Harden the pre-tyctxt query system against accidental recomputation

compiler/rustc_data_structures/src/steal.rs

@@ -40,6 +40,11 @@ impl<T> Steal<T> {
         ReadGuard::map(borrow, |opt| opt.as_ref().unwrap())
     }
 
+    #[track_caller]
+    pub fn get_mut(&mut self) -> &mut T {
+        self.value.get_mut().as_mut().expect("attempt to read from stolen value")
+    }
+
     #[track_caller]
     pub fn steal(&self) -> T {
         let value_ref = &mut *self.value.try_write().expect("stealing value which is locked");

compiler/rustc_driver/src/lib.rs

@@ -309,8 +309,8 @@ fn run_compiler(
 
             if let Some(ppm) = &sess.opts.pretty {
                 if ppm.needs_ast_map() {
-                    let expanded_crate = queries.expansion()?.peek().0.clone();
-                    queries.global_ctxt()?.peek_mut().enter(|tcx| {
+                    let expanded_crate = queries.expansion()?.borrow().0.clone();
+                    queries.global_ctxt()?.enter(|tcx| {
                         pretty::print_after_hir_lowering(
                             tcx,
                             compiler.input(),
@@ -321,7 +321,7 @@ fn run_compiler(
                         Ok(())
                     })?;
                 } else {
-                    let krate = queries.parse()?.take();
+                    let krate = queries.parse()?.steal();
                     pretty::print_after_parsing(
                         sess,
                         compiler.input(),
@@ -343,7 +343,8 @@ fn run_compiler(
             }
 
             {
-                let (_, lint_store) = &*queries.register_plugins()?.peek();
+                let plugins = queries.register_plugins()?;
+                let (_, lint_store) = &*plugins.borrow();
 
                 // Lint plugins are registered; now we can process command line flags.
                 if sess.opts.describe_lints {
@@ -371,7 +372,7 @@ fn run_compiler(
                 return early_exit();
             }
 
-            queries.global_ctxt()?.peek_mut().enter(|tcx| {
+            queries.global_ctxt()?.enter(|tcx| {
                 let result = tcx.analysis(());
                 if sess.opts.unstable_opts.save_analysis {
                     let crate_name = tcx.crate_name(LOCAL_CRATE);

compiler/rustc_interface/src/queries.rs

@@ -5,6 +5,7 @@ use crate::passes::{self, BoxedResolver, QueryContext};
 use rustc_ast as ast;
 use rustc_codegen_ssa::traits::CodegenBackend;
 use rustc_codegen_ssa::CodegenResults;
+use rustc_data_structures::steal::Steal;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::{Lrc, OnceCell, WorkerLocal};
 use rustc_hir::def_id::LOCAL_CRATE;
@@ -19,43 +20,53 @@ use rustc_session::{output::find_crate_name, Session};
 use rustc_span::symbol::sym;
 use rustc_span::Symbol;
 use std::any::Any;
-use std::cell::{Ref, RefCell, RefMut};
+use std::cell::{RefCell, RefMut};
 use std::rc::Rc;
 use std::sync::Arc;
 
 /// Represent the result of a query.
 ///
-/// This result can be stolen with the [`take`] method and generated with the [`compute`] method.
+/// This result can be stolen once with the [`steal`] method and generated with the [`compute`] method.
 ///
-/// [`take`]: Self::take
+/// [`steal`]: Steal::steal
 /// [`compute`]: Self::compute
 pub struct Query<T> {
-    result: RefCell<Option<Result<T>>>,
+    /// `None` means no value has been computed yet.
+    result: RefCell<Option<Result<Steal<T>>>>,
 }
 
 impl<T> Query<T> {
-    fn compute<F: FnOnce() -> Result<T>>(&self, f: F) -> Result<&Query<T>> {
-        self.result.borrow_mut().get_or_insert_with(f).as_ref().map(|_| self).map_err(|&err| err)
+    fn compute<F: FnOnce() -> Result<T>>(&self, f: F) -> Result<QueryResult<'_, T>> {
+        RefMut::filter_map(
+            self.result.borrow_mut(),
+            |r: &mut Option<Result<Steal<T>>>| -> Option<&mut Steal<T>> {
+                r.get_or_insert_with(|| f().map(Steal::new)).as_mut().ok()
+            },
+        )
+        .map_err(|r| *r.as_ref().unwrap().as_ref().map(|_| ()).unwrap_err())
+        .map(QueryResult)
     }
+}
+
+pub struct QueryResult<'a, T>(RefMut<'a, Steal<T>>);
+
+impl<'a, T> std::ops::Deref for QueryResult<'a, T> {
+    type Target = RefMut<'a, Steal<T>>;
 
-    /// Takes ownership of the query result. Further attempts to take or peek the query
-    /// result will panic unless it is generated by calling the `compute` method.
-    pub fn take(&self) -> T {
-        self.result.borrow_mut().take().expect("missing query result").unwrap()
+    fn deref(&self) -> &Self::Target {
+        &self.0
     }
+}
 
-    /// Borrows the query result using the RefCell. Panics if the result is stolen.
-    pub fn peek(&self) -> Ref<'_, T> {
-        Ref::map(self.result.borrow(), |r| {
-            r.as_ref().unwrap().as_ref().expect("missing query result")
-        })
+impl<'a, T> std::ops::DerefMut for QueryResult<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
     }
+}
 
-    /// Mutably borrows the query result using the RefCell. Panics if the result is stolen.
-    pub fn peek_mut(&self) -> RefMut<'_, T> {
-        RefMut::map(self.result.borrow_mut(), |r| {
-            r.as_mut().unwrap().as_mut().expect("missing query result")
-        })
+impl<'a, 'tcx> QueryResult<'a, QueryContext<'tcx>> {
+    pub fn enter<T>(mut self, f: impl FnOnce(TyCtxt<'tcx>) -> T) -> T {
+        (*self.0).get_mut().enter(f)
     }
 }
 
@@ -111,24 +122,24 @@ impl<'tcx> Queries<'tcx> {
         self.compiler.codegen_backend()
     }
 
-    fn dep_graph_future(&self) -> Result<&Query<Option<DepGraphFuture>>> {
+    fn dep_graph_future(&self) -> Result<QueryResult<'_, Option<DepGraphFuture>>> {
         self.dep_graph_future.compute(|| {
             let sess = self.session();
             Ok(sess.opts.build_dep_graph().then(|| rustc_incremental::load_dep_graph(sess)))
         })
     }
 
-    pub fn parse(&self) -> Result<&Query<ast::Crate>> {
+    pub fn parse(&self) -> Result<QueryResult<'_, ast::Crate>> {
         self.parse.compute(|| {
             passes::parse(self.session(), &self.compiler.input)
                 .map_err(|mut parse_error| parse_error.emit())
         })
     }
 
-    pub fn register_plugins(&self) -> Result<&Query<(ast::Crate, Lrc<LintStore>)>> {
+    pub fn register_plugins(&self) -> Result<QueryResult<'_, (ast::Crate, Lrc<LintStore>)>> {
         self.register_plugins.compute(|| {
-            let crate_name = *self.crate_name()?.peek();
-            let krate = self.parse()?.take();
+            let crate_name = *self.crate_name()?.borrow();
+            let krate = self.parse()?.steal();
 
             let empty: &(dyn Fn(&Session, &mut LintStore) + Sync + Send) = &|_, _| {};
             let (krate, lint_store) = passes::register_plugins(
@@ -150,11 +161,11 @@ impl<'tcx> Queries<'tcx> {
         })
     }
 
-    pub fn crate_name(&self) -> Result<&Query<Symbol>> {
+    pub fn crate_name(&self) -> Result<QueryResult<'_, Symbol>> {
         self.crate_name.compute(|| {
             Ok({
                 let parse_result = self.parse()?;
-                let krate = parse_result.peek();
+                let krate = parse_result.borrow();
                 // parse `#[crate_name]` even if `--crate-name` was passed, to make sure it matches.
                 find_crate_name(self.session(), &krate.attrs, &self.compiler.input)
             })
@@ -163,11 +174,12 @@ impl<'tcx> Queries<'tcx> {
 
     pub fn expansion(
         &self,
-    ) -> Result<&Query<(Lrc<ast::Crate>, Rc<RefCell<BoxedResolver>>, Lrc<LintStore>)>> {
+    ) -> Result<QueryResult<'_, (Lrc<ast::Crate>, Rc<RefCell<BoxedResolver>>, Lrc<LintStore>)>>
+    {
         trace!("expansion");
         self.expansion.compute(|| {
-            let crate_name = *self.crate_name()?.peek();
-            let (krate, lint_store) = self.register_plugins()?.take();
+            let crate_name = *self.crate_name()?.borrow();
+            let (krate, lint_store) = self.register_plugins()?.steal();
             let _timer = self.session().timer("configure_and_expand");
             let sess = self.session();
             let mut resolver = passes::create_resolver(
@@ -183,10 +195,10 @@ impl<'tcx> Queries<'tcx> {
         })
     }
 
-    fn dep_graph(&self) -> Result<&Query<DepGraph>> {
+    fn dep_graph(&self) -> Result<QueryResult<'_, DepGraph>> {
         self.dep_graph.compute(|| {
             let sess = self.session();
-            let future_opt = self.dep_graph_future()?.take();
+            let future_opt = self.dep_graph_future()?.steal();
             let dep_graph = future_opt
                 .and_then(|future| {
                     let (prev_graph, prev_work_products) =
@@ -199,10 +211,11 @@ impl<'tcx> Queries<'tcx> {
         })
     }
 
-    pub fn prepare_outputs(&self) -> Result<&Query<OutputFilenames>> {
+    pub fn prepare_outputs(&self) -> Result<QueryResult<'_, OutputFilenames>> {
         self.prepare_outputs.compute(|| {
-            let (krate, boxed_resolver, _) = &*self.expansion()?.peek();
-            let crate_name = *self.crate_name()?.peek();
+            let expansion = self.expansion()?;
+            let (krate, boxed_resolver, _) = &*expansion.borrow();
+            let crate_name = *self.crate_name()?.borrow();
             passes::prepare_outputs(
                 self.session(),
                 self.compiler,
@@ -213,12 +226,12 @@ impl<'tcx> Queries<'tcx> {
         })
     }
 
-    pub fn global_ctxt(&'tcx self) -> Result<&Query<QueryContext<'tcx>>> {
+    pub fn global_ctxt(&'tcx self) -> Result<QueryResult<'_, QueryContext<'tcx>>> {
         self.global_ctxt.compute(|| {
-            let crate_name = *self.crate_name()?.peek();
-            let outputs = self.prepare_outputs()?.take();
-            let dep_graph = self.dep_graph()?.peek().clone();
-            let (krate, resolver, lint_store) = self.expansion()?.take();
+            let crate_name = *self.crate_name()?.borrow();
+            let outputs = self.prepare_outputs()?.steal();
+            let dep_graph = self.dep_graph()?.borrow().clone();
+            let (krate, resolver, lint_store) = self.expansion()?.steal();
             Ok(passes::create_global_ctxt(
                 self.compiler,
                 lint_store,
@@ -235,9 +248,9 @@ impl<'tcx> Queries<'tcx> {
         })
     }
 
-    pub fn ongoing_codegen(&'tcx self) -> Result<&Query<Box<dyn Any>>> {
+    pub fn ongoing_codegen(&'tcx self) -> Result<QueryResult<'_, Box<dyn Any>>> {
         self.ongoing_codegen.compute(|| {
-            self.global_ctxt()?.peek_mut().enter(|tcx| {
+            self.global_ctxt()?.enter(|tcx| {
                 tcx.analysis(()).ok();
 
                 // Don't do code generation if there were any errors
@@ -293,12 +306,10 @@ impl<'tcx> Queries<'tcx> {
         let sess = self.session().clone();
         let codegen_backend = self.codegen_backend().clone();
 
-        let dep_graph = self.dep_graph()?.peek().clone();
-        let (crate_hash, prepare_outputs) = self
-            .global_ctxt()?
-            .peek_mut()
-            .enter(|tcx| (tcx.crate_hash(LOCAL_CRATE), tcx.output_filenames(()).clone()));
-        let ongoing_codegen = self.ongoing_codegen()?.take();
+        let (crate_hash, prepare_outputs, dep_graph) = self.global_ctxt()?.enter(|tcx| {
+            (tcx.crate_hash(LOCAL_CRATE), tcx.output_filenames(()).clone(), tcx.dep_graph.clone())
+        });
+        let ongoing_codegen = self.ongoing_codegen()?.steal();
 
         Ok(Linker {
             sess,
@@ -382,6 +393,7 @@ impl Compiler {
         // NOTE: intentionally does not compute the global context if it hasn't been built yet,
         // since that likely means there was a parse error.
         if let Some(Ok(gcx)) = &mut *queries.global_ctxt.result.borrow_mut() {
+            let gcx = gcx.get_mut();
             // We assume that no queries are run past here. If there are new queries
             // after this point, they'll show up as "<unknown>" in self-profiling data.
             {

src/librustdoc/doctest.rs

@@ -115,9 +115,7 @@ pub(crate) fn run(options: RustdocOptions) -> Result<(), ErrorGuaranteed> {
     let (tests, unused_extern_reports, compiling_test_count) =
         interface::run_compiler(config, |compiler| {
             compiler.enter(|queries| {
-                let mut global_ctxt = queries.global_ctxt()?.take();
-
-                let collector = global_ctxt.enter(|tcx| {
+                let collector = queries.global_ctxt()?.enter(|tcx| {
                     let crate_attrs = tcx.hir().attrs(CRATE_HIR_ID);
 
                     let opts = scrape_test_config(crate_attrs);
@@ -156,9 +154,7 @@ pub(crate) fn run(options: RustdocOptions) -> Result<(), ErrorGuaranteed> {
 
                 let unused_extern_reports = collector.unused_extern_reports.clone();
                 let compiling_test_count = collector.compiling_test_count.load(Ordering::SeqCst);
-                let ret: Result<_, ErrorGuaranteed> =
-                    Ok((collector.tests, unused_extern_reports, compiling_test_count));
-                ret
+                Ok((collector.tests, unused_extern_reports, compiling_test_count))
             })
         })?;
 

src/librustdoc/lib.rs

@@ -800,7 +800,8 @@ fn main_args(at_args: &[String]) -> MainResult {
             // FIXME(#83761): Resolver cloning can lead to inconsistencies between data in the
             // two copies because one of the copies can be modified after `TyCtxt` construction.
             let (resolver, resolver_caches) = {
-                let (krate, resolver, _) = &*abort_on_err(queries.expansion(), sess).peek();
+                let expansion = abort_on_err(queries.expansion(), sess);
+                let (krate, resolver, _) = &*expansion.borrow();
                 let resolver_caches = resolver.borrow_mut().access(|resolver| {
                     collect_intra_doc_links::early_resolve_intra_doc_links(
                         resolver,
@@ -817,7 +818,7 @@ fn main_args(at_args: &[String]) -> MainResult {
                 sess.fatal("Compilation failed, aborting rustdoc");
             }
 
-            let mut global_ctxt = abort_on_err(queries.global_ctxt(), sess).peek_mut();
+            let global_ctxt = abort_on_err(queries.global_ctxt(), sess);
 
             global_ctxt.enter(|tcx| {
                 let (krate, render_opts, mut cache) = sess.time("run_global_ctxt", || {

src/tools/miri/src/bin/miri.rs

@@ -61,7 +61,7 @@ impl rustc_driver::Callbacks for MiriCompilerCalls {
     ) -> Compilation {
         compiler.session().abort_if_errors();
 
-        queries.global_ctxt().unwrap().peek_mut().enter(|tcx| {
+        queries.global_ctxt().unwrap().enter(|tcx| {
             init_late_loggers(tcx);
             if !tcx.sess.crate_types().contains(&CrateType::Executable) {
                 tcx.sess.fatal("miri only makes sense on bin crates");

tests/run-make-fulldeps/obtain-borrowck/driver.rs

@@ -62,7 +62,7 @@ impl rustc_driver::Callbacks for CompilerCalls {
         queries: &'tcx Queries<'tcx>,
     ) -> Compilation {
         compiler.session().abort_if_errors();
-        queries.global_ctxt().unwrap().peek_mut().enter(|tcx| {
+        queries.global_ctxt().unwrap().enter(|tcx| {
             // Collect definition ids of MIR bodies.
             let hir = tcx.hir();
             let mut bodies = Vec::new();