Merge pull request #21752 from ChayimFriedman2/question-mark-conversion

feat: When going to def on `?` on `Result` that goes through `From`, go to the `From` impl

crates/hir/src/lib.rs

@@ -6158,6 +6158,13 @@ impl<'db> Type<'db> {
         Some(adt.into())
     }
 
+    /// Holes in the args can come from lifetime/const params.
+    pub fn as_adt_with_args(&self) -> Option<(Adt, Vec<Option<Type<'db>>>)> {
+        let (adt, args) = self.ty.as_adt()?;
+        let args = args.iter().map(|arg| Some(self.derived(arg.ty()?))).collect();
+        Some((adt.into(), args))
+    }
+
     pub fn as_builtin(&self) -> Option<BuiltinType> {
         self.ty.as_builtin().map(|inner| BuiltinType { inner })
     }

crates/hir/src/semantics.rs

@@ -1819,6 +1819,28 @@ impl<'db> SemanticsImpl<'db> {
         self.analyze(try_expr.syntax())?.resolve_try_expr(self.db, try_expr)
     }
 
+    /// The type that the associated `try` block, closure or function expects.
+    pub fn try_expr_returned_type(&self, try_expr: &ast::TryExpr) -> Option<Type<'db>> {
+        self.ancestors_with_macros(try_expr.syntax().clone()).find_map(|parent| {
+            if let Some(try_block) = ast::BlockExpr::cast(parent.clone())
+                && try_block.try_block_modifier().is_some()
+            {
+                Some(self.type_of_expr(&try_block.into())?.original)
+            } else if let Some(closure) = ast::ClosureExpr::cast(parent.clone()) {
+                Some(
+                    self.type_of_expr(&closure.into())?
+                        .original
+                        .as_callable(self.db)?
+                        .return_type(),
+                )
+            } else if let Some(function) = ast::Fn::cast(parent) {
+                Some(self.to_def(&function)?.ret_type(self.db))
+            } else {
+                None
+            }
+        })
+    }
+
     // This does not resolve the method call to the correct trait impl!
     // We should probably fix that.
     pub fn resolve_method_call_as_callable(

crates/ide/src/goto_definition.rs

@@ -95,6 +95,13 @@ pub(crate) fn goto_definition(
             continue;
         }
 
+        let parent = token.value.parent()?;
+
+        if let Some(question_mark_conversion) = goto_question_mark_conversions(sema, &parent) {
+            navs.extend(def_to_nav(sema, question_mark_conversion.into()));
+            continue;
+        }
+
         if let Some(token) = ast::String::cast(token.value.clone())
             && let Some(original_token) = ast::String::cast(original_token.clone())
             && let Some((analysis, fixture_analysis)) =
@@ -113,8 +120,6 @@ pub(crate) fn goto_definition(
             });
         }
 
-        let parent = token.value.parent()?;
-
         let token_file_id = token.file_id;
         if let Some(token) = ast::String::cast(token.value.clone())
             && let Some(x) =
@@ -149,6 +154,45 @@ pub(crate) fn goto_definition(
     Some(RangeInfo::new(original_token.text_range(), navs))
 }
 
+/// When the `?` operator is used on `Result`, go to the `From` impl if it exists as this provides more value.
+fn goto_question_mark_conversions(
+    sema: &Semantics<'_, RootDatabase>,
+    node: &SyntaxNode,
+) -> Option<hir::Function> {
+    let node = ast::TryExpr::cast(node.clone())?;
+    let try_expr_ty = sema.type_of_expr(&node.expr()?)?.adjusted();
+
+    let fd = FamousDefs(sema, try_expr_ty.krate(sema.db));
+    let result_enum = fd.core_result_Result()?.into();
+
+    let (try_expr_ty_adt, try_expr_ty_args) = try_expr_ty.as_adt_with_args()?;
+    if try_expr_ty_adt != result_enum {
+        // FIXME: Support `Poll<Result>`.
+        return None;
+    }
+    let original_err_ty = try_expr_ty_args.get(1)?.clone()?;
+
+    let returned_ty = sema.try_expr_returned_type(&node)?;
+    let (returned_adt, returned_ty_args) = returned_ty.as_adt_with_args()?;
+    if returned_adt != result_enum {
+        return None;
+    }
+    let returned_err_ty = returned_ty_args.get(1)?.clone()?;
+
+    if returned_err_ty.could_unify_with_deeply(sema.db, &original_err_ty) {
+        return None;
+    }
+
+    let from_trait = fd.core_convert_From()?;
+    let from_fn = from_trait.function(sema.db, sym::from)?;
+    sema.resolve_trait_impl_method(
+        returned_err_ty.clone(),
+        from_trait,
+        from_fn,
+        [returned_err_ty, original_err_ty],
+    )
+}
+
 // If the token is into(), try_into(), search the definition of From, TryFrom.
 fn find_definition_for_known_blanket_dual_impls(
     sema: &Semantics<'_, RootDatabase>,
@@ -4034,4 +4078,25 @@ where
 "#,
         )
     }
+
+    #[test]
+    fn question_mark_on_result_goes_to_conversion() {
+        check(
+            r#"
+//- minicore: try, result, from
+
+struct Foo;
+struct Bar;
+impl From<Foo> for Bar {
+    fn from(_: Foo) -> Bar { Bar }
+    // ^^^^
+}
+
+fn foo() -> Result<(), Bar> {
+    Err(Foo)?$0;
+    Ok(())
+}
+        "#,
+        );
+    }
 }