Improve GeneratorLayout debug output

src/librustc_index/bit_set.rs

@@ -700,7 +700,7 @@ impl<T: Idx> GrowableBitSet<T> {
 ///
 /// All operations that involve a row and/or column index will panic if the
 /// index exceeds the relevant bound.
-#[derive(Clone, Debug, Eq, PartialEq, RustcDecodable, RustcEncodable)]
+#[derive(Clone, Eq, PartialEq, RustcDecodable, RustcEncodable)]
 pub struct BitMatrix<R: Idx, C: Idx> {
     num_rows: usize,
     num_columns: usize,
@@ -876,6 +876,22 @@ impl<R: Idx, C: Idx> BitMatrix<R, C> {
     }
 }
 
+impl<R: Idx, C: Idx> fmt::Debug for BitMatrix<R, C> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        /// Forces its contents to print in regular mode instead of alternate mode.
+        struct OneLinePrinter<T>(T);
+        impl<T: fmt::Debug> fmt::Debug for OneLinePrinter<T> {
+            fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+                write!(fmt, "{:?}", self.0)
+            }
+        }
+
+        write!(fmt, "BitMatrix({}x{}) ", self.num_rows, self.num_columns)?;
+        let items = self.rows().flat_map(|r| self.iter(r).map(move |c| (r, c)));
+        fmt.debug_set().entries(items.map(OneLinePrinter)).finish()
+    }
+}
+
 /// A fixed-column-size, variable-row-size 2D bit matrix with a moderately
 /// sparse representation.
 ///

src/librustc_middle/mir/query.rs

@@ -10,6 +10,8 @@ use rustc_index::vec::IndexVec;
 use rustc_span::{Span, Symbol};
 use rustc_target::abi::VariantIdx;
 use smallvec::SmallVec;
+use std::cell::Cell;
+use std::fmt::{self, Debug};
 
 use super::{Field, SourceInfo};
 
@@ -58,7 +60,7 @@ rustc_index::newtype_index! {
 }
 
 /// The layout of generator state.
-#[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
+#[derive(Clone, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
 pub struct GeneratorLayout<'tcx> {
     /// The type of every local stored inside the generator.
     pub field_tys: IndexVec<GeneratorSavedLocal, Ty<'tcx>>,
@@ -77,6 +79,62 @@ pub struct GeneratorLayout<'tcx> {
     pub storage_conflicts: BitMatrix<GeneratorSavedLocal, GeneratorSavedLocal>,
 }
 
+impl Debug for GeneratorLayout<'_> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        /// Prints an iterator of (key, value) tuples as a map.
+        struct MapPrinter<'a, K, V>(Cell<Option<Box<dyn Iterator<Item = (K, V)> + 'a>>>);
+        impl<'a, K, V> MapPrinter<'a, K, V> {
+            fn new(iter: impl Iterator<Item = (K, V)> + 'a) -> Self {
+                Self(Cell::new(Some(Box::new(iter))))
+            }
+        }
+        impl<'a, K: Debug, V: Debug> Debug for MapPrinter<'a, K, V> {
+            fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+                fmt.debug_map().entries(self.0.take().unwrap()).finish()
+            }
+        }
+
+        /// Prints the generator variant name.
+        struct GenVariantPrinter(VariantIdx);
+        impl From<VariantIdx> for GenVariantPrinter {
+            fn from(idx: VariantIdx) -> Self {
+                GenVariantPrinter(idx)
+            }
+        }
+        impl Debug for GenVariantPrinter {
+            fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+                let variant_name = ty::GeneratorSubsts::variant_name(self.0);
+                if fmt.alternate() {
+                    write!(fmt, "{:9}({:?})", variant_name, self.0)
+                } else {
+                    write!(fmt, "{}", variant_name)
+                }
+            }
+        }
+
+        /// Forces its contents to print in regular mode instead of alternate mode.
+        struct OneLinePrinter<T>(T);
+        impl<T: Debug> Debug for OneLinePrinter<T> {
+            fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+                write!(fmt, "{:?}", self.0)
+            }
+        }
+
+        fmt.debug_struct("GeneratorLayout")
+            .field("field_tys", &MapPrinter::new(self.field_tys.iter_enumerated()))
+            .field(
+                "variant_fields",
+                &MapPrinter::new(
+                    self.variant_fields
+                        .iter_enumerated()
+                        .map(|(k, v)| (GenVariantPrinter(k), OneLinePrinter(v))),
+                ),
+            )
+            .field("storage_conflicts", &self.storage_conflicts)
+            .finish()
+    }
+}
+
 #[derive(Debug, RustcEncodable, RustcDecodable, HashStable)]
 pub struct BorrowCheckResult<'tcx> {
     /// All the opaque types that are restricted to concrete types

src/librustc_middle/ty/sty.rs

@@ -522,7 +522,6 @@ impl<'tcx> GeneratorSubsts<'tcx> {
 
     /// Calls `f` with a reference to the name of the enumerator for the given
     /// variant `v`.
-    #[inline]
     pub fn variant_name(v: VariantIdx) -> Cow<'static, str> {
         match v.as_usize() {
             Self::UNRESUMED => Cow::from(Self::UNRESUMED_NAME),

src/librustc_mir/util/pretty.rs

@@ -131,7 +131,7 @@ fn dump_matched_mir_node<'tcx, F>(
         }
         writeln!(file, " {} {}", disambiguator, pass_name)?;
         if let Some(ref layout) = body.generator_layout {
-            writeln!(file, "// generator_layout = {:?}", layout)?;
+            writeln!(file, "/* generator_layout = {:#?} */", layout)?;
         }
         writeln!(file)?;
         extra_data(PassWhere::BeforeCFG, &mut file)?;

src/test/mir-opt/generator-drop-cleanup/rustc.main-{{closure}}.generator_drop.0.mir

@@ -1,5 +1,18 @@
 // MIR for `main::{{closure}}#0` 0 generator_drop
-// generator_layout = GeneratorLayout { field_tys: [std::string::String], variant_fields: [[], [], [], [_0]], variant_source_info: [SourceInfo { span: $DIR/generator-drop-cleanup.rs:10:15: 10:15 (#0), scope: scope[0] }, SourceInfo { span: $DIR/generator-drop-cleanup.rs:13:6: 13:6 (#0), scope: scope[0] }, SourceInfo { span: $DIR/generator-drop-cleanup.rs:13:6: 13:6 (#0), scope: scope[0] }, SourceInfo { span: $DIR/generator-drop-cleanup.rs:12:9: 12:14 (#0), scope: scope[1] }], storage_conflicts: BitMatrix { num_rows: 1, num_columns: 1, words: [1], marker: PhantomData } }
+/* generator_layout = GeneratorLayout {
+    field_tys: {
+        _0: std::string::String,
+    },
+    variant_fields: {
+        Unresumed(0): [],
+        Returned (1): [],
+        Panicked (2): [],
+        Suspend0 (3): [_0],
+    },
+    storage_conflicts: BitMatrix(1x1) {
+        (_0, _0),
+    },
+} */
 
 fn main::{{closure}}#0(_1: *mut [generator@$DIR/generator-drop-cleanup.rs:10:15: 13:6 {std::string::String, ()}]) -> () {
     let mut _0: ();                      // return place in scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6

src/test/mir-opt/generator-tiny/rustc.main-{{closure}}.generator_resume.0.mir

@@ -1,5 +1,18 @@
 // MIR for `main::{{closure}}#0` 0 generator_resume
-// generator_layout = GeneratorLayout { field_tys: [HasDrop], variant_fields: [[], [], [], [_0]], variant_source_info: [SourceInfo { span: $DIR/generator-tiny.rs:19:16: 19:16 (#0), scope: scope[0] }, SourceInfo { span: $DIR/generator-tiny.rs:25:6: 25:6 (#0), scope: scope[0] }, SourceInfo { span: $DIR/generator-tiny.rs:25:6: 25:6 (#0), scope: scope[0] }, SourceInfo { span: $DIR/generator-tiny.rs:22:13: 22:18 (#0), scope: scope[1] }], storage_conflicts: BitMatrix { num_rows: 1, num_columns: 1, words: [1], marker: PhantomData } }
+/* generator_layout = GeneratorLayout {
+    field_tys: {
+        _0: HasDrop,
+    },
+    variant_fields: {
+        Unresumed(0): [],
+        Returned (1): [],
+        Panicked (2): [],
+        Suspend0 (3): [_0],
+    },
+    storage_conflicts: BitMatrix(1x1) {
+        (_0, _0),
+    },
+} */
 
 fn main::{{closure}}#0(_1: std::pin::Pin<&mut [generator@$DIR/generator-tiny.rs:19:16: 25:6 {u8, HasDrop, ()}]>, _2: u8) -> std::ops::GeneratorState<(), ()> {
     debug _x => _10;                     // in scope 0 at $DIR/generator-tiny.rs:19:17: 19:19