2 files changed, 436 insertions, 5 deletions

diff --git a/crates/ra_ide/src/hover.rs b/crates/ra_ide/src/hover.rs
index aa48cb412..ad68bc43c 100644
--- a/crates/ra_ide/src/hover.rs
+++ b/crates/ra_ide/src/hover.rs
@@ -1,16 +1,26 @@
+use std::collections::{HashMap, HashSet};
+use std::iter::once;
+
 use hir::{
-    Adt, AsAssocItem, AssocItemContainer, Documentation, FieldSource, HasSource, HirDisplay,
-    Module, ModuleDef, ModuleSource, Semantics,
+    db::DefDatabase, Adt, AsAssocItem, AsName, AssocItemContainer, AttrDef, Crate, Documentation,
+    FieldSource, HasSource, HirDisplay, Hygiene, ItemInNs, ModPath, Module, ModuleDef,
+    ModuleSource, Semantics,
 };
 use itertools::Itertools;
+use lazy_static::lazy_static;
+use maplit::{hashmap, hashset};
+use pulldown_cmark::{CowStr, Event, Options, Parser, Tag};
+use pulldown_cmark_to_cmark::cmark;
 use ra_db::SourceDatabase;
 use ra_ide_db::{
     defs::{classify_name, classify_name_ref, Definition},
     RootDatabase,
 };
-use ra_syntax::{ast, match_ast, AstNode, SyntaxKind::*, SyntaxToken, TokenAtOffset, T};
+use ra_syntax::{ast, ast::Path, match_ast, AstNode, SyntaxKind::*, SyntaxToken, TokenAtOffset, T};
+use ra_tt::{Ident, Leaf, Literal, TokenTree};
 use stdx::format_to;
 use test_utils::mark;
+use url::Url;
 
 use crate::{
     display::{macro_label, ShortLabel, ToNav, TryToNav},
@@ -92,7 +102,8 @@ pub(crate) fn hover(db: &RootDatabase, position: FilePosition) -> Option<RangeIn
     };
     if let Some(definition) = definition {
         if let Some(markup) = hover_for_definition(db, definition) {
-            res.markup = markup;
+            let markup = rewrite_links(db, &markup.as_str(), &definition);
+            res.markup = Markup::from(markup);
             if let Some(action) = show_implementations_action(db, definition) {
                 res.actions.push(action);
             }
@@ -335,6 +346,277 @@ fn hover_for_definition(db: &RootDatabase, def: Definition) -> Option<Markup> {
     }
 }
 
+// Rewrites a markdown document, resolving links using `callback` and additionally striping prefixes/suffixes on link titles.
+fn map_links<'e>(
+    events: impl Iterator<Item = Event<'e>>,
+    callback: impl Fn(&str, &str) -> (String, String),
+) -> impl Iterator<Item = Event<'e>> {
+    let mut in_link = false;
+    let mut link_target: Option<CowStr> = None;
+
+    events.map(move |evt| match evt {
+        Event::Start(Tag::Link(_link_type, ref target, _)) => {
+            in_link = true;
+            link_target = Some(target.clone());
+            evt
+        }
+        Event::End(Tag::Link(link_type, _target, _)) => {
+            in_link = false;
+            Event::End(Tag::Link(link_type, link_target.take().unwrap(), CowStr::Borrowed("")))
+        }
+        Event::Text(s) if in_link => {
+            let (link_target_s, link_name) = callback(&link_target.take().unwrap(), &s);
+            link_target = Some(CowStr::Boxed(link_target_s.into()));
+            Event::Text(CowStr::Boxed(link_name.into()))
+        }
+        Event::Code(s) if in_link => {
+            let (link_target_s, link_name) = callback(&link_target.take().unwrap(), &s);
+            link_target = Some(CowStr::Boxed(link_target_s.into()));
+            Event::Code(CowStr::Boxed(link_name.into()))
+        }
+        _ => evt,
+    })
+}
+
+/// Rewrite documentation links in markdown to point to an online host (e.g. docs.rs)
+fn rewrite_links(db: &RootDatabase, markdown: &str, definition: &Definition) -> String {
+    let doc = Parser::new_with_broken_link_callback(
+        markdown,
+        Options::empty(),
+        Some(&|label, _| Some((/*url*/ label.to_string(), /*title*/ label.to_string()))),
+    );
+
+    let doc = map_links(doc, |target, title: &str| {
+        // This check is imperfect, there's some overlap between valid intra-doc links
+        // and valid URLs so we choose to be too eager to try to resolve what might be
+        // a URL.
+        if target.contains("://") {
+            (target.to_string(), title.to_string())
+        } else {
+            // Two posibilities:
+            // * path-based links: `../../module/struct.MyStruct.html`
+            // * module-based links (AKA intra-doc links): `super::super::module::MyStruct`
+            let resolved = try_resolve_intra(db, definition, title, &target).or_else(|| {
+                try_resolve_path(db, definition, &target).map(|target| (target, title.to_string()))
+            });
+
+            if let Some((target, title)) = resolved {
+                (target, title)
+            } else {
+                (target.to_string(), title.to_string())
+            }
+        }
+    });
+    let mut out = String::new();
+    cmark(doc, &mut out, None).ok();
+    out
+}
+
+#[derive(PartialEq, Eq, Hash, Copy, Clone, Debug)]
+enum Namespace {
+    Types,
+    Values,
+    Macros,
+}
+
+lazy_static!(
+    /// Map of namespaces to identifying prefixes and suffixes as defined by RFC1946.
+    static ref NS_MAP: HashMap<Namespace, (HashSet<&'static str>, HashSet<&'static str>)> = hashmap!{
+        Namespace::Types => (hashset!{"type", "struct", "enum", "mod", "trait", "union", "module"}, hashset!{}),
+        Namespace::Values => (hashset!{"value", "function", "fn", "method", "const", "static", "mod", "module"}, hashset!{"()"}),
+        Namespace::Macros => (hashset!{"macro"}, hashset!{"!"})
+    };
+);
+
+impl Namespace {
+    /// Extract the specified namespace from an intra-doc-link if one exists.
+    fn from_intra_spec(s: &str) -> Option<Self> {
+        NS_MAP
+            .iter()
+            .filter(|(_ns, (prefixes, suffixes))| {
+                prefixes
+                    .iter()
+                    .map(|prefix| {
+                        s.starts_with(prefix)
+                            && s.chars()
+                                .nth(prefix.len() + 1)
+                                .map(|c| c == '@' || c == ' ')
+                                .unwrap_or(false)
+                    })
+                    .any(|cond| cond)
+                    || suffixes
+                        .iter()
+                        .map(|suffix| {
+                            s.starts_with(suffix)
+                                && s.chars()
+                                    .nth(suffix.len() + 1)
+                                    .map(|c| c == '@' || c == ' ')
+                                    .unwrap_or(false)
+                        })
+                        .any(|cond| cond)
+            })
+            .map(|(ns, (_, _))| *ns)
+            .next()
+    }
+}
+
+// Strip prefixes, suffixes, and inline code marks from the given string.
+fn strip_prefixes_suffixes(mut s: &str) -> &str {
+    s = s.trim_matches('`');
+    NS_MAP.iter().for_each(|(_, (prefixes, suffixes))| {
+        prefixes.iter().for_each(|prefix| s = s.trim_start_matches(prefix));
+        suffixes.iter().for_each(|suffix| s = s.trim_end_matches(suffix));
+    });
+    s.trim_start_matches("@").trim()
+}
+
+/// Try to resolve path to local documentation via intra-doc-links (i.e. `super::gateway::Shard`).
+///
+/// See [RFC1946](https://github.com/rust-lang/rfcs/blob/master/text/1946-intra-rustdoc-links.md).
+fn try_resolve_intra(
+    db: &RootDatabase,
+    definition: &Definition,
+    link_text: &str,
+    link_target: &str,
+) -> Option<(String, String)> {
+    // Set link_target for implied shortlinks
+    let link_target =
+        if link_target.is_empty() { link_text.trim_matches('`') } else { link_target };
+
+    // Namespace disambiguation
+    let namespace = Namespace::from_intra_spec(link_target);
+
+    // Strip prefixes/suffixes
+    let link_target = strip_prefixes_suffixes(link_target);
+
+    // Parse link as a module path
+    let path = Path::parse(link_target).ok()?;
+    let modpath = ModPath::from_src(path, &Hygiene::new_unhygienic()).unwrap();
+
+    // Resolve it relative to symbol's location (according to the RFC this should consider small scopes
+    let resolver = definition.resolver(db)?;
+
+    let resolved = resolver.resolve_module_path_in_items(db, &modpath);
+    let (defid, namespace) = match namespace {
+        // FIXME: .or(resolved.macros)
+        None => resolved
+            .types
+            .map(|t| (t.0, Namespace::Types))
+            .or(resolved.values.map(|t| (t.0, Namespace::Values)))?,
+        Some(ns @ Namespace::Types) => (resolved.types?.0, ns),
+        Some(ns @ Namespace::Values) => (resolved.values?.0, ns),
+        // FIXME:
+        Some(Namespace::Macros) => None?,
+    };
+
+    // Get the filepath of the final symbol
+    let def: ModuleDef = defid.into();
+    let module = def.module(db)?;
+    let krate = module.krate();
+    let ns = match namespace {
+        Namespace::Types => ItemInNs::Types(defid),
+        Namespace::Values => ItemInNs::Values(defid),
+        // FIXME:
+        Namespace::Macros => None?,
+    };
+    let import_map = db.import_map(krate.into());
+    let path = import_map.path_of(ns)?;
+
+    Some((
+        get_doc_url(db, &krate)?
+            .join(&format!("{}/", krate.display_name(db)?))
+            .ok()?
+            .join(&path.segments.iter().map(|name| format!("{}", name)).join("/"))
+            .ok()?
+            .join(&get_symbol_filename(db, &Definition::ModuleDef(def))?)
+            .ok()?
+            .into_string(),
+        strip_prefixes_suffixes(link_text).to_string(),
+    ))
+}
+
+/// Try to resolve path to local documentation via path-based links (i.e. `../gateway/struct.Shard.html`).
+fn try_resolve_path(db: &RootDatabase, definition: &Definition, link: &str) -> Option<String> {
+    if !link.contains("#") && !link.contains(".html") {
+        return None;
+    }
+    let ns = if let Definition::ModuleDef(moddef) = definition {
+        ItemInNs::Types(moddef.clone().into())
+    } else {
+        return None;
+    };
+    let module = definition.module(db)?;
+    let krate = module.krate();
+    let import_map = db.import_map(krate.into());
+    let base = once(format!("{}", krate.display_name(db)?))
+        .chain(import_map.path_of(ns)?.segments.iter().map(|name| format!("{}", name)))
+        .join("/");
+
+    get_doc_url(db, &krate)
+        .and_then(|url| url.join(&base).ok())
+        .and_then(|url| {
+            get_symbol_filename(db, definition).as_deref().map(|f| url.join(f).ok()).flatten()
+        })
+        .and_then(|url| url.join(link).ok())
+        .map(|url| url.into_string())
+}
+
+/// Try to get the root URL of the documentation of a crate.
+fn get_doc_url(db: &RootDatabase, krate: &Crate) -> Option<Url> {
+    // Look for #![doc(html_root_url = "...")]
+    let attrs = db.attrs(AttrDef::from(krate.root_module(db)?).into());
+    let doc_attr_q = attrs.by_key("doc");
+
+    let doc_url = if doc_attr_q.exists() {
+        doc_attr_q.tt_values().map(|tt| {
+            let name = tt.token_trees.iter()
+                .skip_while(|tt| !matches!(tt, TokenTree::Leaf(Leaf::Ident(Ident{text: ref ident, ..})) if ident == "html_root_url"))
+                .skip(2)
+                .next();
+
+            match name {
+                Some(TokenTree::Leaf(Leaf::Literal(Literal{ref text, ..}))) => Some(text),
+                _ => None
+            }
+        }).flat_map(|t| t).next().map(|s| s.to_string())
+    } else {
+        // Fallback to docs.rs
+        // FIXME: Specify an exact version here (from Cargo.lock)
+        Some(format!("https://docs.rs/{}/*", krate.display_name(db)?))
+    };
+
+    doc_url
+        .map(|s| s.trim_matches('"').trim_end_matches("/").to_owned() + "/")
+        .and_then(|s| Url::parse(&s).ok())
+}
+
+/// Get the filename and extension generated for a symbol by rustdoc.
+///
+/// Example: `struct.Shard.html`
+fn get_symbol_filename(db: &RootDatabase, definition: &Definition) -> Option<String> {
+    Some(match definition {
+        Definition::ModuleDef(def) => match def {
+            ModuleDef::Adt(adt) => match adt {
+                Adt::Struct(s) => format!("struct.{}.html", s.name(db)),
+                Adt::Enum(e) => format!("enum.{}.html", e.name(db)),
+                Adt::Union(u) => format!("union.{}.html", u.name(db)),
+            },
+            ModuleDef::Module(_) => "index.html".to_string(),
+            ModuleDef::Trait(t) => format!("trait.{}.html", t.name(db)),
+            ModuleDef::TypeAlias(t) => format!("type.{}.html", t.name(db)),
+            ModuleDef::BuiltinType(t) => format!("primitive.{}.html", t.as_name()),
+            ModuleDef::Function(f) => format!("fn.{}.html", f.name(db)),
+            ModuleDef::EnumVariant(ev) => {
+                format!("enum.{}.html#variant.{}", ev.parent_enum(db).name(db), ev.name(db))
+            }
+            ModuleDef::Const(c) => format!("const.{}.html", c.name(db)?),
+            ModuleDef::Static(s) => format!("static.{}.html", s.name(db)?),
+        },
+        Definition::Macro(m) => format!("macro.{}.html", m.name(db)?),
+        _ => None?,
+    })
+}
+
 fn pick_best(tokens: TokenAtOffset<SyntaxToken>) -> Option<SyntaxToken> {
     return tokens.max_by_key(priority);
     fn priority(n: &SyntaxToken) -> usize {
@@ -1194,6 +1476,155 @@ fn foo() { let bar = Ba<|>r; }
     }
 
     #[test]
+    fn test_hover_path_link() {
+        check_hover_result(
+            r"
+            //- /lib.rs
+            pub struct Foo;
+            /// [Foo](struct.Foo.html)
+            pub struct B<|>ar
+            ",
+            &["pub struct Bar\n```\n___\n\n[Foo](https://docs.rs/test/*/test/struct.Foo.html)"],
+        );
+    }
+
+    #[test]
+    fn test_hover_path_link_no_strip() {
+        check_hover_result(
+            r"
+            //- /lib.rs
+            pub struct Foo;
+            /// [struct Foo](struct.Foo.html)
+            pub struct B<|>ar
+            ",
+            &["pub struct Bar\n```\n___\n\n[struct Foo](https://docs.rs/test/*/test/struct.Foo.html)"],
+        );
+    }
+
+    #[test]
+    fn test_hover_intra_link() {
+        check_hover_result(
+            r"
+            //- /lib.rs
+            pub mod foo {
+                pub struct Foo;
+            }
+            /// [Foo](foo::Foo)
+            pub struct B<|>ar
+            ",
+            &["pub struct Bar\n```\n___\n\n[Foo](https://docs.rs/test/*/test/foo/struct.Foo.html)"],
+        );
+    }
+
+    #[test]
+    fn test_hover_intra_link_shortlink() {
+        check_hover_result(
+            r"
+            //- /lib.rs
+            pub struct Foo;
+            /// [Foo]
+            pub struct B<|>ar
+            ",
+            &["pub struct Bar\n```\n___\n\n[Foo](https://docs.rs/test/*/test/struct.Foo.html)"],
+        );
+    }
+
+    #[test]
+    fn test_hover_intra_link_shortlink_code() {
+        check_hover_result(
+            r"
+            //- /lib.rs
+            pub struct Foo;
+            /// [`Foo`]
+            pub struct B<|>ar
+            ",
+            &["pub struct Bar\n```\n___\n\n[`Foo`](https://docs.rs/test/*/test/struct.Foo.html)"],
+        );
+    }
+
+    #[test]
+    fn test_hover_intra_link_namespaced() {
+        check_hover_result(
+            r"
+            //- /lib.rs
+            pub struct Foo;
+            fn Foo() {}
+            /// [Foo()]
+            pub struct B<|>ar
+            ",
+            &["pub struct Bar\n```\n___\n\n[Foo](https://docs.rs/test/*/test/struct.Foo.html)"],
+        );
+    }
+
+    #[test]
+    fn test_hover_intra_link_shortlink_namspaced_code() {
+        check_hover_result(
+            r"
+            //- /lib.rs
+            pub struct Foo;
+            /// [`struct Foo`]
+            pub struct B<|>ar
+            ",
+            &["pub struct Bar\n```\n___\n\n[`Foo`](https://docs.rs/test/*/test/struct.Foo.html)"],
+        );
+    }
+
+    #[test]
+    fn test_hover_intra_link_shortlink_namspaced_code_with_at() {
+        check_hover_result(
+            r"
+            //- /lib.rs
+            pub struct Foo;
+            /// [`struct@Foo`]
+            pub struct B<|>ar
+            ",
+            &["pub struct Bar\n```\n___\n\n[`Foo`](https://docs.rs/test/*/test/struct.Foo.html)"],
+        );
+    }
+
+    #[test]
+    fn test_hover_intra_link_reference() {
+        check_hover_result(
+            r"
+            //- /lib.rs
+            pub struct Foo;
+            /// [my Foo][foo]
+            ///
+            /// [foo]: Foo
+            pub struct B<|>ar
+            ",
+            &["pub struct Bar\n```\n___\n\n[my Foo](https://docs.rs/test/*/test/struct.Foo.html)"],
+        );
+    }
+
+    #[test]
+    fn test_hover_external_url() {
+        check_hover_result(
+            r"
+            //- /lib.rs
+            pub struct Foo;
+            /// [external](https://www.google.com)
+            pub struct B<|>ar
+            ",
+            &["pub struct Bar\n```\n___\n\n[external](https://www.google.com)"],
+        );
+    }
+
+    // Check that we don't rewrite links which we can't identify
+    #[test]
+    fn test_hover_unknown_target() {
+        check_hover_result(
+            r"
+            //- /lib.rs
+            pub struct Foo;
+            /// [baz](Baz)
+            pub struct B<|>ar
+            ",
+            &["pub struct Bar\n```\n___\n\n[baz](Baz)"],
+        );
+    }
+
+    #[test]
     fn test_hover_macro_generated_struct_fn_doc_comment() {
         mark::check!(hover_macro_generated_struct_fn_doc_comment);
 
diff --git a/crates/ra_ide/src/mock_analysis.rs b/crates/ra_ide/src/mock_analysis.rs
index c7e0f4b58..cf2ee1bfa 100644
--- a/crates/ra_ide/src/mock_analysis.rs
+++ b/crates/ra_ide/src/mock_analysis.rs
@@ -115,7 +115,7 @@ impl MockAnalysis {
                 root_crate = Some(crate_graph.add_crate_root(
                     file_id,
                     edition,
-                    None,
+                    Some("test".to_string()),
                     cfg,
                     env,
                     Default::default(),