Rollup of 6 pull requests

compiler/rustc_feature/src/unstable.rs

@@ -579,6 +579,9 @@ declare_features! (
     (incomplete, repr128, "1.16.0", Some(56071)),
     /// Allows `repr(simd)` and importing the various simd intrinsics.
     (unstable, repr_simd, "1.4.0", Some(27731)),
+    /// Allows enums like Result<T, E> to be used across FFI, if T's niche value can
+    /// be used to describe E or vise-versa.
+    (unstable, result_ffi_guarantees, "CURRENT_RUSTC_VERSION", Some(110503)),
     /// Allows bounding the return type of AFIT/RPITIT.
     (incomplete, return_type_notation, "1.70.0", Some(109417)),
     /// Allows `extern "rust-cold"`.

compiler/rustc_lint/src/types.rs

@@ -1101,6 +1101,32 @@ fn get_nullable_type<'tcx>(
     })
 }
 
+/// A type is niche-optimization candidate iff:
+/// - Is a zero-sized type with alignment 1 (a “1-ZST”).
+/// - Has no fields.
+/// - Does not have the `#[non_exhaustive]` attribute.
+fn is_niche_optimization_candidate<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    ty: Ty<'tcx>,
+) -> bool {
+    if tcx.layout_of(param_env.and(ty)).is_ok_and(|layout| !layout.is_1zst()) {
+        return false;
+    }
+
+    match ty.kind() {
+        ty::Adt(ty_def, _) => {
+            let non_exhaustive = ty_def.is_variant_list_non_exhaustive();
+            let empty = (ty_def.is_struct() && ty_def.all_fields().next().is_none())
+                || (ty_def.is_enum() && ty_def.variants().is_empty());
+
+            !non_exhaustive && empty
+        }
+        ty::Tuple(tys) => tys.is_empty(),
+        _ => false,
+    }
+}
+
 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero`,
@@ -1117,6 +1143,22 @@ pub(crate) fn repr_nullable_ptr<'tcx>(
         let field_ty = match &ty_def.variants().raw[..] {
             [var_one, var_two] => match (&var_one.fields.raw[..], &var_two.fields.raw[..]) {
                 ([], [field]) | ([field], []) => field.ty(tcx, args),
+                ([field1], [field2]) => {
+                    if !tcx.features().result_ffi_guarantees {
+                        return None;
+                    }
+
+                    let ty1 = field1.ty(tcx, args);
+                    let ty2 = field2.ty(tcx, args);
+
+                    if is_niche_optimization_candidate(tcx, param_env, ty1) {
+                        ty2
+                    } else if is_niche_optimization_candidate(tcx, param_env, ty2) {
+                        ty1
+                    } else {
+                        return None;
+                    }
+                }
                 _ => return None,
             },
             _ => return None,
@@ -1202,7 +1244,6 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
         args: GenericArgsRef<'tcx>,
     ) -> FfiResult<'tcx> {
         use FfiResult::*;
-
         let transparent_with_all_zst_fields = if def.repr().transparent() {
             if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
                 // Transparent newtypes have at most one non-ZST field which needs to be checked..
@@ -1329,27 +1370,29 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
                             return FfiSafe;
                         }
 
+                        if def.is_variant_list_non_exhaustive() && !def.did().is_local() {
+                            return FfiUnsafe {
+                                ty,
+                                reason: fluent::lint_improper_ctypes_non_exhaustive,
+                                help: None,
+                            };
+                        }
+
                         // Check for a repr() attribute to specify the size of the
                         // discriminant.
                         if !def.repr().c() && !def.repr().transparent() && def.repr().int.is_none()
                         {
-                            // Special-case types like `Option<extern fn()>`.
-                            if repr_nullable_ptr(self.cx.tcx, self.cx.param_env, ty, self.mode)
-                                .is_none()
+                            // Special-case types like `Option<extern fn()>` and `Result<extern fn(), ()>`
+                            if let Some(ty) =
+                                repr_nullable_ptr(self.cx.tcx, self.cx.param_env, ty, self.mode)
                             {
-                                return FfiUnsafe {
-                                    ty,
-                                    reason: fluent::lint_improper_ctypes_enum_repr_reason,
-                                    help: Some(fluent::lint_improper_ctypes_enum_repr_help),
-                                };
+                                return self.check_type_for_ffi(cache, ty);
                             }
-                        }
 
-                        if def.is_variant_list_non_exhaustive() && !def.did().is_local() {
                             return FfiUnsafe {
                                 ty,
-                                reason: fluent::lint_improper_ctypes_non_exhaustive,
-                                help: None,
+                                reason: fluent::lint_improper_ctypes_enum_repr_reason,
+                                help: Some(fluent::lint_improper_ctypes_enum_repr_help),
                             };
                         }
 

compiler/rustc_session/src/config/cfg.rs

@@ -262,13 +262,15 @@ impl CheckCfg {
 
         ins!(sym::debug_assertions, no_values);
 
-        // These four are never set by rustc, but we set them anyway: they
-        // should not trigger a lint because `cargo clippy`, `cargo doc`,
-        // `cargo test` and `cargo miri run` (respectively) can set them.
+        // These four are never set by rustc, but we set them anyway; they
+        // should not trigger the lint because `cargo clippy`, `cargo doc`,
+        // `cargo test`, `cargo miri run` and `cargo fmt` (respectively)
+        // can set them.
         ins!(sym::clippy, no_values);
         ins!(sym::doc, no_values);
         ins!(sym::doctest, no_values);
         ins!(sym::miri, no_values);
+        ins!(sym::rustfmt, no_values);
 
         ins!(sym::overflow_checks, no_values);
 

compiler/rustc_span/src/symbol.rs

@@ -1511,6 +1511,7 @@ symbols! {
         require,
         residual,
         result,
+        result_ffi_guarantees,
         resume,
         return_position_impl_trait_in_trait,
         return_type_notation,

src/doc/rustc/src/check-cfg.md

@@ -71,7 +71,7 @@ Those well known names and values follows the same stability as what they refer
 Well known names and values checking is always enabled as long as at least one
 `--check-cfg` argument is present.
 
-As of `2024-04-06T`, the list of known names is as follows:
+As of `2024-05-06T`, the list of known names is as follows:
 
 <!--- See CheckCfg::fill_well_known in compiler/rustc_session/src/config.rs -->
 
@@ -84,6 +84,7 @@ As of `2024-04-06T`, the list of known names is as follows:
  - `panic`
  - `proc_macro`
  - `relocation_model`
+ - `rustfmt`
  - `sanitize`
  - `sanitizer_cfi_generalize_pointers`
  - `sanitizer_cfi_normalize_integers`

src/doc/unstable-book/src/language-features/result-ffi-guarantees.md

@@ -0,0 +1,14 @@
+# `result_ffi_guarantees`
+
+The tracking issue for this feature is: [#110503]
+
+[#110503]: https://github.com/rust-lang/rust/issues/110503
+
+------------------------
+
+This feature adds the possibility of using `Result<T, E>` in FFI if T's niche
+value can be used to describe E or vise-versa.
+
+See [RFC 3391] for more information.
+
+[RFC 3391]: https://github.com/rust-lang/rfcs/blob/master/text/3391-result_ffi_guarantees.md

src/etc/lldb_lookup.py

@@ -86,7 +86,8 @@ def synthetic_lookup(valobj, dict):
         return synthetic_lookup(valobj.GetChildAtIndex(discriminant), dict)
     if rust_type == RustType.SINGLETON_ENUM:
         return synthetic_lookup(valobj.GetChildAtIndex(0), dict)
-
+    if rust_type == RustType.ENUM:
+        return ClangEncodedEnumProvider(valobj, dict)
     if rust_type == RustType.STD_VEC:
         return StdVecSyntheticProvider(valobj, dict)
     if rust_type == RustType.STD_VEC_DEQUE:

src/etc/lldb_providers.py

@@ -247,6 +247,58 @@ def has_children(self):
         # type: () -> bool
         return True
 
+class ClangEncodedEnumProvider:
+    """Pretty-printer for 'clang-encoded' enums support implemented in LLDB"""
+    DISCRIMINANT_MEMBER_NAME = "$discr$"
+    VALUE_MEMBER_NAME = "value"
+
+    def __init__(self, valobj, dict):
+        self.valobj = valobj
+        self.update()
+
+    def has_children(self):
+       return True
+
+    def num_children(self):
+        if self.is_default:
+            return 1
+        return 2
+
+    def get_child_index(self, name):
+        if name == ClangEncodedEnumProvider.VALUE_MEMBER_NAME:
+            return 0
+        if name == ClangEncodedEnumProvider.DISCRIMINANT_MEMBER_NAME:
+            return 1
+        return -1
+
+    def get_child_at_index(self, index):
+        if index == 0:
+            return self.variant.GetChildMemberWithName(ClangEncodedEnumProvider.VALUE_MEMBER_NAME)
+        if index == 1:
+            return self.variant.GetChildMemberWithName(
+                ClangEncodedEnumProvider.DISCRIMINANT_MEMBER_NAME)
+
+
+    def update(self):
+        all_variants = self.valobj.GetChildAtIndex(0)
+        index = self._getCurrentVariantIndex(all_variants)
+        self.variant = all_variants.GetChildAtIndex(index)
+        self.is_default = self.variant.GetIndexOfChildWithName(
+            ClangEncodedEnumProvider.DISCRIMINANT_MEMBER_NAME) == -1
+
+    def _getCurrentVariantIndex(self, all_variants):
+        default_index = 0
+        for i in range(all_variants.GetNumChildren()):
+            variant = all_variants.GetChildAtIndex(i)
+            discr = variant.GetChildMemberWithName(
+                ClangEncodedEnumProvider.DISCRIMINANT_MEMBER_NAME)
+            if discr.IsValid():
+                discr_unsigned_value = discr.GetValueAsUnsigned()
+                if variant.GetName() == f"$variant${discr_unsigned_value}":
+                    return i
+            else:
+                default_index = i
+        return default_index
 
 class TupleSyntheticProvider:
     """Pretty-printer for tuples and tuple enum variants"""

src/etc/rust_types.py

@@ -60,6 +60,7 @@ class RustType(object):
 
 ENCODED_ENUM_PREFIX = "RUST$ENCODED$ENUM$"
 ENUM_DISR_FIELD_NAME = "<<variant>>"
+ENUM_LLDB_ENCODED_VARIANTS = "$variants$"
 
 STD_TYPE_TO_REGEX = {
     RustType.STD_STRING: STD_STRING_REGEX,
@@ -96,7 +97,11 @@ def classify_struct(name, fields):
         if regex.match(name):
             return ty
 
-    if fields[0].name == ENUM_DISR_FIELD_NAME:
+    # <<variant>> is emitted by GDB while LLDB(18.1+) emits "$variants$"
+    if (
+        fields[0].name == ENUM_DISR_FIELD_NAME
+        or fields[0].name == ENUM_LLDB_ENCODED_VARIANTS
+    ):
         return RustType.ENUM
 
     if is_tuple_fields(fields):

src/librustdoc/html/static/css/noscript.css

@@ -85,6 +85,7 @@ nav.sub {
 	--search-tab-button-not-selected-background: #e6e6e6;
 	--search-tab-button-selected-border-top-color: #0089ff;
 	--search-tab-button-selected-background: #fff;
+	--settings-menu-filter: none;
 	--stab-background-color: #fff5d6;
 	--stab-code-color: #000;
 	--code-highlight-kw-color: #8959a8;

src/librustdoc/html/static/css/rustdoc.css

@@ -1625,6 +1625,7 @@ a.tooltip:hover::after {
 	,5.1715698,7.5,6  S6.8284302,7.5,6,7.5z" fill="black"/></svg>');
 	width: 22px;
 	height: 22px;
+	filter: var(--settings-menu-filter);
 }
 
 #sidebar-button > a:before {
@@ -2419,6 +2420,7 @@ by default.
 	--search-tab-button-not-selected-background: #e6e6e6;
 	--search-tab-button-selected-border-top-color: #0089ff;
 	--search-tab-button-selected-background: #fff;
+	--settings-menu-filter: none;
 	--stab-background-color: #fff5d6;
 	--stab-code-color: #000;
 	--code-highlight-kw-color: #8959a8;
@@ -2524,6 +2526,7 @@ by default.
 	--search-tab-button-not-selected-background: #252525;
 	--search-tab-button-selected-border-top-color: #0089ff;
 	--search-tab-button-selected-background: #353535;
+	--settings-menu-filter: none;
 	--stab-background-color: #314559;
 	--stab-code-color: #e6e1cf;
 	--code-highlight-kw-color: #ab8ac1;
@@ -2636,6 +2639,7 @@ Original by Dempfi (https://github.com/dempfi/ayu)
 	--search-tab-button-not-selected-background: transparent !important;
 	--search-tab-button-selected-border-top-color: none;
 	--search-tab-button-selected-background: #141920 !important;
+	--settings-menu-filter: invert(100%);
 	--stab-background-color: #314559;
 	--stab-code-color: #e6e1cf;
 	--code-highlight-kw-color: #ff7733;

tests/debuginfo/borrowed-enum.rs

@@ -1,6 +1,6 @@
 // Require a gdb or lldb that can read DW_TAG_variant_part.
 //@ min-gdb-version: 8.2
-//@ needs-rust-lldb
+//@ min-lldb-version: 1800
 
 //@ compile-flags:-g
 
@@ -23,10 +23,13 @@
 // lldb-command:run
 
 // lldb-command:v *the_a_ref
+// lldbg-check:(borrowed_enum::ABC) *the_a_ref = { value = { x = 0 y = 8970181431921507452 } $discr$ = 0 }
 // lldbr-check:(borrowed_enum::ABC::TheA) *the_a_ref = TheA { TheA: 0, TheB: 8970181431921507452 }
 // lldb-command:v *the_b_ref
+// lldbg-check:(borrowed_enum::ABC) *the_b_ref = { value = { 0 = 0 1 = 286331153 2 = 286331153 } $discr$ = 1 }
 // lldbr-check:(borrowed_enum::ABC::TheB) *the_b_ref = { = 0 = 286331153 = 286331153 }
 // lldb-command:v *univariant_ref
+// lldbg-check:(borrowed_enum::Univariant) *univariant_ref = { value = { 0 = 4820353753753434 } }
 // lldbr-check:(borrowed_enum::Univariant) *univariant_ref = { TheOnlyCase = { = 4820353753753434 } }
 
 #![allow(unused_variables)]

tests/debuginfo/coroutine-objects.rs

@@ -1,8 +1,9 @@
 // Require a gdb that can read DW_TAG_variant_part.
 //@ min-gdb-version: 8.2
+//@ min-lldb-version: 1800
 
-// LLDB without native Rust support cannot read DW_TAG_variant_part,
-// so it prints nothing for coroutines. But those tests are kept to
+// LLDB (18.1+) now supports DW_TAG_variant_part, but there is some bug in either compiler or LLDB
+// with memory layout of discriminant for this particular enum
 // ensure that LLDB won't crash at least (like #57822).
 
 //@ compile-flags:-g
@@ -26,16 +27,7 @@
 
 // lldb-command:run
 // lldb-command:v b
-// lldbg-check:(coroutine_objects::main::{coroutine_env#0}) b =
-// lldb-command:continue
-// lldb-command:v b
-// lldbg-check:(coroutine_objects::main::{coroutine_env#0}) b =
-// lldb-command:continue
-// lldb-command:v b
-// lldbg-check:(coroutine_objects::main::{coroutine_env#0}) b =
-// lldb-command:continue
-// lldb-command:v b
-// lldbg-check:(coroutine_objects::main::{coroutine_env#0}) b =
+// lldb-check:(coroutine_objects::main::{coroutine_env#0}) b = { value = { _ref__a = 0x[...] } $discr$ = ',' }
 
 // === CDB TESTS ===================================================================================
 

tests/debuginfo/enum-thinlto.rs

@@ -1,6 +1,6 @@
 // Require a gdb that can read DW_TAG_variant_part.
 //@ min-gdb-version: 8.2
-
+//@ min-lldb-version: 1800
 //@ compile-flags:-g -Z thinlto
 
 // === GDB TESTS ===================================================================================
@@ -15,7 +15,7 @@
 // lldb-command:run
 
 // lldb-command:v *abc
-// lldbg-check:(enum_thinlto::ABC) *abc =
+// lldbg-check:(enum_thinlto::ABC) *abc = { value = { x = 0 y = 8970181431921507452 } $discr$ = 0 }
 // lldbr-check:(enum_thinlto::ABC) *abc = (x = 0, y = 8970181431921507452)
 
 #![allow(unused_variables)]

tests/debuginfo/issue-57822.rs

@@ -3,7 +3,7 @@
 
 // Require a gdb that can read DW_TAG_variant_part.
 //@ min-gdb-version: 8.2
-
+//@ min-lldb-version: 1800
 //@ compile-flags:-g
 
 // === GDB TESTS ===================================================================================
@@ -24,7 +24,7 @@
 // lldbg-check:(issue_57822::main::{closure_env#1}) g = { f = { x = 1 } }
 
 // lldb-command:v b
-// lldbg-check:(issue_57822::main::{coroutine_env#3}) b =
+// lldbg-check:(issue_57822::main::{coroutine_env#3}) b = { value = { a = { value = { y = 2 } $discr$ = '\x02' } } $discr$ = '\x02' }
 
 #![feature(omit_gdb_pretty_printer_section, coroutines, coroutine_trait, stmt_expr_attributes)]
 #![omit_gdb_pretty_printer_section]