Auto merge of #45605 - Nashenas88:derive-newtype, r=nikomatsakis

Add derive and doc comment capabilities to newtype_index macro

This moves `RustcDecodable` and `RustcEncodable` out of the macro definition and into the macro uses. They were conflicting with `CrateNum`'s impls of `serialize::UseSpecializedEncodable` and `serialize::UseSpecializedDecodable`, and now it's not :). `CrateNum` is now defined with the `newtype_index` macro. I also added support for doc comments on constant definitions and allowed a type to remove the pub specification on the tuple param (otherwise a LOT of code would refuse to compile for `CrateNum`). I was getting dozens of errors like this if `CrateNum` was defined as `pub struct CrateNum(pub u32)`:
```
error[E0530]: match bindings cannot shadow tuple structs
   --> src/librustc/dep_graph/dep_node.rs:624:25
    |
63  | use hir::def_id::{CrateNum, DefId, DefIndex, CRATE_DEF_INDEX};
    |                   -------- a tuple struct `CrateNum` is imported here
...
624 |     [] MissingLangItems(CrateNum),
    |                         ^^^^^^^^ cannot be named the same as a tuple struct
```

I also cleaned up the formatting of the macro bodies as they were getting impossibly long. Should I go back and fix the matching rules to this style too?

I also want to see what the test results look like because `CrateNum` used to just derive `Debug`, but the `newtype_index` macro has a custom implementation. This might require further pushes.

Feel free to bikeshed on the macro language, I have no preference here.

src/librustc/hir/def_id.rs

@@ -16,30 +16,23 @@ use serialize::{self, Encoder, Decoder};
 use std::fmt;
 use std::u32;
 
-#[derive(Clone, Copy, Eq, Ord, PartialOrd, PartialEq, Hash, Debug)]
-pub struct CrateNum(u32);
+newtype_index!(CrateNum
+    {
+        derive[Debug]
+        ENCODABLE = custom
 
-impl Idx for CrateNum {
-    fn new(value: usize) -> Self {
-        assert!(value < (u32::MAX) as usize);
-        CrateNum(value as u32)
-    }
+        /// Item definitions in the currently-compiled crate would have the CrateNum
+        /// LOCAL_CRATE in their DefId.
+        const LOCAL_CRATE = 0,
 
-    fn index(self) -> usize {
-        self.0 as usize
-    }
-}
+        /// Virtual crate for builtin macros
+        // FIXME(jseyfried): this is also used for custom derives until proc-macro crates get
+        // `CrateNum`s.
+        const BUILTIN_MACROS_CRATE = u32::MAX,
 
-/// Item definitions in the currently-compiled crate would have the CrateNum
-/// LOCAL_CRATE in their DefId.
-pub const LOCAL_CRATE: CrateNum = CrateNum(0);
-
-/// Virtual crate for builtin macros
-// FIXME(jseyfried): this is also used for custom derives until proc-macro crates get `CrateNum`s.
-pub const BUILTIN_MACROS_CRATE: CrateNum = CrateNum(u32::MAX);
-
-/// A CrateNum value that indicates that something is wrong.
-pub const INVALID_CRATE: CrateNum = CrateNum(u32::MAX - 1);
+        /// A CrateNum value that indicates that something is wrong.
+        const INVALID_CRATE = u32::MAX - 1,
+    });
 
 impl CrateNum {
     pub fn new(x: usize) -> CrateNum {

src/librustc/middle/region.rs

@@ -158,8 +158,8 @@ pub struct BlockRemainder {
 
 newtype_index!(FirstStatementIndex
     {
-        DEBUG_FORMAT = "{}",
-        MAX = SCOPE_DATA_REMAINDER_MAX,
+        pub idx
+        MAX = SCOPE_DATA_REMAINDER_MAX
     });
 
 impl From<ScopeData> for Scope {

src/librustc/mir/mod.rs

@@ -1552,6 +1552,7 @@ pub struct Constant<'tcx> {
 
 newtype_index!(Promoted { DEBUG_FORMAT = "promoted[{}]" });
 
+
 #[derive(Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub enum Literal<'tcx> {
     Value {