Enable documentation for types

Summary:
Since OTP 27, [it's possible to use `-doc` attributes for user defined types](https://www.erlang.org/doc/system/documentation.html).

This diff enables extraction of type documentation for both local and remote types, ensuring documentation is visible on hover.

Since no test cases were covering documentation extraction, I also added a couple of them for functions.

Reviewed By: alanz

Differential Revision: D84680999

fbshipit-source-id: 120dbfab0e046e34363563c7139369cb36de202b

Author: robertoaloi

crates/ide/src/handlers/get_docs.rs

@@ -22,3 +22,100 @@ pub(crate) fn get_doc_for_token(
     let docs = elp_ide_db::docs::Documentation::new(db, sema);
     Doc::from_reference(&docs, token)
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::fixture;
+
+    #[track_caller]
+    fn check(fixture: &str, expected: &str) {
+        let (analysis, fixture) = fixture::with_fixture(fixture);
+        let docs = analysis
+            .get_docs_at_position(fixture.position())
+            .unwrap()
+            .unwrap();
+        let doc = docs.doc.unwrap();
+        assert_eq!(doc.markdown_text(), expected);
+    }
+
+    #[test]
+    fn local_type() {
+        check(
+            r#"
+-module(main).
+-export([main/0]).
+-doc """
+My integer
+""".
+-type my_integer() :: integer().
+
+-spec main() -> my_in~teger().
+main() -> 42.
+"#,
+            "\
+```erlang
+-type my_integer() :: integer().
+```
+
+-----
+
+My integer",
+        );
+    }
+
+    #[test]
+    fn remote_type() {
+        check(
+            r#"
+//- /src/main.erl
+-module(main).
+-export([main/0]).
+-spec main() -> other:my_in~teger().
+main() -> 42.
+
+//- /src/other.erl
+-module(other).
+-doc """
+My integer
+""".
+-export_type([my_integer/0]).
+-type my_integer() :: integer().
+"#,
+            "\
+```erlang
+-type my_integer() :: integer().
+```
+
+-----
+
+My integer",
+        );
+    }
+
+    #[test]
+    fn local_function() {
+        check(
+            r#"
+-module(main).
+-export([main/0]).
+
+-doc """
+My function
+""".
+-spec main() -> ok.
+main() -> ok.
+
+-spec caller() -> ok.
+caller() -> ma~in().
+"#,
+            "\
+```erlang
+-spec main() -> ok.
+```
+
+-----
+
+My function",
+        );
+    }
+}

crates/ide/src/lib.rs

@@ -170,6 +170,7 @@ pub struct AnalysisHost {
     db: RootDatabase,
 }
 
+#[derive(Debug)]
 pub struct DocResult {
     pub doc: Option<Doc>,
     pub token_kind: SyntaxKind,

crates/ide_db/src/docs.rs

@@ -137,7 +137,9 @@ impl ToDoc for InFile<&ast::Remote> {
                     let name_arity = fun_def.name;
                     docs.function_doc(file_id, name_arity)
                 }
-                CallDef::Type(_) | CallDef::FuzzyType(_) => None,
+                CallDef::Type(type_def) | CallDef::FuzzyType(type_def) => {
+                    docs.type_doc(type_def.file.file_id, type_def.name().clone())
+                }
             }
         } else {
             None
@@ -152,7 +154,9 @@ impl ToDoc for InFile<&ast::Call> {
                 CallDef::Function(fun_def) | CallDef::FuzzyFunction(fun_def) => {
                     docs.function_doc(fun_def.file.file_id, fun_def.name)
                 }
-                CallDef::Type(_) | CallDef::FuzzyType(_) => None,
+                CallDef::Type(type_def) | CallDef::FuzzyType(type_def) => {
+                    docs.type_doc(type_def.file.file_id, type_def.name().clone())
+                }
             }
         } else {
             None