Tease apart orthogonal concerns in markdown link rewriting

`hir` should know nothing about URLs, markdown and html. It should
only be able to:

* resolve stringy path from documentation
* generate canonical stringy path for a def

In contrast, link rewriting should not care about semantics of paths
and names resolution, and should be concern only with text mangling
bits.

9 files changed, 297 insertions, 337 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 015f84ba8..f1a17fa90 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -498,7 +498,6 @@ dependencies = [
  "stdx",
  "syntax",
  "tt",
- "url",
 ]
 
 [[package]]
@@ -606,6 +605,7 @@ dependencies = [
  "syntax",
  "test_utils",
  "text_edit",
+ "url",
 ]
 
 [[package]]
diff --git a/crates/hir/Cargo.toml b/crates/hir/Cargo.toml
index 72f941c46..6dc5ad63b 100644
--- a/crates/hir/Cargo.toml
+++ b/crates/hir/Cargo.toml
@@ -15,7 +15,6 @@ rustc-hash = "1.1.0"
 either = "1.5.3"
 arrayvec = "0.5.1"
 itertools = "0.9.0"
-url = "2.1.1"
 
 stdx = { path = "../stdx", version = "0.0.0" }
 syntax = { path = "../syntax", version = "0.0.0" }
diff --git a/crates/hir/src/attrs.rs b/crates/hir/src/attrs.rs
index e5a539cb8..c3e820d89 100644
--- a/crates/hir/src/attrs.rs
+++ b/crates/hir/src/attrs.rs
@@ -1,20 +1,32 @@
 //! Attributes & documentation for hir types.
 use hir_def::{
-    attr::Attrs,
-    docs::Documentation,
-    resolver::{HasResolver, Resolver},
-    AdtId, AttrDefId, FunctionId, GenericDefId, ModuleId, StaticId, TraitId, VariantId,
+    attr::Attrs, docs::Documentation, path::ModPath, resolver::HasResolver, AttrDefId, ModuleDefId,
 };
+use hir_expand::hygiene::Hygiene;
 use hir_ty::db::HirDatabase;
+use syntax::ast;
 
 use crate::{
-    doc_links::Resolvable, Adt, Const, Enum, EnumVariant, Field, Function, GenericDef, ImplDef,
-    Local, MacroDef, Module, ModuleDef, Static, Struct, Trait, TypeAlias, TypeParam, Union,
+    Adt, Const, Enum, EnumVariant, Field, Function, MacroDef, Module, ModuleDef, Static, Struct,
+    Trait, TypeAlias, Union,
 };
 
 pub trait HasAttrs {
     fn attrs(self, db: &dyn HirDatabase) -> Attrs;
     fn docs(self, db: &dyn HirDatabase) -> Option<Documentation>;
+    fn resolve_doc_path(
+        self,
+        db: &dyn HirDatabase,
+        link: &str,
+        ns: Option<Namespace>,
+    ) -> Option<ModuleDef>;
+}
+
+#[derive(PartialEq, Eq, Hash, Copy, Clone, Debug)]
+pub enum Namespace {
+    Types,
+    Values,
+    Macros,
 }
 
 macro_rules! impl_has_attrs {
@@ -28,6 +40,10 @@ macro_rules! impl_has_attrs {
                 let def = AttrDefId::$def_id(self.into());
                 db.documentation(def)
             }
+            fn resolve_doc_path(self, db: &dyn HirDatabase, link: &str, ns: Option<Namespace>) -> Option<ModuleDef> {
+                let def = AttrDefId::$def_id(self.into());
+                resolve_doc_path(db, def, link, ns).map(ModuleDef::from)
+            }
         }
     )*};
 }
@@ -54,83 +70,42 @@ macro_rules! impl_has_attrs_adt {
             fn docs(self, db: &dyn HirDatabase) -> Option<Documentation> {
                 Adt::$adt(self).docs(db)
             }
+            fn resolve_doc_path(self, db: &dyn HirDatabase, link: &str, ns: Option<Namespace>) -> Option<ModuleDef> {
+                Adt::$adt(self).resolve_doc_path(db, link, ns)
+            }
         }
     )*};
 }
 
 impl_has_attrs_adt![Struct, Union, Enum];
 
-impl Resolvable for ModuleDef {
-    fn resolver(&self, db: &dyn HirDatabase) -> Option<Resolver> {
-        Some(match self {
-            ModuleDef::Module(m) => ModuleId::from(m.clone()).resolver(db.upcast()),
-            ModuleDef::Function(f) => FunctionId::from(f.clone()).resolver(db.upcast()),
-            ModuleDef::Adt(adt) => AdtId::from(adt.clone()).resolver(db.upcast()),
-            ModuleDef::EnumVariant(ev) => {
-                GenericDefId::from(GenericDef::from(ev.clone())).resolver(db.upcast())
-            }
-            ModuleDef::Const(c) => {
-                GenericDefId::from(GenericDef::from(c.clone())).resolver(db.upcast())
-            }
-            ModuleDef::Static(s) => StaticId::from(s.clone()).resolver(db.upcast()),
-            ModuleDef::Trait(t) => TraitId::from(t.clone()).resolver(db.upcast()),
-            ModuleDef::TypeAlias(t) => ModuleId::from(t.module(db)).resolver(db.upcast()),
-            // FIXME: This should be a resolver relative to `std/core`
-            ModuleDef::BuiltinType(_t) => None?,
-        })
-    }
-
-    fn try_into_module_def(self) -> Option<ModuleDef> {
-        Some(self)
-    }
-}
-
-impl Resolvable for TypeParam {
-    fn resolver(&self, db: &dyn HirDatabase) -> Option<Resolver> {
-        Some(ModuleId::from(self.module(db)).resolver(db.upcast()))
-    }
-
-    fn try_into_module_def(self) -> Option<ModuleDef> {
-        None
-    }
-}
-
-impl Resolvable for MacroDef {
-    fn resolver(&self, db: &dyn HirDatabase) -> Option<Resolver> {
-        Some(ModuleId::from(self.module(db)?).resolver(db.upcast()))
-    }
-
-    fn try_into_module_def(self) -> Option<ModuleDef> {
-        None
-    }
-}
-
-impl Resolvable for Field {
-    fn resolver(&self, db: &dyn HirDatabase) -> Option<Resolver> {
-        Some(VariantId::from(self.parent_def(db)).resolver(db.upcast()))
-    }
-
-    fn try_into_module_def(self) -> Option<ModuleDef> {
-        None
-    }
-}
-
-impl Resolvable for ImplDef {
-    fn resolver(&self, db: &dyn HirDatabase) -> Option<Resolver> {
-        Some(ModuleId::from(self.module(db)).resolver(db.upcast()))
-    }
-
-    fn try_into_module_def(self) -> Option<ModuleDef> {
-        None
-    }
-}
-
-impl Resolvable for Local {
-    fn resolver(&self, db: &dyn HirDatabase) -> Option<Resolver> {
-        Some(ModuleId::from(self.module(db)).resolver(db.upcast()))
-    }
-
-    fn try_into_module_def(self) -> Option<ModuleDef> {
-        None
-    }
+fn resolve_doc_path(
+    db: &dyn HirDatabase,
+    def: AttrDefId,
+    link: &str,
+    ns: Option<Namespace>,
+) -> Option<ModuleDefId> {
+    let resolver = match def {
+        AttrDefId::ModuleId(it) => it.resolver(db.upcast()),
+        AttrDefId::FieldId(it) => it.parent.resolver(db.upcast()),
+        AttrDefId::AdtId(it) => it.resolver(db.upcast()),
+        AttrDefId::FunctionId(it) => it.resolver(db.upcast()),
+        AttrDefId::EnumVariantId(it) => it.parent.resolver(db.upcast()),
+        AttrDefId::StaticId(it) => it.resolver(db.upcast()),
+        AttrDefId::ConstId(it) => it.resolver(db.upcast()),
+        AttrDefId::TraitId(it) => it.resolver(db.upcast()),
+        AttrDefId::TypeAliasId(it) => it.resolver(db.upcast()),
+        AttrDefId::ImplId(it) => it.resolver(db.upcast()),
+        AttrDefId::MacroDefId(_) => return None,
+    };
+    let path = ast::Path::parse(link).ok()?;
+    let modpath = ModPath::from_src(path, &Hygiene::new_unhygienic()).unwrap();
+    let resolved = resolver.resolve_module_path_in_items(db.upcast(), &modpath);
+    let def = match ns {
+        Some(Namespace::Types) => resolved.take_types()?,
+        Some(Namespace::Values) => resolved.take_values()?,
+        Some(Namespace::Macros) => return None,
+        None => resolved.iter_items().find_map(|it| it.as_module_def_id())?,
+    };
+    Some(def.into())
 }
diff --git a/crates/hir/src/code_model.rs b/crates/hir/src/code_model.rs
index c2ee20dbb..c2fc819e7 100644
--- a/crates/hir/src/code_model.rs
+++ b/crates/hir/src/code_model.rs
@@ -196,6 +196,16 @@ impl ModuleDef {
         }
     }
 
+    pub fn canonical_path(&self, db: &dyn HirDatabase) -> Option<String> {
+        let mut segments = Vec::new();
+        segments.push(self.name(db)?.to_string());
+        for m in self.module(db)?.path_to_root(db) {
+            segments.extend(m.name(db).map(|it| it.to_string()))
+        }
+        segments.reverse();
+        Some(segments.join("::"))
+    }
+
     pub fn definition_visibility(&self, db: &dyn HirDatabase) -> Option<Visibility> {
         let module = match self {
             ModuleDef::Module(it) => it.parent(db)?,
diff --git a/crates/hir/src/doc_links.rs b/crates/hir/src/doc_links.rs
deleted file mode 100644
index ddaffbec2..000000000
--- a/crates/hir/src/doc_links.rs
+++ /dev/null
@@ -1,238 +0,0 @@
-//! Resolves links in markdown documentation.
-
-use std::iter::once;
-
-use hir_def::resolver::Resolver;
-use itertools::Itertools;
-use syntax::ast::Path;
-use url::Url;
-
-use crate::{db::HirDatabase, Adt, AsName, Crate, Hygiene, ItemInNs, ModPath, ModuleDef};
-
-pub fn resolve_doc_link<T: Resolvable + Clone>(
-    db: &dyn HirDatabase,
-    definition: &T,
-    link_text: &str,
-    link_target: &str,
-) -> Option<(String, String)> {
-    let resolver = definition.resolver(db)?;
-    let module_def = definition.clone().try_into_module_def();
-    resolve_doc_link_impl(db, &resolver, module_def, link_text, link_target)
-}
-
-fn resolve_doc_link_impl(
-    db: &dyn HirDatabase,
-    resolver: &Resolver,
-    module_def: Option<ModuleDef>,
-    link_text: &str,
-    link_target: &str,
-) -> Option<(String, String)> {
-    try_resolve_intra(db, &resolver, link_text, &link_target).or_else(|| {
-        try_resolve_path(db, &module_def?, &link_target)
-            .map(|target| (target, link_text.to_string()))
-    })
-}
-
-/// 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: &dyn HirDatabase,
-    resolver: &Resolver,
-    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 };
-
-    let doclink = IntraDocLink::from(link_target);
-
-    // Parse link as a module path
-    let path = Path::parse(doclink.path).ok()?;
-    let modpath = ModPath::from_src(path, &Hygiene::new_unhygienic()).unwrap();
-
-    let resolved = resolver.resolve_module_path_in_items(db.upcast(), &modpath);
-    let (defid, namespace) = match doclink.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) => return 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| name.to_string()).join("/"))
-            .ok()?
-            .join(&get_symbol_filename(db, &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: &dyn HirDatabase, moddef: &ModuleDef, link_target: &str) -> Option<String> {
-    if !link_target.contains("#") && !link_target.contains(".html") {
-        return None;
-    }
-    let ns = ItemInNs::Types(moddef.clone().into());
-
-    let module = moddef.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, moddef).as_deref().map(|f| url.join(f).ok()).flatten()
-        })
-        .and_then(|url| url.join(link_target).ok())
-        .map(|url| url.into_string())
-}
-
-/// Strip prefixes, suffixes, and inline code marks from the given string.
-fn strip_prefixes_suffixes(mut s: &str) -> &str {
-    s = s.trim_matches('`');
-
-    [
-        (TYPES.0.iter(), TYPES.1.iter()),
-        (VALUES.0.iter(), VALUES.1.iter()),
-        (MACROS.0.iter(), MACROS.1.iter()),
-    ]
-    .iter()
-    .for_each(|(prefixes, suffixes)| {
-        prefixes.clone().for_each(|prefix| s = s.trim_start_matches(*prefix));
-        suffixes.clone().for_each(|suffix| s = s.trim_end_matches(*suffix));
-    });
-    let s = s.trim_start_matches("@").trim();
-    s
-}
-
-fn get_doc_url(db: &dyn HirDatabase, krate: &Crate) -> Option<Url> {
-    krate
-        .get_html_root_url(db)
-        .or_else(||
-        // Fallback to docs.rs
-        // FIXME: Specify an exact version here. This may be difficult, as multiple versions of the same crate could exist.
-        Some(format!("https://docs.rs/{}/*/", krate.display_name(db)?)))
-        .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: &dyn HirDatabase, definition: &ModuleDef) -> Option<String> {
-    Some(match definition {
-        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)?),
-    })
-}
-
-struct IntraDocLink<'s> {
-    path: &'s str,
-    namespace: Option<Namespace>,
-}
-
-impl<'s> From<&'s str> for IntraDocLink<'s> {
-    fn from(s: &'s str) -> Self {
-        Self { path: strip_prefixes_suffixes(s), namespace: Namespace::from_intra_spec(s) }
-    }
-}
-
-#[derive(PartialEq, Eq, Hash, Copy, Clone, Debug)]
-enum Namespace {
-    Types,
-    Values,
-    Macros,
-}
-
-static TYPES: ([&str; 7], [&str; 0]) =
-    (["type", "struct", "enum", "mod", "trait", "union", "module"], []);
-static VALUES: ([&str; 8], [&str; 1]) =
-    (["value", "function", "fn", "method", "const", "static", "mod", "module"], ["()"]);
-static MACROS: ([&str; 1], [&str; 1]) = (["macro"], ["!"]);
-
-impl Namespace {
-    /// Extract the specified namespace from an intra-doc-link if one exists.
-    ///
-    /// # Examples
-    ///
-    /// * `struct MyStruct` -> `Namespace::Types`
-    /// * `panic!` -> `Namespace::Macros`
-    /// * `fn@from_intra_spec` -> `Namespace::Values`
-    fn from_intra_spec(s: &str) -> Option<Self> {
-        [
-            (Namespace::Types, (TYPES.0.iter(), TYPES.1.iter())),
-            (Namespace::Values, (VALUES.0.iter(), VALUES.1.iter())),
-            (Namespace::Macros, (MACROS.0.iter(), MACROS.1.iter())),
-        ]
-        .iter()
-        .filter(|(_ns, (prefixes, suffixes))| {
-            prefixes
-                .clone()
-                .map(|prefix| {
-                    s.starts_with(*prefix)
-                        && s.chars()
-                            .nth(prefix.len() + 1)
-                            .map(|c| c == '@' || c == ' ')
-                            .unwrap_or(false)
-                })
-                .any(|cond| cond)
-                || suffixes
-                    .clone()
-                    .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()
-    }
-}
-
-/// Sealed trait used solely for the generic bound on [`resolve_doc_link`].
-pub trait Resolvable {
-    fn resolver(&self, db: &dyn HirDatabase) -> Option<Resolver>;
-    fn try_into_module_def(self) -> Option<ModuleDef>;
-}
diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 03915ea1b..b9d9c7e25 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -27,19 +27,17 @@ pub mod diagnostics;
 
 mod from_id;
 mod code_model;
-mod doc_links;
 mod attrs;
 mod has_source;
 
 pub use crate::{
-    attrs::HasAttrs,
+    attrs::{HasAttrs, Namespace},
     code_model::{
         Access, Adt, AsAssocItem, AssocItem, AssocItemContainer, Callable, CallableKind, Const,
         Crate, CrateDependency, DefWithBody, Enum, EnumVariant, Field, FieldSource, Function,
         GenericDef, HasVisibility, ImplDef, Local, MacroDef, Module, ModuleDef, ScopeDef, Static,
         Struct, Trait, Type, TypeAlias, TypeParam, Union, VariantDef, Visibility,
     },
-    doc_links::resolve_doc_link,
     has_source::HasSource,
     semantics::{original_range, PathResolution, Semantics, SemanticsScope},
 };
diff --git a/crates/ide/Cargo.toml b/crates/ide/Cargo.toml
index e61c276df..a15f704ca 100644
--- a/crates/ide/Cargo.toml
+++ b/crates/ide/Cargo.toml
@@ -18,6 +18,7 @@ rustc-hash = "1.1.0"
 oorandom = "11.1.2"
 pulldown-cmark-to-cmark = "5.0.0"
 pulldown-cmark = {version = "0.7.2", default-features = false}
+url = "2.1.1"
 
 stdx = { path = "../stdx", version = "0.0.0" }
 syntax = { path = "../syntax", version = "0.0.0" }
diff --git a/crates/ide/src/hover.rs b/crates/ide/src/hover.rs
index 536411704..efec0184e 100644
--- a/crates/ide/src/hover.rs
+++ b/crates/ide/src/hover.rs
@@ -1756,6 +1756,60 @@ pub struct B<|>ar
     }
 
     #[test]
+    fn test_doc_links_enum_variant() {
+        check(
+            r#"
+enum E {
+    /// [E]
+    V<|> { field: i32 }
+}
+"#,
+            expect![[r#"
+                *V*
+
+                ```rust
+                test::E
+                ```
+
+                ```rust
+                V
+                ```
+
+                ---
+
+                [E](https://docs.rs/test/*/test/enum.E.html)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_doc_links_field() {
+        check(
+            r#"
+struct S {
+    /// [`S`]
+    field<|>: i32
+}
+"#,
+            expect![[r#"
+                *field*
+
+                ```rust
+                test::S
+                ```
+
+                ```rust
+                field: i32
+                ```
+
+                ---
+
+                [`S`](https://docs.rs/test/*/test/struct.S.html)
+            "#]],
+        );
+    }
+
+    #[test]
     fn test_hover_macro_generated_struct_fn_doc_comment() {
         mark::check!(hover_macro_generated_struct_fn_doc_comment);
 
diff --git a/crates/ide/src/link_rewrite.rs b/crates/ide/src/link_rewrite.rs
index ff3200eef..acedea71b 100644
--- a/crates/ide/src/link_rewrite.rs
+++ b/crates/ide/src/link_rewrite.rs
@@ -2,11 +2,11 @@
 //!
 //! Most of the implementation can be found in [`hir::doc_links`].
 
+use hir::{Adt, Crate, HasAttrs, ModuleDef};
+use ide_db::{defs::Definition, RootDatabase};
 use pulldown_cmark::{CowStr, Event, Options, Parser, Tag};
 use pulldown_cmark_to_cmark::{cmark_with_options, Options as CmarkOptions};
-
-use hir::resolve_doc_link;
-use ide_db::{defs::Definition, RootDatabase};
+use url::Url;
 
 /// Rewrite documentation links in markdown to point to an online host (e.g. docs.rs)
 pub fn rewrite_links(db: &RootDatabase, markdown: &str, definition: &Definition) -> String {
@@ -26,19 +26,16 @@ pub fn rewrite_links(db: &RootDatabase, markdown: &str, definition: &Definition)
             // Two posibilities:
             // * path-based links: `../../module/struct.MyStruct.html`
             // * module-based links (AKA intra-doc links): `super::super::module::MyStruct`
-            let resolved = match definition {
-                Definition::ModuleDef(t) => resolve_doc_link(db, t, title, target),
-                Definition::Macro(t) => resolve_doc_link(db, t, title, target),
-                Definition::Field(t) => resolve_doc_link(db, t, title, target),
-                Definition::SelfType(t) => resolve_doc_link(db, t, title, target),
-                Definition::Local(t) => resolve_doc_link(db, t, title, target),
-                Definition::TypeParam(t) => resolve_doc_link(db, t, title, target),
-            };
-
-            match resolved {
-                Some((target, title)) => (target, title),
-                None => (target.to_string(), title.to_string()),
+            if let Some(rewritten) = rewrite_intra_doc_link(db, *definition, target, title) {
+                return rewritten;
+            }
+            if let Definition::ModuleDef(def) = *definition {
+                if let Some(target) = rewrite_url_link(db, def, target) {
+                    return (target, title.to_string());
+                }
             }
+
+            (target.to_string(), title.to_string())
         }
     });
     let mut out = String::new();
@@ -48,6 +45,64 @@ pub fn rewrite_links(db: &RootDatabase, markdown: &str, definition: &Definition)
     out
 }
 
+fn rewrite_intra_doc_link(
+    db: &RootDatabase,
+    def: Definition,
+    target: &str,
+    title: &str,
+) -> Option<(String, String)> {
+    let link = if target.is_empty() { title } else { target };
+    let (link, ns) = parse_link(link);
+    let resolved = match def {
+        Definition::ModuleDef(def) => match def {
+            ModuleDef::Module(it) => it.resolve_doc_path(db, link, ns),
+            ModuleDef::Function(it) => it.resolve_doc_path(db, link, ns),
+            ModuleDef::Adt(it) => it.resolve_doc_path(db, link, ns),
+            ModuleDef::EnumVariant(it) => it.resolve_doc_path(db, link, ns),
+            ModuleDef::Const(it) => it.resolve_doc_path(db, link, ns),
+            ModuleDef::Static(it) => it.resolve_doc_path(db, link, ns),
+            ModuleDef::Trait(it) => it.resolve_doc_path(db, link, ns),
+            ModuleDef::TypeAlias(it) => it.resolve_doc_path(db, link, ns),
+            ModuleDef::BuiltinType(_) => return None,
+        },
+        Definition::Macro(it) => it.resolve_doc_path(db, link, ns),
+        Definition::Field(it) => it.resolve_doc_path(db, link, ns),
+        Definition::SelfType(_) | Definition::Local(_) | Definition::TypeParam(_) => return None,
+    }?;
+    let krate = resolved.module(db)?.krate();
+    let canonical_path = resolved.canonical_path(db)?;
+    let new_target = get_doc_url(db, &krate)?
+        .join(&format!("{}/", krate.display_name(db)?))
+        .ok()?
+        .join(&canonical_path.replace("::", "/"))
+        .ok()?
+        .join(&get_symbol_filename(db, &resolved)?)
+        .ok()?
+        .into_string();
+    let new_title = strip_prefixes_suffixes(title);
+    Some((new_target, new_title.to_string()))
+}
+
+/// Try to resolve path to local documentation via path-based links (i.e. `../gateway/struct.Shard.html`).
+fn rewrite_url_link(db: &RootDatabase, def: ModuleDef, target: &str) -> Option<String> {
+    if !(target.contains("#") || target.contains(".html")) {
+        return None;
+    }
+
+    let module = def.module(db)?;
+    let krate = module.krate();
+    let canonical_path = def.canonical_path(db)?;
+    let base = format!("{}/{}", krate.display_name(db)?, canonical_path.replace("::", "/"));
+
+    get_doc_url(db, &krate)
+        .and_then(|url| url.join(&base).ok())
+        .and_then(|url| {
+            get_symbol_filename(db, &def).as_deref().map(|f| url.join(f).ok()).flatten()
+        })
+        .and_then(|url| url.join(target).ok())
+        .map(|url| url.into_string())
+}
+
 // 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>>,
@@ -79,3 +134,109 @@ fn map_links<'e>(
         _ => evt,
     })
 }
+
+fn parse_link(s: &str) -> (&str, Option<hir::Namespace>) {
+    let path = strip_prefixes_suffixes(s);
+    let ns = ns_from_intra_spec(s);
+    (path, ns)
+}
+
+/// Strip prefixes, suffixes, and inline code marks from the given string.
+fn strip_prefixes_suffixes(mut s: &str) -> &str {
+    s = s.trim_matches('`');
+
+    [
+        (TYPES.0.iter(), TYPES.1.iter()),
+        (VALUES.0.iter(), VALUES.1.iter()),
+        (MACROS.0.iter(), MACROS.1.iter()),
+    ]
+    .iter()
+    .for_each(|(prefixes, suffixes)| {
+        prefixes.clone().for_each(|prefix| s = s.trim_start_matches(*prefix));
+        suffixes.clone().for_each(|suffix| s = s.trim_end_matches(*suffix));
+    });
+    s.trim_start_matches("@").trim()
+}
+
+static TYPES: ([&str; 7], [&str; 0]) =
+    (["type", "struct", "enum", "mod", "trait", "union", "module"], []);
+static VALUES: ([&str; 8], [&str; 1]) =
+    (["value", "function", "fn", "method", "const", "static", "mod", "module"], ["()"]);
+static MACROS: ([&str; 1], [&str; 1]) = (["macro"], ["!"]);
+
+/// Extract the specified namespace from an intra-doc-link if one exists.
+///
+/// # Examples
+///
+/// * `struct MyStruct` -> `Namespace::Types`
+/// * `panic!` -> `Namespace::Macros`
+/// * `fn@from_intra_spec` -> `Namespace::Values`
+fn ns_from_intra_spec(s: &str) -> Option<hir::Namespace> {
+    [
+        (hir::Namespace::Types, (TYPES.0.iter(), TYPES.1.iter())),
+        (hir::Namespace::Values, (VALUES.0.iter(), VALUES.1.iter())),
+        (hir::Namespace::Macros, (MACROS.0.iter(), MACROS.1.iter())),
+    ]
+    .iter()
+    .filter(|(_ns, (prefixes, suffixes))| {
+        prefixes
+            .clone()
+            .map(|prefix| {
+                s.starts_with(*prefix)
+                    && s.chars()
+                        .nth(prefix.len() + 1)
+                        .map(|c| c == '@' || c == ' ')
+                        .unwrap_or(false)
+            })
+            .any(|cond| cond)
+            || suffixes
+                .clone()
+                .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()
+}
+
+fn get_doc_url(db: &RootDatabase, krate: &Crate) -> Option<Url> {
+    krate
+        .get_html_root_url(db)
+        .or_else(|| {
+            // Fallback to docs.rs. This uses `display_name` and can never be
+            // correct, but that's what fallbacks are about.
+            //
+            // FIXME: clicking on the link should just open the file in the editor,
+            // instead of falling back to external urls.
+            Some(format!("https://docs.rs/{}/*/", krate.display_name(db)?))
+        })
+        .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: &ModuleDef) -> Option<String> {
+    Some(match definition {
+        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),
+        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)?),
+    })
+}