[do not merge] Preparation for LLD stabilization

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1414,7 +1414,7 @@ pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
         }
     }
 
-    let features = sess.opts.unstable_opts.linker_features;
+    let features = sess.opts.cg.linker_features;
 
     // linker and linker flavor specified via command line have precedence over what the target
     // specification specifies

compiler/rustc_session/src/config.rs

@@ -362,9 +362,14 @@ impl LinkSelfContained {
     /// 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.enabled_components.is_empty() || !self.disabled_components.is_empty();
-        self.explicitly_set.is_none() && any_component_set
+        if self.explicitly_set.is_some() {
+            return false;
+        }
+
+        // Only the linker component is stable, anything else is thus unstable.
+        let mentioned_components = self.enabled_components.union(self.disabled_components);
+        let unstable_components = mentioned_components - LinkSelfContainedComponents::LINKER;
+        !unstable_components.is_empty()
     }
 
     /// Returns whether the self-contained linker component was enabled on the CLI, using the
@@ -391,7 +396,7 @@ impl LinkSelfContained {
     }
 }
 
-/// The different values that `-Z linker-features` can take on the CLI: a list of individually
+/// The different values that `-C linker-features` can take on the CLI: a list of individually
 /// enabled or disabled features used during linking.
 ///
 /// There is no need to enable or disable them in bulk. Each feature is fine-grained, and can be
@@ -431,6 +436,44 @@ impl LinkerFeaturesCli {
             _ => None,
         }
     }
+
+    /// When *not* using `-Z unstable-options` on the CLI, ensure only stable linker features are
+    /// used, for the given `TargetTuple`. Returns `Ok` if no unstable variants are used.
+    /// The caller should ensure that e.g. `nightly_options::is_unstable_enabled()`
+    /// returns false.
+    pub(crate) fn check_unstable_variants(&self, target_tuple: &TargetTuple) -> Result<(), String> {
+        // `-C linker-features=[-+]lld` is only stable on x64 linux.
+        let check_lld = |features: LinkerFeatures, polarity: &str| {
+            let has_lld = features.is_lld_enabled();
+            if has_lld && target_tuple.tuple() != "x86_64-unknown-linux-gnu" {
+                return Err(format!(
+                    "`-C linker-features={polarity}lld` is unstable on the `{target_tuple}` \
+                    target. The `-Z unstable-options` flag must also be passed to use it on this target",
+                ));
+            }
+            Ok(())
+        };
+        check_lld(self.enabled, "+")?;
+        check_lld(self.disabled, "-")?;
+
+        // Since only lld is stable, any non-lld feature used is unstable, and that's an error.
+        let unstable_enabled = self.enabled - LinkerFeatures::LLD;
+        let unstable_disabled = self.disabled - LinkerFeatures::LLD;
+        if !unstable_enabled.union(unstable_disabled).is_empty() {
+            let unstable_features: Vec<_> = unstable_enabled
+                .iter()
+                .map(|f| format!("+{}", f.as_str().unwrap()))
+                .chain(unstable_disabled.iter().map(|f| format!("-{}", f.as_str().unwrap())))
+                .collect();
+            return Err(format!(
+                "the requested `-C linker-features={}` are unstable, and also require the \
+                `-Z unstable-options` flag to be usable",
+                unstable_features.join(","),
+            ));
+        }
+
+        Ok(())
+    }
 }
 
 /// Used with `-Z assert-incr-state`.
@@ -2486,9 +2529,8 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
         }
     }
 
-    if !nightly_options::is_unstable_enabled(matches)
-        && cg.force_frame_pointers == FramePointer::NonLeaf
-    {
+    let unstable_options_enabled = nightly_options::is_unstable_enabled(matches);
+    if !unstable_options_enabled && cg.force_frame_pointers == FramePointer::NonLeaf {
         early_dcx.early_fatal(
             "`-Cforce-frame-pointers=non-leaf` or `always` also requires `-Zunstable-options` \
                 and a nightly compiler",
@@ -2498,12 +2540,12 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
     // For testing purposes, until we have more feedback about these options: ensure `-Z
     // unstable-options` is required when using the unstable `-C link-self-contained` and `-C
     // linker-flavor` options.
-    if !nightly_options::is_unstable_enabled(matches) {
+    if !unstable_options_enabled {
         let uses_unstable_self_contained_option =
             cg.link_self_contained.are_unstable_variants_set();
         if uses_unstable_self_contained_option {
             early_dcx.early_fatal(
-                "only `-C link-self-contained` values `y`/`yes`/`on`/`n`/`no`/`off` are stable, \
+                "only `-C link-self-contained` values `y`/`yes`/`on`/`n`/`no`/`off`/`-linker`/`+linker` are stable, \
                 the `-Z unstable-options` flag must also be passed to use the unstable values",
             );
         }
@@ -2546,6 +2588,12 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
     let debuginfo = select_debuginfo(matches, &cg);
     let debuginfo_compression = unstable_opts.debuginfo_compression;
 
+    if !unstable_options_enabled {
+        if let Err(error) = cg.linker_features.check_unstable_variants(&target_triple) {
+            early_dcx.early_fatal(error);
+        }
+    }
+
     let crate_name = matches.opt_str("crate-name");
     let unstable_features = UnstableFeatures::from_environment(crate_name.as_deref());
     // Parse any `-l` flags, which link to native libraries.

compiler/rustc_session/src/options.rs

@@ -1988,6 +1988,8 @@ options! {
         on a C toolchain or linker installed in the system"),
     linker: Option<PathBuf> = (None, parse_opt_pathbuf, [UNTRACKED],
         "system linker to link outputs with"),
+    linker_features: LinkerFeaturesCli = (LinkerFeaturesCli::default(), parse_linker_features, [UNTRACKED],
+        "a comma-separated list of linker features to enable (+) or disable (-): `lld`"),
     linker_flavor: Option<LinkerFlavorCli> = (None, parse_linker_flavor, [UNTRACKED],
         "linker flavor"),
     linker_plugin_lto: LinkerPluginLto = (LinkerPluginLto::Disabled,
@@ -2273,8 +2275,6 @@ options! {
         "link native libraries in the linker invocation (default: yes)"),
     link_only: bool = (false, parse_bool, [TRACKED],
         "link the `.rlink` file generated by `-Z no-link` (default: no)"),
-    linker_features: LinkerFeaturesCli = (LinkerFeaturesCli::default(), parse_linker_features, [UNTRACKED],
-        "a comma-separated list of linker features to enable (+) or disable (-): `lld`"),
     lint_llvm_ir: bool = (false, parse_bool, [TRACKED],
         "lint LLVM IR (default: no)"),
     lint_mir: bool = (false, parse_bool, [UNTRACKED],

compiler/rustc_target/src/spec/mod.rs

@@ -718,7 +718,7 @@ impl ToJson for LinkSelfContainedComponents {
 }
 
 bitflags::bitflags! {
-    /// The `-Z linker-features` components that can individually be enabled or disabled.
+    /// The `-C linker-features` components that can individually be enabled or disabled.
     ///
     /// They are feature flags intended to be a more flexible mechanism than linker flavors, and
     /// also to prevent a combinatorial explosion of flavors whenever a new linker feature is
@@ -749,7 +749,7 @@ bitflags::bitflags! {
 rustc_data_structures::external_bitflags_debug! { LinkerFeatures }
 
 impl LinkerFeatures {
-    /// Parses a single `-Z linker-features` well-known feature, not a set of flags.
+    /// Parses a single `-C linker-features` well-known feature, not a set of flags.
     pub fn from_str(s: &str) -> Option<LinkerFeatures> {
         Some(match s {
             "cc" => LinkerFeatures::CC,
@@ -758,6 +758,17 @@ impl LinkerFeatures {
         })
     }
 
+    /// Return the linker feature name, as would be passed on the CLI.
+    ///
+    /// Returns `None` if the bitflags aren't a singular component (but a mix of multiple flags).
+    pub fn as_str(self) -> Option<&'static str> {
+        Some(match self {
+            LinkerFeatures::CC => "cc",
+            LinkerFeatures::LLD => "lld",
+            _ => return None,
+        })
+    }
+
     /// Returns whether the `lld` linker feature is enabled.
     pub fn is_lld_enabled(self) -> bool {
         self.contains(LinkerFeatures::LLD)

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

@@ -1331,9 +1331,7 @@ pub fn rustc_cargo_env(
     }
 
     // Enable rustc's env var for `rust-lld` when requested.
-    if builder.config.lld_enabled
-        && (builder.config.channel == "dev" || builder.config.channel == "nightly")
-    {
+    if builder.config.lld_enabled {
         cargo.env("CFG_USE_SELF_CONTAINED_LINKER", "1");
     }
 

src/bootstrap/src/core/config/config.rs

@@ -2356,7 +2356,6 @@ impl Config {
         // build our internal lld and use it as the default linker, by setting the `rust.lld` config
         // to true by default:
         // - on the `x86_64-unknown-linux-gnu` target
-        // - on the `dev` and `nightly` channels
         // - when building our in-tree llvm (i.e. the target has not set an `llvm-config`), so that
         //   we're also able to build the corresponding lld
         // - or when using an external llvm that's downloaded from CI, which also contains our prebuilt
@@ -2365,10 +2364,7 @@ impl Config {
         //   thus, disabled
         // - similarly, lld will not be built nor used by default when explicitly asked not to, e.g.
         //   when the config sets `rust.lld = false`
-        if config.build.triple == "x86_64-unknown-linux-gnu"
-            && config.hosts == [config.build]
-            && (config.channel == "dev" || config.channel == "nightly")
-        {
+        if config.build.triple == "x86_64-unknown-linux-gnu" && config.hosts == [config.build] {
             let no_llvm_config = config
                 .target_config
                 .get(&config.build)

src/doc/rustc/src/codegen-options/index.md

@@ -218,15 +218,22 @@ coverage measurement. Its use is not recommended.
 
 ## link-self-contained
 
-On `windows-gnu`, `linux-musl`, and `wasi` targets, this flag controls whether the
-linker will use libraries and objects shipped with Rust instead of those in the system.
-It takes one of the following values:
+This flag controls whether the linker will use libraries and objects shipped with Rust instead
+of those in the system. This allows overriding cases when detection fails or user wants to use shipped
+libraries.
+
+You can enable or disable the usage of any self-contained objects using one of the following values:
 
 * no value: rustc will use heuristic to disable self-contained mode if system has necessary tools.
 * `y`, `yes`, `on`, `true`: use only libraries/objects shipped with Rust.
 * `n`, `no`, `off` or `false`: rely on the user or the linker to provide non-Rust libraries/objects.
 
-This allows overriding cases when detection fails or user wants to use shipped libraries.
+It is also possible to enable or disable specific self-contained objects in a more granular way.
+You can pass a comma-separated list of self-contained objects, individually enabled (`+object`) or
+disabled (`-object`).
+
+Currently, only the `linker` granular option is stabilized:
+- `linker`: toggle the usage of self-contained linker objects (linker, dlltool, and their necessary libraries)
 
 ## linker
 
@@ -235,6 +242,25 @@ path to the linker executable. If this flag is not specified, the linker will
 be inferred based on the target. See also the [linker-flavor](#linker-flavor)
 flag for another way to specify the linker.
 
+## linker-features
+
+The `-Clinker-features` flag allows enabling or disabling specific features used during linking.
+
+These feature flags are a flexible extension mechanism that is complementary to linker flavors,
+designed to avoid the combinatorial explosion of having to create a new set of flavors for each
+linker feature we'd want to use.
+
+The flag accepts a comma-separated list of features, individually enabled (`+feature`) or disabled
+(`-feature`).
+
+Currently only one is stable, and only on the `x86_64-unknown-linux-gnu` target:
+- `lld`: to toggle using the lld linker, either the system-installed binary, or the self-contained
+  `rust-lld` linker (via the `-Clink-self-contained=+linker` flag).
+
+For example, use:
+- `-Clinker-features=+lld` to opt in to using the `lld` linker
+- `-Clinker-features=-lld` to opt out instead, for targets where it is configured as the default linker
+
 ## linker-flavor
 
 This flag controls the linker flavor used by `rustc`. If a linker is given with

src/doc/unstable-book/src/compiler-flags/codegen-options.md

@@ -51,10 +51,10 @@ instead of those in the system. The stable boolean values for this flag are coar
 - `mingw`: other MinGW libs and Windows import libs
 
 Out of the above self-contained linking components, `linker` is the only one currently implemented
-(beyond parsing the CLI options).
+(beyond parsing the CLI options) and stabilized.
 
 It refers to the LLD linker, built from the same LLVM revision used by rustc (named `rust-lld` to
 avoid naming conflicts), that is distributed via `rustup` with the compiler (and is used by default
-for the wasm targets). One can also opt-in to use it by combining this flag with an appropriate
+for the wasm targets). One can also opt in to use it by combining this flag with an appropriate
 linker flavor: for example, `-Clinker-flavor=gnu-lld-cc -Clink-self-contained=+linker` will use the
 toolchain's `rust-lld` as the linker.

src/tools/opt-dist/src/tests.rs

@@ -104,7 +104,10 @@ llvm-config = "{llvm_config}"
             "tests/incremental",
             "tests/mir-opt",
             "tests/pretty",
+            // Make sure that we don't use too new GLIBC symbols on x64
             "tests/run-make/glibc-symbols-x86_64-unknown-linux-gnu",
+            // Make sure that we use LLD by default on x64
+            "tests/run-make/rust-lld-x86_64-unknown-linux-gnu-dist",
             "tests/ui",
             "tests/crashes",
         ];

tests/run-make/compressed-debuginfo-zstd/rmake.rs

@@ -26,9 +26,8 @@ fn prepare_and_check<F: FnOnce(&mut Rustc) -> &mut Rustc>(to_find: &str, prepare
     run_in_tmpdir(|| {
         let mut rustc = Rustc::new();
         rustc
-            .arg("-Zlinker-features=+lld")
+            .arg("-Clinker-features=+lld")
             .arg("-Clink-self-contained=+linker")
-            .arg("-Zunstable-options")
             .arg("-Cdebuginfo=full")
             .input("main.rs");
         prepare_rustc(&mut rustc).run();

tests/run-make/rust-lld-custom-target/rmake.rs

@@ -23,7 +23,8 @@ fn main() {
         rustc()
             .crate_type("cdylib")
             .target("custom-target.json")
-            .arg("-Zlinker-features=-lld")
+            .arg("-Clinker-features=-lld")
+            .arg("-Zunstable-options")
             .input("lib.rs"),
     );
 }

tests/run-make/rust-lld-link-script-provide/rmake.rs

@@ -10,7 +10,7 @@ use run_make_support::rustc;
 fn main() {
     rustc()
         .input("main.rs")
-        .arg("-Zlinker-features=+lld")
+        .arg("-Clinker-features=+lld")
         .arg("-Clink-self-contained=+linker")
         .arg("-Zunstable-options")
         .link_arg("-Tscript.t")

tests/run-make/rust-lld-by-default-nightly/rmake.rs → tests/run-make/rust-lld-x86_64-unknown-linux-gnu-dist/rmake.rs

@@ -1,19 +1,16 @@
-// Ensure that rust-lld is used as the default linker on `x86_64-unknown-linux-gnu` on the nightly
-// channel, and that it can also be turned off with a CLI flag.
+// Ensure that rust-lld is used as the default linker on `x86_64-unknown-linux-gnu`
+// dist artifacts and that it can also be turned off with a CLI flag.
 
-//@ needs-rust-lld
-//@ ignore-beta
-//@ ignore-stable
+//@ only-dist
 //@ only-x86_64-unknown-linux-gnu
 
 use run_make_support::linker::{assert_rustc_doesnt_use_lld, assert_rustc_uses_lld};
 use run_make_support::rustc;
 
 fn main() {
-    // A regular compilation should use rust-lld by default. We'll check that by asking the linker
-    // to display its version number with a link-arg.
+    // A regular compilation should use rust-lld by default.
     assert_rustc_uses_lld(rustc().input("main.rs"));
 
     // But it can still be disabled by turning the linker feature off.
-    assert_rustc_doesnt_use_lld(rustc().arg("-Zlinker-features=-lld").input("main.rs"));
+    assert_rustc_doesnt_use_lld(rustc().arg("-Clinker-features=-lld").input("main.rs"));
 }

tests/run-make/rust-lld-x86_64-unknown-linux-gnu/main.rs

@@ -0,0 +1,5 @@
+// Test linking using `cc` with `rust-lld`, which is on by default on the x86_64-unknown-linux-gnu
+// target.
+// See https://github.com/rust-lang/compiler-team/issues/510 for more info
+
+fn main() {}