refactor!: make Position generic over offset type

Previously Span was generic over R just
so that it could provide the method:

    fn from_reader(reader: &R) -> Self;

and properly implementing that method again
relied on R implementing the Position trait:

    impl<P: Position> Span<P> for Range<usize> { .. }

which was a very roundabout and awkward way of doing things.

It makes much more sense to make the Position trait generic
over the return type of its method (which previously always had
to be usize). Which lets us provide a blanket implementation:

    impl<R: Reader> Position<NoopOffset> for R { .. }

1 files changed, 11 insertions, 8 deletions

diff --git a/src/emitter.rs b/src/emitter.rs
index e441eb7..18b2539 100644
--- a/src/emitter.rs
+++ b/src/emitter.rs
@@ -5,6 +5,7 @@ use std::collections::VecDeque;
 use std::marker::PhantomData;
 use std::mem;
 
+use crate::spans::Position;
 use crate::spans::Span;
 use crate::Error;
 
@@ -183,7 +184,7 @@ impl<R, S> Default for DefaultEmitter<R, S> {
     }
 }
 
-impl<R, S: Span<R>> DefaultEmitter<R, S> {
+impl<R, S: Span> DefaultEmitter<R, S> {
     fn emit_token(&mut self, token: Token<S>) {
         self.flush_current_characters();
         self.emitted_tokens.push_front(token);
@@ -229,7 +230,7 @@ impl<R, S: Span<R>> DefaultEmitter<R, S> {
     }
 }
 
-impl<R, S: Span<R>> Emitter<R> for DefaultEmitter<R, S> {
+impl<R: Position<S::Offset>, S: Span> Emitter<R> for DefaultEmitter<R, S> {
     type Token = Token<S>;
 
     fn emit_eof(&mut self) {
@@ -237,7 +238,7 @@ impl<R, S: Span<R>> Emitter<R> for DefaultEmitter<R, S> {
     }
 
     fn emit_error(&mut self, error: Error, reader: &R) {
-        self.push_error(error, S::from_reader(reader));
+        self.push_error(error, S::new(reader.position(), reader.position()));
     }
 
     fn pop_token(&mut self) -> Option<Self::Token> {
@@ -250,7 +251,7 @@ impl<R, S: Span<R>> Emitter<R> for DefaultEmitter<R, S> {
 
     fn init_start_tag(&mut self, reader: &R) {
         self.current_token = Some(Token::StartTag(StartTag {
-            name_span: S::from_reader(reader),
+            name_span: S::new(reader.position(), reader.position()),
             self_closing: false,
             name: String::new(),
             attributes: Default::default(),
@@ -258,7 +259,7 @@ impl<R, S: Span<R>> Emitter<R> for DefaultEmitter<R, S> {
     }
     fn init_end_tag(&mut self, reader: &R) {
         self.current_token = Some(Token::EndTag(EndTag {
-            name_span: S::from_reader(reader),
+            name_span: S::new(reader.position(), reader.position()),
             name: String::new(),
         }));
         self.seen_attributes.clear();
@@ -367,15 +368,17 @@ impl<R, S: Span<R>> Emitter<R> for DefaultEmitter<R, S> {
         self.current_attribute = Some((
             String::new(),
             Attribute {
-                name_span: S::from_reader(reader),
+                name_span: S::new(reader.position(), reader.position()),
                 value: String::new(),
                 value_span: S::default(),
             },
         ));
     }
     fn init_attribute_value(&mut self, reader: &R, quoted: bool) {
-        self.current_attribute.as_mut().unwrap().1.value_span =
-            S::from_reader_with_offset(reader, quoted as usize);
+        self.current_attribute.as_mut().unwrap().1.value_span = S::new(
+            reader.position() + quoted as usize,
+            reader.position() + quoted as usize,
+        );
     }
 
     fn push_attribute_name(&mut self, s: &str) {