Merge branch 'rust-lang:master' into feature-rustdoc-sort-traits

Author: MeetThePatel

compiler/rustc_abi/src/layout.rs

@@ -26,7 +26,7 @@ mod layout;
 #[cfg(test)]
 mod tests;
 
-pub use layout::LayoutCalculator;
+pub use layout::{LayoutCalculator, LayoutCalculatorError};
 
 /// Requirements for a `StableHashingContext` to be used in this crate.
 /// This is a hack to allow using the `HashStable_Generic` derive macro
@@ -393,6 +393,14 @@ impl HasDataLayout for TargetDataLayout {
     }
 }
 
+// used by rust-analyzer
+impl HasDataLayout for &TargetDataLayout {
+    #[inline]
+    fn data_layout(&self) -> &TargetDataLayout {
+        (**self).data_layout()
+    }
+}
+
 /// Endianness of the target, which must match cfg(target-endian).
 #[derive(Copy, Clone, PartialEq, Eq)]
 pub enum Endian {
@@ -781,6 +789,14 @@ impl Align {
 }
 
 /// A pair of alignments, ABI-mandated and preferred.
+///
+/// The "preferred" alignment is an LLVM concept that is virtually meaningless to Rust code:
+/// it is not exposed semantically to programmers nor can they meaningfully affect it.
+/// The only concern for us is that preferred alignment must not be less than the mandated alignment
+/// and thus in practice the two values are almost always identical.
+///
+/// An example of a rare thing actually affected by preferred alignment is aligning of statics.
+/// It is of effectively no consequence for layout in structs and on the stack.
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 #[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
 pub struct AbiAndPrefAlign {