From 44e48d75dd3e08d4fea4654b9e970a0bb4ce2d5b Mon Sep 17 00:00:00 2001
From: Khanh Duong Quoc <dqkqdlot@gmail.com>
Date: Tue, 22 Oct 2024 20:23:05 +0900
Subject: [PATCH] feat: render docs from aliased type when docs are missing

---
 crates/ide-db/src/defs.rs     |  14 +++-
 crates/ide/src/hover/tests.rs | 153 ++++++++++++++++++++++++++++++++++
 2 files changed, 166 insertions(+), 1 deletion(-)

diff --git a/crates/ide-db/src/defs.rs b/crates/ide-db/src/defs.rs
index 099f26eba7..0372a58281 100644
--- a/crates/ide-db/src/defs.rs
+++ b/crates/ide-db/src/defs.rs
@@ -179,7 +179,19 @@ impl Definition {
             Definition::Static(it) => it.docs(db),
             Definition::Trait(it) => it.docs(db),
             Definition::TraitAlias(it) => it.docs(db),
-            Definition::TypeAlias(it) => it.docs(db),
+            Definition::TypeAlias(it) => {
+                it.docs(db).or_else(|| {
+                    // docs are missing, try to fall back to the docs of the aliased item.
+                    let adt = it.ty(db).as_adt()?;
+                    let docs = adt.docs(db)?;
+                    let docs = format!(
+                        "*This is the documentation for* `{}`\n\n{}",
+                        adt.display(db, edition),
+                        docs.as_str()
+                    );
+                    Some(Documentation::new(docs))
+                })
+            }
             Definition::BuiltinType(it) => {
                 famous_defs.and_then(|fd| {
                     // std exposes prim_{} modules with docstrings on the root to document the builtins
diff --git a/crates/ide/src/hover/tests.rs b/crates/ide/src/hover/tests.rs
index 81397b0785..ef835f5bef 100644
--- a/crates/ide/src/hover/tests.rs
+++ b/crates/ide/src/hover/tests.rs
@@ -9018,3 +9018,156 @@ foo!(BAR_$0);
         "#]],
     );
 }
+
+#[test]
+fn type_alias_without_docs() {
+    // Simple.
+    check(
+        r#"
+/// Docs for B
+struct B;
+
+type A$0 = B;
+"#,
+        expect![[r#"
+            *A*
+
+            ```rust
+            test
+            ```
+
+            ```rust
+            // size = 0, align = 1
+            type A = B
+            ```
+
+            ---
+
+            *This is the documentation for* `struct B`
+
+            Docs for B
+        "#]],
+    );
+
+    // Nested.
+    check(
+        r#"
+/// Docs for C
+struct C;
+
+type B = C;
+
+type A$0 = B;
+"#,
+        expect![[r#"
+            *A*
+
+            ```rust
+            test
+            ```
+
+            ```rust
+            // size = 0, align = 1
+            type A = B
+            ```
+
+            ---
+
+            *This is the documentation for* `struct C`
+
+            Docs for C
+        "#]],
+    );
+
+    // Showing the docs for aliased struct instead of intermediate type.
+    check(
+        r#"
+/// Docs for C
+struct C;
+
+/// Docs for B
+type B = C;
+
+type A$0 = B;
+"#,
+        expect![[r#"
+            *A*
+
+            ```rust
+            test
+            ```
+
+            ```rust
+            // size = 0, align = 1
+            type A = B
+            ```
+
+            ---
+
+            *This is the documentation for* `struct C`
+
+            Docs for C
+        "#]],
+    );
+
+    // No docs found.
+    check(
+        r#"
+struct C;
+
+type B = C;
+
+type A$0 = B;
+"#,
+        expect![[r#"
+            *A*
+
+            ```rust
+            test
+            ```
+
+            ```rust
+            // size = 0, align = 1
+            type A = B
+            ```
+        "#]],
+    );
+
+    // Multiple nested crate.
+    check(
+        r#"
+//- /lib.rs crate:c
+/// Docs for C
+pub struct C;
+
+//- /lib.rs crate:b deps:c
+pub use c::C;
+pub type B = C;
+
+//- /lib.rs crate:a deps:b
+pub use b::B;
+pub type A = B;
+
+//- /main.rs crate:main deps:a
+use a::A$0;
+"#,
+        expect![[r#"
+            *A*
+
+            ```rust
+            a
+            ```
+
+            ```rust
+            // size = 0, align = 1
+            pub type A = B
+            ```
+
+            ---
+
+            *This is the documentation for* `pub struct C`
+
+            Docs for C
+        "#]],
+    );
+}