Merge pull request #145 from dtolnay/addrof

Eliminate functionally duplicate vtable methods on rustc 1.51+

Author: dtolnay

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [nightly, beta, stable]
+        rust: [nightly, beta, stable, 1.51.0, 1.50.0]
     steps:
       - uses: actions/checkout@v2
       - uses: dtolnay/rust-toolchain@master

build.rs

@@ -56,6 +56,10 @@ fn main() {
     if rustc < 38 {
         println!("cargo:rustc-cfg=anyhow_no_macro_reexport");
     }
+
+    if rustc < 51 {
+        println!("cargo:rustc-cfg=anyhow_no_ptr_addr_of");
+    }
 }
 
 fn compile_probe() -> Option<ExitStatus> {

src/error.rs

@@ -1,11 +1,15 @@
 use crate::alloc::Box;
 use crate::backtrace::Backtrace;
 use crate::chain::Chain;
-use crate::ptr::{Mut, Own, Ref};
+#[cfg(any(feature = "std", anyhow_no_ptr_addr_of))]
+use crate::ptr::Mut;
+use crate::ptr::{Own, Ref};
 use crate::{Error, StdError};
 use core::any::TypeId;
 use core::fmt::{self, Debug, Display};
 use core::mem::ManuallyDrop;
+#[cfg(not(anyhow_no_ptr_addr_of))]
+use core::ptr;
 use core::ptr::NonNull;
 
 #[cfg(feature = "std")]
@@ -81,9 +85,11 @@ impl Error {
         let vtable = &ErrorVTable {
             object_drop: object_drop::<E>,
             object_ref: object_ref::<E>,
+            #[cfg(anyhow_no_ptr_addr_of)]
             object_mut: object_mut::<E>,
             object_boxed: object_boxed::<E>,
             object_downcast: object_downcast::<E>,
+            #[cfg(anyhow_no_ptr_addr_of)]
             object_downcast_mut: object_downcast_mut::<E>,
             object_drop_rest: object_drop_front::<E>,
             #[cfg(all(not(backtrace), feature = "backtrace"))]
@@ -103,10 +109,11 @@ impl Error {
         let vtable = &ErrorVTable {
             object_drop: object_drop::<MessageError<M>>,
             object_ref: object_ref::<MessageError<M>>,
-            #[cfg(feature = "std")]
+            #[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
             object_mut: object_mut::<MessageError<M>>,
             object_boxed: object_boxed::<MessageError<M>>,
             object_downcast: object_downcast::<M>,
+            #[cfg(anyhow_no_ptr_addr_of)]
             object_downcast_mut: object_downcast_mut::<M>,
             object_drop_rest: object_drop_front::<M>,
             #[cfg(all(not(backtrace), feature = "backtrace"))]
@@ -127,10 +134,11 @@ impl Error {
         let vtable = &ErrorVTable {
             object_drop: object_drop::<DisplayError<M>>,
             object_ref: object_ref::<DisplayError<M>>,
-            #[cfg(feature = "std")]
+            #[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
             object_mut: object_mut::<DisplayError<M>>,
             object_boxed: object_boxed::<DisplayError<M>>,
             object_downcast: object_downcast::<M>,
+            #[cfg(anyhow_no_ptr_addr_of)]
             object_downcast_mut: object_downcast_mut::<M>,
             object_drop_rest: object_drop_front::<M>,
             #[cfg(all(not(backtrace), feature = "backtrace"))]
@@ -153,9 +161,11 @@ impl Error {
         let vtable = &ErrorVTable {
             object_drop: object_drop::<ContextError<C, E>>,
             object_ref: object_ref::<ContextError<C, E>>,
+            #[cfg(anyhow_no_ptr_addr_of)]
             object_mut: object_mut::<ContextError<C, E>>,
             object_boxed: object_boxed::<ContextError<C, E>>,
             object_downcast: context_downcast::<C, E>,
+            #[cfg(anyhow_no_ptr_addr_of)]
             object_downcast_mut: context_downcast_mut::<C, E>,
             object_drop_rest: context_drop_rest::<C, E>,
             #[cfg(all(not(backtrace), feature = "backtrace"))]
@@ -176,9 +186,11 @@ impl Error {
         let vtable = &ErrorVTable {
             object_drop: object_drop::<BoxedError>,
             object_ref: object_ref::<BoxedError>,
+            #[cfg(anyhow_no_ptr_addr_of)]
             object_mut: object_mut::<BoxedError>,
             object_boxed: object_boxed::<BoxedError>,
             object_downcast: object_downcast::<Box<dyn StdError + Send + Sync>>,
+            #[cfg(anyhow_no_ptr_addr_of)]
             object_downcast_mut: object_downcast_mut::<Box<dyn StdError + Send + Sync>>,
             object_drop_rest: object_drop_front::<Box<dyn StdError + Send + Sync>>,
             #[cfg(all(not(backtrace), feature = "backtrace"))]
@@ -284,10 +296,11 @@ impl Error {
         let vtable = &ErrorVTable {
             object_drop: object_drop::<ContextError<C, Error>>,
             object_ref: object_ref::<ContextError<C, Error>>,
-            #[cfg(feature = "std")]
+            #[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
             object_mut: object_mut::<ContextError<C, Error>>,
             object_boxed: object_boxed::<ContextError<C, Error>>,
             object_downcast: context_chain_downcast::<C>,
+            #[cfg(anyhow_no_ptr_addr_of)]
             object_downcast_mut: context_chain_downcast_mut::<C>,
             object_drop_rest: context_chain_drop_rest::<C>,
             #[cfg(all(not(backtrace), feature = "backtrace"))]
@@ -396,14 +409,20 @@ impl Error {
         E: Display + Debug + Send + Sync + 'static,
     {
         let target = TypeId::of::<E>();
+        let inner = self.inner.by_mut();
         unsafe {
             // Use vtable to find NonNull<()> which points to a value of type E
             // somewhere inside the data structure.
-            let addr =
-                match (vtable(self.inner.ptr).object_downcast_mut)(self.inner.by_mut(), target) {
-                    Some(addr) => addr.extend(),
-                    None => return Err(self),
-                };
+            #[cfg(not(anyhow_no_ptr_addr_of))]
+            let addr = match (vtable(inner.ptr).object_downcast)(inner.by_ref(), target) {
+                Some(addr) => addr.by_mut().extend(),
+                None => return Err(self),
+            };
+            #[cfg(anyhow_no_ptr_addr_of)]
+            let addr = match (vtable(inner.ptr).object_downcast_mut)(inner, target) {
+                Some(addr) => addr.extend(),
+                None => return Err(self),
+            };
 
             // Prepare to read E out of the data structure. We'll drop the rest
             // of the data structure separately so that E is not dropped.
@@ -477,7 +496,14 @@ impl Error {
         unsafe {
             // Use vtable to find NonNull<()> which points to a value of type E
             // somewhere inside the data structure.
+
+            #[cfg(not(anyhow_no_ptr_addr_of))]
+            let addr =
+                (vtable(self.inner.ptr).object_downcast)(self.inner.by_ref(), target)?.by_mut();
+
+            #[cfg(anyhow_no_ptr_addr_of)]
             let addr = (vtable(self.inner.ptr).object_downcast_mut)(self.inner.by_mut(), target)?;
+
             Some(addr.cast::<E>().deref_mut())
         }
     }
@@ -536,11 +562,12 @@ impl Drop for Error {
 
 struct ErrorVTable {
     object_drop: unsafe fn(Own<ErrorImpl>),
-    object_ref: unsafe fn(Ref<ErrorImpl>) -> &(dyn StdError + Send + Sync + 'static),
-    #[cfg(feature = "std")]
+    object_ref: unsafe fn(Ref<ErrorImpl>) -> Ref<dyn StdError + Send + Sync + 'static>,
+    #[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
     object_mut: unsafe fn(Mut<ErrorImpl>) -> &mut (dyn StdError + Send + Sync + 'static),
     object_boxed: unsafe fn(Own<ErrorImpl>) -> Box<dyn StdError + Send + Sync + 'static>,
     object_downcast: unsafe fn(Ref<ErrorImpl>, TypeId) -> Option<Ref<()>>,
+    #[cfg(anyhow_no_ptr_addr_of)]
     object_downcast_mut: unsafe fn(Mut<ErrorImpl>, TypeId) -> Option<Mut<()>>,
     object_drop_rest: unsafe fn(Own<ErrorImpl>, TypeId),
     #[cfg(all(not(backtrace), feature = "backtrace"))]
@@ -566,17 +593,26 @@ unsafe fn object_drop_front<E>(e: Own<ErrorImpl>, target: TypeId) {
 }
 
 // Safety: requires layout of *e to match ErrorImpl<E>.
-unsafe fn object_ref<E>(e: Ref<ErrorImpl>) -> &(dyn StdError + Send + Sync + 'static)
+unsafe fn object_ref<E>(e: Ref<ErrorImpl>) -> Ref<dyn StdError + Send + Sync + 'static>
 where
     E: StdError + Send + Sync + 'static,
 {
     // Attach E's native StdError vtable onto a pointer to self._object.
-    &e.cast::<ErrorImpl<E>>().deref()._object
+
+    let unerased = e.cast::<ErrorImpl<E>>();
+
+    #[cfg(not(anyhow_no_ptr_addr_of))]
+    return Ref::from_raw(NonNull::new_unchecked(
+        ptr::addr_of!((*unerased.as_ptr())._object) as *mut E,
+    ));
+
+    #[cfg(anyhow_no_ptr_addr_of)]
+    return Ref::new(&unerased.deref()._object);
 }
 
 // Safety: requires layout of *e to match ErrorImpl<E>, and for `e` to be derived
 // from a `&mut`
-#[cfg(feature = "std")]
+#[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
 unsafe fn object_mut<E>(e: Mut<ErrorImpl>) -> &mut (dyn StdError + Send + Sync + 'static)
 where
     E: StdError + Send + Sync + 'static,
@@ -602,14 +638,26 @@ where
     if TypeId::of::<E>() == target {
         // Caller is looking for an E pointer and e is ErrorImpl<E>, take a
         // pointer to its E field.
-        let unerased = e.cast::<ErrorImpl<E>>().deref();
-        Some(Ref::new(&unerased._object).cast::<()>())
+
+        let unerased = e.cast::<ErrorImpl<E>>();
+
+        #[cfg(not(anyhow_no_ptr_addr_of))]
+        return Some(
+            Ref::from_raw(NonNull::new_unchecked(
+                ptr::addr_of!((*unerased.as_ptr())._object) as *mut E,
+            ))
+            .cast::<()>(),
+        );
+
+        #[cfg(anyhow_no_ptr_addr_of)]
+        return Some(Ref::new(&unerased.deref()._object).cast::<()>());
     } else {
         None
     }
 }
 
 // Safety: requires layout of *e to match ErrorImpl<E>.
+#[cfg(anyhow_no_ptr_addr_of)]
 unsafe fn object_downcast_mut<E>(e: Mut<ErrorImpl>, target: TypeId) -> Option<Mut<()>>
 where
     E: 'static,
@@ -649,7 +697,7 @@ where
 }
 
 // Safety: requires layout of *e to match ErrorImpl<ContextError<C, E>>.
-#[cfg(feature = "std")]
+#[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
 unsafe fn context_downcast_mut<C, E>(e: Mut<ErrorImpl>, target: TypeId) -> Option<Mut<()>>
 where
     C: 'static,
@@ -705,6 +753,7 @@ where
 }
 
 // Safety: requires layout of *e to match ErrorImpl<ContextError<C, Error>>.
+#[cfg(anyhow_no_ptr_addr_of)]
 unsafe fn context_chain_downcast_mut<C>(e: Mut<ErrorImpl>, target: TypeId) -> Option<Mut<()>>
 where
     C: 'static,
@@ -798,14 +847,21 @@ impl ErrorImpl {
     pub(crate) unsafe fn error(this: Ref<Self>) -> &(dyn StdError + Send + Sync + 'static) {
         // Use vtable to attach E's native StdError vtable for the right
         // original type E.
-        (vtable(this.ptr).object_ref)(this)
+        (vtable(this.ptr).object_ref)(this).deref()
     }
 
     #[cfg(feature = "std")]
     pub(crate) unsafe fn error_mut(this: Mut<Self>) -> &mut (dyn StdError + Send + Sync + 'static) {
         // Use vtable to attach E's native StdError vtable for the right
         // original type E.
-        (vtable(this.ptr).object_mut)(this)
+
+        #[cfg(not(anyhow_no_ptr_addr_of))]
+        return (vtable(this.ptr).object_ref)(this.by_ref())
+            .by_mut()
+            .deref_mut();
+
+        #[cfg(anyhow_no_ptr_addr_of)]
+        return (vtable(this.ptr).object_mut)(this);
     }
 
     #[cfg(any(backtrace, feature = "backtrace"))]

src/ptr.rs

@@ -91,13 +91,34 @@ where
         }
     }
 
+    #[cfg(not(anyhow_no_ptr_addr_of))]
+    pub fn from_raw(ptr: NonNull<T>) -> Self {
+        Ref {
+            ptr,
+            lifetime: PhantomData,
+        }
+    }
+
     pub fn cast<U: CastTo>(self) -> Ref<'a, U::Target> {
         Ref {
             ptr: self.ptr.cast(),
             lifetime: PhantomData,
         }
     }
 
+    #[cfg(not(anyhow_no_ptr_addr_of))]
+    pub fn by_mut(self) -> Mut<'a, T> {
+        Mut {
+            ptr: self.ptr,
+            lifetime: PhantomData,
+        }
+    }
+
+    #[cfg(not(anyhow_no_ptr_addr_of))]
+    pub fn as_ptr(self) -> *const T {
+        self.ptr.as_ptr() as *const T
+    }
+
     pub unsafe fn deref(self) -> &'a T {
         &*self.ptr.as_ptr()
     }
@@ -127,6 +148,7 @@ impl<'a, T> Mut<'a, T>
 where
     T: ?Sized,
 {
+    #[cfg(anyhow_no_ptr_addr_of)]
     pub fn new(ptr: &'a mut T) -> Self {
         Mut {
             ptr: NonNull::from(ptr),
@@ -141,6 +163,14 @@ where
         }
     }
 
+    #[cfg(not(anyhow_no_ptr_addr_of))]
+    pub fn by_ref(self) -> Ref<'a, T> {
+        Ref {
+            ptr: self.ptr,
+            lifetime: PhantomData,
+        }
+    }
+
     pub fn extend<'b>(self) -> Mut<'b, T> {
         Mut {
             ptr: self.ptr,