diff --git a/compiler/rustc_hir/src/tests.rs b/compiler/rustc_hir/src/tests.rs
index 74b8e88a97790..571923b546293 100644
--- a/compiler/rustc_hir/src/tests.rs
+++ b/compiler/rustc_hir/src/tests.rs
@@ -14,7 +14,7 @@ fn def_path_hash_depends_on_crate_id() {
     // the crate by changing the crate disambiguator (e.g. via bumping the
     // crate's version number).
 
-    create_session_globals_then(Edition::Edition2024, || {
+    create_session_globals_then(Edition::Edition2024, None, || {
         let id0 = StableCrateId::new(Symbol::intern("foo"), false, vec!["1".to_string()], "");
         let id1 = StableCrateId::new(Symbol::intern("foo"), false, vec!["2".to_string()], "");
 
diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index da2fb490a36f2..c5b81dbd67919 100644
--- a/compiler/rustc_interface/src/interface.rs
+++ b/compiler/rustc_interface/src/interface.rs
@@ -5,6 +5,7 @@ use rustc_ast::{LitKind, MetaItemKind};
 use rustc_codegen_ssa::traits::CodegenBackend;
 use rustc_data_structures::defer;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::jobserver;
 use rustc_data_structures::stable_hasher::StableHasher;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::registry::Registry;
@@ -21,7 +22,7 @@ use rustc_session::config::{self, Cfg, CheckCfg, ExpectedValues, Input, OutFileN
 use rustc_session::filesearch::{self, sysroot_candidates};
 use rustc_session::parse::ParseSess;
 use rustc_session::{lint, CompilerIO, EarlyDiagCtxt, Session};
-use rustc_span::source_map::FileLoader;
+use rustc_span::source_map::{FileLoader, RealFileLoader, SourceMapInputs};
 use rustc_span::symbol::sym;
 use rustc_span::FileName;
 use std::path::PathBuf;
@@ -323,6 +324,18 @@ pub struct Config {
     pub expanded_args: Vec<String>,
 }
 
+/// Initialize jobserver before getting `jobserver::client` and `build_session`.
+pub(crate) fn initialize_checked_jobserver(early_dcx: &EarlyDiagCtxt) {
+    jobserver::initialize_checked(|err| {
+        #[allow(rustc::untranslatable_diagnostic)]
+        #[allow(rustc::diagnostic_outside_of_impl)]
+        early_dcx
+            .early_struct_warn(err)
+            .with_note("the build environment is likely misconfigured")
+            .emit()
+    });
+}
+
 // JUSTIFICATION: before session exists, only config
 #[allow(rustc::bad_opt_access)]
 #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
@@ -334,20 +347,25 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
 
     // Check jobserver before run_in_thread_pool_with_globals, which call jobserver::acquire_thread
     let early_dcx = EarlyDiagCtxt::new(config.opts.error_format);
-    early_dcx.initialize_checked_jobserver();
+    initialize_checked_jobserver(&early_dcx);
+
+    crate::callbacks::setup_callbacks();
+
+    let sysroot = filesearch::materialize_sysroot(config.opts.maybe_sysroot.clone());
+    let target = config::build_target_config(&early_dcx, &config.opts, &sysroot);
+    let file_loader = config.file_loader.unwrap_or_else(|| Box::new(RealFileLoader));
+    let path_mapping = config.opts.file_path_mapping();
+    let hash_kind = config.opts.unstable_opts.src_hash_algorithm(&target);
 
     util::run_in_thread_pool_with_globals(
         config.opts.edition,
         config.opts.unstable_opts.threads,
+        SourceMapInputs { file_loader, path_mapping, hash_kind },
         |current_gcx| {
-            crate::callbacks::setup_callbacks();
-
+            // The previous `early_dcx` can't be reused here because it doesn't
+            // impl `Send`. Creating a new one is fine.
             let early_dcx = EarlyDiagCtxt::new(config.opts.error_format);
 
-            let sysroot = filesearch::materialize_sysroot(config.opts.maybe_sysroot.clone());
-
-            let target = config::build_target_config(&early_dcx, &config.opts, &sysroot);
-
             let codegen_backend = match config.make_codegen_backend {
                 None => util::get_codegen_backend(
                     &early_dcx,
@@ -372,9 +390,7 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
                 config.opts.unstable_opts.translate_directionality_markers,
             ) {
                 Ok(bundle) => bundle,
-                Err(e) => {
-                    early_dcx.early_fatal(format!("failed to load fluent bundle: {e}"));
-                }
+                Err(e) => early_dcx.early_fatal(format!("failed to load fluent bundle: {e}")),
             };
 
             let mut locale_resources = Vec::from(config.locale_resources);
@@ -393,7 +409,6 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
                 config.registry.clone(),
                 locale_resources,
                 config.lint_caps,
-                config.file_loader,
                 target,
                 sysroot,
                 util::rustc_version_str().unwrap_or("unknown"),
@@ -440,45 +455,43 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
                 current_gcx,
             };
 
-            rustc_span::set_source_map(compiler.sess.psess.clone_source_map(), move || {
-                // There are two paths out of `f`.
-                // - Normal exit.
-                // - Panic, e.g. triggered by `abort_if_errors`.
-                //
-                // We must run `finish_diagnostics` in both cases.
-                let res = {
-                    // If `f` panics, `finish_diagnostics` will run during
-                    // unwinding because of the `defer`.
-                    let mut guar = None;
-                    let sess_abort_guard = defer(|| {
-                        guar = compiler.sess.finish_diagnostics(&config.registry);
-                    });
-
-                    let res = f(&compiler);
-
-                    // If `f` doesn't panic, `finish_diagnostics` will run
-                    // normally when `sess_abort_guard` is dropped.
-                    drop(sess_abort_guard);
-
-                    // If `finish_diagnostics` emits errors (e.g. stashed
-                    // errors) we can't return an error directly, because the
-                    // return type of this function is `R`, not `Result<R, E>`.
-                    // But we need to communicate the errors' existence to the
-                    // caller, otherwise the caller might mistakenly think that
-                    // no errors occurred and return a zero exit code. So we
-                    // abort (panic) instead, similar to if `f` had panicked.
-                    if guar.is_some() {
-                        compiler.sess.dcx().abort_if_errors();
-                    }
+            // There are two paths out of `f`.
+            // - Normal exit.
+            // - Panic, e.g. triggered by `abort_if_errors`.
+            //
+            // We must run `finish_diagnostics` in both cases.
+            let res = {
+                // If `f` panics, `finish_diagnostics` will run during
+                // unwinding because of the `defer`.
+                let mut guar = None;
+                let sess_abort_guard = defer(|| {
+                    guar = compiler.sess.finish_diagnostics(&config.registry);
+                });
+
+                let res = f(&compiler);
+
+                // If `f` doesn't panic, `finish_diagnostics` will run
+                // normally when `sess_abort_guard` is dropped.
+                drop(sess_abort_guard);
+
+                // If `finish_diagnostics` emits errors (e.g. stashed
+                // errors) we can't return an error directly, because the
+                // return type of this function is `R`, not `Result<R, E>`.
+                // But we need to communicate the errors' existence to the
+                // caller, otherwise the caller might mistakenly think that
+                // no errors occurred and return a zero exit code. So we
+                // abort (panic) instead, similar to if `f` had panicked.
+                if guar.is_some() {
+                    compiler.sess.dcx().abort_if_errors();
+                }
 
-                    res
-                };
+                res
+            };
 
-                let prof = compiler.sess.prof.clone();
-                prof.generic_activity("drop_compiler").run(move || drop(compiler));
+            let prof = compiler.sess.prof.clone();
+            prof.generic_activity("drop_compiler").run(move || drop(compiler));
 
-                res
-            })
+            res
         },
     )
 }
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index 923581d1cb696..e563728c893d6 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -1,5 +1,5 @@
 #![allow(rustc::bad_opt_access)]
-use crate::interface::parse_cfg;
+use crate::interface::{initialize_checked_jobserver, parse_cfg};
 use rustc_data_structures::profiling::TimePassesFormat;
 use rustc_errors::{emitter::HumanReadableErrorType, registry, ColorConfig};
 use rustc_session::config::{
@@ -16,6 +16,7 @@ use rustc_session::search_paths::SearchPath;
 use rustc_session::utils::{CanonicalizedPath, NativeLib, NativeLibKind};
 use rustc_session::{build_session, filesearch, getopts, CompilerIO, EarlyDiagCtxt, Session};
 use rustc_span::edition::{Edition, DEFAULT_EDITION};
+use rustc_span::source_map::{RealFileLoader, SourceMapInputs};
 use rustc_span::symbol::sym;
 use rustc_span::{FileName, SourceFileHashAlgorithm};
 use rustc_target::spec::{CodeModel, LinkerFlavorCli, MergeFunctions, PanicStrategy, RelocModel};
@@ -25,42 +26,52 @@ use std::num::NonZero;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
-fn mk_session(matches: getopts::Matches) -> (Session, Cfg) {
+fn sess_and_cfg<F>(args: &[&'static str], f: F)
+where
+    F: FnOnce(Session, Cfg),
+{
     let mut early_dcx = EarlyDiagCtxt::new(ErrorOutputType::default());
-    early_dcx.initialize_checked_jobserver();
+    initialize_checked_jobserver(&early_dcx);
 
-    let registry = registry::Registry::new(&[]);
+    let matches = optgroups().parse(args).unwrap();
     let sessopts = build_session_options(&mut early_dcx, &matches);
-    let temps_dir = sessopts.unstable_opts.temps_dir.as_deref().map(PathBuf::from);
-    let io = CompilerIO {
-        input: Input::Str { name: FileName::Custom(String::new()), input: String::new() },
-        output_dir: None,
-        output_file: None,
-        temps_dir,
-    };
-
     let sysroot = filesearch::materialize_sysroot(sessopts.maybe_sysroot.clone());
-
     let target = rustc_session::config::build_target_config(&early_dcx, &sessopts, &sysroot);
+    let hash_kind = sessopts.unstable_opts.src_hash_algorithm(&target);
+    let sm_inputs = Some(SourceMapInputs {
+        file_loader: Box::new(RealFileLoader) as _,
+        path_mapping: sessopts.file_path_mapping(),
+        hash_kind,
+    });
 
-    let sess = build_session(
-        early_dcx,
-        sessopts,
-        io,
-        None,
-        registry,
-        vec![],
-        Default::default(),
-        None,
-        target,
-        sysroot,
-        "",
-        None,
-        Arc::default(),
-        Default::default(),
-    );
-    let cfg = parse_cfg(&sess.dcx(), matches.opt_strs("cfg"));
-    (sess, cfg)
+    rustc_span::create_session_globals_then(DEFAULT_EDITION, sm_inputs, || {
+        let temps_dir = sessopts.unstable_opts.temps_dir.as_deref().map(PathBuf::from);
+        let io = CompilerIO {
+            input: Input::Str { name: FileName::Custom(String::new()), input: String::new() },
+            output_dir: None,
+            output_file: None,
+            temps_dir,
+        };
+
+        let sess = build_session(
+            early_dcx,
+            sessopts,
+            io,
+            None,
+            registry::Registry::new(&[]),
+            vec![],
+            Default::default(),
+            target,
+            sysroot,
+            "",
+            None,
+            Arc::default(),
+            Default::default(),
+        );
+        let cfg = parse_cfg(&sess.dcx(), matches.opt_strs("cfg"));
+        let cfg = build_configuration(&sess, cfg);
+        f(sess, cfg)
+    });
 }
 
 fn new_public_extern_entry<S, I>(locations: I) -> ExternEntry
@@ -125,21 +136,15 @@ fn assert_non_crate_hash_different(x: &Options, y: &Options) {
 // When the user supplies --test we should implicitly supply --cfg test
 #[test]
 fn test_switch_implies_cfg_test() {
-    rustc_span::create_default_session_globals_then(|| {
-        let matches = optgroups().parse(&["--test".to_string()]).unwrap();
-        let (sess, cfg) = mk_session(matches);
-        let cfg = build_configuration(&sess, cfg);
+    sess_and_cfg(&["--test"], |_sess, cfg| {
         assert!(cfg.contains(&(sym::test, None)));
-    });
+    })
 }
 
 // When the user supplies --test and --cfg test, don't implicitly add another --cfg test
 #[test]
 fn test_switch_implies_cfg_test_unless_cfg_test() {
-    rustc_span::create_default_session_globals_then(|| {
-        let matches = optgroups().parse(&["--test".to_string(), "--cfg=test".to_string()]).unwrap();
-        let (sess, cfg) = mk_session(matches);
-        let cfg = build_configuration(&sess, cfg);
+    sess_and_cfg(&["--test", "--cfg=test"], |_sess, cfg| {
         let mut test_items = cfg.iter().filter(|&&(name, _)| name == sym::test);
         assert!(test_items.next().is_some());
         assert!(test_items.next().is_none());
@@ -148,22 +153,15 @@ fn test_switch_implies_cfg_test_unless_cfg_test() {
 
 #[test]
 fn test_can_print_warnings() {
-    rustc_span::create_default_session_globals_then(|| {
-        let matches = optgroups().parse(&["-Awarnings".to_string()]).unwrap();
-        let (sess, _) = mk_session(matches);
+    sess_and_cfg(&["-Awarnings"], |sess, _cfg| {
         assert!(!sess.dcx().can_emit_warnings());
     });
 
-    rustc_span::create_default_session_globals_then(|| {
-        let matches =
-            optgroups().parse(&["-Awarnings".to_string(), "-Dwarnings".to_string()]).unwrap();
-        let (sess, _) = mk_session(matches);
+    sess_and_cfg(&["-Awarnings", "-Dwarnings"], |sess, _cfg| {
         assert!(sess.dcx().can_emit_warnings());
     });
 
-    rustc_span::create_default_session_globals_then(|| {
-        let matches = optgroups().parse(&["-Adead_code".to_string()]).unwrap();
-        let (sess, _) = mk_session(matches);
+    sess_and_cfg(&["-Adead_code"], |sess, _cfg| {
         assert!(sess.dcx().can_emit_warnings());
     });
 }
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index d0f04fccc4810..02dcfe9c8dffb 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -14,6 +14,7 @@ use rustc_session::lint::{self, BuiltinLintDiag, LintBuffer};
 use rustc_session::{filesearch, Session};
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::edition::Edition;
+use rustc_span::source_map::SourceMapInputs;
 use rustc_span::symbol::sym;
 use rustc_target::spec::Target;
 use session::output::{categorize_crate_type, CRATE_TYPES};
@@ -65,8 +66,9 @@ fn init_stack_size() -> usize {
     })
 }
 
-pub(crate) fn run_in_thread_with_globals<F: FnOnce(CurrentGcx) -> R + Send, R: Send>(
+fn run_in_thread_with_globals<F: FnOnce(CurrentGcx) -> R + Send, R: Send>(
     edition: Edition,
+    sm_inputs: SourceMapInputs,
     f: F,
 ) -> R {
     // The "thread pool" is a single spawned thread in the non-parallel
@@ -84,7 +86,9 @@ pub(crate) fn run_in_thread_with_globals<F: FnOnce(CurrentGcx) -> R + Send, R: S
         // name contains null bytes.
         let r = builder
             .spawn_scoped(s, move || {
-                rustc_span::create_session_globals_then(edition, || f(CurrentGcx::new()))
+                rustc_span::create_session_globals_then(edition, Some(sm_inputs), || {
+                    f(CurrentGcx::new())
+                })
             })
             .unwrap()
             .join();
@@ -100,15 +104,17 @@ pub(crate) fn run_in_thread_with_globals<F: FnOnce(CurrentGcx) -> R + Send, R: S
 pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce(CurrentGcx) -> R + Send, R: Send>(
     edition: Edition,
     _threads: usize,
+    sm_inputs: SourceMapInputs,
     f: F,
 ) -> R {
-    run_in_thread_with_globals(edition, f)
+    run_in_thread_with_globals(edition, sm_inputs, f)
 }
 
 #[cfg(parallel_compiler)]
 pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce(CurrentGcx) -> R + Send, R: Send>(
     edition: Edition,
     threads: usize,
+    sm_inputs: SourceMapInputs,
     f: F,
 ) -> R {
     use rustc_data_structures::{defer, jobserver, sync::FromDyn};
@@ -120,7 +126,7 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce(CurrentGcx) -> R + Send,
     let registry = sync::Registry::new(std::num::NonZero::new(threads).unwrap());
 
     if !sync::is_dyn_thread_safe() {
-        return run_in_thread_with_globals(edition, |current_gcx| {
+        return run_in_thread_with_globals(edition, sm_inputs, |current_gcx| {
             // Register the thread for use with the `WorkerLocal` type.
             registry.register();
 
@@ -169,7 +175,7 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce(CurrentGcx) -> R + Send,
     // pool. Upon creation, each worker thread created gets a copy of the
     // session globals in TLS. This is possible because `SessionGlobals` impls
     // `Send` in the parallel compiler.
-    rustc_span::create_session_globals_then(edition, || {
+    rustc_span::create_session_globals_then(edition, Some(sm_inputs), || {
         rustc_span::with_session_globals(|session_globals| {
             let session_globals = FromDyn::from(session_globals);
             builder
diff --git a/compiler/rustc_log/src/lib.rs b/compiler/rustc_log/src/lib.rs
index e4b67cde244fb..81257f9be8823 100644
--- a/compiler/rustc_log/src/lib.rs
+++ b/compiler/rustc_log/src/lib.rs
@@ -17,7 +17,7 @@
 //!     rustc_log::init_logger(rustc_log::LoggerConfig::from_env("LOG")).unwrap();
 //!
 //!     let edition = rustc_span::edition::Edition::Edition2021;
-//!     rustc_span::create_session_globals_then(edition, || {
+//!     rustc_span::create_session_globals_then(edition, None, || {
 //!         /* ... */
 //!     });
 //! }
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index d9fc43625ef5f..2a7b5650fc214 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -1125,7 +1125,7 @@ impl Options {
             || self.unstable_opts.query_dep_graph
     }
 
-    pub(crate) fn file_path_mapping(&self) -> FilePathMapping {
+    pub fn file_path_mapping(&self) -> FilePathMapping {
         file_path_mapping(self.remap_path_prefix.clone(), &self.unstable_opts)
     }
 
@@ -1162,6 +1162,16 @@ impl UnstableOptions {
             track_diagnostics: self.track_diagnostics,
         }
     }
+
+    pub fn src_hash_algorithm(&self, target: &Target) -> SourceFileHashAlgorithm {
+        self.src_hash_algorithm.unwrap_or_else(|| {
+            if target.is_like_msvc {
+                SourceFileHashAlgorithm::Sha256
+            } else {
+                SourceFileHashAlgorithm::Md5
+            }
+        })
+    }
 }
 
 // The type of entry function, so users can have their own entry functions
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 38642efadbd80..b63c119eee0e4 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -28,9 +28,9 @@ use rustc_errors::{
 use rustc_macros::HashStable_Generic;
 pub use rustc_span::def_id::StableCrateId;
 use rustc_span::edition::Edition;
-use rustc_span::source_map::{FileLoader, FilePathMapping, RealFileLoader, SourceMap};
+use rustc_span::source_map::{FilePathMapping, SourceMap};
 use rustc_span::{FileNameDisplayPreference, RealFileName};
-use rustc_span::{SourceFileHashAlgorithm, Span, Symbol};
+use rustc_span::{Span, Symbol};
 use rustc_target::asm::InlineAsmArch;
 use rustc_target::spec::{CodeModel, PanicStrategy, RelocModel, RelroLevel};
 use rustc_target::spec::{
@@ -988,7 +988,6 @@ pub fn build_session(
     registry: rustc_errors::registry::Registry,
     fluent_resources: Vec<&'static str>,
     driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
-    file_loader: Option<Box<dyn FileLoader + Send + Sync + 'static>>,
     target: Target,
     sysroot: PathBuf,
     cfg_version: &'static str,
@@ -1015,24 +1014,11 @@ pub fn build_session(
         early_dcx.early_warn(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.is_like_msvc {
-            SourceFileHashAlgorithm::Sha256
-        } 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(
         fluent_resources,
         sopts.unstable_opts.translate_directionality_markers,
     );
+    let source_map = rustc_span::source_map::get_source_map().unwrap();
     let emitter = default_emitter(&sopts, registry, source_map.clone(), bundle, fallback_bundle);
 
     let mut dcx =
@@ -1411,16 +1397,10 @@ impl EarlyDiagCtxt {
         self.dcx.warn(msg)
     }
 
-    pub fn initialize_checked_jobserver(&self) {
-        // initialize jobserver before getting `jobserver::client` and `build_session`.
-        jobserver::initialize_checked(|err| {
-            #[allow(rustc::untranslatable_diagnostic)]
-            #[allow(rustc::diagnostic_outside_of_impl)]
-            self.dcx
-                .struct_warn(err)
-                .with_note("the build environment is likely misconfigured")
-                .emit()
-        });
+    #[allow(rustc::untranslatable_diagnostic)]
+    #[allow(rustc::diagnostic_outside_of_impl)]
+    pub fn early_struct_warn(&self, msg: impl Into<DiagMessage>) -> Diag<'_, ()> {
+        self.dcx.struct_warn(msg)
     }
 }
 
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index c1e1175b4bd6b..f749d4eb83368 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -49,7 +49,7 @@ use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 mod caching_source_map_view;
 pub mod source_map;
 pub use self::caching_source_map_view::CachingSourceMapView;
-use source_map::SourceMap;
+use source_map::{SourceMap, SourceMapInputs};
 
 pub mod edition;
 use edition::Edition;
@@ -104,35 +104,35 @@ pub struct SessionGlobals {
     metavar_spans: Lock<FxHashMap<Span, Span>>,
     hygiene_data: Lock<hygiene::HygieneData>,
 
-    /// A reference to the source map in the `Session`. It's an `Option`
-    /// because it can't be initialized until `Session` is created, which
-    /// happens after `SessionGlobals`. `set_source_map` does the
-    /// initialization.
-    ///
-    /// This field should only be used in places where the `Session` is truly
-    /// not available, such as `<Span as Debug>::fmt`.
-    source_map: Lock<Option<Lrc<SourceMap>>>,
+    /// The session's source map, if there is one. This field should only be
+    /// used in places where the `Session` is truly not available, such as
+    /// `<Span as Debug>::fmt`.
+    source_map: Option<Lrc<SourceMap>>,
 }
 
 impl SessionGlobals {
-    pub fn new(edition: Edition) -> SessionGlobals {
+    pub fn new(edition: Edition, sm_inputs: Option<SourceMapInputs>) -> SessionGlobals {
         SessionGlobals {
             symbol_interner: symbol::Interner::fresh(),
             span_interner: Lock::new(span_encoding::SpanInterner::default()),
             metavar_spans: Default::default(),
             hygiene_data: Lock::new(hygiene::HygieneData::new(edition)),
-            source_map: Lock::new(None),
+            source_map: sm_inputs.map(|inputs| Lrc::new(SourceMap::with_inputs(inputs))),
         }
     }
 }
 
-pub fn create_session_globals_then<R>(edition: Edition, f: impl FnOnce() -> R) -> R {
+pub fn create_session_globals_then<R>(
+    edition: Edition,
+    sm_inputs: Option<SourceMapInputs>,
+    f: impl FnOnce() -> R,
+) -> R {
     assert!(
         !SESSION_GLOBALS.is_set(),
         "SESSION_GLOBALS should never be overwritten! \
          Use another thread if you need another SessionGlobals"
     );
-    let session_globals = SessionGlobals::new(edition);
+    let session_globals = SessionGlobals::new(edition, sm_inputs);
     SESSION_GLOBALS.set(&session_globals, f)
 }
 
@@ -145,12 +145,13 @@ pub fn set_session_globals_then<R>(session_globals: &SessionGlobals, f: impl FnO
     SESSION_GLOBALS.set(session_globals, f)
 }
 
+/// No source map.
 pub fn create_session_if_not_set_then<R, F>(edition: Edition, f: F) -> R
 where
     F: FnOnce(&SessionGlobals) -> R,
 {
     if !SESSION_GLOBALS.is_set() {
-        let session_globals = SessionGlobals::new(edition);
+        let session_globals = SessionGlobals::new(edition, None);
         SESSION_GLOBALS.set(&session_globals, || SESSION_GLOBALS.with(f))
     } else {
         SESSION_GLOBALS.with(f)
@@ -164,8 +165,9 @@ where
     SESSION_GLOBALS.with(f)
 }
 
+/// Default edition, no source map.
 pub fn create_default_session_globals_then<R>(f: impl FnOnce() -> R) -> R {
-    create_session_globals_then(edition::DEFAULT_EDITION, f)
+    create_session_globals_then(edition::DEFAULT_EDITION, None, f)
 }
 
 // If this ever becomes non thread-local, `decode_syntax_context`
@@ -1318,25 +1320,6 @@ impl<D: SpanDecoder> Decodable<D> for AttrId {
     }
 }
 
-/// Insert `source_map` into the session globals for the duration of the
-/// closure's execution.
-pub fn set_source_map<T, F: FnOnce() -> T>(source_map: Lrc<SourceMap>, f: F) -> T {
-    with_session_globals(|session_globals| {
-        *session_globals.source_map.borrow_mut() = Some(source_map);
-    });
-    struct ClearSourceMap;
-    impl Drop for ClearSourceMap {
-        fn drop(&mut self) {
-            with_session_globals(|session_globals| {
-                session_globals.source_map.borrow_mut().take();
-            });
-        }
-    }
-
-    let _guard = ClearSourceMap;
-    f()
-}
-
 impl fmt::Debug for Span {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         // Use the global `SourceMap` to print the span. If that's not
@@ -1352,7 +1335,7 @@ impl fmt::Debug for Span {
 
         if SESSION_GLOBALS.is_set() {
             with_session_globals(|session_globals| {
-                if let Some(source_map) = &*session_globals.source_map.borrow() {
+                if let Some(source_map) = &session_globals.source_map {
                     write!(f, "{} ({:?})", source_map.span_to_diagnostic_string(*self), self.ctxt())
                 } else {
                     fallback(*self, f)
diff --git a/compiler/rustc_span/src/source_map.rs b/compiler/rustc_span/src/source_map.rs
index 93d5f06a16736..e3e76caebaf00 100644
--- a/compiler/rustc_span/src/source_map.rs
+++ b/compiler/rustc_span/src/source_map.rs
@@ -167,9 +167,17 @@ struct SourceMapFiles {
     stable_id_to_source_file: UnhashMap<StableSourceFileId, Lrc<SourceFile>>,
 }
 
+/// Used to construct a `SourceMap` with `SourceMap::with_inputs`.
+pub struct SourceMapInputs {
+    pub file_loader: Box<dyn FileLoader + Send + Sync>,
+    pub path_mapping: FilePathMapping,
+    pub hash_kind: SourceFileHashAlgorithm,
+}
+
 pub struct SourceMap {
     files: RwLock<SourceMapFiles>,
     file_loader: IntoDynSyncSend<Box<dyn FileLoader + Sync + Send>>,
+
     // This is used to apply the file path remapping as specified via
     // `--remap-path-prefix` to all `SourceFile`s allocated within this `SourceMap`.
     path_mapping: FilePathMapping,
@@ -180,17 +188,15 @@ pub struct SourceMap {
 
 impl SourceMap {
     pub fn new(path_mapping: FilePathMapping) -> SourceMap {
-        Self::with_file_loader_and_hash_kind(
-            Box::new(RealFileLoader),
+        Self::with_inputs(SourceMapInputs {
+            file_loader: Box::new(RealFileLoader),
             path_mapping,
-            SourceFileHashAlgorithm::Md5,
-        )
+            hash_kind: SourceFileHashAlgorithm::Md5,
+        })
     }
 
-    pub fn with_file_loader_and_hash_kind(
-        file_loader: Box<dyn FileLoader + Sync + Send>,
-        path_mapping: FilePathMapping,
-        hash_kind: SourceFileHashAlgorithm,
+    pub fn with_inputs(
+        SourceMapInputs { file_loader, path_mapping, hash_kind }: SourceMapInputs,
     ) -> SourceMap {
         SourceMap {
             files: Default::default(),
@@ -1054,6 +1060,10 @@ impl SourceMap {
     }
 }
 
+pub fn get_source_map() -> Option<Lrc<SourceMap>> {
+    with_session_globals(|session_globals| session_globals.source_map.clone())
+}
+
 #[derive(Clone)]
 pub struct FilePathMapping {
     mapping: Vec<(PathBuf, PathBuf)>,
diff --git a/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs b/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs
index e55a988321b34..651f2ebaee6f4 100644
--- a/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs
+++ b/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs
@@ -38,7 +38,7 @@ pub fn check(
     // of all `#[test]` attributes in not ignored code examples
     fn check_code_sample(code: String, edition: Edition, ignore: bool) -> (bool, Vec<Range<usize>>) {
         rustc_driver::catch_fatal_errors(|| {
-            rustc_span::create_session_globals_then(edition, || {
+            rustc_span::create_session_globals_then(edition, None, || {
                 let mut test_attr_spans = vec![];
                 let filename = FileName::anon_source_code(&code);