fix: correct broken logic for return complition

It seems that we've accidentally deleted the tests here couple of years
ago, and then fairly recently made a typo during refactor as well.

Reinstall tests, with coverage marks this time :-)

Author: matklad

crates/ide-completion/src/completions/expr.rs

@@ -282,14 +282,26 @@ pub(crate) fn complete_expr_path(
                         }
                     }
 
-                    if let Some(ty) = innermost_ret_ty {
+                    if let Some(ret_ty) = innermost_ret_ty {
                         add_keyword(
                             "return",
-                            match (in_block_expr, ty.is_unit()) {
-                                (true, true) => "return ;",
-                                (true, false) => "return;",
-                                (false, true) => "return $0",
-                                (false, false) => "return",
+                            match (ret_ty.is_unit(), in_block_expr) {
+                                (true, true) => {
+                                    cov_mark::hit!(return_unit_block);
+                                    "return;"
+                                }
+                                (true, false) => {
+                                    cov_mark::hit!(return_unit_no_block);
+                                    "return"
+                                }
+                                (false, true) => {
+                                    cov_mark::hit!(return_value_block);
+                                    "return $0;"
+                                }
+                                (false, false) => {
+                                    cov_mark::hit!(return_value_no_block);
+                                    "return $0"
+                                }
                             },
                         );
                     }

crates/ide-completion/src/tests/expression.rs

@@ -1,7 +1,7 @@
 //! Completion tests for expressions.
 use expect_test::{expect, Expect};
 
-use crate::tests::{completion_list, BASE_ITEMS_FIXTURE};
+use crate::tests::{check_edit, completion_list, BASE_ITEMS_FIXTURE};
 
 fn check(ra_fixture: &str, expect: Expect) {
     let actual = completion_list(&format!("{}{}", BASE_ITEMS_FIXTURE, ra_fixture));
@@ -670,3 +670,39 @@ fn main() {
         "#]],
     );
 }
+
+#[test]
+fn return_unit_block() {
+    cov_mark::check!(return_unit_block);
+    check_edit("return", r#"fn f() { if true { $0 } }"#, r#"fn f() { if true { return; } }"#);
+}
+
+#[test]
+fn return_unit_no_block() {
+    cov_mark::check!(return_unit_no_block);
+    check_edit(
+        "return",
+        r#"fn f() { match () { () => $0 } }"#,
+        r#"fn f() { match () { () => return } }"#,
+    );
+}
+
+#[test]
+fn return_value_block() {
+    cov_mark::check!(return_value_block);
+    check_edit(
+        "return",
+        r#"fn f() -> i32 { if true { $0 } }"#,
+        r#"fn f() -> i32 { if true { return $0; } }"#,
+    );
+}
+
+#[test]
+fn return_value_no_block() {
+    cov_mark::check!(return_value_no_block);
+    check_edit(
+        "return",
+        r#"fn f() -> i32 { match () { () => $0 } }"#,
+        r#"fn f() -> i32 { match () { () => return $0 } }"#,
+    );
+}