From b4b4a2f0927d2d1d838da1e128472ff8bf64e98b Mon Sep 17 00:00:00 2001
From: James Whaley <juicy66173@gmail.com>
Date: Mon, 21 Sep 2020 18:27:43 +0100
Subject: [PATCH] Reduce boilerplate for BytePos and CharPos

---
 compiler/rustc_span/src/lib.rs | 137 +++++++++++++--------------------
 1 file changed, 55 insertions(+), 82 deletions(-)

diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index a730c30378827..ad3a866463d45 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -1558,58 +1558,71 @@ pub trait Pos {
     fn to_u32(&self) -> u32;
 }
 
-/// A byte offset. Keep this small (currently 32-bits), as AST contains
-/// a lot of them.
-#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Debug)]
-pub struct BytePos(pub u32);
-
-/// A character offset. Because of multibyte UTF-8 characters, a byte offset
-/// is not equivalent to a character offset. The `SourceMap` will convert `BytePos`
-/// values to `CharPos` values as necessary.
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
-pub struct CharPos(pub usize);
+macro_rules! impl_pos {
+    (
+        $(
+            $(#[$attr:meta])*
+            $vis:vis struct $ident:ident($inner_vis:vis $inner_ty:ty);
+        )*
+    ) => {
+        $(
+            $(#[$attr])*
+            $vis struct $ident($inner_vis $inner_ty);
+
+            impl Pos for $ident {
+                #[inline(always)]
+                fn from_usize(n: usize) -> $ident {
+                    $ident(n as $inner_ty)
+                }
 
-// FIXME: lots of boilerplate in these impls, but so far my attempts to fix
-// have been unsuccessful.
+                #[inline(always)]
+                fn to_usize(&self) -> usize {
+                    self.0 as usize
+                }
 
-impl Pos for BytePos {
-    #[inline(always)]
-    fn from_usize(n: usize) -> BytePos {
-        BytePos(n as u32)
-    }
+                #[inline(always)]
+                fn from_u32(n: u32) -> $ident {
+                    $ident(n as $inner_ty)
+                }
 
-    #[inline(always)]
-    fn to_usize(&self) -> usize {
-        self.0 as usize
-    }
+                #[inline(always)]
+                fn to_u32(&self) -> u32 {
+                    self.0 as u32
+                }
+            }
 
-    #[inline(always)]
-    fn from_u32(n: u32) -> BytePos {
-        BytePos(n)
-    }
+            impl Add for $ident {
+                type Output = $ident;
 
-    #[inline(always)]
-    fn to_u32(&self) -> u32 {
-        self.0
-    }
-}
+                #[inline(always)]
+                fn add(self, rhs: $ident) -> $ident {
+                    $ident((self.to_usize() + rhs.to_usize()) as $inner_ty)
+                }
+            }
 
-impl Add for BytePos {
-    type Output = BytePos;
+            impl Sub for $ident {
+                type Output = $ident;
 
-    #[inline(always)]
-    fn add(self, rhs: BytePos) -> BytePos {
-        BytePos((self.to_usize() + rhs.to_usize()) as u32)
-    }
+                #[inline(always)]
+                fn sub(self, rhs: $ident) -> $ident {
+                    $ident((self.to_usize() - rhs.to_usize()) as $inner_ty)
+                }
+            }
+        )*
+    };
 }
 
-impl Sub for BytePos {
-    type Output = BytePos;
+impl_pos! {
+    /// A byte offset. Keep this small (currently 32-bits), as AST contains
+    /// a lot of them.
+    #[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Debug)]
+    pub struct BytePos(pub u32);
 
-    #[inline(always)]
-    fn sub(self, rhs: BytePos) -> BytePos {
-        BytePos((self.to_usize() - rhs.to_usize()) as u32)
-    }
+    /// A character offset. Because of multibyte UTF-8 characters, a byte offset
+    /// is not equivalent to a character offset. The `SourceMap` will convert `BytePos`
+    /// values to `CharPos` values as necessary.
+    #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
+    pub struct CharPos(pub usize);
 }
 
 impl<S: rustc_serialize::Encoder> Encodable<S> for BytePos {
@@ -1624,46 +1637,6 @@ impl<D: rustc_serialize::Decoder> Decodable<D> for BytePos {
     }
 }
 
-impl Pos for CharPos {
-    #[inline(always)]
-    fn from_usize(n: usize) -> CharPos {
-        CharPos(n)
-    }
-
-    #[inline(always)]
-    fn to_usize(&self) -> usize {
-        self.0
-    }
-
-    #[inline(always)]
-    fn from_u32(n: u32) -> CharPos {
-        CharPos(n as usize)
-    }
-
-    #[inline(always)]
-    fn to_u32(&self) -> u32 {
-        self.0 as u32
-    }
-}
-
-impl Add for CharPos {
-    type Output = CharPos;
-
-    #[inline(always)]
-    fn add(self, rhs: CharPos) -> CharPos {
-        CharPos(self.to_usize() + rhs.to_usize())
-    }
-}
-
-impl Sub for CharPos {
-    type Output = CharPos;
-
-    #[inline(always)]
-    fn sub(self, rhs: CharPos) -> CharPos {
-        CharPos(self.to_usize() - rhs.to_usize())
-    }
-}
-
 // _____________________________________________________________________________
 // Loc, SourceFileAndLine, SourceFileAndBytePos
 //