Add basic pin sugar support to rustfmt

Author: eholk

src/tools/rustfmt/src/types.rs

@@ -829,7 +829,6 @@ impl Rewrite for ast::Ty {
             }
             ast::TyKind::Ref(ref lifetime, ref mt)
             | ast::TyKind::PinnedRef(ref lifetime, ref mt) => {
-                // FIXME(pin_ergonomics): correctly format pinned reference syntax
                 let mut_str = format_mutability(mt.mutbl);
                 let mut_len = mut_str.len();
                 let mut result = String::with_capacity(128);
@@ -863,6 +862,13 @@ impl Rewrite for ast::Ty {
                     cmnt_lo = lifetime.ident.span.hi();
                 }
 
+                if let ast::TyKind::PinnedRef(..) = self.kind {
+                    result.push_str("pin ");
+                    if ast::Mutability::Not == mt.mutbl {
+                        result.push_str("const ");
+                    }
+                }
+
                 if ast::Mutability::Mut == mt.mutbl {
                     let mut_hi = context.snippet_provider.span_after(self.span(), "mut");
                     let before_mut_span = mk_sp(cmnt_lo, mut_hi - BytePos::from_usize(3));

src/tools/rustfmt/tests/source/pin_sugar.rs

@@ -0,0 +1,10 @@
+// See #130494
+
+#![feature(pin_ergonomics)]
+#![allow(incomplete_features)]
+
+fn f(x: &pin  const i32) {}
+fn g<'a>(x: &  'a pin const  i32) {}
+fn h<'a>(x: &  'a pin  
+mut i32) {}
+fn i(x: &pin      mut  i32) {}

src/tools/rustfmt/tests/target/pin_sugar.rs

@@ -0,0 +1,9 @@
+// See #130494
+
+#![feature(pin_ergonomics)]
+#![allow(incomplete_features)]
+
+fn f(x: &pin const i32) {}
+fn g<'a>(x: &'a pin const i32) {}
+fn h<'a>(x: &'a pin mut i32) {}
+fn i(x: &pin mut i32) {}