add flag to dump unstable feature status information

Cargo.lock

@@ -3596,6 +3596,7 @@ dependencies = [
  "rustc_target",
  "rustc_trait_selection",
  "rustc_ty_utils",
+ "serde",
  "serde_json",
  "shlex",
  "time",
@@ -4012,6 +4013,7 @@ dependencies = [
  "rustc_span",
  "rustc_target",
  "rustc_type_ir",
+ "serde",
  "tempfile",
  "tracing",
 ]

compiler/rustc_driver_impl/Cargo.toml

@@ -47,6 +47,7 @@ rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
 rustc_ty_utils = { path = "../rustc_ty_utils" }
+serde = { version = "1.0.125", features = [ "derive" ] }
 serde_json = "1.0.59"
 shlex = "1.0"
 time = { version = "0.3.36", default-features = false, features = ["alloc", "formatting", "macros"] }

compiler/rustc_driver_impl/src/lib.rs

@@ -21,10 +21,11 @@
 
 use std::cmp::max;
 use std::collections::BTreeMap;
+use std::error::Error;
 use std::ffi::OsString;
 use std::fmt::Write as _;
 use std::fs::{self, File};
-use std::io::{self, IsTerminal, Read, Write};
+use std::io::{self, BufWriter, IsTerminal, Read, Write, stdout};
 use std::panic::{self, PanicHookInfo, catch_unwind};
 use std::path::PathBuf;
 use std::process::{self, Command, Stdio};
@@ -45,7 +46,7 @@ use rustc_errors::registry::Registry;
 use rustc_errors::{
     ColorConfig, DiagCtxt, ErrCode, ErrorGuaranteed, FatalError, PResult, markdown,
 };
-use rustc_feature::find_gated_cfg;
+use rustc_feature::{LangFeaturesStatus, find_gated_cfg};
 use rustc_interface::util::{self, get_codegen_backend};
 use rustc_interface::{Linker, Queries, interface, passes};
 use rustc_lint::unerased_lint_store;
@@ -377,6 +378,11 @@ fn run_compiler(
             return early_exit();
         }
 
+        if sess.opts.unstable_opts.dump_features_status {
+            dump_features_status(sess, codegen_backend);
+            return early_exit();
+        }
+
         if !has_input {
             #[allow(rustc::diagnostic_outside_of_impl)]
             sess.dcx().fatal("no input filename given"); // this is fatal
@@ -1571,6 +1577,30 @@ fn report_ice(
     }
 }
 
+fn dump_features_status(sess: &Session, codegen_backend: &dyn CodegenBackend) {
+    #[derive(serde::Serialize)]
+    struct FeaturesStatus {
+        lang_features_status: LangFeaturesStatus,
+        lib_features_status: locator::LibFeaturesStatus,
+    }
+
+    let result: Result<(), Box<dyn Error>> = try {
+        let lang_features_status = rustc_feature::lang_features_status();
+        let lib_features_status =
+            rustc_metadata::lib_features_status(sess, &*codegen_backend.metadata_loader())?;
+        let value = FeaturesStatus { lang_features_status, lib_features_status };
+        let writer = stdout();
+        let writer = BufWriter::new(writer);
+        serde_json::to_writer_pretty(writer, &value)?;
+    };
+
+    // this happens before the global context and more importantly the diagnostic context is setup,
+    // so we can't report with the proper machinery
+    if let Err(error) = result {
+        panic!("cannot emit feature status json: {error}")
+    }
+}
+
 /// This allows tools to enable rust logging without having to magically match rustc's
 /// tracing crate version.
 pub fn init_rustc_env_logger(early_dcx: &EarlyDiagCtxt) {

compiler/rustc_feature/src/lib.rs

@@ -132,6 +132,62 @@ pub fn find_feature_issue(feature: Symbol, issue: GateIssue) -> Option<NonZero<u
     }
 }
 
+#[derive(serde::Serialize)]
+enum LangFeature {
+    Unstable {
+        status: &'static str,
+        symbol: String,
+        since: &'static str,
+        issue: Option<NonZero<u32>>,
+    },
+    Accepted {
+        symbol: String,
+        since: &'static str,
+        issue: Option<NonZero<u32>>,
+    },
+    Removed {
+        symbol: String,
+        since: &'static str,
+        issue: Option<NonZero<u32>>,
+        reason: Option<&'static str>,
+    },
+}
+
+#[derive(serde::Serialize)]
+pub struct LangFeaturesStatus {
+    lang_features: Vec<LangFeature>,
+}
+
+/// Extract the status of all lang features as a json serializable struct
+pub fn lang_features_status() -> LangFeaturesStatus {
+    let unstable_lang_features =
+        UNSTABLE_LANG_FEATURES.iter().map(|feature| LangFeature::Unstable {
+            status: Features::feature_status(feature.name),
+            symbol: feature.name.to_string(),
+            since: feature.since,
+            issue: feature.issue,
+        });
+
+    let accepted_lang_features =
+        ACCEPTED_LANG_FEATURES.iter().map(|feature| LangFeature::Accepted {
+            symbol: feature.name.to_string(),
+            since: feature.since,
+            issue: feature.issue,
+        });
+
+    let removed_lang_features = REMOVED_LANG_FEATURES.iter().map(|removed| LangFeature::Removed {
+        symbol: removed.feature.name.to_string(),
+        since: removed.feature.since,
+        issue: removed.feature.issue,
+        reason: removed.reason,
+    });
+
+    let lang_features =
+        unstable_lang_features.chain(accepted_lang_features).chain(removed_lang_features).collect();
+
+    LangFeaturesStatus { lang_features }
+}
+
 pub use accepted::ACCEPTED_LANG_FEATURES;
 pub use builtin_attrs::{
     AttributeDuplicates, AttributeGate, AttributeSafety, AttributeTemplate, AttributeType,

compiler/rustc_feature/src/unstable.rs

@@ -99,6 +99,18 @@ impl Features {
     }
 }
 
+macro_rules! status_to_str {
+    (unstable) => {
+        "default"
+    };
+    (incomplete) => {
+        "incomplete"
+    };
+    (internal) => {
+        "internal"
+    };
+}
+
 macro_rules! declare_features {
     ($(
         $(#[doc = $doc:tt])* ($status:ident, $feature:ident, $ver:expr, $issue:expr),
@@ -159,6 +171,15 @@ macro_rules! declare_features {
                     _ => panic!("`{}` was not listed in `declare_features`", feature),
                 }
             }
+
+            pub fn feature_status(feature: Symbol) -> &'static str {
+                match feature {
+                    $(
+                    sym::$feature => status_to_str!($status),
+                    )*
+                    _ => panic!("`{}` was not listed in `declare_features`", feature),
+                }
+            }
         }
     };
 }

compiler/rustc_metadata/Cargo.toml

@@ -28,6 +28,7 @@ rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
 rustc_type_ir = { path = "../rustc_type_ir" }
+serde = { version = "1.0.125", features = [ "derive" ] }
 tempfile = "3.2"
 tracing = "0.1"
 # tidy-alphabetical-end

compiler/rustc_metadata/src/lib.rs

@@ -5,6 +5,7 @@
 #![feature(coroutines)]
 #![feature(decl_macro)]
 #![feature(error_iter)]
+#![feature(error_reporter)]
 #![feature(extract_if)]
 #![feature(file_buffered)]
 #![feature(if_let_guard)]
@@ -35,6 +36,7 @@ pub mod locator;
 
 pub use creader::{DylibError, load_symbol_from_dylib};
 pub use fs::{METADATA_FILENAME, emit_wrapper_file};
+pub use locator::lib_features_status;
 pub use native_libs::{
     find_native_static_library, try_find_native_dynamic_library, try_find_native_static_library,
     walk_native_lib_search_dirs,

compiler/rustc_metadata/src/locator.rs

@@ -213,6 +213,7 @@
 //! metadata::locator or metadata::creader for all the juicy details!
 
 use std::borrow::Cow;
+use std::error::Error;
 use std::io::{Result as IoResult, Write};
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
@@ -224,6 +225,7 @@ use rustc_data_structures::owned_slice::slice_owned;
 use rustc_data_structures::svh::Svh;
 use rustc_errors::{DiagArgValue, IntoDiagArg};
 use rustc_fs_util::try_canonicalize;
+use rustc_middle::middle::lib_features::FeatureStability;
 use rustc_session::Session;
 use rustc_session::cstore::CrateSource;
 use rustc_session::filesearch::FileSearch;
@@ -864,6 +866,88 @@ fn get_metadata_section<'p>(
     }
 }
 
+#[derive(serde::Serialize)]
+enum LibFeature {
+    Core { name: String, status: Status },
+    Std { name: String, status: Status },
+}
+
+#[derive(serde::Serialize)]
+enum Status {
+    AcceptedSince(String),
+    Unstable,
+}
+
+#[derive(serde::Serialize)]
+pub struct LibFeaturesStatus {
+    lib_features: Vec<LibFeature>,
+}
+
+pub fn lib_features_status(
+    sess: &Session,
+    metadata_loader: &dyn MetadataLoader,
+) -> Result<LibFeaturesStatus, Box<dyn Error>> {
+    let is_rlib = true;
+    let hash = None;
+    let extra_filename = None;
+    let path_kind = PathKind::Crate;
+    let extra_prefix = "";
+
+    let mut core_locator = CrateLocator::new(
+        sess,
+        metadata_loader,
+        rustc_span::sym::core,
+        is_rlib,
+        hash,
+        extra_filename,
+        path_kind,
+    );
+    let Ok(Some(core)) = core_locator.find_library_crate(extra_prefix, &mut FxHashSet::default())
+    else {
+        Err("unable to locate core library")?
+    };
+    let mut std_locator = CrateLocator::new(
+        sess,
+        metadata_loader,
+        rustc_span::sym::std,
+        is_rlib,
+        hash,
+        extra_filename,
+        path_kind,
+    );
+    let Ok(Some(std)) = std_locator.find_library_crate(extra_prefix, &mut FxHashSet::default())
+    else {
+        Err("unable to locate standard library")?
+    };
+
+    let core_features =
+        core.metadata.dump_crate_features_json().into_iter().map(|(name, status)| {
+            LibFeature::Core {
+                name,
+                status: match status {
+                    FeatureStability::AcceptedSince(symbol) => {
+                        Status::AcceptedSince(symbol.to_string())
+                    }
+                    FeatureStability::Unstable => Status::Unstable,
+                },
+            }
+        });
+    let std_features =
+        std.metadata.dump_crate_features_json().into_iter().map(|(name, status)| LibFeature::Std {
+            name,
+            status: match status {
+                FeatureStability::AcceptedSince(symbol) => {
+                    Status::AcceptedSince(symbol.to_string())
+                }
+                FeatureStability::Unstable => Status::Unstable,
+            },
+        });
+
+    let lib_features = core_features.chain(std_features).collect();
+
+    Ok(LibFeaturesStatus { lib_features })
+}
+
 /// A diagnostic function for dumping crate metadata to an output stream.
 pub fn list_file_metadata(
     target: &Target,

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -935,6 +935,14 @@ impl MetadataBlob {
 
         Ok(())
     }
+
+    pub(crate) fn dump_crate_features_json(&self) -> Vec<(String, FeatureStability)> {
+        let root = self.get_root();
+        root.lib_features
+            .decode(self)
+            .map(|(symbol, status)| (symbol.to_string(), status))
+            .collect()
+    }
 }
 
 impl CrateRoot {

compiler/rustc_session/src/options.rs

@@ -1730,6 +1730,8 @@ options! {
     dump_dep_graph: bool = (false, parse_bool, [UNTRACKED],
         "dump the dependency graph to $RUST_DEP_GRAPH (default: /tmp/dep_graph.gv) \
         (default: no)"),
+    dump_features_status: bool = (false, parse_bool, [UNTRACKED],
+        "dump the status of rust language and library features as json"),
     dump_mir: Option<String> = (None, parse_opt_string, [UNTRACKED],
         "dump MIR state to file.
         `val` is used to select which passes and functions to dump. For example: