Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1599 insertions, 0 deletions

diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
new file mode 100644
index 000000000..9669287b3
--- /dev/null
+++ b/compiler/rustc_session/src/session.rs
@@ -0,0 +1,1599 @@
+use crate::cgu_reuse_tracker::CguReuseTracker;
+use crate::code_stats::CodeStats;
+pub use crate::code_stats::{DataTypeKind, FieldInfo, SizeKind, VariantInfo};
+use crate::config::{self, CrateType, InstrumentCoverage, OptLevel, OutputType, SwitchWithOptPath};
+use crate::parse::{add_feature_diagnostics, ParseSess};
+use crate::search_paths::{PathKind, SearchPath};
+use crate::{filesearch, lint};
+
+pub use rustc_ast::attr::MarkedAttrs;
+pub use rustc_ast::Attribute;
+use rustc_data_structures::flock;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::jobserver::{self, Client};
+use rustc_data_structures::profiling::{duration_to_secs_str, SelfProfiler, SelfProfilerRef};
+use rustc_data_structures::sync::{
+    self, AtomicU64, AtomicUsize, Lock, Lrc, OnceCell, OneThread, Ordering, Ordering::SeqCst,
+};
+use rustc_errors::annotate_snippet_emitter_writer::AnnotateSnippetEmitterWriter;
+use rustc_errors::emitter::{Emitter, EmitterWriter, HumanReadableErrorType};
+use rustc_errors::json::JsonEmitter;
+use rustc_errors::registry::Registry;
+use rustc_errors::{
+    fallback_fluent_bundle, DiagnosticBuilder, DiagnosticId, DiagnosticMessage, EmissionGuarantee,
+    ErrorGuaranteed, FluentBundle, LazyFallbackBundle, MultiSpan,
+};
+use rustc_macros::HashStable_Generic;
+pub use rustc_span::def_id::StableCrateId;
+use rustc_span::edition::Edition;
+use rustc_span::source_map::{FileLoader, RealFileLoader, SourceMap, Span};
+use rustc_span::{sym, SourceFileHashAlgorithm, Symbol};
+use rustc_target::asm::InlineAsmArch;
+use rustc_target::spec::{CodeModel, PanicStrategy, RelocModel, RelroLevel};
+use rustc_target::spec::{
+    SanitizerSet, SplitDebuginfo, StackProtector, Target, TargetTriple, TlsModel,
+};
+
+use std::cell::{self, RefCell};
+use std::env;
+use std::fmt;
+use std::io::Write;
+use std::ops::{Div, Mul};
+use std::path::{Path, PathBuf};
+use std::str::FromStr;
+use std::sync::Arc;
+use std::time::Duration;
+
+pub struct OptimizationFuel {
+    /// If `-zfuel=crate=n` is specified, initially set to `n`, otherwise `0`.
+    remaining: u64,
+    /// We're rejecting all further optimizations.
+    out_of_fuel: bool,
+}
+
+/// The behavior of the CTFE engine when an error occurs with regards to backtraces.
+#[derive(Clone, Copy)]
+pub enum CtfeBacktrace {
+    /// Do nothing special, return the error as usual without a backtrace.
+    Disabled,
+    /// Capture a backtrace at the point the error is created and return it in the error
+    /// (to be printed later if/when the error ever actually gets shown to the user).
+    Capture,
+    /// Capture a backtrace at the point the error is created and immediately print it out.
+    Immediate,
+}
+
+/// New-type wrapper around `usize` for representing limits. Ensures that comparisons against
+/// limits are consistent throughout the compiler.
+#[derive(Clone, Copy, Debug, HashStable_Generic)]
+pub struct Limit(pub usize);
+
+impl Limit {
+    /// Create a new limit from a `usize`.
+    pub fn new(value: usize) -> Self {
+        Limit(value)
+    }
+
+    /// Check that `value` is within the limit. Ensures that the same comparisons are used
+    /// throughout the compiler, as mismatches can cause ICEs, see #72540.
+    #[inline]
+    pub fn value_within_limit(&self, value: usize) -> bool {
+        value <= self.0
+    }
+}
+
+impl From<usize> for Limit {
+    fn from(value: usize) -> Self {
+        Self::new(value)
+    }
+}
+
+impl fmt::Display for Limit {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+impl Div<usize> for Limit {
+    type Output = Limit;
+
+    fn div(self, rhs: usize) -> Self::Output {
+        Limit::new(self.0 / rhs)
+    }
+}
+
+impl Mul<usize> for Limit {
+    type Output = Limit;
+
+    fn mul(self, rhs: usize) -> Self::Output {
+        Limit::new(self.0 * rhs)
+    }
+}
+
+#[derive(Clone, Copy, Debug, HashStable_Generic)]
+pub struct Limits {
+    /// The maximum recursion limit for potentially infinitely recursive
+    /// operations such as auto-dereference and monomorphization.
+    pub recursion_limit: Limit,
+    /// The size at which the `large_assignments` lint starts
+    /// being emitted.
+    pub move_size_limit: Limit,
+    /// The maximum length of types during monomorphization.
+    pub type_length_limit: Limit,
+    /// The maximum blocks a const expression can evaluate.
+    pub const_eval_limit: Limit,
+}
+
+/// Represents the data associated with a compilation
+/// session for a single crate.
+pub struct Session {
+    pub target: Target,
+    pub host: Target,
+    pub opts: config::Options,
+    pub host_tlib_path: Lrc<SearchPath>,
+    pub target_tlib_path: Lrc<SearchPath>,
+    pub parse_sess: ParseSess,
+    pub sysroot: PathBuf,
+    /// The name of the root source file of the crate, in the local file system.
+    /// `None` means that there is no source file.
+    pub local_crate_source_file: Option<PathBuf>,
+
+    crate_types: OnceCell<Vec<CrateType>>,
+    /// The `stable_crate_id` is constructed out of the crate name and all the
+    /// `-C metadata` arguments passed to the compiler. Its value forms a unique
+    /// global identifier for the crate. It is used to allow multiple crates
+    /// with the same name to coexist. See the
+    /// `rustc_codegen_llvm::back::symbol_names` module for more information.
+    pub stable_crate_id: OnceCell<StableCrateId>,
+
+    features: OnceCell<rustc_feature::Features>,
+
+    incr_comp_session: OneThread<RefCell<IncrCompSession>>,
+    /// Used for incremental compilation tests. Will only be populated if
+    /// `-Zquery-dep-graph` is specified.
+    pub cgu_reuse_tracker: CguReuseTracker,
+
+    /// Used by `-Z self-profile`.
+    pub prof: SelfProfilerRef,
+
+    /// Some measurements that are being gathered during compilation.
+    pub perf_stats: PerfStats,
+
+    /// Data about code being compiled, gathered during compilation.
+    pub code_stats: CodeStats,
+
+    /// Tracks fuel info if `-zfuel=crate=n` is specified.
+    optimization_fuel: Lock<OptimizationFuel>,
+
+    /// Always set to zero and incremented so that we can print fuel expended by a crate.
+    pub print_fuel: AtomicU64,
+
+    /// Loaded up early on in the initialization of this `Session` to avoid
+    /// false positives about a job server in our environment.
+    pub jobserver: Client,
+
+    /// Cap lint level specified by a driver specifically.
+    pub driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
+
+    /// Tracks the current behavior of the CTFE engine when an error occurs.
+    /// Options range from returning the error without a backtrace to returning an error
+    /// and immediately printing the backtrace to stderr.
+    /// The `Lock` is only used by miri to allow setting `ctfe_backtrace` after analysis when
+    /// `MIRI_BACKTRACE` is set. This makes it only apply to miri's errors and not to all CTFE
+    /// errors.
+    pub ctfe_backtrace: Lock<CtfeBacktrace>,
+
+    /// This tracks where `-Zunleash-the-miri-inside-of-you` was used to get around a
+    /// const check, optionally with the relevant feature gate.  We use this to
+    /// warn about unleashing, but with a single diagnostic instead of dozens that
+    /// drown everything else in noise.
+    miri_unleashed_features: Lock<Vec<(Span, Option<Symbol>)>>,
+
+    /// Architecture to use for interpreting asm!.
+    pub asm_arch: Option<InlineAsmArch>,
+
+    /// Set of enabled features for the current target.
+    pub target_features: FxHashSet<Symbol>,
+
+    /// Set of enabled features for the current target, including unstable ones.
+    pub unstable_target_features: FxHashSet<Symbol>,
+}
+
+pub struct PerfStats {
+    /// The accumulated time spent on computing symbol hashes.
+    pub symbol_hash_time: Lock<Duration>,
+    /// Total number of values canonicalized queries constructed.
+    pub queries_canonicalized: AtomicUsize,
+    /// Number of times this query is invoked.
+    pub normalize_generic_arg_after_erasing_regions: AtomicUsize,
+    /// Number of times this query is invoked.
+    pub normalize_projection_ty: AtomicUsize,
+}
+
+/// Trait implemented by error types. This should not be implemented manually. Instead, use
+/// `#[derive(SessionDiagnostic)]` -- see [rustc_macros::SessionDiagnostic].
+#[rustc_diagnostic_item = "SessionDiagnostic"]
+pub trait SessionDiagnostic<'a, T: EmissionGuarantee = ErrorGuaranteed> {
+    /// Write out as a diagnostic out of `sess`.
+    #[must_use]
+    fn into_diagnostic(self, sess: &'a ParseSess) -> DiagnosticBuilder<'a, T>;
+}
+
+impl Session {
+    pub fn miri_unleashed_feature(&self, span: Span, feature_gate: Option<Symbol>) {
+        self.miri_unleashed_features.lock().push((span, feature_gate));
+    }
+
+    fn check_miri_unleashed_features(&self) {
+        let unleashed_features = self.miri_unleashed_features.lock();
+        if !unleashed_features.is_empty() {
+            let mut must_err = false;
+            // Create a diagnostic pointing at where things got unleashed.
+            let mut diag = self.struct_warn("skipping const checks");
+            for &(span, feature_gate) in unleashed_features.iter() {
+                // FIXME: `span_label` doesn't do anything, so we use "help" as a hack.
+                if let Some(gate) = feature_gate {
+                    diag.span_help(span, &format!("skipping check for `{gate}` feature"));
+                    // The unleash flag must *not* be used to just "hack around" feature gates.
+                    must_err = true;
+                } else {
+                    diag.span_help(span, "skipping check that does not even have a feature gate");
+                }
+            }
+            diag.emit();
+            // If we should err, make sure we did.
+            if must_err && self.has_errors().is_none() {
+                // We have skipped a feature gate, and not run into other errors... reject.
+                self.err(
+                    "`-Zunleash-the-miri-inside-of-you` may not be used to circumvent feature \
+                     gates, except when testing error paths in the CTFE engine",
+                );
+            }
+        }
+    }
+
+    /// Invoked all the way at the end to finish off diagnostics printing.
+    pub fn finish_diagnostics(&self, registry: &Registry) {
+        self.check_miri_unleashed_features();
+        self.diagnostic().print_error_count(registry);
+        self.emit_future_breakage();
+    }
+
+    fn emit_future_breakage(&self) {
+        if !self.opts.json_future_incompat {
+            return;
+        }
+
+        let diags = self.diagnostic().take_future_breakage_diagnostics();
+        if diags.is_empty() {
+            return;
+        }
+        self.parse_sess.span_diagnostic.emit_future_breakage_report(diags);
+    }
+
+    pub fn local_stable_crate_id(&self) -> StableCrateId {
+        self.stable_crate_id.get().copied().unwrap()
+    }
+
+    pub fn crate_types(&self) -> &[CrateType] {
+        self.crate_types.get().unwrap().as_slice()
+    }
+
+    pub fn init_crate_types(&self, crate_types: Vec<CrateType>) {
+        self.crate_types.set(crate_types).expect("`crate_types` was initialized twice")
+    }
+
+    #[rustc_lint_diagnostics]
+    pub fn struct_span_warn<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> DiagnosticBuilder<'_, ()> {
+        self.diagnostic().struct_span_warn(sp, msg)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_span_warn_with_expectation<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+        id: lint::LintExpectationId,
+    ) -> DiagnosticBuilder<'_, ()> {
+        self.diagnostic().struct_span_warn_with_expectation(sp, msg, id)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_span_warn_with_code<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+        code: DiagnosticId,
+    ) -> DiagnosticBuilder<'_, ()> {
+        self.diagnostic().struct_span_warn_with_code(sp, msg, code)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_warn(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, ()> {
+        self.diagnostic().struct_warn(msg)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_warn_with_expectation(
+        &self,
+        msg: impl Into<DiagnosticMessage>,
+        id: lint::LintExpectationId,
+    ) -> DiagnosticBuilder<'_, ()> {
+        self.diagnostic().struct_warn_with_expectation(msg, id)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_span_allow<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> DiagnosticBuilder<'_, ()> {
+        self.diagnostic().struct_span_allow(sp, msg)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_allow(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, ()> {
+        self.diagnostic().struct_allow(msg)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_expect(
+        &self,
+        msg: impl Into<DiagnosticMessage>,
+        id: lint::LintExpectationId,
+    ) -> DiagnosticBuilder<'_, ()> {
+        self.diagnostic().struct_expect(msg, id)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_span_err<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+        self.diagnostic().struct_span_err(sp, msg)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_span_err_with_code<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+        code: DiagnosticId,
+    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+        self.diagnostic().struct_span_err_with_code(sp, msg, code)
+    }
+    // FIXME: This method should be removed (every error should have an associated error code).
+    #[rustc_lint_diagnostics]
+    pub fn struct_err(
+        &self,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+        self.parse_sess.struct_err(msg)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_err_with_code(
+        &self,
+        msg: impl Into<DiagnosticMessage>,
+        code: DiagnosticId,
+    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+        self.diagnostic().struct_err_with_code(msg, code)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_warn_with_code(
+        &self,
+        msg: impl Into<DiagnosticMessage>,
+        code: DiagnosticId,
+    ) -> DiagnosticBuilder<'_, ()> {
+        self.diagnostic().struct_warn_with_code(msg, code)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_span_fatal<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> DiagnosticBuilder<'_, !> {
+        self.diagnostic().struct_span_fatal(sp, msg)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_span_fatal_with_code<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+        code: DiagnosticId,
+    ) -> DiagnosticBuilder<'_, !> {
+        self.diagnostic().struct_span_fatal_with_code(sp, msg, code)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn struct_fatal(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, !> {
+        self.diagnostic().struct_fatal(msg)
+    }
+
+    #[rustc_lint_diagnostics]
+    pub fn span_fatal<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<DiagnosticMessage>) -> ! {
+        self.diagnostic().span_fatal(sp, msg)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn span_fatal_with_code<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+        code: DiagnosticId,
+    ) -> ! {
+        self.diagnostic().span_fatal_with_code(sp, msg, code)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn fatal(&self, msg: impl Into<DiagnosticMessage>) -> ! {
+        self.diagnostic().fatal(msg).raise()
+    }
+    #[rustc_lint_diagnostics]
+    pub fn span_err_or_warn<S: Into<MultiSpan>>(
+        &self,
+        is_warning: bool,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+    ) {
+        if is_warning {
+            self.span_warn(sp, msg);
+        } else {
+            self.span_err(sp, msg);
+        }
+    }
+    #[rustc_lint_diagnostics]
+    pub fn span_err<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> ErrorGuaranteed {
+        self.diagnostic().span_err(sp, msg)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn span_err_with_code<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+        code: DiagnosticId,
+    ) {
+        self.diagnostic().span_err_with_code(sp, msg, code)
+    }
+    #[rustc_lint_diagnostics]
+    pub fn err(&self, msg: impl Into<DiagnosticMessage>) -> ErrorGuaranteed {
+        self.diagnostic().err(msg)
+    }
+    pub fn create_err<'a>(
+        &'a self,
+        err: impl SessionDiagnostic<'a>,
+    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+        self.parse_sess.create_err(err)
+    }
+    pub fn create_feature_err<'a>(
+        &'a self,
+        err: impl SessionDiagnostic<'a>,
+        feature: Symbol,
+    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+        let mut err = self.parse_sess.create_err(err);
+        add_feature_diagnostics(&mut err, &self.parse_sess, feature);
+        err
+    }
+    pub fn emit_err<'a>(&'a self, err: impl SessionDiagnostic<'a>) -> ErrorGuaranteed {
+        self.parse_sess.emit_err(err)
+    }
+    pub fn create_warning<'a>(
+        &'a self,
+        err: impl SessionDiagnostic<'a, ()>,
+    ) -> DiagnosticBuilder<'a, ()> {
+        self.parse_sess.create_warning(err)
+    }
+    pub fn emit_warning<'a>(&'a self, warning: impl SessionDiagnostic<'a, ()>) {
+        self.parse_sess.emit_warning(warning)
+    }
+    #[inline]
+    pub fn err_count(&self) -> usize {
+        self.diagnostic().err_count()
+    }
+    pub fn has_errors(&self) -> Option<ErrorGuaranteed> {
+        self.diagnostic().has_errors()
+    }
+    pub fn has_errors_or_delayed_span_bugs(&self) -> bool {
+        self.diagnostic().has_errors_or_delayed_span_bugs()
+    }
+    pub fn abort_if_errors(&self) {
+        self.diagnostic().abort_if_errors();
+    }
+    pub fn compile_status(&self) -> Result<(), ErrorGuaranteed> {
+        if let Some(reported) = self.diagnostic().has_errors_or_lint_errors() {
+            let _ = self.diagnostic().emit_stashed_diagnostics();
+            Err(reported)
+        } else {
+            Ok(())
+        }
+    }
+    // FIXME(matthewjasper) Remove this method, it should never be needed.
+    pub fn track_errors<F, T>(&self, f: F) -> Result<T, ErrorGuaranteed>
+    where
+        F: FnOnce() -> T,
+    {
+        let old_count = self.err_count();
+        let result = f();
+        if self.err_count() == old_count {
+            Ok(result)
+        } else {
+            Err(ErrorGuaranteed::unchecked_claim_error_was_emitted())
+        }
+    }
+    pub fn span_warn<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<DiagnosticMessage>) {
+        self.diagnostic().span_warn(sp, msg)
+    }
+    pub fn span_warn_with_code<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+        code: DiagnosticId,
+    ) {
+        self.diagnostic().span_warn_with_code(sp, msg, code)
+    }
+    pub fn warn(&self, msg: impl Into<DiagnosticMessage>) {
+        self.diagnostic().warn(msg)
+    }
+    /// Delay a span_bug() call until abort_if_errors()
+    #[track_caller]
+    pub fn delay_span_bug<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> ErrorGuaranteed {
+        self.diagnostic().delay_span_bug(sp, msg)
+    }
+
+    /// Used for code paths of expensive computations that should only take place when
+    /// warnings or errors are emitted. If no messages are emitted ("good path"), then
+    /// it's likely a bug.
+    pub fn delay_good_path_bug(&self, msg: impl Into<DiagnosticMessage>) {
+        if self.opts.unstable_opts.print_type_sizes
+            || self.opts.unstable_opts.query_dep_graph
+            || self.opts.unstable_opts.dump_mir.is_some()
+            || self.opts.unstable_opts.unpretty.is_some()
+            || self.opts.output_types.contains_key(&OutputType::Mir)
+            || std::env::var_os("RUSTC_LOG").is_some()
+        {
+            return;
+        }
+
+        self.diagnostic().delay_good_path_bug(msg)
+    }
+
+    pub fn note_without_error(&self, msg: impl Into<DiagnosticMessage>) {
+        self.diagnostic().note_without_error(msg)
+    }
+    pub fn span_note_without_error<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        msg: impl Into<DiagnosticMessage>,
+    ) {
+        self.diagnostic().span_note_without_error(sp, msg)
+    }
+    pub fn struct_note_without_error(
+        &self,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> DiagnosticBuilder<'_, ()> {
+        self.diagnostic().struct_note_without_error(msg)
+    }
+
+    #[inline]
+    pub fn diagnostic(&self) -> &rustc_errors::Handler {
+        &self.parse_sess.span_diagnostic
+    }
+
+    #[inline]
+    pub fn source_map(&self) -> &SourceMap {
+        self.parse_sess.source_map()
+    }
+
+    pub fn time_passes(&self) -> bool {
+        self.opts.time_passes()
+    }
+
+    /// Returns `true` if internal lints should be added to the lint store - i.e. if
+    /// `-Zunstable-options` is provided and this isn't rustdoc (internal lints can trigger errors
+    /// to be emitted under rustdoc).
+    pub fn enable_internal_lints(&self) -> bool {
+        self.unstable_options() && !self.opts.actually_rustdoc
+    }
+
+    pub fn instrument_coverage(&self) -> bool {
+        self.opts.cg.instrument_coverage() != InstrumentCoverage::Off
+    }
+
+    pub fn instrument_coverage_except_unused_generics(&self) -> bool {
+        self.opts.cg.instrument_coverage() == InstrumentCoverage::ExceptUnusedGenerics
+    }
+
+    pub fn instrument_coverage_except_unused_functions(&self) -> bool {
+        self.opts.cg.instrument_coverage() == InstrumentCoverage::ExceptUnusedFunctions
+    }
+
+    /// Gets the features enabled for the current compilation session.
+    /// DO NOT USE THIS METHOD if there is a TyCtxt available, as it circumvents
+    /// dependency tracking. Use tcx.features() instead.
+    #[inline]
+    pub fn features_untracked(&self) -> &rustc_feature::Features {
+        self.features.get().unwrap()
+    }
+
+    pub fn init_features(&self, features: rustc_feature::Features) {
+        match self.features.set(features) {
+            Ok(()) => {}
+            Err(_) => panic!("`features` was initialized twice"),
+        }
+    }
+
+    pub fn is_sanitizer_cfi_enabled(&self) -> bool {
+        self.opts.unstable_opts.sanitizer.contains(SanitizerSet::CFI)
+    }
+
+    /// Check whether this compile session and crate type use static crt.
+    pub fn crt_static(&self, crate_type: Option<CrateType>) -> bool {
+        if !self.target.crt_static_respected {
+            // If the target does not opt in to crt-static support, use its default.
+            return self.target.crt_static_default;
+        }
+
+        let requested_features = self.opts.cg.target_feature.split(',');
+        let found_negative = requested_features.clone().any(|r| r == "-crt-static");
+        let found_positive = requested_features.clone().any(|r| r == "+crt-static");
+
+        // JUSTIFICATION: necessary use of crate_types directly (see FIXME below)
+        #[cfg_attr(not(bootstrap), allow(rustc::bad_opt_access))]
+        if found_positive || found_negative {
+            found_positive
+        } else if crate_type == Some(CrateType::ProcMacro)
+            || crate_type == None && self.opts.crate_types.contains(&CrateType::ProcMacro)
+        {
+            // FIXME: When crate_type is not available,
+            // we use compiler options to determine the crate_type.
+            // We can't check `#![crate_type = "proc-macro"]` here.
+            false
+        } else {
+            self.target.crt_static_default
+        }
+    }
+
+    pub fn is_wasi_reactor(&self) -> bool {
+        self.target.options.os == "wasi"
+            && matches!(
+                self.opts.unstable_opts.wasi_exec_model,
+                Some(config::WasiExecModel::Reactor)
+            )
+    }
+
+    pub fn target_can_use_split_dwarf(&self) -> bool {
+        !self.target.is_like_windows && !self.target.is_like_osx
+    }
+
+    pub fn generate_proc_macro_decls_symbol(&self, stable_crate_id: StableCrateId) -> String {
+        format!("__rustc_proc_macro_decls_{:08x}__", stable_crate_id.to_u64())
+    }
+
+    pub fn target_filesearch(&self, kind: PathKind) -> filesearch::FileSearch<'_> {
+        filesearch::FileSearch::new(
+            &self.sysroot,
+            self.opts.target_triple.triple(),
+            &self.opts.search_paths,
+            &self.target_tlib_path,
+            kind,
+        )
+    }
+    pub fn host_filesearch(&self, kind: PathKind) -> filesearch::FileSearch<'_> {
+        filesearch::FileSearch::new(
+            &self.sysroot,
+            config::host_triple(),
+            &self.opts.search_paths,
+            &self.host_tlib_path,
+            kind,
+        )
+    }
+
+    /// Returns a list of directories where target-specific tool binaries are located.
+    pub fn get_tools_search_paths(&self, self_contained: bool) -> Vec<PathBuf> {
+        let rustlib_path = rustc_target::target_rustlib_path(&self.sysroot, &config::host_triple());
+        let p = PathBuf::from_iter([
+            Path::new(&self.sysroot),
+            Path::new(&rustlib_path),
+            Path::new("bin"),
+        ]);
+        if self_contained { vec![p.clone(), p.join("self-contained")] } else { vec![p] }
+    }
+
+    pub fn init_incr_comp_session(
+        &self,
+        session_dir: PathBuf,
+        lock_file: flock::Lock,
+        load_dep_graph: bool,
+    ) {
+        let mut incr_comp_session = self.incr_comp_session.borrow_mut();
+
+        if let IncrCompSession::NotInitialized = *incr_comp_session {
+        } else {
+            panic!("Trying to initialize IncrCompSession `{:?}`", *incr_comp_session)
+        }
+
+        *incr_comp_session =
+            IncrCompSession::Active { session_directory: session_dir, lock_file, load_dep_graph };
+    }
+
+    pub fn finalize_incr_comp_session(&self, new_directory_path: PathBuf) {
+        let mut incr_comp_session = self.incr_comp_session.borrow_mut();
+
+        if let IncrCompSession::Active { .. } = *incr_comp_session {
+        } else {
+            panic!("trying to finalize `IncrCompSession` `{:?}`", *incr_comp_session);
+        }
+
+        // Note: this will also drop the lock file, thus unlocking the directory.
+        *incr_comp_session = IncrCompSession::Finalized { session_directory: new_directory_path };
+    }
+
+    pub fn mark_incr_comp_session_as_invalid(&self) {
+        let mut incr_comp_session = self.incr_comp_session.borrow_mut();
+
+        let session_directory = match *incr_comp_session {
+            IncrCompSession::Active { ref session_directory, .. } => session_directory.clone(),
+            IncrCompSession::InvalidBecauseOfErrors { .. } => return,
+            _ => panic!("trying to invalidate `IncrCompSession` `{:?}`", *incr_comp_session),
+        };
+
+        // Note: this will also drop the lock file, thus unlocking the directory.
+        *incr_comp_session = IncrCompSession::InvalidBecauseOfErrors { session_directory };
+    }
+
+    pub fn incr_comp_session_dir(&self) -> cell::Ref<'_, PathBuf> {
+        let incr_comp_session = self.incr_comp_session.borrow();
+        cell::Ref::map(incr_comp_session, |incr_comp_session| match *incr_comp_session {
+            IncrCompSession::NotInitialized => panic!(
+                "trying to get session directory from `IncrCompSession`: {:?}",
+                *incr_comp_session,
+            ),
+            IncrCompSession::Active { ref session_directory, .. }
+            | IncrCompSession::Finalized { ref session_directory }
+            | IncrCompSession::InvalidBecauseOfErrors { ref session_directory } => {
+                session_directory
+            }
+        })
+    }
+
+    pub fn incr_comp_session_dir_opt(&self) -> Option<cell::Ref<'_, PathBuf>> {
+        self.opts.incremental.as_ref().map(|_| self.incr_comp_session_dir())
+    }
+
+    pub fn print_perf_stats(&self) {
+        eprintln!(
+            "Total time spent computing symbol hashes:      {}",
+            duration_to_secs_str(*self.perf_stats.symbol_hash_time.lock())
+        );
+        eprintln!(
+            "Total queries canonicalized:                   {}",
+            self.perf_stats.queries_canonicalized.load(Ordering::Relaxed)
+        );
+        eprintln!(
+            "normalize_generic_arg_after_erasing_regions:   {}",
+            self.perf_stats.normalize_generic_arg_after_erasing_regions.load(Ordering::Relaxed)
+        );
+        eprintln!(
+            "normalize_projection_ty:                       {}",
+            self.perf_stats.normalize_projection_ty.load(Ordering::Relaxed)
+        );
+    }
+
+    /// We want to know if we're allowed to do an optimization for crate foo from -z fuel=foo=n.
+    /// This expends fuel if applicable, and records fuel if applicable.
+    pub fn consider_optimizing<T: Fn() -> String>(&self, crate_name: &str, msg: T) -> bool {
+        let mut ret = true;
+        if let Some((ref c, _)) = self.opts.unstable_opts.fuel {
+            if c == crate_name {
+                assert_eq!(self.threads(), 1);
+                let mut fuel = self.optimization_fuel.lock();
+                ret = fuel.remaining != 0;
+                if fuel.remaining == 0 && !fuel.out_of_fuel {
+                    if self.diagnostic().can_emit_warnings() {
+                        // We only call `msg` in case we can actually emit warnings.
+                        // Otherwise, this could cause a `delay_good_path_bug` to
+                        // trigger (issue #79546).
+                        self.warn(&format!("optimization-fuel-exhausted: {}", msg()));
+                    }
+                    fuel.out_of_fuel = true;
+                } else if fuel.remaining > 0 {
+                    fuel.remaining -= 1;
+                }
+            }
+        }
+        if let Some(ref c) = self.opts.unstable_opts.print_fuel {
+            if c == crate_name {
+                assert_eq!(self.threads(), 1);
+                self.print_fuel.fetch_add(1, SeqCst);
+            }
+        }
+        ret
+    }
+
+    pub fn rust_2015(&self) -> bool {
+        self.edition() == Edition::Edition2015
+    }
+
+    /// Are we allowed to use features from the Rust 2018 edition?
+    pub fn rust_2018(&self) -> bool {
+        self.edition() >= Edition::Edition2018
+    }
+
+    /// Are we allowed to use features from the Rust 2021 edition?
+    pub fn rust_2021(&self) -> bool {
+        self.edition() >= Edition::Edition2021
+    }
+
+    /// Are we allowed to use features from the Rust 2024 edition?
+    pub fn rust_2024(&self) -> bool {
+        self.edition() >= Edition::Edition2024
+    }
+
+    /// Returns `true` if we cannot skip the PLT for shared library calls.
+    pub fn needs_plt(&self) -> bool {
+        // Check if the current target usually needs PLT to be enabled.
+        // The user can use the command line flag to override it.
+        let needs_plt = self.target.needs_plt;
+
+        let dbg_opts = &self.opts.unstable_opts;
+
+        let relro_level = dbg_opts.relro_level.unwrap_or(self.target.relro_level);
+
+        // Only enable this optimization by default if full relro is also enabled.
+        // In this case, lazy binding was already unavailable, so nothing is lost.
+        // This also ensures `-Wl,-z,now` is supported by the linker.
+        let full_relro = RelroLevel::Full == relro_level;
+
+        // If user didn't explicitly forced us to use / skip the PLT,
+        // then try to skip it where possible.
+        dbg_opts.plt.unwrap_or(needs_plt || !full_relro)
+    }
+
+    /// Checks if LLVM lifetime markers should be emitted.
+    pub fn emit_lifetime_markers(&self) -> bool {
+        self.opts.optimize != config::OptLevel::No
+        // AddressSanitizer uses lifetimes to detect use after scope bugs.
+        // MemorySanitizer uses lifetimes to detect use of uninitialized stack variables.
+        // HWAddressSanitizer will use lifetimes to detect use after scope bugs in the future.
+        || self.opts.unstable_opts.sanitizer.intersects(SanitizerSet::ADDRESS | SanitizerSet::MEMORY | SanitizerSet::HWADDRESS)
+    }
+
+    pub fn is_proc_macro_attr(&self, attr: &Attribute) -> bool {
+        [sym::proc_macro, sym::proc_macro_attribute, sym::proc_macro_derive]
+            .iter()
+            .any(|kind| attr.has_name(*kind))
+    }
+
+    pub fn contains_name(&self, attrs: &[Attribute], name: Symbol) -> bool {
+        attrs.iter().any(|item| item.has_name(name))
+    }
+
+    pub fn find_by_name<'a>(
+        &'a self,
+        attrs: &'a [Attribute],
+        name: Symbol,
+    ) -> Option<&'a Attribute> {
+        attrs.iter().find(|attr| attr.has_name(name))
+    }
+
+    pub fn filter_by_name<'a>(
+        &'a self,
+        attrs: &'a [Attribute],
+        name: Symbol,
+    ) -> impl Iterator<Item = &'a Attribute> {
+        attrs.iter().filter(move |attr| attr.has_name(name))
+    }
+
+    pub fn first_attr_value_str_by_name(
+        &self,
+        attrs: &[Attribute],
+        name: Symbol,
+    ) -> Option<Symbol> {
+        attrs.iter().find(|at| at.has_name(name)).and_then(|at| at.value_str())
+    }
+}
+
+// JUSTIFICATION: defn of the suggested wrapper fns
+#[cfg_attr(not(bootstrap), allow(rustc::bad_opt_access))]
+impl Session {
+    pub fn verbose(&self) -> bool {
+        self.opts.unstable_opts.verbose
+    }
+
+    pub fn instrument_mcount(&self) -> bool {
+        self.opts.unstable_opts.instrument_mcount
+    }
+
+    pub fn time_llvm_passes(&self) -> bool {
+        self.opts.unstable_opts.time_llvm_passes
+    }
+
+    pub fn meta_stats(&self) -> bool {
+        self.opts.unstable_opts.meta_stats
+    }
+
+    pub fn asm_comments(&self) -> bool {
+        self.opts.unstable_opts.asm_comments
+    }
+
+    pub fn verify_llvm_ir(&self) -> bool {
+        self.opts.unstable_opts.verify_llvm_ir || option_env!("RUSTC_VERIFY_LLVM_IR").is_some()
+    }
+
+    pub fn print_llvm_passes(&self) -> bool {
+        self.opts.unstable_opts.print_llvm_passes
+    }
+
+    pub fn binary_dep_depinfo(&self) -> bool {
+        self.opts.unstable_opts.binary_dep_depinfo
+    }
+
+    pub fn mir_opt_level(&self) -> usize {
+        self.opts
+            .unstable_opts
+            .mir_opt_level
+            .unwrap_or_else(|| if self.opts.optimize != OptLevel::No { 2 } else { 1 })
+    }
+
+    /// Calculates the flavor of LTO to use for this compilation.
+    pub fn lto(&self) -> config::Lto {
+        // If our target has codegen requirements ignore the command line
+        if self.target.requires_lto {
+            return config::Lto::Fat;
+        }
+
+        // If the user specified something, return that. If they only said `-C
+        // lto` and we've for whatever reason forced off ThinLTO via the CLI,
+        // then ensure we can't use a ThinLTO.
+        match self.opts.cg.lto {
+            config::LtoCli::Unspecified => {
+                // The compiler was invoked without the `-Clto` flag. Fall
+                // through to the default handling
+            }
+            config::LtoCli::No => {
+                // The user explicitly opted out of any kind of LTO
+                return config::Lto::No;
+            }
+            config::LtoCli::Yes | config::LtoCli::Fat | config::LtoCli::NoParam => {
+                // All of these mean fat LTO
+                return config::Lto::Fat;
+            }
+            config::LtoCli::Thin => {
+                return if self.opts.cli_forced_thinlto_off {
+                    config::Lto::Fat
+                } else {
+                    config::Lto::Thin
+                };
+            }
+        }
+
+        // Ok at this point the target doesn't require anything and the user
+        // hasn't asked for anything. Our next decision is whether or not
+        // we enable "auto" ThinLTO where we use multiple codegen units and
+        // then do ThinLTO over those codegen units. The logic below will
+        // either return `No` or `ThinLocal`.
+
+        // If processing command line options determined that we're incompatible
+        // with ThinLTO (e.g., `-C lto --emit llvm-ir`) then return that option.
+        if self.opts.cli_forced_thinlto_off {
+            return config::Lto::No;
+        }
+
+        // If `-Z thinlto` specified process that, but note that this is mostly
+        // a deprecated option now that `-C lto=thin` exists.
+        if let Some(enabled) = self.opts.unstable_opts.thinlto {
+            if enabled {
+                return config::Lto::ThinLocal;
+            } else {
+                return config::Lto::No;
+            }
+        }
+
+        // If there's only one codegen unit and LTO isn't enabled then there's
+        // no need for ThinLTO so just return false.
+        if self.codegen_units() == 1 {
+            return config::Lto::No;
+        }
+
+        // Now we're in "defaults" territory. By default we enable ThinLTO for
+        // optimized compiles (anything greater than O0).
+        match self.opts.optimize {
+            config::OptLevel::No => config::Lto::No,
+            _ => config::Lto::ThinLocal,
+        }
+    }
+
+    /// Returns the panic strategy for this compile session. If the user explicitly selected one
+    /// using '-C panic', use that, otherwise use the panic strategy defined by the target.
+    pub fn panic_strategy(&self) -> PanicStrategy {
+        self.opts.cg.panic.unwrap_or(self.target.panic_strategy)
+    }
+
+    pub fn fewer_names(&self) -> bool {
+        if let Some(fewer_names) = self.opts.unstable_opts.fewer_names {
+            fewer_names
+        } else {
+            let more_names = self.opts.output_types.contains_key(&OutputType::LlvmAssembly)
+                || self.opts.output_types.contains_key(&OutputType::Bitcode)
+                // AddressSanitizer and MemorySanitizer use alloca name when reporting an issue.
+                || self.opts.unstable_opts.sanitizer.intersects(SanitizerSet::ADDRESS | SanitizerSet::MEMORY);
+            !more_names
+        }
+    }
+
+    pub fn unstable_options(&self) -> bool {
+        self.opts.unstable_opts.unstable_options
+    }
+
+    pub fn is_nightly_build(&self) -> bool {
+        self.opts.unstable_features.is_nightly_build()
+    }
+
+    pub fn overflow_checks(&self) -> bool {
+        self.opts.cg.overflow_checks.unwrap_or(self.opts.debug_assertions)
+    }
+
+    pub fn relocation_model(&self) -> RelocModel {
+        self.opts.cg.relocation_model.unwrap_or(self.target.relocation_model)
+    }
+
+    pub fn code_model(&self) -> Option<CodeModel> {
+        self.opts.cg.code_model.or(self.target.code_model)
+    }
+
+    pub fn tls_model(&self) -> TlsModel {
+        self.opts.unstable_opts.tls_model.unwrap_or(self.target.tls_model)
+    }
+
+    pub fn split_debuginfo(&self) -> SplitDebuginfo {
+        self.opts.cg.split_debuginfo.unwrap_or(self.target.split_debuginfo)
+    }
+
+    pub fn stack_protector(&self) -> StackProtector {
+        if self.target.options.supports_stack_protector {
+            self.opts.unstable_opts.stack_protector
+        } else {
+            StackProtector::None
+        }
+    }
+
+    pub fn must_emit_unwind_tables(&self) -> bool {
+        // This is used to control the emission of the `uwtable` attribute on
+        // LLVM functions.
+        //
+        // Unwind tables are needed when compiling with `-C panic=unwind`, but
+        // LLVM won't omit unwind tables unless the function is also marked as
+        // `nounwind`, so users are allowed to disable `uwtable` emission.
+        // Historically rustc always emits `uwtable` attributes by default, so
+        // even they can be disabled, they're still emitted by default.
+        //
+        // On some targets (including windows), however, exceptions include
+        // other events such as illegal instructions, segfaults, etc. This means
+        // that on Windows we end up still needing unwind tables even if the `-C
+        // panic=abort` flag is passed.
+        //
+        // You can also find more info on why Windows needs unwind tables in:
+        //      https://bugzilla.mozilla.org/show_bug.cgi?id=1302078
+        //
+        // If a target requires unwind tables, then they must be emitted.
+        // Otherwise, we can defer to the `-C force-unwind-tables=<yes/no>`
+        // value, if it is provided, or disable them, if not.
+        self.target.requires_uwtable
+            || self.opts.cg.force_unwind_tables.unwrap_or(
+                self.panic_strategy() == PanicStrategy::Unwind || self.target.default_uwtable,
+            )
+    }
+
+    /// Returns the number of query threads that should be used for this
+    /// compilation
+    pub fn threads(&self) -> usize {
+        self.opts.unstable_opts.threads
+    }
+
+    /// Returns the number of codegen units that should be used for this
+    /// compilation
+    pub fn codegen_units(&self) -> usize {
+        if let Some(n) = self.opts.cli_forced_codegen_units {
+            return n;
+        }
+        if let Some(n) = self.target.default_codegen_units {
+            return n as usize;
+        }
+
+        // If incremental compilation is turned on, we default to a high number
+        // codegen units in order to reduce the "collateral damage" small
+        // changes cause.
+        if self.opts.incremental.is_some() {
+            return 256;
+        }
+
+        // Why is 16 codegen units the default all the time?
+        //
+        // The main reason for enabling multiple codegen units by default is to
+        // leverage the ability for the codegen backend to do codegen and
+        // optimization in parallel. This allows us, especially for large crates, to
+        // make good use of all available resources on the machine once we've
+        // hit that stage of compilation. Large crates especially then often
+        // take a long time in codegen/optimization and this helps us amortize that
+        // cost.
+        //
+        // Note that a high number here doesn't mean that we'll be spawning a
+        // large number of threads in parallel. The backend of rustc contains
+        // global rate limiting through the `jobserver` crate so we'll never
+        // overload the system with too much work, but rather we'll only be
+        // optimizing when we're otherwise cooperating with other instances of
+        // rustc.
+        //
+        // Rather a high number here means that we should be able to keep a lot
+        // of idle cpus busy. By ensuring that no codegen unit takes *too* long
+        // to build we'll be guaranteed that all cpus will finish pretty closely
+        // to one another and we should make relatively optimal use of system
+        // resources
+        //
+        // Note that the main cost of codegen units is that it prevents LLVM
+        // from inlining across codegen units. Users in general don't have a lot
+        // of control over how codegen units are split up so it's our job in the
+        // compiler to ensure that undue performance isn't lost when using
+        // codegen units (aka we can't require everyone to slap `#[inline]` on
+        // everything).
+        //
+        // If we're compiling at `-O0` then the number doesn't really matter too
+        // much because performance doesn't matter and inlining is ok to lose.
+        // In debug mode we just want to try to guarantee that no cpu is stuck
+        // doing work that could otherwise be farmed to others.
+        //
+        // In release mode, however (O1 and above) performance does indeed
+        // matter! To recover the loss in performance due to inlining we'll be
+        // enabling ThinLTO by default (the function for which is just below).
+        // This will ensure that we recover any inlining wins we otherwise lost
+        // through codegen unit partitioning.
+        //
+        // ---
+        //
+        // Ok that's a lot of words but the basic tl;dr; is that we want a high
+        // number here -- but not too high. Additionally we're "safe" to have it
+        // always at the same number at all optimization levels.
+        //
+        // As a result 16 was chosen here! Mostly because it was a power of 2
+        // and most benchmarks agreed it was roughly a local optimum. Not very
+        // scientific.
+        16
+    }
+
+    pub fn teach(&self, code: &DiagnosticId) -> bool {
+        self.opts.unstable_opts.teach && self.diagnostic().must_teach(code)
+    }
+
+    pub fn edition(&self) -> Edition {
+        self.opts.edition
+    }
+
+    pub fn link_dead_code(&self) -> bool {
+        self.opts.cg.link_dead_code.unwrap_or(false)
+    }
+}
+
+// JUSTIFICATION: part of session construction
+#[cfg_attr(not(bootstrap), allow(rustc::bad_opt_access))]
+fn default_emitter(
+    sopts: &config::Options,
+    registry: rustc_errors::registry::Registry,
+    source_map: Lrc<SourceMap>,
+    bundle: Option<Lrc<FluentBundle>>,
+    fallback_bundle: LazyFallbackBundle,
+    emitter_dest: Option<Box<dyn Write + Send>>,
+) -> Box<dyn Emitter + sync::Send> {
+    let macro_backtrace = sopts.unstable_opts.macro_backtrace;
+    match (sopts.error_format, emitter_dest) {
+        (config::ErrorOutputType::HumanReadable(kind), dst) => {
+            let (short, color_config) = kind.unzip();
+
+            if let HumanReadableErrorType::AnnotateSnippet(_) = kind {
+                let emitter = AnnotateSnippetEmitterWriter::new(
+                    Some(source_map),
+                    bundle,
+                    fallback_bundle,
+                    short,
+                    macro_backtrace,
+                );
+                Box::new(emitter.ui_testing(sopts.unstable_opts.ui_testing))
+            } else {
+                let emitter = match dst {
+                    None => EmitterWriter::stderr(
+                        color_config,
+                        Some(source_map),
+                        bundle,
+                        fallback_bundle,
+                        short,
+                        sopts.unstable_opts.teach,
+                        sopts.diagnostic_width,
+                        macro_backtrace,
+                    ),
+                    Some(dst) => EmitterWriter::new(
+                        dst,
+                        Some(source_map),
+                        bundle,
+                        fallback_bundle,
+                        short,
+                        false, // no teach messages when writing to a buffer
+                        false, // no colors when writing to a buffer
+                        None,  // no diagnostic width
+                        macro_backtrace,
+                    ),
+                };
+                Box::new(emitter.ui_testing(sopts.unstable_opts.ui_testing))
+            }
+        }
+        (config::ErrorOutputType::Json { pretty, json_rendered }, None) => Box::new(
+            JsonEmitter::stderr(
+                Some(registry),
+                source_map,
+                bundle,
+                fallback_bundle,
+                pretty,
+                json_rendered,
+                sopts.diagnostic_width,
+                macro_backtrace,
+            )
+            .ui_testing(sopts.unstable_opts.ui_testing),
+        ),
+        (config::ErrorOutputType::Json { pretty, json_rendered }, Some(dst)) => Box::new(
+            JsonEmitter::new(
+                dst,
+                Some(registry),
+                source_map,
+                bundle,
+                fallback_bundle,
+                pretty,
+                json_rendered,
+                sopts.diagnostic_width,
+                macro_backtrace,
+            )
+            .ui_testing(sopts.unstable_opts.ui_testing),
+        ),
+    }
+}
+
+pub enum DiagnosticOutput {
+    Default,
+    Raw(Box<dyn Write + Send>),
+}
+
+// JUSTIFICATION: literally session construction
+#[cfg_attr(not(bootstrap), allow(rustc::bad_opt_access))]
+pub fn build_session(
+    sopts: config::Options,
+    local_crate_source_file: Option<PathBuf>,
+    bundle: Option<Lrc<rustc_errors::FluentBundle>>,
+    registry: rustc_errors::registry::Registry,
+    diagnostics_output: DiagnosticOutput,
+    driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
+    file_loader: Option<Box<dyn FileLoader + Send + Sync + 'static>>,
+    target_override: Option<Target>,
+) -> Session {
+    // FIXME: This is not general enough to make the warning lint completely override
+    // normal diagnostic warnings, since the warning lint can also be denied and changed
+    // later via the source code.
+    let warnings_allow = sopts
+        .lint_opts
+        .iter()
+        .filter(|&&(ref key, _)| *key == "warnings")
+        .map(|&(_, ref level)| *level == lint::Allow)
+        .last()
+        .unwrap_or(false);
+    let cap_lints_allow = sopts.lint_cap.map_or(false, |cap| cap == lint::Allow);
+    let can_emit_warnings = !(warnings_allow || cap_lints_allow);
+
+    let write_dest = match diagnostics_output {
+        DiagnosticOutput::Default => None,
+        DiagnosticOutput::Raw(write) => Some(write),
+    };
+
+    let sysroot = match &sopts.maybe_sysroot {
+        Some(sysroot) => sysroot.clone(),
+        None => filesearch::get_or_default_sysroot(),
+    };
+
+    let target_cfg = config::build_target_config(&sopts, target_override, &sysroot);
+    let host_triple = TargetTriple::from_triple(config::host_triple());
+    let (host, target_warnings) = Target::search(&host_triple, &sysroot).unwrap_or_else(|e| {
+        early_error(sopts.error_format, &format!("Error loading host specification: {e}"))
+    });
+    for warning in target_warnings.warning_messages() {
+        early_warn(sopts.error_format, &warning)
+    }
+
+    let loader = file_loader.unwrap_or_else(|| Box::new(RealFileLoader));
+    let hash_kind = sopts.unstable_opts.src_hash_algorithm.unwrap_or_else(|| {
+        if target_cfg.is_like_msvc {
+            SourceFileHashAlgorithm::Sha1
+        } else {
+            SourceFileHashAlgorithm::Md5
+        }
+    });
+    let source_map = Lrc::new(SourceMap::with_file_loader_and_hash_kind(
+        loader,
+        sopts.file_path_mapping(),
+        hash_kind,
+    ));
+
+    let fallback_bundle = fallback_fluent_bundle(
+        rustc_errors::DEFAULT_LOCALE_RESOURCES,
+        sopts.unstable_opts.translate_directionality_markers,
+    );
+    let emitter =
+        default_emitter(&sopts, registry, source_map.clone(), bundle, fallback_bundle, write_dest);
+
+    let span_diagnostic = rustc_errors::Handler::with_emitter_and_flags(
+        emitter,
+        sopts.unstable_opts.diagnostic_handler_flags(can_emit_warnings),
+    );
+
+    let self_profiler = if let SwitchWithOptPath::Enabled(ref d) = sopts.unstable_opts.self_profile
+    {
+        let directory =
+            if let Some(ref directory) = d { directory } else { std::path::Path::new(".") };
+
+        let profiler = SelfProfiler::new(
+            directory,
+            sopts.crate_name.as_deref(),
+            sopts.unstable_opts.self_profile_events.as_ref().map(|xs| &xs[..]),
+            &sopts.unstable_opts.self_profile_counter,
+        );
+        match profiler {
+            Ok(profiler) => Some(Arc::new(profiler)),
+            Err(e) => {
+                early_warn(sopts.error_format, &format!("failed to create profiler: {e}"));
+                None
+            }
+        }
+    } else {
+        None
+    };
+
+    let mut parse_sess = ParseSess::with_span_handler(span_diagnostic, source_map);
+    parse_sess.assume_incomplete_release = sopts.unstable_opts.assume_incomplete_release;
+
+    let host_triple = config::host_triple();
+    let target_triple = sopts.target_triple.triple();
+    let host_tlib_path = Lrc::new(SearchPath::from_sysroot_and_triple(&sysroot, host_triple));
+    let target_tlib_path = if host_triple == target_triple {
+        // Use the same `SearchPath` if host and target triple are identical to avoid unnecessary
+        // rescanning of the target lib path and an unnecessary allocation.
+        host_tlib_path.clone()
+    } else {
+        Lrc::new(SearchPath::from_sysroot_and_triple(&sysroot, target_triple))
+    };
+
+    let file_path_mapping = sopts.file_path_mapping();
+
+    let local_crate_source_file =
+        local_crate_source_file.map(|path| file_path_mapping.map_prefix(path).0);
+
+    let optimization_fuel = Lock::new(OptimizationFuel {
+        remaining: sopts.unstable_opts.fuel.as_ref().map_or(0, |i| i.1),
+        out_of_fuel: false,
+    });
+    let print_fuel = AtomicU64::new(0);
+
+    let cgu_reuse_tracker = if sopts.unstable_opts.query_dep_graph {
+        CguReuseTracker::new()
+    } else {
+        CguReuseTracker::new_disabled()
+    };
+
+    let prof =
+        SelfProfilerRef::new(self_profiler, sopts.time_passes(), sopts.unstable_opts.time_passes);
+
+    let ctfe_backtrace = Lock::new(match env::var("RUSTC_CTFE_BACKTRACE") {
+        Ok(ref val) if val == "immediate" => CtfeBacktrace::Immediate,
+        Ok(ref val) if val != "0" => CtfeBacktrace::Capture,
+        _ => CtfeBacktrace::Disabled,
+    });
+
+    let asm_arch =
+        if target_cfg.allow_asm { InlineAsmArch::from_str(&target_cfg.arch).ok() } else { None };
+
+    let sess = Session {
+        target: target_cfg,
+        host,
+        opts: sopts,
+        host_tlib_path,
+        target_tlib_path,
+        parse_sess,
+        sysroot,
+        local_crate_source_file,
+        crate_types: OnceCell::new(),
+        stable_crate_id: OnceCell::new(),
+        features: OnceCell::new(),
+        incr_comp_session: OneThread::new(RefCell::new(IncrCompSession::NotInitialized)),
+        cgu_reuse_tracker,
+        prof,
+        perf_stats: PerfStats {
+            symbol_hash_time: Lock::new(Duration::from_secs(0)),
+            queries_canonicalized: AtomicUsize::new(0),
+            normalize_generic_arg_after_erasing_regions: AtomicUsize::new(0),
+            normalize_projection_ty: AtomicUsize::new(0),
+        },
+        code_stats: Default::default(),
+        optimization_fuel,
+        print_fuel,
+        jobserver: jobserver::client(),
+        driver_lint_caps,
+        ctfe_backtrace,
+        miri_unleashed_features: Lock::new(Default::default()),
+        asm_arch,
+        target_features: FxHashSet::default(),
+        unstable_target_features: FxHashSet::default(),
+    };
+
+    validate_commandline_args_with_session_available(&sess);
+
+    sess
+}
+
+/// Validate command line arguments with a `Session`.
+///
+/// If it is useful to have a Session available already for validating a commandline argument, you
+/// can do so here.
+// JUSTIFICATION: needs to access args to validate them
+#[cfg_attr(not(bootstrap), allow(rustc::bad_opt_access))]
+fn validate_commandline_args_with_session_available(sess: &Session) {
+    // Since we don't know if code in an rlib will be linked to statically or
+    // dynamically downstream, rustc generates `__imp_` symbols that help linkers
+    // on Windows deal with this lack of knowledge (#27438). Unfortunately,
+    // these manually generated symbols confuse LLD when it tries to merge
+    // bitcode during ThinLTO. Therefore we disallow dynamic linking on Windows
+    // when compiling for LLD ThinLTO. This way we can validly just not generate
+    // the `dllimport` attributes and `__imp_` symbols in that case.
+    if sess.opts.cg.linker_plugin_lto.enabled()
+        && sess.opts.cg.prefer_dynamic
+        && sess.target.is_like_windows
+    {
+        sess.err(
+            "Linker plugin based LTO is not supported together with \
+                  `-C prefer-dynamic` when targeting Windows-like targets",
+        );
+    }
+
+    // Make sure that any given profiling data actually exists so LLVM can't
+    // decide to silently skip PGO.
+    if let Some(ref path) = sess.opts.cg.profile_use {
+        if !path.exists() {
+            sess.err(&format!(
+                "File `{}` passed to `-C profile-use` does not exist.",
+                path.display()
+            ));
+        }
+    }
+
+    // Do the same for sample profile data.
+    if let Some(ref path) = sess.opts.unstable_opts.profile_sample_use {
+        if !path.exists() {
+            sess.err(&format!(
+                "File `{}` passed to `-C profile-sample-use` does not exist.",
+                path.display()
+            ));
+        }
+    }
+
+    // Unwind tables cannot be disabled if the target requires them.
+    if let Some(include_uwtables) = sess.opts.cg.force_unwind_tables {
+        if sess.target.requires_uwtable && !include_uwtables {
+            sess.err(
+                "target requires unwind tables, they cannot be disabled with \
+                     `-C force-unwind-tables=no`.",
+            );
+        }
+    }
+
+    // Sanitizers can only be used on platforms that we know have working sanitizer codegen.
+    let supported_sanitizers = sess.target.options.supported_sanitizers;
+    let unsupported_sanitizers = sess.opts.unstable_opts.sanitizer - supported_sanitizers;
+    match unsupported_sanitizers.into_iter().count() {
+        0 => {}
+        1 => {
+            sess.err(&format!(
+                "{} sanitizer is not supported for this target",
+                unsupported_sanitizers
+            ));
+        }
+        _ => {
+            sess.err(&format!(
+                "{} sanitizers are not supported for this target",
+                unsupported_sanitizers
+            ));
+        }
+    }
+    // Cannot mix and match sanitizers.
+    let mut sanitizer_iter = sess.opts.unstable_opts.sanitizer.into_iter();
+    if let (Some(first), Some(second)) = (sanitizer_iter.next(), sanitizer_iter.next()) {
+        sess.err(&format!("`-Zsanitizer={first}` is incompatible with `-Zsanitizer={second}`"));
+    }
+
+    // Cannot enable crt-static with sanitizers on Linux
+    if sess.crt_static(None) && !sess.opts.unstable_opts.sanitizer.is_empty() {
+        sess.err(
+            "sanitizer is incompatible with statically linked libc, \
+                                disable it using `-C target-feature=-crt-static`",
+        );
+    }
+
+    // LLVM CFI and VFE both require LTO.
+    if sess.lto() != config::Lto::Fat {
+        if sess.is_sanitizer_cfi_enabled() {
+            sess.err("`-Zsanitizer=cfi` requires `-Clto`");
+        }
+        if sess.opts.unstable_opts.virtual_function_elimination {
+            sess.err("`-Zvirtual-function-elimination` requires `-Clto`");
+        }
+    }
+
+    if sess.opts.unstable_opts.stack_protector != StackProtector::None {
+        if !sess.target.options.supports_stack_protector {
+            sess.warn(&format!(
+                "`-Z stack-protector={}` is not supported for target {} and will be ignored",
+                sess.opts.unstable_opts.stack_protector, sess.opts.target_triple
+            ))
+        }
+    }
+
+    if let Some(dwarf_version) = sess.opts.unstable_opts.dwarf_version {
+        if dwarf_version > 5 {
+            sess.err(&format!("requested DWARF version {} is greater than 5", dwarf_version));
+        }
+    }
+}
+
+/// Holds data on the current incremental compilation session, if there is one.
+#[derive(Debug)]
+pub enum IncrCompSession {
+    /// This is the state the session will be in until the incr. comp. dir is
+    /// needed.
+    NotInitialized,
+    /// This is the state during which the session directory is private and can
+    /// be modified.
+    Active { session_directory: PathBuf, lock_file: flock::Lock, load_dep_graph: bool },
+    /// This is the state after the session directory has been finalized. In this
+    /// state, the contents of the directory must not be modified any more.
+    Finalized { session_directory: PathBuf },
+    /// This is an error state that is reached when some compilation error has
+    /// occurred. It indicates that the contents of the session directory must
+    /// not be used, since they might be invalid.
+    InvalidBecauseOfErrors { session_directory: PathBuf },
+}
+
+fn early_error_handler(output: config::ErrorOutputType) -> rustc_errors::Handler {
+    let fallback_bundle = fallback_fluent_bundle(rustc_errors::DEFAULT_LOCALE_RESOURCES, false);
+    let emitter: Box<dyn Emitter + sync::Send> = match output {
+        config::ErrorOutputType::HumanReadable(kind) => {
+            let (short, color_config) = kind.unzip();
+            Box::new(EmitterWriter::stderr(
+                color_config,
+                None,
+                None,
+                fallback_bundle,
+                short,
+                false,
+                None,
+                false,
+            ))
+        }
+        config::ErrorOutputType::Json { pretty, json_rendered } => {
+            Box::new(JsonEmitter::basic(pretty, json_rendered, None, fallback_bundle, None, false))
+        }
+    };
+    rustc_errors::Handler::with_emitter(true, None, emitter)
+}
+
+pub fn early_error_no_abort(output: config::ErrorOutputType, msg: &str) -> ErrorGuaranteed {
+    early_error_handler(output).struct_err(msg).emit()
+}
+
+pub fn early_error(output: config::ErrorOutputType, msg: &str) -> ! {
+    early_error_handler(output).struct_fatal(msg).emit()
+}
+
+pub fn early_warn(output: config::ErrorOutputType, msg: &str) {
+    early_error_handler(output).struct_warn(msg).emit()
+}