rustc: use FromPrimitive for decoding astencode_tag.

Author: eddyb

src/librustc/metadata/common.rs

@@ -12,7 +12,6 @@
 
 pub use self::astencode_tag::*;
 
-use std::mem;
 use back::svh::Svh;
 
 // EBML enum definitions and utils shared by the encoder and decoder
@@ -113,7 +112,7 @@ pub const tag_items_data_item_reexport_def_id: uint = 0x39;
 pub const tag_items_data_item_reexport_name: uint = 0x3a;
 
 // used to encode crate_ctxt side tables
-#[derive(Copy, PartialEq)]
+#[derive(Copy, PartialEq, FromPrimitive)]
 #[repr(uint)]
 pub enum astencode_tag { // Reserves 0x40 -- 0x5f
     tag_ast = 0x40,
@@ -145,17 +144,6 @@ pub enum astencode_tag { // Reserves 0x40 -- 0x5f
     tag_table_object_cast_map = 0x57,
 }
 
-static first_astencode_tag: uint = tag_ast as uint;
-static last_astencode_tag: uint = tag_table_object_cast_map as uint;
-impl astencode_tag {
-    pub fn from_uint(value : uint) -> Option<astencode_tag> {
-        let is_a_tag = first_astencode_tag <= value && value <= last_astencode_tag;
-        if !is_a_tag { None } else {
-            Some(unsafe { mem::transmute::<uint, astencode_tag>(value) })
-        }
-    }
-}
-
 pub const tag_item_trait_item_sort: uint = 0x60;
 
 pub const tag_item_trait_parent_sort: uint = 0x61;

src/librustc/middle/astencode.rs

@@ -38,6 +38,7 @@ use syntax::ptr::P;
 use syntax;
 
 use std::old_io::Seek;
+use std::num::FromPrimitive;
 use std::rc::Rc;
 
 use rbml::io::SeekableMemWriter;
@@ -1875,8 +1876,8 @@ fn decode_side_tables(dcx: &DecodeContext,
         debug!(">> Side table document with tag 0x{:x} \
                 found for id {} (orig {})",
                tag, id, id0);
-
-        match c::astencode_tag::from_uint(tag) {
+        let decoded_tag: Option<c::astencode_tag> = FromPrimitive::from_uint(tag);
+        match decoded_tag {
             None => {
                 dcx.tcx.sess.bug(
                     &format!("unknown tag found in side tables: {:x}",