Rollup merge of rust-lang#56059 - alexcrichton:fix-tests, r=sfackler

Increase `Duration` approximate equal threshold to 1us

Previously this threshold when testing was 100ns, but the Windows
documentation states:

> which is a high resolution (<1us) time stamp

which presumably means that we could have up to 1us resolution, which
means that 100ns doesn't capture "equivalent" time intervals due to
various bits of rounding here and there.

It's hoped that this..

Closes rust-lang#56034

src/librustc_mir/interpret/eval_context.rs

@@ -340,8 +340,21 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tc
                 // the last field).  Can't have foreign types here, how would we
                 // adjust alignment and size for them?
                 let field = layout.field(self, layout.fields.count() - 1)?;
-                let (unsized_size, unsized_align) = self.size_and_align_of(metadata, field)?
-                    .expect("Fields cannot be extern types");
+                let (unsized_size, unsized_align) = match self.size_and_align_of(metadata, field)? {
+                    Some(size_and_align) => size_and_align,
+                    None => {
+                        // A field with extern type.  If this field is at offset 0, we behave
+                        // like the underlying extern type.
+                        // FIXME: Once we have made decisions for how to handle size and alignment
+                        // of `extern type`, this should be adapted.  It is just a temporary hack
+                        // to get some code to work that probably ought to work.
+                        if sized_size == Size::ZERO {
+                            return Ok(None)
+                        } else {
+                            bug!("Fields cannot be extern types, unless they are at offset 0")
+                        }
+                    }
+                };
 
                 // FIXME (#26403, #27023): We should be adding padding
                 // to `sized_size` (to accommodate the `unsized_align`

src/librustc_mir/interpret/place.rs

@@ -351,8 +351,17 @@ where
         // Offset may need adjustment for unsized fields
         let (meta, offset) = if field_layout.is_unsized() {
             // re-use parent metadata to determine dynamic field layout
-            let (_, align) = self.size_and_align_of(base.meta, field_layout)?
-                .expect("Fields cannot be extern types");
+            let align = match self.size_and_align_of(base.meta, field_layout)? {
+                Some((_, align)) => align,
+                None if offset == Size::ZERO =>
+                    // An extern type at offset 0, we fall back to its static alignment.
+                    // FIXME: Once we have made decisions for how to handle size and alignment
+                    // of `extern type`, this should be adapted.  It is just a temporary hack
+                    // to get some code to work that probably ought to work.
+                    field_layout.align,
+                None =>
+                    bug!("Cannot compute offset for extern type field at non-0 offset"),
+            };
             (base.meta, offset.abi_align(align))
         } else {
             // base.meta could be present; we might be accessing a sized field of an unsized

src/libstd/time.rs

@@ -481,7 +481,7 @@ mod tests {
             let (a, b) = ($a, $b);
             if a != b {
                 let (a, b) = if a > b {(a, b)} else {(b, a)};
-                assert!(a - Duration::new(0, 100) <= b,
+                assert!(a - Duration::new(0, 1000) <= b,
                         "{:?} is not almost equal to {:?}", a, b);
             }
         })

src/test/ui/consts/const-eval/issue-55541.rs

@@ -0,0 +1,27 @@
+// compile-pass
+
+// Test that we can handle newtypes wrapping extern types
+
+#![feature(extern_types, const_transmute)]
+
+use std::marker::PhantomData;
+
+extern "C" {
+  pub type ExternType;
+}
+unsafe impl Sync for ExternType {}
+static MAGIC_FFI_STATIC: u8 = 42;
+
+#[repr(transparent)]
+pub struct Wrapper(ExternType);
+pub static MAGIC_FFI_REF: &'static Wrapper = unsafe {
+  std::mem::transmute(&MAGIC_FFI_STATIC)
+};
+
+#[repr(transparent)]
+pub struct Wrapper2(PhantomData<Vec<i32>>, ExternType);
+pub static MAGIC_FFI_REF2: &'static Wrapper2 = unsafe {
+  std::mem::transmute(&MAGIC_FFI_STATIC)
+};
+
+fn main() {}