Rollup merge of #81008 - tmiasko:generator-layout-err, r=tmandry

Don't ICE when computing a layout of a generator tainted by errors

Fixes #80998.

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -1832,8 +1832,9 @@ fn field_name(&self, i: usize) -> String {
     fn source_info(&self, cx: &CodegenCx<'ll, 'tcx>) -> Option<SourceInfo<'ll>> {
         match self {
             VariantInfo::Generator { def_id, variant_index, .. } => {
-                let span =
-                    cx.tcx.generator_layout(*def_id).variant_source_info[*variant_index].span;
+                let span = cx.tcx.generator_layout(*def_id).unwrap().variant_source_info
+                    [*variant_index]
+                    .span;
                 if !span.is_dummy() {
                     let loc = cx.lookup_debug_loc(span.lo());
                     return Some(SourceInfo {

compiler/rustc_middle/src/ty/layout.rs

@@ -1466,10 +1466,12 @@ fn generator_layout(
     ) -> Result<&'tcx Layout, LayoutError<'tcx>> {
         use SavedLocalEligibility::*;
         let tcx = self.tcx;
-
         let subst_field = |ty: Ty<'tcx>| ty.subst(tcx, substs);
 
-        let info = tcx.generator_layout(def_id);
+        let info = match tcx.generator_layout(def_id) {
+            None => return Err(LayoutError::Unknown(ty)),
+            Some(info) => info,
+        };
         let (ineligible_locals, assignments) = self.generator_saved_local_eligibility(&info);
 
         // Build a prefix layout, including "promoting" all ineligible

compiler/rustc_middle/src/ty/mod.rs

@@ -3068,8 +3068,10 @@ pub fn trait_is_auto(self, trait_def_id: DefId) -> bool {
         self.trait_def(trait_def_id).has_auto_impl
     }
 
-    pub fn generator_layout(self, def_id: DefId) -> &'tcx GeneratorLayout<'tcx> {
-        self.optimized_mir(def_id).generator_layout.as_ref().unwrap()
+    /// Returns layout of a generator. Layout might be unavailable if the
+    /// generator is tainted by errors.
+    pub fn generator_layout(self, def_id: DefId) -> Option<&'tcx GeneratorLayout<'tcx>> {
+        self.optimized_mir(def_id).generator_layout.as_ref()
     }
 
     /// Given the `DefId` of an impl, returns the `DefId` of the trait it implements.

compiler/rustc_middle/src/ty/sty.rs

@@ -605,7 +605,7 @@ impl<'tcx> GeneratorSubsts<'tcx> {
     #[inline]
     pub fn variant_range(&self, def_id: DefId, tcx: TyCtxt<'tcx>) -> Range<VariantIdx> {
         // FIXME requires optimized MIR
-        let num_variants = tcx.generator_layout(def_id).variant_fields.len();
+        let num_variants = tcx.generator_layout(def_id).unwrap().variant_fields.len();
         VariantIdx::new(0)..VariantIdx::new(num_variants)
     }
 
@@ -666,7 +666,7 @@ pub fn state_tys(
         def_id: DefId,
         tcx: TyCtxt<'tcx>,
     ) -> impl Iterator<Item = impl Iterator<Item = Ty<'tcx>> + Captures<'tcx>> {
-        let layout = tcx.generator_layout(def_id);
+        let layout = tcx.generator_layout(def_id).unwrap();
         layout.variant_fields.iter().map(move |variant| {
             variant.iter().map(move |field| layout.field_tys[*field].subst(tcx, self.substs))
         })

src/test/ui/generator/layout-error.rs

@@ -0,0 +1,28 @@
+// Verifies that computing a layout of a generator tainted by type errors
+// doesn't ICE. Regression test for #80998.
+//
+// edition:2018
+
+#![feature(type_alias_impl_trait)]
+use std::future::Future;
+
+pub struct Task<F: Future>(F);
+impl<F: Future> Task<F> {
+    fn new() -> Self {
+        todo!()
+    }
+    fn spawn(&self, _: impl FnOnce() -> F) {
+        todo!()
+    }
+}
+
+fn main() {
+    async fn cb() {
+        let a = Foo; //~ ERROR cannot find value `Foo` in this scope
+    }
+
+    type F = impl Future;
+    // Check that statics are inhabited computes they layout.
+    static POOL: Task<F> = Task::new();
+    Task::spawn(&POOL, || cb());
+}

src/test/ui/generator/layout-error.stderr

@@ -0,0 +1,9 @@
+error[E0425]: cannot find value `Foo` in this scope
+  --> $DIR/layout-error.rs:21:17
+   |
+LL |         let a = Foo;
+   |                 ^^^ not found in this scope
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0425`.