Rollup of 13 pull requests

compiler/rustc_ast/src/lib.rs

@@ -7,6 +7,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/", test(attr(deny(warnings))))]
 #![feature(box_syntax)]
 #![feature(const_fn)] // For the `transmute` in `P::new`
+#![feature(const_fn_transmute)]
 #![feature(const_panic)]
 #![feature(crate_visibility_modifier)]
 #![feature(label_break_value)]

compiler/rustc_attr/src/builtin.rs

@@ -301,7 +301,7 @@ where
                                                 .emit();
                                             };
                                             match issue.parse() {
-                                                Ok(num) if num == 0 => {
+                                                Ok(0) => {
                                                     emit_diag(
                                                         "`issue` must not be \"0\", \
                                                         use \"none\" instead",

compiler/rustc_builtin_macros/src/format_foreign.rs

@@ -518,8 +518,7 @@ pub mod printf {
                         .and_then(|end| end.at_next_cp())
                         .map(|end| (next.slice_between(end).unwrap(), end));
                     let end = match end {
-                        Some(("32", end)) => end,
-                        Some(("64", end)) => end,
+                        Some(("32" | "64", end)) => end,
                         _ => next,
                     };
                     state = Type;

compiler/rustc_lint/src/lib.rs

@@ -49,6 +49,7 @@ mod early;
 mod internal;
 mod late;
 mod levels;
+mod methods;
 mod non_ascii_idents;
 mod nonstandard_style;
 mod passes;
@@ -72,6 +73,7 @@ use rustc_span::Span;
 use array_into_iter::ArrayIntoIter;
 use builtin::*;
 use internal::*;
+use methods::*;
 use non_ascii_idents::*;
 use nonstandard_style::*;
 use redundant_semicolon::*;
@@ -157,6 +159,7 @@ macro_rules! late_lint_passes {
                 MissingDebugImplementations: MissingDebugImplementations::default(),
                 ArrayIntoIter: ArrayIntoIter,
                 ClashingExternDeclarations: ClashingExternDeclarations::new(),
+                TemporaryCStringAsPtr: TemporaryCStringAsPtr,
             ]
         );
     };

compiler/rustc_lint/src/methods.rs

@@ -0,0 +1,106 @@
+use crate::LateContext;
+use crate::LateLintPass;
+use crate::LintContext;
+use rustc_hir::{Expr, ExprKind, PathSegment};
+use rustc_middle::ty;
+use rustc_span::{symbol::sym, ExpnKind, Span};
+
+declare_lint! {
+    /// The `temporary_cstring_as_ptr` lint detects getting the inner pointer of
+    /// a temporary `CString`.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// # #![allow(unused)]
+    /// # use std::ffi::CString;
+    /// let c_str = CString::new("foo").unwrap().as_ptr();
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// The inner pointer of a `CString` lives only as long as the `CString` it
+    /// points to. Getting the inner pointer of a *temporary* `CString` allows the `CString`
+    /// to be dropped at the end of the statement, as it is not being referenced as far as the typesystem
+    /// is concerned. This means outside of the statement the pointer will point to freed memory, which
+    /// causes undefined behavior if the pointer is later dereferenced.
+    pub TEMPORARY_CSTRING_AS_PTR,
+    Warn,
+    "detects getting the inner pointer of a temporary `CString`"
+}
+
+declare_lint_pass!(TemporaryCStringAsPtr => [TEMPORARY_CSTRING_AS_PTR]);
+
+fn in_macro(span: Span) -> bool {
+    if span.from_expansion() {
+        !matches!(span.ctxt().outer_expn_data().kind, ExpnKind::Desugaring(..))
+    } else {
+        false
+    }
+}
+
+fn first_method_call<'tcx>(
+    expr: &'tcx Expr<'tcx>,
+) -> Option<(&'tcx PathSegment<'tcx>, &'tcx [Expr<'tcx>])> {
+    if let ExprKind::MethodCall(path, _, args, _) = &expr.kind {
+        if args.iter().any(|e| e.span.from_expansion()) { None } else { Some((path, *args)) }
+    } else {
+        None
+    }
+}
+
+impl<'tcx> LateLintPass<'tcx> for TemporaryCStringAsPtr {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if in_macro(expr.span) {
+            return;
+        }
+
+        match first_method_call(expr) {
+            Some((path, args)) if path.ident.name == sym::as_ptr => {
+                let unwrap_arg = &args[0];
+                let as_ptr_span = path.ident.span;
+                match first_method_call(unwrap_arg) {
+                    Some((path, args))
+                        if path.ident.name == sym::unwrap || path.ident.name == sym::expect =>
+                    {
+                        let source_arg = &args[0];
+                        lint_cstring_as_ptr(cx, as_ptr_span, source_arg, unwrap_arg);
+                    }
+                    _ => return,
+                }
+            }
+            _ => return,
+        }
+    }
+}
+
+fn lint_cstring_as_ptr(
+    cx: &LateContext<'_>,
+    as_ptr_span: Span,
+    source: &rustc_hir::Expr<'_>,
+    unwrap: &rustc_hir::Expr<'_>,
+) {
+    let source_type = cx.typeck_results().expr_ty(source);
+    if let ty::Adt(def, substs) = source_type.kind() {
+        if cx.tcx.is_diagnostic_item(sym::result_type, def.did) {
+            if let ty::Adt(adt, _) = substs.type_at(0).kind() {
+                if cx.tcx.is_diagnostic_item(sym::cstring_type, adt.did) {
+                    cx.struct_span_lint(TEMPORARY_CSTRING_AS_PTR, as_ptr_span, |diag| {
+                        let mut diag = diag
+                            .build("getting the inner pointer of a temporary `CString`");
+                        diag.span_label(as_ptr_span, "this pointer will be invalid");
+                        diag.span_label(
+                            unwrap.span,
+                            "this `CString` is deallocated at the end of the statement, bind it to a variable to extend its lifetime",
+                        );
+                        diag.note("pointers do not have a lifetime; when calling `as_ptr` the `CString` will be deallocated at the end of the statement because nothing is referencing it as far as the type system is concerned");
+                        diag.help("for more information, see https://doc.rust-lang.org/reference/destructors.html");
+                        diag.emit();
+                    });
+                }
+            }
+        }
+    }
+}

compiler/rustc_lint/src/types.rs

@@ -733,7 +733,7 @@ fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'t
 }
 
 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
-/// can, return the the type that `ty` can be safely converted to, otherwise return `None`.
+/// can, return the type that `ty` can be safely converted to, otherwise return `None`.
 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
 /// FIXME: This duplicates code in codegen.

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -11,6 +11,7 @@ use rustc_data_structures::fingerprint::{Fingerprint, FingerprintDecoder};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::{AtomicCell, Lock, LockGuard, Lrc, OnceCell};
+use rustc_errors::ErrorReported;
 use rustc_expand::base::{SyntaxExtension, SyntaxExtensionKind};
 use rustc_expand::proc_macro::{AttrProcMacro, BangProcMacro, ProcMacroDerive};
 use rustc_hir as hir;
@@ -1201,13 +1202,13 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         &self,
         tcx: TyCtxt<'tcx>,
         id: DefIndex,
-    ) -> Option<&'tcx [mir::abstract_const::Node<'tcx>]> {
+    ) -> Result<Option<&'tcx [mir::abstract_const::Node<'tcx>]>, ErrorReported> {
         self.root
             .tables
             .mir_abstract_consts
             .get(self, id)
             .filter(|_| !self.is_proc_macro(id))
-            .map_or(None, |v| Some(v.decode((self, tcx))))
+            .map_or(Ok(None), |v| Ok(Some(v.decode((self, tcx)))))
     }
 
     fn get_unused_generic_params(&self, id: DefIndex) -> FiniteBitSet<u32> {

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1117,7 +1117,7 @@ impl EncodeContext<'a, 'tcx> {
             }
 
             let abstract_const = self.tcx.mir_abstract_const(def_id);
-            if let Some(abstract_const) = abstract_const {
+            if let Ok(Some(abstract_const)) = abstract_const {
                 record!(self.tables.mir_abstract_consts[def_id.to_def_id()] <- abstract_const);
             }
         }
@@ -1300,7 +1300,7 @@ impl EncodeContext<'a, 'tcx> {
         });
         record!(self.tables.visibility[def_id] <-
             ty::Visibility::from_hir(&item.vis, item.hir_id, tcx));
-        record!(self.tables.span[def_id] <- item.span);
+        record!(self.tables.span[def_id] <- self.tcx.def_span(def_id));
         record!(self.tables.attributes[def_id] <- item.attrs);
         // FIXME(eddyb) there should be a nicer way to do this.
         match item.kind {

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -23,6 +23,12 @@ pub enum ErrorHandled {
     TooGeneric,
 }
 
+impl From<ErrorReported> for ErrorHandled {
+    fn from(err: ErrorReported) -> ErrorHandled {
+        ErrorHandled::Reported(err)
+    }
+}
+
 CloneTypeFoldableAndLiftImpls! {
     ErrorHandled,
 }

compiler/rustc_middle/src/mir/predecessors.rs

@@ -33,7 +33,7 @@ impl PredecessorCache {
         self.cache = OnceCell::new();
     }
 
-    /// Returns the the predecessor graph for this MIR.
+    /// Returns the predecessor graph for this MIR.
     #[inline]
     pub(super) fn compute(
         &self,

compiler/rustc_middle/src/query/mod.rs

@@ -247,15 +247,15 @@ rustc_queries! {
         /// Try to build an abstract representation of the given constant.
         query mir_abstract_const(
             key: DefId
-        ) -> Option<&'tcx [mir::abstract_const::Node<'tcx>]> {
+        ) -> Result<Option<&'tcx [mir::abstract_const::Node<'tcx>]>, ErrorReported> {
             desc {
                 |tcx| "building an abstract representation for {}", tcx.def_path_str(key),
             }
         }
         /// Try to build an abstract representation of the given constant.
         query mir_abstract_const_of_const_arg(
             key: (LocalDefId, DefId)
-        ) -> Option<&'tcx [mir::abstract_const::Node<'tcx>]> {
+        ) -> Result<Option<&'tcx [mir::abstract_const::Node<'tcx>]>, ErrorReported> {
             desc {
                 |tcx|
                 "building an abstract representation for the const argument {}",

compiler/rustc_mir/src/borrow_check/member_constraints.rs

@@ -71,7 +71,7 @@ impl<'tcx> MemberConstraintSet<'tcx, ty::RegionVid> {
     /// Pushes a member constraint into the set.
     ///
     /// The input member constraint `m_c` is in the form produced by
-    /// the the `rustc_middle::infer` code.
+    /// the `rustc_middle::infer` code.
     ///
     /// The `to_region_vid` callback fn is used to convert the regions
     /// within into `RegionVid` format -- it typically consults the

compiler/rustc_mir/src/interpret/memory.rs

@@ -285,9 +285,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             None => {
                 // Deallocating global memory -- always an error
                 return Err(match self.tcx.get_global_alloc(ptr.alloc_id) {
-                    Some(GlobalAlloc::Function(..)) => err_ub_format!("deallocating a function"),
+                    Some(GlobalAlloc::Function(..)) => {
+                        err_ub_format!("deallocating {}, which is a function", ptr.alloc_id)
+                    }
                     Some(GlobalAlloc::Static(..) | GlobalAlloc::Memory(..)) => {
-                        err_ub_format!("deallocating static memory")
+                        err_ub_format!("deallocating {}, which is static memory", ptr.alloc_id)
                     }
                     None => err_ub!(PointerUseAfterFree(ptr.alloc_id)),
                 }
@@ -297,15 +299,17 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
 
         if alloc_kind != kind {
             throw_ub_format!(
-                "deallocating {} memory using {} deallocation operation",
+                "deallocating {}, which is {} memory, using {} deallocation operation",
+                ptr.alloc_id,
                 alloc_kind,
                 kind
             );
         }
         if let Some((size, align)) = old_size_and_align {
             if size != alloc.size || align != alloc.align {
                 throw_ub_format!(
-                    "incorrect layout on deallocation: allocation has size {} and alignment {}, but gave size {} and alignment {}",
+                    "incorrect layout on deallocation: {} has size {} and alignment {}, but gave size {} and alignment {}",
+                    ptr.alloc_id,
                     alloc.size.bytes(),
                     alloc.align.bytes(),
                     size.bytes(),

compiler/rustc_mir/src/transform/check_consts/mod.rs

@@ -51,6 +51,12 @@ impl ConstCx<'mir, 'tcx> {
     pub fn const_kind(&self) -> hir::ConstContext {
         self.const_kind.expect("`const_kind` must not be called on a non-const fn")
     }
+
+    pub fn is_const_stable_const_fn(&self) -> bool {
+        self.const_kind == Some(hir::ConstContext::ConstFn)
+            && self.tcx.features().staged_api
+            && is_const_stable_const_fn(self.tcx, self.def_id.to_def_id())
+    }
 }
 
 /// Returns `true` if this `DefId` points to one of the official `panic` lang items.
@@ -63,3 +69,37 @@ pub fn allow_internal_unstable(tcx: TyCtxt<'tcx>, def_id: DefId, feature_gate: S
     attr::allow_internal_unstable(&tcx.sess, attrs)
         .map_or(false, |mut features| features.any(|name| name == feature_gate))
 }
+
+// Returns `true` if the given `const fn` is "const-stable".
+//
+// Panics if the given `DefId` does not refer to a `const fn`.
+//
+// Const-stability is only relevant for `const fn` within a `staged_api` crate. Only "const-stable"
+// functions can be called in a const-context by users of the stable compiler. "const-stable"
+// functions are subject to more stringent restrictions than "const-unstable" functions: They
+// cannot use unstable features and can only call other "const-stable" functions.
+pub fn is_const_stable_const_fn(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
+    use attr::{ConstStability, Stability, StabilityLevel};
+
+    // Const-stability is only relevant for `const fn`.
+    assert!(tcx.is_const_fn_raw(def_id));
+
+    // Functions with `#[rustc_const_unstable]` are const-unstable.
+    match tcx.lookup_const_stability(def_id) {
+        Some(ConstStability { level: StabilityLevel::Unstable { .. }, .. }) => return false,
+        Some(ConstStability { level: StabilityLevel::Stable { .. }, .. }) => return true,
+        None => {}
+    }
+
+    // Functions with `#[unstable]` are const-unstable.
+    //
+    // FIXME(ecstaticmorse): We should keep const-stability attributes wholly separate from normal stability
+    // attributes. `#[unstable]` should be irrelevant.
+    if let Some(Stability { level: StabilityLevel::Unstable { .. }, .. }) =
+        tcx.lookup_stability(def_id)
+    {
+        return false;
+    }
+
+    true
+}