Fix the JSON backend

This was simpler than expected.

src/librustdoc/json/conversions.rs

@@ -6,14 +6,16 @@ use std::convert::From;
 
 use rustc_ast::ast;
 use rustc_span::def_id::{DefId, CRATE_DEF_INDEX};
+use rustc_span::Pos;
 
 use crate::clean;
 use crate::doctree;
 use crate::formats::item_type::ItemType;
 use crate::json::types::*;
+use crate::json::JsonRenderer;
 
-impl From<clean::Item> for Option<Item> {
-    fn from(item: clean::Item) -> Self {
+impl JsonRenderer {
+    pub(super) fn convert_item(&self, item: clean::Item) -> Option<Item> {
         let item_type = ItemType::from(&item);
         let clean::Item {
             source,
@@ -32,7 +34,7 @@ impl From<clean::Item> for Option<Item> {
                 id: def_id.into(),
                 crate_id: def_id.krate.as_u32(),
                 name,
-                source: source.into(),
+                source: self.convert_span(source),
                 visibility: visibility.into(),
                 docs: attrs.collapsed_doc_value().unwrap_or_default(),
                 links: attrs
@@ -53,25 +55,23 @@ impl From<clean::Item> for Option<Item> {
             }),
         }
     }
-}
 
-impl From<clean::Span> for Option<Span> {
-    #[allow(unreachable_code)]
-    fn from(span: clean::Span) -> Self {
-        // TODO: this should actually work
-        // Unfortunately this requires rethinking the whole framework,
-        // since this now needs a context and not just .into().
-        match span.filename(todo!()) {
-            rustc_span::FileName::Real(name) => Some(Span {
+    fn convert_span(&self, span: clean::Span) -> Option<Span> {
+        match span.filename(&self.sess) {
+            rustc_span::FileName::Real(name) => {
+                let hi = span.hi(&self.sess);
+                let lo = span.lo(&self.sess);
+                Some(Span {
                     filename: match name {
                         rustc_span::RealFileName::Named(path) => path,
                         rustc_span::RealFileName::Devirtualized { local_path, virtual_name: _ } => {
                             local_path
                         }
                     },
-                begin: todo!(),
-                end: todo!(),
-            }),
+                    begin: (lo.line, lo.col.to_usize()),
+                    end: (hi.line, hi.col.to_usize()),
+                })
+            }
             _ => None,
         }
     }

src/librustdoc/json/mod.rs

@@ -26,6 +26,7 @@ use crate::html::render::cache::ExternalLocation;
 
 #[derive(Clone)]
 crate struct JsonRenderer {
+    sess: Lrc<Session>,
     /// A mapping of IDs that contains all local items for this crate which gets output as a top
     /// level field of the JSON blob.
     index: Rc<RefCell<FxHashMap<types::Id, types::Item>>>,
@@ -126,11 +127,12 @@ impl FormatRenderer for JsonRenderer {
         _render_info: RenderInfo,
         _edition: Edition,
         _cache: &mut Cache,
-        _sess: Lrc<Session>,
+        sess: Lrc<Session>,
     ) -> Result<(Self, clean::Crate), Error> {
         debug!("Initializing json renderer");
         Ok((
             JsonRenderer {
+                sess,
                 index: Rc::new(RefCell::new(FxHashMap::default())),
                 out_path: options.output,
             },
@@ -146,7 +148,7 @@ impl FormatRenderer for JsonRenderer {
         item.kind.inner_items().for_each(|i| self.item(i.clone(), cache).unwrap());
 
         let id = item.def_id;
-        if let Some(mut new_item) = item.into(): Option<types::Item> {
+        if let Some(mut new_item) = self.convert_item(item) {
             if let types::ItemEnum::TraitItem(ref mut t) = new_item.inner {
                 t.implementors = self.get_trait_implementors(id, cache)
             } else if let types::ItemEnum::StructItem(ref mut s) = new_item.inner {