Auto merge of #71232 - eddyb:print-const-adts, r=oli-obk

ty/print: pretty-print constant aggregates (arrays, tuples and ADTs).

Oddly enough, we don't have any UI tests showing this off in types, only `mir-opt` tests.
However, the pretty form should show up in the test output diff of #71018, if this PR is merged first.

<hr/>

Examples of before/after:
|`Option<bool>`|
|:-:|
|`{transmute(0x01): std::option::Option<bool>}`|
| :sparkles: ↓↓↓ :sparkles: |
|`std::option::Option::<bool>::Some(true)`|

| `RawVec<u32>` |
|:-:|
| `ByRef { alloc: Allocation { bytes: [4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], relocations: Relocations(SortedMap { data: [] }), undef_mask: UndefMask { blocks: [65535], len: Size { raw: 16 } }, size: Size { raw: 16 }, align: Align { pow2: 3 }, mutability: Not, extra: () }, offset: Size { raw: 0 } }: alloc::raw_vec::RawVec::<u32>`|
| :sparkles: ↓↓↓ :sparkles: |
|`alloc::raw_vec::RawVec::<u32> { ptr: std::ptr::Unique::<u32> { pointer: {0x4 as *const u32}, _marker: std::marker::PhantomData::<u32> }, cap: 0usize, alloc: std::alloc::Global }`|

<hr/>

This PR is a prerequisite for #61486, *sort of*, in that we need to be able to pretty-print values in order to even consider how we might mangle them.
We still don't have pretty-printing for constants of reference types, @oli-obk has the necessary support logic in a PR but I didn't want to interfere with that.

<hr/>

Each commit should be reviewed separately, as I've fixed a couple deficiencies along the way.

r? @oli-obk cc @rust-lang/wg-mir-opt @varkor @yodaldevoid

src/librustc_middle/mir/mod.rs

@@ -2242,39 +2242,41 @@ impl<'tcx> Debug for Rvalue<'tcx> {
             }
 
             Aggregate(ref kind, ref places) => {
-                fn fmt_tuple(fmt: &mut Formatter<'_>, places: &[Operand<'_>]) -> fmt::Result {
-                    let mut tuple_fmt = fmt.debug_tuple("");
+                let fmt_tuple = |fmt: &mut Formatter<'_>, name: &str| {
+                    let mut tuple_fmt = fmt.debug_tuple(name);
                     for place in places {
                         tuple_fmt.field(place);
                     }
                     tuple_fmt.finish()
-                }
+                };
 
                 match **kind {
                     AggregateKind::Array(_) => write!(fmt, "{:?}", places),
 
-                    AggregateKind::Tuple => match places.len() {
-                        0 => write!(fmt, "()"),
-                        1 => write!(fmt, "({:?},)", places[0]),
-                        _ => fmt_tuple(fmt, places),
-                    },
+                    AggregateKind::Tuple => {
+                        if places.is_empty() {
+                            write!(fmt, "()")
+                        } else {
+                            fmt_tuple(fmt, "")
+                        }
+                    }
 
                     AggregateKind::Adt(adt_def, variant, substs, _user_ty, _) => {
                         let variant_def = &adt_def.variants[variant];
 
-                        let f = &mut *fmt;
-                        ty::tls::with(|tcx| {
+                        let name = ty::tls::with(|tcx| {
+                            let mut name = String::new();
                             let substs = tcx.lift(&substs).expect("could not lift for printing");
-                            FmtPrinter::new(tcx, f, Namespace::ValueNS)
+                            FmtPrinter::new(tcx, &mut name, Namespace::ValueNS)
                                 .print_def_path(variant_def.def_id, substs)?;
-                            Ok(())
+                            Ok(name)
                         })?;
 
                         match variant_def.ctor_kind {
-                            CtorKind::Const => Ok(()),
-                            CtorKind::Fn => fmt_tuple(fmt, places),
+                            CtorKind::Const => fmt.write_str(&name),
+                            CtorKind::Fn => fmt_tuple(fmt, &name),
                             CtorKind::Fictive => {
-                                let mut struct_fmt = fmt.debug_struct("");
+                                let mut struct_fmt = fmt.debug_struct(&name);
                                 for (field, place) in variant_def.fields.iter().zip(places) {
                                     struct_fmt.field(&field.ident.as_str(), place);
                                 }

src/librustc_middle/query/mod.rs

@@ -574,7 +574,7 @@ rustc_queries! {
             desc { "extract field of const" }
         }
 
-        /// Destructure a constant ADT or array into its variant indent and its
+        /// Destructure a constant ADT or array into its variant index and its
         /// field values.
         query destructure_const(
             key: ty::ParamEnvAnd<'tcx, &'tcx ty::Const<'tcx>>

src/librustc_middle/ty/print/pretty.rs

@@ -9,7 +9,7 @@ use rustc_apfloat::Float;
 use rustc_ast::ast;
 use rustc_attr::{SignedInt, UnsignedInt};
 use rustc_hir as hir;
-use rustc_hir::def::{DefKind, Namespace};
+use rustc_hir::def::{CtorKind, DefKind, Namespace};
 use rustc_hir::def_id::{CrateNum, DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
 use rustc_span::symbol::{kw, Symbol};
@@ -498,16 +498,9 @@ pub trait PrettyPrinter<'tcx>:
             }
             ty::Never => p!(write("!")),
             ty::Tuple(ref tys) => {
-                p!(write("("));
-                let mut tys = tys.iter();
-                if let Some(&ty) = tys.next() {
-                    p!(print(ty), write(","));
-                    if let Some(&ty) = tys.next() {
-                        p!(write(" "), print(ty));
-                        for &ty in tys {
-                            p!(write(", "), print(ty));
-                        }
-                    }
+                p!(write("("), comma_sep(tys.iter().copied()));
+                if tys.len() == 1 {
+                    p!(write(","));
                 }
                 p!(write(")"))
             }
@@ -570,15 +563,10 @@ pub trait PrettyPrinter<'tcx>:
                     let def_key = self.tcx().def_key(def_id);
                     if let Some(name) = def_key.disambiguated_data.data.get_opt_name() {
                         p!(write("{}", name));
-                        let mut substs = substs.iter();
                         // FIXME(eddyb) print this with `print_def_path`.
-                        if let Some(first) = substs.next() {
-                            p!(write("::<"));
-                            p!(print(first));
-                            for subst in substs {
-                                p!(write(", "), print(subst));
-                            }
-                            p!(write(">"));
+                        if !substs.is_empty() {
+                            p!(write("::"));
+                            p!(generic_delimiters(|cx| cx.comma_sep(substs.iter().copied())));
                         }
                         return Ok(self);
                     }
@@ -850,16 +838,12 @@ pub trait PrettyPrinter<'tcx>:
     ) -> Result<Self, Self::Error> {
         define_scoped_cx!(self);
 
-        p!(write("("));
-        let mut inputs = inputs.iter();
-        if let Some(&ty) = inputs.next() {
-            p!(print(ty));
-            for &ty in inputs {
-                p!(write(", "), print(ty));
-            }
-            if c_variadic {
-                p!(write(", ..."));
+        p!(write("("), comma_sep(inputs.iter().copied()));
+        if c_variadic {
+            if !inputs.is_empty() {
+                p!(write(", "));
             }
+            p!(write("..."));
         }
         p!(write(")"));
         if !output.is_unit() {
@@ -1050,19 +1034,6 @@ pub trait PrettyPrinter<'tcx>:
             }
             // For function type zsts just printing the path is enough
             (Scalar::Raw { size: 0, .. }, ty::FnDef(d, s)) => p!(print_value_path(*d, s)),
-            // Empty tuples are frequently occurring, so don't print the fallback.
-            (Scalar::Raw { size: 0, .. }, ty::Tuple(ts)) if ts.is_empty() => p!(write("()")),
-            // Zero element arrays have a trivial representation.
-            (
-                Scalar::Raw { size: 0, .. },
-                ty::Array(
-                    _,
-                    ty::Const {
-                        val: ty::ConstKind::Value(ConstValue::Scalar(Scalar::Raw { data: 0, .. })),
-                        ..
-                    },
-                ),
-            ) => p!(write("[]")),
             // Nontrivial types with scalar bit representation
             (Scalar::Raw { data, size }, _) => {
                 let print = |mut this: Self| {
@@ -1131,14 +1102,14 @@ pub trait PrettyPrinter<'tcx>:
         define_scoped_cx!(self);
 
         if self.tcx().sess.verbose() {
-            p!(write("ConstValue({:?}: {:?})", ct, ty));
+            p!(write("ConstValue({:?}: ", ct), print(ty), write(")"));
             return Ok(self);
         }
 
         let u8_type = self.tcx().types.u8;
 
         match (ct, &ty.kind) {
-            (ConstValue::Scalar(scalar), _) => self.pretty_print_const_scalar(scalar, ty, print_ty),
+            // Byte/string slices, printed as (byte) string literals.
             (
                 ConstValue::Slice { data, start, end },
                 ty::Ref(_, ty::TyS { kind: ty::Slice(t), .. }, _),
@@ -1172,6 +1143,66 @@ pub trait PrettyPrinter<'tcx>:
                 p!(pretty_print_byte_str(byte_str));
                 Ok(self)
             }
+
+            // Aggregates, printed as array/tuple/struct/variant construction syntax.
+            //
+            // NB: the `has_param_types_or_consts` check ensures that we can use
+            // the `destructure_const` query with an empty `ty::ParamEnv` without
+            // introducing ICEs (e.g. via `layout_of`) from missing bounds.
+            // E.g. `transmute([0usize; 2]): (u8, *mut T)` needs to know `T: Sized`
+            // to be able to destructure the tuple into `(0u8, *mut T)
+            //
+            // FIXME(eddyb) for `--emit=mir`/`-Z dump-mir`, we should provide the
+            // correct `ty::ParamEnv` to allow printing *all* constant values.
+            (_, ty::Array(..) | ty::Tuple(..) | ty::Adt(..)) if !ty.has_param_types_or_consts() => {
+                let contents = self.tcx().destructure_const(
+                    ty::ParamEnv::reveal_all()
+                        .and(self.tcx().mk_const(ty::Const { val: ty::ConstKind::Value(ct), ty })),
+                );
+                let fields = contents.fields.iter().copied();
+
+                match ty.kind {
+                    ty::Array(..) => {
+                        p!(write("["), comma_sep(fields), write("]"));
+                    }
+                    ty::Tuple(..) => {
+                        p!(write("("), comma_sep(fields));
+                        if contents.fields.len() == 1 {
+                            p!(write(","));
+                        }
+                        p!(write(")"));
+                    }
+                    ty::Adt(def, substs) => {
+                        let variant_def = &def.variants[contents.variant];
+                        p!(print_value_path(variant_def.def_id, substs));
+
+                        match variant_def.ctor_kind {
+                            CtorKind::Const => {}
+                            CtorKind::Fn => {
+                                p!(write("("), comma_sep(fields), write(")"));
+                            }
+                            CtorKind::Fictive => {
+                                p!(write(" {{ "));
+                                let mut first = true;
+                                for (field_def, field) in variant_def.fields.iter().zip(fields) {
+                                    if !first {
+                                        p!(write(", "));
+                                    }
+                                    p!(write("{}: ", field_def.ident), print(field));
+                                    first = false;
+                                }
+                                p!(write(" }}"));
+                            }
+                        }
+                    }
+                    _ => unreachable!(),
+                }
+
+                Ok(self)
+            }
+
+            (ConstValue::Scalar(scalar), _) => self.pretty_print_const_scalar(scalar, ty, print_ty),
+
             // FIXME(oli-obk): also pretty print arrays and other aggregate constants by reading
             // their fields instead of just dumping the memory.
             _ => {
@@ -1910,15 +1941,7 @@ define_print_and_forward_display! {
     (self, cx):
 
     &'tcx ty::List<Ty<'tcx>> {
-        p!(write("{{"));
-        let mut tys = self.iter();
-        if let Some(&ty) = tys.next() {
-            p!(print(ty));
-            for &ty in tys {
-                p!(write(", "), print(ty));
-            }
-        }
-        p!(write("}}"))
+        p!(write("{{"), comma_sep(self.iter().copied()), write("}}"))
     }
 
     ty::TypeAndMut<'tcx> {

src/test/mir-opt/const_prop/discriminant/32bit/rustc.main.ConstProp.diff

@@ -15,8 +15,8 @@
           StorageLive(_1);                 // bb0[0]: scope 0 at $DIR/discriminant.rs:6:9: 6:10
           StorageLive(_2);                 // bb0[1]: scope 0 at $DIR/discriminant.rs:6:13: 6:64
           StorageLive(_3);                 // bb0[2]: scope 0 at $DIR/discriminant.rs:6:34: 6:44
--         _3 = std::option::Option::<bool>::Some(const true,); // bb0[3]: scope 0 at $DIR/discriminant.rs:6:34: 6:44
-+         _3 = const {transmute(0x01): std::option::Option<bool>}; // bb0[3]: scope 0 at $DIR/discriminant.rs:6:34: 6:44
+-         _3 = std::option::Option::<bool>::Some(const true); // bb0[3]: scope 0 at $DIR/discriminant.rs:6:34: 6:44
++         _3 = const std::option::Option::<bool>::Some(true); // bb0[3]: scope 0 at $DIR/discriminant.rs:6:34: 6:44
                                            // ty::Const
 -                                          // + ty: bool
 +                                          // + ty: std::option::Option<bool>

src/test/mir-opt/const_prop/discriminant/64bit/rustc.main.ConstProp.diff

@@ -15,8 +15,8 @@
           StorageLive(_1);                 // bb0[0]: scope 0 at $DIR/discriminant.rs:6:9: 6:10
           StorageLive(_2);                 // bb0[1]: scope 0 at $DIR/discriminant.rs:6:13: 6:64
           StorageLive(_3);                 // bb0[2]: scope 0 at $DIR/discriminant.rs:6:34: 6:44
--         _3 = std::option::Option::<bool>::Some(const true,); // bb0[3]: scope 0 at $DIR/discriminant.rs:6:34: 6:44
-+         _3 = const {transmute(0x01): std::option::Option<bool>}; // bb0[3]: scope 0 at $DIR/discriminant.rs:6:34: 6:44
+-         _3 = std::option::Option::<bool>::Some(const true); // bb0[3]: scope 0 at $DIR/discriminant.rs:6:34: 6:44
++         _3 = const std::option::Option::<bool>::Some(true); // bb0[3]: scope 0 at $DIR/discriminant.rs:6:34: 6:44
                                            // ty::Const
 -                                          // + ty: bool
 +                                          // + ty: std::option::Option<bool>

src/test/mir-opt/deaggregator_test_enum_2/rustc.test1.Deaggregator.diff

@@ -18,7 +18,7 @@
       bb1: {
           StorageLive(_5);                 // bb1[0]: scope 0 at $DIR/deaggregator_test_enum_2.rs:13:16: 13:17
           _5 = _2;                         // bb1[1]: scope 0 at $DIR/deaggregator_test_enum_2.rs:13:16: 13:17
--         _0 = Foo::B(move _5,);           // bb1[2]: scope 0 at $DIR/deaggregator_test_enum_2.rs:13:9: 13:18
+-         _0 = Foo::B(move _5);            // bb1[2]: scope 0 at $DIR/deaggregator_test_enum_2.rs:13:9: 13:18
 -         StorageDead(_5);                 // bb1[3]: scope 0 at $DIR/deaggregator_test_enum_2.rs:13:17: 13:18
 -         goto -> bb3;                     // bb1[4]: scope 0 at $DIR/deaggregator_test_enum_2.rs:10:5: 14:6
 +         ((_0 as B).0: i32) = move _5;    // bb1[2]: scope 0 at $DIR/deaggregator_test_enum_2.rs:13:9: 13:18
@@ -30,7 +30,7 @@
       bb2: {
           StorageLive(_4);                 // bb2[0]: scope 0 at $DIR/deaggregator_test_enum_2.rs:11:16: 11:17
           _4 = _2;                         // bb2[1]: scope 0 at $DIR/deaggregator_test_enum_2.rs:11:16: 11:17
--         _0 = Foo::A(move _4,);           // bb2[2]: scope 0 at $DIR/deaggregator_test_enum_2.rs:11:9: 11:18
+-         _0 = Foo::A(move _4);            // bb2[2]: scope 0 at $DIR/deaggregator_test_enum_2.rs:11:9: 11:18
 -         StorageDead(_4);                 // bb2[3]: scope 0 at $DIR/deaggregator_test_enum_2.rs:11:17: 11:18
 -         goto -> bb3;                     // bb2[4]: scope 0 at $DIR/deaggregator_test_enum_2.rs:10:5: 14:6
 +         ((_0 as A).0: i32) = move _4;    // bb2[2]: scope 0 at $DIR/deaggregator_test_enum_2.rs:11:9: 11:18

src/test/mir-opt/deaggregator_test_multiple/rustc.test.Deaggregator.diff

@@ -13,12 +13,12 @@
           StorageLive(_2);                 // bb0[0]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:6: 10:15
           StorageLive(_3);                 // bb0[1]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:13: 10:14
           _3 = _1;                         // bb0[2]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:13: 10:14
--         _2 = Foo::A(move _3,);           // bb0[3]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:6: 10:15
+-         _2 = Foo::A(move _3);            // bb0[3]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:6: 10:15
 -         StorageDead(_3);                 // bb0[4]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:14: 10:15
 -         StorageLive(_4);                 // bb0[5]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:17: 10:26
 -         StorageLive(_5);                 // bb0[6]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:24: 10:25
 -         _5 = _1;                         // bb0[7]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:24: 10:25
--         _4 = Foo::A(move _5,);           // bb0[8]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:17: 10:26
+-         _4 = Foo::A(move _5);            // bb0[8]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:17: 10:26
 -         StorageDead(_5);                 // bb0[9]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:25: 10:26
 -         _0 = [move _2, move _4];         // bb0[10]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:5: 10:27
 -         StorageDead(_4);                 // bb0[11]: scope 0 at $DIR/deaggregator_test_multiple.rs:10:26: 10:27

src/test/mir-opt/generator-storage-dead-unwind/rustc.main-{{closure}}.StateTransform.before.mir

@@ -21,15 +21,15 @@ yields ()
 
     bb0: {
         StorageLive(_3);                 // bb0[0]: scope 0 at $DIR/generator-storage-dead-unwind.rs:23:13: 23:14
-        _3 = Foo(const 5i32,);           // bb0[1]: scope 0 at $DIR/generator-storage-dead-unwind.rs:23:17: 23:23
+        _3 = Foo(const 5i32);            // bb0[1]: scope 0 at $DIR/generator-storage-dead-unwind.rs:23:17: 23:23
                                          // ty::Const
                                          // + ty: i32
                                          // + val: Value(Scalar(0x00000005))
                                          // mir::Constant
                                          // + span: $DIR/generator-storage-dead-unwind.rs:23:21: 23:22
                                          // + literal: Const { ty: i32, val: Value(Scalar(0x00000005)) }
         StorageLive(_4);                 // bb0[2]: scope 1 at $DIR/generator-storage-dead-unwind.rs:24:13: 24:14
-        _4 = Bar(const 6i32,);           // bb0[3]: scope 1 at $DIR/generator-storage-dead-unwind.rs:24:17: 24:23
+        _4 = Bar(const 6i32);            // bb0[3]: scope 1 at $DIR/generator-storage-dead-unwind.rs:24:17: 24:23
                                          // ty::Const
                                          // + ty: i32
                                          // + val: Value(Scalar(0x00000006))

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

@@ -34,7 +34,7 @@ fn main::{{closure}}#0(_1: std::pin::Pin<&mut [generator@$DIR/generator-tiny.rs:
         StorageLive(_6);                 // bb2[0]: scope 1 at $DIR/generator-tiny.rs:21:13: 21:18
         StorageLive(_7);                 // bb2[1]: scope 1 at $DIR/generator-tiny.rs:21:13: 21:18
         _7 = ();                         // bb2[2]: scope 1 at $DIR/generator-tiny.rs:21:13: 21:18
-        _0 = std::ops::GeneratorState::<(), ()>::Yielded(move _7,); // bb2[3]: scope 1 at $DIR/generator-tiny.rs:21:13: 21:18
+        _0 = std::ops::GeneratorState::<(), ()>::Yielded(move _7); // bb2[3]: scope 1 at $DIR/generator-tiny.rs:21:13: 21:18
         discriminant((*(_1.0: &mut [generator@$DIR/generator-tiny.rs:18:16: 24:6 {u8, HasDrop, ()}]))) = 3; // bb2[4]: scope 1 at $DIR/generator-tiny.rs:21:13: 21:18
         return;                          // bb2[5]: scope 1 at $DIR/generator-tiny.rs:21:13: 21:18
     }

src/test/mir-opt/inline/inline-into-box-place/32bit/rustc.main.Inline.diff

@@ -19,7 +19,7 @@
           _2 = Box(std::vec::Vec<u32>);    // bb0[2]: scope 0 at $DIR/inline-into-box-place.rs:8:29: 8:43
 -         (*_2) = const std::vec::Vec::<u32>::new() -> [return: bb2, unwind: bb4]; // bb0[3]: scope 0 at $DIR/inline-into-box-place.rs:8:33: 8:43
 +         _4 = &mut (*_2);                 // bb0[3]: scope 0 at $DIR/inline-into-box-place.rs:8:33: 8:43
-+         ((*_4).0: alloc::raw_vec::RawVec<u32>) = const ByRef { alloc: Allocation { bytes: [4, 0, 0, 0, 0, 0, 0, 0], relocations: Relocations(SortedMap { data: [] }), undef_mask: UndefMask { blocks: [255], len: Size { raw: 8 } }, size: Size { raw: 8 }, align: Align { pow2: 2 }, mutability: Not, extra: () }, offset: Size { raw: 0 } }: alloc::raw_vec::RawVec::<u32>; // bb0[4]: scope 2 at $SRC_DIR/liballoc/vec.rs:LL:COL
++         ((*_4).0: alloc::raw_vec::RawVec<u32>) = const alloc::raw_vec::RawVec::<u32> { ptr: std::ptr::Unique::<u32> { pointer: {0x4 as *const u32}, _marker: std::marker::PhantomData::<u32> }, cap: 0usize, alloc: std::alloc::Global }; // bb0[4]: scope 2 at $SRC_DIR/liballoc/vec.rs:LL:COL
                                            // ty::Const
 -                                          // + ty: fn() -> std::vec::Vec<u32> {std::vec::Vec::<u32>::new}
 -                                          // + val: Value(Scalar(<ZST>))