1 files changed, 226 insertions, 0 deletions

diff --git a/crates/hir/src/link_rewrite.rs b/crates/hir/src/link_rewrite.rs
new file mode 100644
index 000000000..dad3a39cf
--- /dev/null
+++ b/crates/hir/src/link_rewrite.rs
@@ -0,0 +1,226 @@
+//! Resolves and rewrites links in markdown documentation for hovers/completion windows.
+
+use std::iter::once;
+
+use itertools::Itertools;
+use url::Url;
+
+use crate::{db::HirDatabase, Adt, AsName, Crate, Hygiene, ItemInNs, ModPath, ModuleDef};
+use hir_def::{db::DefDatabase, resolver::Resolver};
+use syntax::ast::Path;
+
+pub fn resolve_doc_link<T: Resolvable + Clone, D: DefDatabase + HirDatabase>(
+    db: &D,
+    definition: &T,
+    link_text: &str,
+    link_target: &str,
+) -> Option<(String, String)> {
+    try_resolve_intra(db, definition, link_text, &link_target).or_else(|| {
+        if let Some(definition) = definition.clone().try_into_module_def() {
+            try_resolve_path(db, &definition, &link_target)
+                .map(|target| (target, link_text.to_string()))
+        } else {
+            None
+        }
+    })
+}
+
+/// 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<T: Resolvable, D: DefDatabase + HirDatabase>(
+    db: &D,
+    definition: &T,
+    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| 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_doc_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)?),
+    })
+}
+
+#[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<D: DefDatabase + HirDatabase>(&self, db: &D) -> Option<Resolver>;
+    fn try_into_module_def(self) -> Option<ModuleDef>;
+}