9 files changed, 628 insertions, 9 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 234c31406..572fb868e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -400,6 +400,26 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3dcaa9ae7725d12cdb85b3ad99a434db70b468c09ded17e012d86b5c1010f7a7"
 
 [[package]]
+name = "getopts"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "14dbbfd5c71d70241ecf9e6f13737f7b5ce823821063188d7e46c41d371eebd5"
+dependencies = [
+ "unicode-width",
+]
+
+[[package]]
+name = "getrandom"
+version = "0.1.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7abc8dd8451921606d809ba32e95b6111925cd2906060d2dcc29c070220503eb"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "wasi",
+]
+
+[[package]]
 name = "gimli"
 version = "0.22.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -620,6 +640,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "maplit"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3e2e65a1a2e43cfcb47a895c4c8b10d1f4a61097f9f254f183aee60cad9c651d"
+
+[[package]]
 name = "matchers"
 version = "0.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -882,6 +908,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b4596b6d070b27117e987119b4dac604f3c58cfb0b191112e24771b2faeac1a6"
 
 [[package]]
+name = "ppv-lite86"
+version = "0.2.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "237a5ed80e274dbc66f86bd59c1e25edc039660be53194b5fe0a482e0f2612ea"
+
+[[package]]
 name = "proc-macro2"
 version = "1.0.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -891,6 +923,27 @@ dependencies = [
 ]
 
 [[package]]
+name = "pulldown-cmark"
+version = "0.7.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca36dea94d187597e104a5c8e4b07576a8a45aa5db48a65e12940d3eb7461f55"
+dependencies = [
+ "bitflags",
+ "getopts",
+ "memchr",
+ "unicase",
+]
+
+[[package]]
+name = "pulldown-cmark-to-cmark"
+version = "4.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cffb594e453d29e238ac190362a4a291daec00396717a8d1670863121ac56958"
+dependencies = [
+ "pulldown-cmark",
+]
+
+[[package]]
 name = "quote"
 version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1052,21 +1105,30 @@ dependencies = [
  "expect",
  "indexmap",
  "itertools",
+ "lazy_static",
  "log",
+ "maplit",
  "oorandom",
+ "pulldown-cmark",
+ "pulldown-cmark-to-cmark",
  "ra_assists",
  "ra_cfg",
  "ra_db",
  "ra_fmt",
  "ra_hir",
+ "ra_hir_def",
  "ra_ide_db",
+ "ra_parser",
  "ra_prof",
  "ra_ssr",
  "ra_syntax",
  "ra_text_edit",
+ "ra_tt",
+ "rand",
  "rustc-hash",
  "stdx",
  "test_utils",
+ "url",
 ]
 
 [[package]]
@@ -1079,6 +1141,7 @@ dependencies = [
  "once_cell",
  "ra_db",
  "ra_hir",
+ "ra_hir_def",
  "ra_prof",
  "ra_syntax",
  "ra_text_edit",
@@ -1226,6 +1289,57 @@ dependencies = [
 ]
 
 [[package]]
+name = "rand"
+version = "0.7.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6a6b1679d49b24bbfe0c803429aa1874472f50d9b363131f0e89fc356b544d03"
+dependencies = [
+ "getrandom",
+ "libc",
+ "rand_chacha",
+ "rand_core",
+ "rand_hc",
+ "rand_pcg",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f4c8ed856279c9737206bf725bf36935d8666ead7aa69b52be55af369d193402"
+dependencies = [
+ "ppv-lite86",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "90bde5296fc891b0cef12a6d03ddccc162ce7b2aff54160af9338f8d40df6d19"
+dependencies = [
+ "getrandom",
+]
+
+[[package]]
+name = "rand_hc"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca3129af7b92a17112d59ad498c6f81eaf463253766b90396d39ea7a39d6613c"
+dependencies = [
+ "rand_core",
+]
+
+[[package]]
+name = "rand_pcg"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "16abd0c1b639e9eb4d7c50c0b8100b0d0f849be2349829c740fe8e6eb4816429"
+dependencies = [
+ "rand_core",
+]
+
+[[package]]
 name = "rayon"
 version = "1.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1713,6 +1827,15 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0ee12e4891ab3acc2d95d5023022ace22020247bb8a8d1ece875a443f7dab37d"
 
 [[package]]
+name = "unicase"
+version = "2.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "50f37be617794602aabbeee0be4f259dc1778fabe05e2d67ee8f79326d5cb4f6"
+dependencies = [
+ "version_check",
+]
+
+[[package]]
 name = "unicode-bidi"
 version = "0.3.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1737,6 +1860,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e83e153d1053cbb5a118eeff7fd5be06ed99153f00dbcd8ae310c5fb2b22edc0"
 
 [[package]]
+name = "unicode-width"
+version = "0.1.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9337591893a19b88d8d87f2cec1e73fad5cdfd10e5a6f349f498ad6ea2ffb1e3"
+
+[[package]]
 name = "unicode-xid"
 version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1755,6 +1884,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "version_check"
+version = "0.9.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b5a972e5669d67ba988ce3dc826706fb0a8b01471c088cb0b6110b805cc36aed"
+
+[[package]]
 name = "vfs"
 version = "0.1.0"
 dependencies = [
@@ -1789,6 +1924,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "wasi"
+version = "0.9.0+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cccddf32554fecc6acb585f82a32a72e28b48f8c4c1883ddfeeeaa96f7d8e519"
+
+[[package]]
 name = "winapi"
 version = "0.2.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/crates/ra_hir/src/code_model.rs b/crates/ra_hir/src/code_model.rs
index 36c0bdc9e..5d88c5c64 100644
--- a/crates/ra_hir/src/code_model.rs
+++ b/crates/ra_hir/src/code_model.rs
@@ -196,7 +196,6 @@ impl ModuleDef {
             ModuleDef::Function(it) => Some(it.name(db)),
             ModuleDef::EnumVariant(it) => Some(it.name(db)),
             ModuleDef::TypeAlias(it) => Some(it.name(db)),
-
             ModuleDef::Module(it) => it.name(db),
             ModuleDef::Const(it) => it.name(db),
             ModuleDef::Static(it) => it.name(db),
@@ -204,6 +203,25 @@ impl ModuleDef {
             ModuleDef::BuiltinType(it) => Some(it.as_name()),
         }
     }
+
+    pub fn resolver<D: DefDatabase + HirDatabase>(&self, db: &D) -> Option<Resolver> {
+        Some(match self {
+            ModuleDef::Module(m) => ModuleId::from(m.clone()).resolver(db),
+            ModuleDef::Function(f) => FunctionId::from(f.clone()).resolver(db),
+            ModuleDef::Adt(adt) => AdtId::from(adt.clone()).resolver(db),
+            ModuleDef::EnumVariant(ev) => {
+                GenericDefId::from(GenericDef::from(ev.clone())).resolver(db)
+            }
+            ModuleDef::Const(c) => {
+                GenericDefId::from(GenericDef::from(c.clone())).resolver(db)
+            }
+            ModuleDef::Static(s) => StaticId::from(s.clone()).resolver(db),
+            ModuleDef::Trait(t) => TraitId::from(t.clone()).resolver(db),
+            ModuleDef::TypeAlias(t) => ModuleId::from(t.module(db)).resolver(db),
+            // FIXME: This should be a resolver relative to `std/core`
+            ModuleDef::BuiltinType(_t) => None?,
+        })
+    }
 }
 
 pub use hir_def::{
diff --git a/crates/ra_hir/src/lib.rs b/crates/ra_hir/src/lib.rs
index 31f3241c9..e2d13dbfd 100644
--- a/crates/ra_hir/src/lib.rs
+++ b/crates/ra_hir/src/lib.rs
@@ -47,13 +47,15 @@ pub use hir_def::{
     body::scope::ExprScopes,
     builtin_type::BuiltinType,
     docs::Documentation,
+    item_scope::ItemInNs,
     nameres::ModuleSource,
     path::{ModPath, Path, PathKind},
     type_ref::Mutability,
 };
 pub use hir_expand::{
-    hygiene::Hygiene, name::Name, HirFileId, InFile, MacroCallId, MacroCallLoc,
-    MacroDefId, /* FIXME */
+    hygiene::Hygiene,
+    name::{AsName, Name},
+    HirFileId, InFile, MacroCallId, MacroCallLoc, MacroDefId, /* FIXME */
     MacroFile, Origin,
 };
 pub use hir_ty::display::HirDisplay;
diff --git a/crates/ra_ide/Cargo.toml b/crates/ra_ide/Cargo.toml
index f4181c4eb..4e2ba6d61 100644
--- a/crates/ra_ide/Cargo.toml
+++ b/crates/ra_ide/Cargo.toml
@@ -17,6 +17,12 @@ indexmap = "1.3.2"
 itertools = "0.9.0"
 log = "0.4.8"
 rustc-hash = "1.1.0"
+rand = { version = "0.7.3", features = ["small_rng"] }
+url = "*"
+maplit = "*"
+lazy_static = "*"
+pulldown-cmark-to-cmark = "4.0.2"
+pulldown-cmark = "0.7.0"
 oorandom = "11.1.2"
 
 stdx = { path = "../stdx" }
@@ -31,6 +37,9 @@ ra_prof = { path = "../ra_prof" }
 test_utils = { path = "../test_utils" }
 ra_assists = { path = "../ra_assists" }
 ra_ssr = { path = "../ra_ssr" }
+ra_hir_def = { path = "../ra_hir_def" }
+ra_tt = { path = "../ra_tt" }
+ra_parser = { path = "../ra_parser" }
 
 # ra_ide should depend only on the top-level `hir` package. if you need
 # something from some `hir_xxx` subpackage, reexport the API via `hir`.
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(),
diff --git a/crates/ra_ide_db/Cargo.toml b/crates/ra_ide_db/Cargo.toml
index 2716a38cc..f345f1de8 100644
--- a/crates/ra_ide_db/Cargo.toml
+++ b/crates/ra_ide_db/Cargo.toml
@@ -26,6 +26,7 @@ ra_text_edit = { path = "../ra_text_edit" }
 ra_db = { path = "../ra_db" }
 ra_prof = { path = "../ra_prof" }
 test_utils = { path = "../test_utils" }
+ra_hir_def = { path = "../ra_hir_def" }
 
 # ra_ide should depend only on the top-level `hir` package. if you need
 # something from some `hir_xxx` subpackage, reexport the API via `hir`.
diff --git a/crates/ra_ide_db/src/defs.rs b/crates/ra_ide_db/src/defs.rs
index df56f2d9e..80c99935d 100644
--- a/crates/ra_ide_db/src/defs.rs
+++ b/crates/ra_ide_db/src/defs.rs
@@ -6,6 +6,7 @@
 // FIXME: this badly needs rename/rewrite (matklad, 2020-02-06).
 
 use hir::{
+    db::{DefDatabase, HirDatabase},
     Field, HasVisibility, ImplDef, Local, MacroDef, Module, ModuleDef, Name, PathResolution,
     Semantics, TypeParam, Visibility,
 };
@@ -16,6 +17,7 @@ use ra_syntax::{
 };
 
 use crate::RootDatabase;
+use ra_hir_def::resolver::{HasResolver, Resolver};
 
 // FIXME: a more precise name would probably be `Symbol`?
 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
@@ -76,6 +78,21 @@ impl Definition {
         };
         Some(name)
     }
+
+    pub fn resolver<D: HirDatabase + DefDatabase>(&self, db: &D) -> Option<Resolver> {
+        use hir::VariantDef;
+        use ra_hir_def::*;
+        Some(match self {
+            Definition::ModuleDef(def) => def.resolver(db)?,
+            Definition::Field(field) => {
+                Into::<VariantId>::into(Into::<VariantDef>::into(field.parent_def(db))).resolver(db)
+            }
+            Definition::Macro(m) => Into::<ModuleId>::into(m.module(db)?).resolver(db),
+            Definition::SelfType(imp) => Into::<ImplId>::into(imp.clone()).resolver(db),
+            Definition::Local(local) => Into::<DefWithBodyId>::into(local.parent(db)).resolver(db),
+            Definition::TypeParam(tp) => Into::<ModuleId>::into(tp.module(db)).resolver(db),
+        })
+    }
 }
 
 #[derive(Debug)]
diff --git a/crates/rust-analyzer/tests/heavy_tests/main.rs b/crates/rust-analyzer/tests/heavy_tests/main.rs
index 7370505f8..91ce04731 100644
--- a/crates/rust-analyzer/tests/heavy_tests/main.rs
+++ b/crates/rust-analyzer/tests/heavy_tests/main.rs
@@ -680,5 +680,5 @@ pub fn foo(_input: TokenStream) -> TokenStream {
     });
 
     let value = res.get("contents").unwrap().get("value").unwrap().to_string();
-    assert_eq!(value, r#""```rust\nfoo::Bar\n```\n\n```rust\nfn bar()\n```""#)
+    assert_eq!(value, r#""\n````rust\nfoo::Bar\n````\n\n````rust\nfn bar()\n````""#)
 }