+linker`, and when using the unstable `-C linker-flavor` options, like
-        {
+    // `-C linker-flavor=gnu-lld-cc`.
-            let msg = format!(
+    if !nightly_options::is_unstable_enabled(matches) {
-                "linker flavor `{}` is unstable, `-Z unstable-options` \
+        let uses_unstable_self_contained_option =
-                 flag must also be passed to explicitly use it",
+            cg.link_self_contained.are_unstable_variants_set();
-                flavor.desc()
+        if uses_unstable_self_contained_option {
+            handler.early_error(
+                "only `-C link-self-contained` values `y`/`yes`/`on`/`n`/`no`/`off` are stable, \
+                the `-Z unstable-options` flag must also be passed to use the unstable values",
             );
-            handler.early_error(msg);
+        }
+
+        if let Some(flavor) = cg.linker_flavor {
+            if flavor.is_unstable() {
+                handler.early_error(format!(
+                    "the linker flavor `{}` is unstable, the `-Z unstable-options` \
+                        flag must also be passed to use the unstable values",
+                    flavor.desc()
+                ));
+            }
         }
     }
 

compiler/rustc_target/src/spec/mod.rs

@@ -181,6 +181,29 @@ pub enum LinkerFlavorCli {
     PtxLinker,
 }
 
+impl LinkerFlavorCli {
+    /// Returns whether this `-C linker-flavor` option is one of the unstable values.
+    pub fn is_unstable(&self) -> bool {
+        match self {
+            LinkerFlavorCli::Gnu(..)
+            | LinkerFlavorCli::Darwin(..)
+            | LinkerFlavorCli::WasmLld(..)
+            | LinkerFlavorCli::Unix(..)
+            | LinkerFlavorCli::Msvc(Lld::Yes)
+            | LinkerFlavorCli::EmCc
+            | LinkerFlavorCli::Bpf
+            | LinkerFlavorCli::Ptx
+            | LinkerFlavorCli::BpfLinker
+            | LinkerFlavorCli::PtxLinker => true,
+            LinkerFlavorCli::Gcc
+            | LinkerFlavorCli::Ld
+            | LinkerFlavorCli::Lld(..)
+            | LinkerFlavorCli::Msvc(Lld::No)
+            | LinkerFlavorCli::Em => false,
+        }
+    }
+}
+
 #[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
 pub enum LldFlavor {
     Wasm,