Add json backend

Respond to comments and start adding tests

Fix re-exports and extern-crate

Add expected output tests

Add restricted paths

Format

Fix: associated methods missing in output

Ignore stripped items

Mark stripped items

removing them creates dangling references

Fix tests and update conversions

Don't panic if JSON backend fails to create a file

Fix attribute error in JSON testsuite

Move rustdoc-json to rustdoc/

This way it doesn't have to build rustc twice. Eventually it should
probably get its own suite, like rustdoc-js, but that can be fixed in a
follow-up.

Small cleanups

Don't prettify json before printing

This fully halves the size of the emitted JSON.

Add comments

[BREAKING CHANGE] rename version -> crate_version

[BREAKING CHANGE] rename source -> span

Use exhaustive matches

Don't qualify imports for DefId

Rename clean::{ItemEnum -> ItemKind}, clean::Item::{inner -> kind}

Fix Visibility conversion

clean::Visability was changed here:
https://github.com/rust-lang/rust/pull/77820/files#diff-df9f90aae0b7769e1eb6ea6f1d73c1c3f649e1ac48a20e169662a8930eb427beL1467-R1509

More churn catchup

Format

Author: P1n3appl3

src/librustdoc/clean/mod.rs

@@ -2281,7 +2281,7 @@ impl Clean<Vec<Item>> for doctree::Import<'_> {
             name: None,
             attrs: self.attrs.clean(cx),
             source: self.span.clean(cx),
-            def_id: DefId::local(CRATE_DEF_INDEX),
+            def_id: cx.tcx.hir().local_def_id(self.id).to_def_id(),
             visibility: self.vis.clean(cx),
             stability: None,
             const_stability: None,

src/librustdoc/clean/types.rs

@@ -337,6 +337,42 @@ crate enum ItemKind {
 }
 
 impl ItemKind {
+    /// Some items contain others such as structs (for their fields) and Enums
+    /// (for their variants). This method returns those contained items.
+    crate fn inner_items(&self) -> impl Iterator<Item = &Item> {
+        match self {
+            StructItem(s) => s.fields.iter(),
+            UnionItem(u) => u.fields.iter(),
+            VariantItem(Variant { kind: VariantKind::Struct(v) }) => v.fields.iter(),
+            EnumItem(e) => e.variants.iter(),
+            TraitItem(t) => t.items.iter(),
+            ImplItem(i) => i.items.iter(),
+            ModuleItem(m) => m.items.iter(),
+            ExternCrateItem(_, _)
+            | ImportItem(_)
+            | FunctionItem(_)
+            | TypedefItem(_, _)
+            | OpaqueTyItem(_)
+            | StaticItem(_)
+            | ConstantItem(_)
+            | TraitAliasItem(_)
+            | TyMethodItem(_)
+            | MethodItem(_, _)
+            | StructFieldItem(_)
+            | VariantItem(_)
+            | ForeignFunctionItem(_)
+            | ForeignStaticItem(_)
+            | ForeignTypeItem
+            | MacroItem(_)
+            | ProcMacroItem(_)
+            | PrimitiveItem(_)
+            | AssocConstItem(_, _)
+            | AssocTypeItem(_, _)
+            | StrippedItem(_)
+            | KeywordItem(_) => [].iter(),
+        }
+    }
+
     crate fn is_type_alias(&self) -> bool {
         match *self {
             ItemKind::TypedefItem(_, _) | ItemKind::AssocTypeItem(_, _) => true,
@@ -1613,6 +1649,11 @@ impl Path {
     crate fn last_name(&self) -> &str {
         self.segments.last().expect("segments were empty").name.as_str()
     }
+
+    crate fn whole_name(&self) -> String {
+        String::from(if self.global { "::" } else { "" })
+            + &self.segments.iter().map(|s| s.name.clone()).collect::<Vec<_>>().join("::")
+    }
 }
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]