Generate docs for links to private items when passed --document-private

- Pass around document_private a lot more
- Add tests
  + Add tests for intra-doc links to private items
  + Add ignored tests for warnings in reference links

src/librustdoc/html/format.rs

@@ -468,7 +468,7 @@ impl clean::Path {
 
 pub fn href(did: DefId) -> Option<(String, ItemType, Vec<String>)> {
     let cache = cache();
-    if !did.is_local() && !cache.access_levels.is_public(did) {
+    if !did.is_local() && !cache.access_levels.is_public(did) && !cache.document_private {
         return None;
     }
 

src/librustdoc/html/render.rs

@@ -469,6 +469,7 @@ pub fn run(
         static_root_path,
         generate_search_filter,
         generate_redirect_pages,
+        document_private,
         ..
     } = options;
 
@@ -546,7 +547,7 @@ pub fn run(
     scx.ensure_dir(&dst)?;
     krate = sources::render(&dst, &mut scx, krate)?;
     let (new_crate, index, cache) =
-        Cache::from_krate(renderinfo, &extern_html_root_urls, &dst, krate);
+        Cache::from_krate(renderinfo, document_private, &extern_html_root_urls, &dst, krate);
     krate = new_crate;
     let cache = Arc::new(cache);
     let mut cx = Context {

src/librustdoc/html/render/cache.rs

@@ -91,6 +91,10 @@ crate struct Cache {
     /// The version of the crate being documented, if given from the `--crate-version` flag.
     pub crate_version: Option<String>,
 
+    /// Whether to document private items.
+    /// This is stored in `Cache` so it doesn't need to be passed through all rustdoc functions.
+    pub document_private: bool,
+
     // Private fields only used when initially crawling a crate to build a cache
     stack: Vec<String>,
     parent_stack: Vec<DefId>,
@@ -126,6 +130,7 @@ crate struct Cache {
 impl Cache {
     pub fn from_krate(
         renderinfo: RenderInfo,
+        document_private: bool,
         extern_html_root_urls: &BTreeMap<String, String>,
         dst: &Path,
         mut krate: clean::Crate,
@@ -160,6 +165,7 @@ impl Cache {
             stripped_mod: false,
             access_levels,
             crate_version: krate.version.take(),
+            document_private,
             orphan_impl_items: Vec::new(),
             orphan_trait_impls: Vec::new(),
             traits: krate.external_traits.replace(Default::default()),