Make RUSTC_BOOTSTRAP read the crate name from CARGO_CRATE_NAME

compiler/rustc_driver_impl/src/lib.rs

@@ -1211,9 +1211,7 @@ pub fn handle_options(early_dcx: &EarlyDiagCtxt, args: &[String]) -> Option<geto
     if args.is_empty() {
         // user did not write `-v` nor `-Z unstable-options`, so do not
         // include that extra information.
-        let nightly_build =
-            rustc_feature::UnstableFeatures::from_environment(None).is_nightly_build();
-        usage(false, false, nightly_build);
+        usage(false, false, nightly_options::is_nightly_build());
         return None;
     }
 
@@ -1265,7 +1263,7 @@ pub fn handle_options(early_dcx: &EarlyDiagCtxt, args: &[String]) -> Option<geto
     if matches.opt_present("h") || matches.opt_present("help") {
         // Only show unstable options in --help if we accept unstable options.
         let unstable_enabled = nightly_options::is_unstable_enabled(&matches);
-        let nightly_build = nightly_options::match_is_nightly_build(&matches);
+        let nightly_build = nightly_options::is_nightly_build();
         usage(matches.opt_present("verbose"), unstable_enabled, nightly_build);
         return None;
     }
@@ -1337,7 +1335,7 @@ fn ice_path_with_config(config: Option<&UnstableOptions>) -> &'static Option<Pat
     }
 
     ICE_PATH.get_or_init(|| {
-        if !rustc_feature::UnstableFeatures::from_environment(None).is_nightly_build() {
+        if !nightly_options::is_nightly_build() {
             return None;
         }
         let mut path = match std::env::var_os("RUSTC_ICE") {
@@ -1493,7 +1491,7 @@ fn report_ice(
         dcx.emit_note(session_diagnostics::IceBugReport { bug_report_url });
 
         // Only emit update nightly hint for users on nightly builds.
-        if rustc_feature::UnstableFeatures::from_environment(None).is_nightly_build() {
+        if nightly_options::is_nightly_build() {
             dcx.emit_note(session_diagnostics::UpdateNightlyNote);
         }
     }

compiler/rustc_feature/src/lib.rs

@@ -64,38 +64,52 @@ pub enum UnstableFeatures {
 }
 
 impl UnstableFeatures {
-    /// This takes into account `RUSTC_BOOTSTRAP`.
-    ///
-    /// If `krate` is [`Some`], then setting `RUSTC_BOOTSTRAP=krate` will enable the nightly
-    /// features. Otherwise, only `RUSTC_BOOTSTRAP=1` will work.
-    pub fn from_environment(krate: Option<&str>) -> Self {
-        Self::from_environment_inner(krate, |name| env::var(name))
+    /// Determines whether this compiler allows unstable options/features,
+    /// according to whether it was built as a stable/beta compiler or a nightly
+    /// compiler, and taking `RUSTC_BOOTSTRAP` into account.
+    #[inline(never)]
+    pub fn from_environment() -> Self {
+        Self::from_environment_inner(|name| env::var(name))
     }
 
     /// Unit tests can pass a mock `std::env::var` instead of modifying the real environment.
     fn from_environment_inner(
-        krate: Option<&str>,
         env_var: impl Fn(&str) -> Result<String, env::VarError>, // std::env::var
     ) -> Self {
-        // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
+        // If `CFG_DISABLE_UNSTABLE_FEATURES` was true when this compiler was
+        // built, it is a stable/beta compiler that forbids unstable features.
         let disable_unstable_features =
             option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some_and(|s| s != "0");
-        // Returns whether `krate` should be counted as unstable
-        let is_unstable_crate =
-            |var: &str| krate.is_some_and(|name| var.split(',').any(|new_krate| new_krate == name));
-
-        let bootstrap = env_var("RUSTC_BOOTSTRAP").ok();
-        if let Some(val) = bootstrap.as_deref() {
-            match val {
-                val if val == "1" || is_unstable_crate(val) => return UnstableFeatures::Cheat,
-                // Hypnotize ourselves so that we think we are a stable compiler and thus don't
-                // allow any unstable features.
-                "-1" => return UnstableFeatures::Disallow,
-                _ => {}
-            }
+        let default_answer = if disable_unstable_features {
+            UnstableFeatures::Disallow
+        } else {
+            UnstableFeatures::Allow
+        };
+
+        // Returns true if the given list of comma-separated crate names
+        // contains `CARGO_CRATE_NAME`.
+        //
+        // This is not actually used by bootstrap; it only exists so that when
+        // cargo sees a third-party crate trying to set `RUSTC_BOOTSTRAP=1` in
+        // build.rs, it can suggest a somewhat less horrifying alternative.
+        //
+        // See <https://github.com/rust-lang/rust/pull/77802> for context.
+        let includes_current_crate = |names: &str| -> bool {
+            let Ok(crate_name) = env_var("CARGO_CRATE_NAME") else { return false };
+            // Normalize `-` in crate names to `_`.
+            let crate_name = crate_name.replace('-', "_");
+            names.replace('-', "_").split(',').any(|name| name == crate_name)
+        };
+
+        match env_var("RUSTC_BOOTSTRAP").as_deref() {
+            // Force the compiler to act as nightly, even if it's stable.
+            Ok("1") => UnstableFeatures::Cheat,
+            // Force the compiler to act as stable, even if it's nightly.
+            Ok("-1") => UnstableFeatures::Disallow,
+            // Force nightly if `RUSTC_BOOTSTRAP` contains the current crate name.
+            Ok(names) if includes_current_crate(names) => UnstableFeatures::Cheat,
+            _ => default_answer,
         }
-
-        if disable_unstable_features { UnstableFeatures::Disallow } else { UnstableFeatures::Allow }
     }
 
     pub fn is_nightly_build(&self) -> bool {

compiler/rustc_feature/src/tests.rs

@@ -3,8 +3,9 @@ use std::env;
 use super::UnstableFeatures;
 
 fn unstable_features(rustc_bootstrap: &str, crate_name: Option<&str>) -> UnstableFeatures {
-    UnstableFeatures::from_environment_inner(crate_name, |name| match name {
+    UnstableFeatures::from_environment_inner(|name| match name {
         "RUSTC_BOOTSTRAP" => Ok(rustc_bootstrap.to_owned()),
+        "CARGO_CRATE_NAME" => crate_name.map(str::to_owned).ok_or(env::VarError::NotPresent),
         _ => Err(env::VarError::NotPresent),
     })
 }
@@ -21,6 +22,7 @@ fn rustc_bootstrap_parsing() {
     // RUSTC_BOOTSTRAP allows multiple comma-delimited crates
     assert!(is_bootstrap("x,y,z", Some("x")));
     assert!(is_bootstrap("x,y,z", Some("y")));
+    assert!(is_bootstrap("x,y-utils", Some("y_utils")));
     // Crate that aren't specified do not get unstable features
     assert!(!is_bootstrap("x", Some("a")));
     assert!(!is_bootstrap("x,y,z", Some("a")));

compiler/rustc_session/src/config.rs

@@ -1825,7 +1825,7 @@ pub fn parse_crate_edition(early_dcx: &EarlyDiagCtxt, matches: &getopts::Matches
     };
 
     if !edition.is_stable() && !nightly_options::is_unstable_enabled(matches) {
-        let is_nightly = nightly_options::match_is_nightly_build(matches);
+        let is_nightly = nightly_options::is_nightly_build();
         let msg = if !is_nightly {
             format!(
                 "the crate requires edition {edition}, but the latest edition supported by this Rust version is {LATEST_STABLE_EDITION}"
@@ -2510,7 +2510,7 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
     let debuginfo_compression = unstable_opts.debuginfo_compression;
 
     let crate_name = matches.opt_str("crate-name");
-    let unstable_features = UnstableFeatures::from_environment(crate_name.as_deref());
+    let unstable_features = UnstableFeatures::from_environment();
     // Parse any `-l` flags, which link to native libraries.
     let libs = parse_native_libs(early_dcx, &unstable_opts, unstable_features, matches);
 

compiler/rustc_session/src/config/nightly_options.rs

@@ -4,16 +4,11 @@ use crate::EarlyDiagCtxt;
 use crate::config::{OptionStability, RustcOptGroup};
 
 pub fn is_unstable_enabled(matches: &getopts::Matches) -> bool {
-    match_is_nightly_build(matches)
-        && matches.opt_strs("Z").iter().any(|x| *x == "unstable-options")
+    is_nightly_build() && matches.opt_strs("Z").iter().any(|x| *x == "unstable-options")
 }
 
-pub fn match_is_nightly_build(matches: &getopts::Matches) -> bool {
-    is_nightly_build(matches.opt_str("crate-name").as_deref())
-}
-
-fn is_nightly_build(krate: Option<&str>) -> bool {
-    UnstableFeatures::from_environment(krate).is_nightly_build()
+pub fn is_nightly_build() -> bool {
+    UnstableFeatures::from_environment().is_nightly_build()
 }
 
 pub fn check_nightly_options(
@@ -22,7 +17,7 @@ pub fn check_nightly_options(
     flags: &[RustcOptGroup],
 ) {
     let has_z_unstable_option = matches.opt_strs("Z").iter().any(|x| *x == "unstable-options");
-    let really_allows_unstable_options = match_is_nightly_build(matches);
+    let really_allows_unstable_options = is_nightly_build();
     let mut nightly_options_on_stable = 0;
 
     for opt in flags.iter() {

compiler/rustc_session/src/parse.rs

@@ -251,7 +251,7 @@ impl ParseSess {
     pub fn with_dcx(dcx: DiagCtxt, source_map: Lrc<SourceMap>) -> Self {
         Self {
             dcx,
-            unstable_features: UnstableFeatures::from_environment(None),
+            unstable_features: UnstableFeatures::from_environment(),
             config: Cfg::default(),
             check_config: CheckCfg::default(),
             edition: ExpnId::root().expn_data().edition,

src/librustdoc/config.rs

@@ -409,7 +409,7 @@ impl Options {
                 println_condition(p.condition);
             }
 
-            if nightly_options::match_is_nightly_build(matches) {
+            if nightly_options::is_nightly_build() {
                 println!("\nPasses run with `--show-coverage`:");
                 for p in passes::COVERAGE_PASSES {
                     print!("{:>20}", p.pass.name);
@@ -653,7 +653,7 @@ impl Options {
             &matches.opt_strs("html-after-content"),
             &matches.opt_strs("markdown-before-content"),
             &matches.opt_strs("markdown-after-content"),
-            nightly_options::match_is_nightly_build(matches),
+            nightly_options::is_nightly_build(),
             dcx,
             &mut id_map,
             edition,
@@ -775,8 +775,7 @@ impl Options {
         let with_examples = matches.opt_strs("with-examples");
         let call_locations = crate::scrape_examples::load_call_locations(with_examples, dcx);
 
-        let unstable_features =
-            rustc_feature::UnstableFeatures::from_environment(crate_name.as_deref());
+        let unstable_features = rustc_feature::UnstableFeatures::from_environment();
         let options = Options {
             bin_crate,
             proc_macro_crate,

src/librustdoc/core.rs

@@ -260,7 +260,7 @@ pub(crate) fn create_config(
         cg: codegen_options,
         externs,
         target_triple: target,
-        unstable_features: UnstableFeatures::from_environment(crate_name.as_deref()),
+        unstable_features: UnstableFeatures::from_environment(),
         actually_rustdoc: true,
         resolve_doc_links,
         unstable_opts,