No completions in comments (#1999)

Suppress completions inside comments like

```qsharp
import Foo;
// Hello there |
import Bar;
```

language_service/src/completion.rs

@@ -102,6 +102,16 @@ fn expected_word_kinds(
     source_contents: &str,
     cursor_offset: u32,
 ) -> WordKinds {
+    // We should not retun any completions in comments.
+    // This compensates for a bug in [`possible_words_at_offset_in_source`] .
+    // Ideally, that function would be aware of the comment context and not
+    // return any completions, however this is difficult to do today because
+    // of the parser's unawareness of comment tokens.
+    // So we do a simple check here where we have access to the full source contents.
+    if in_comment(source_contents, cursor_offset) {
+        return WordKinds::empty();
+    }
+
     match &compilation.kind {
         CompilationKind::OpenProject {
             package_graph_sources,
@@ -121,6 +131,16 @@ fn expected_word_kinds(
     }
 }
 
+fn in_comment(source_contents: &str, cursor_offset: u32) -> bool {
+    // find the last newline before the cursor
+    let last_line_start = source_contents[..cursor_offset as usize]
+        .rfind('\n')
+        .unwrap_or(0);
+    // find the last comment start before the cursor
+    let last_comment_start = source_contents[last_line_start..cursor_offset as usize].rfind("//");
+    last_comment_start.is_some()
+}
+
 /// Collects hardcoded completions from the given set of parser predictions.
 ///
 /// Hardcoded words are actual keywords (`let`, etc) as well as other words that are

language_service/src/completion/tests.rs

@@ -121,6 +121,13 @@ fn check_with_dependency(
     assert_no_duplicates(actual_completions);
 }
 
+fn check_no_completions(source_with_cursor: &str) {
+    let (compilation, cursor_position, _) = compile_with_markers(source_with_cursor, true);
+    let actual_completions =
+        get_completions(&compilation, "<source>", cursor_position, Encoding::Utf8);
+    assert_eq!(actual_completions.items, Vec::default());
+}
+
 fn assert_no_duplicates(mut actual_completions: CompletionList) {
     actual_completions
         .items
@@ -4075,42 +4082,55 @@ fn incomplete_return_type_in_partial_callable_signature() {
 
 #[test]
 fn no_path_segment_completion_inside_attr() {
-    check(
+    check_no_completions(
         "namespace Test {
 
         @Config(FakeStdLib.↘)
         function Main() : Unit {
         }
     }",
-        &["Fake", "not", "Test"],
-        &expect![[r#"
-            [
-                None,
-                None,
-                None,
-            ]
-        "#]],
     );
 }
 
 #[test]
 fn no_completion_inside_attr() {
-    check(
+    check_no_completions(
         "namespace Test {
 
         @Config(↘)
         function Main() : Unit {
-            let FakeStdLib = new Foo { bar = 3 };
-            FakeStdLib.↘
         }
     }",
-        &["Fake", "not", "Test"],
-        &expect![[r#"
-            [
-                None,
-                None,
-                None,
-            ]
-        "#]],
+    );
+}
+
+#[test]
+fn in_comment() {
+    check_no_completions(
+        "namespace Test {
+            import Foo;
+            // Hello there ↘
+            import Bar;
+        }",
+    );
+}
+
+#[test]
+fn in_doc_comment() {
+    check_no_completions(
+        "namespace Test {
+            import Foo;
+            /// Hello there ↘
+            import Bar;
+        }",
+    );
+}
+
+#[test]
+fn in_trailing_comment() {
+    check_no_completions(
+        "namespace Test {
+            import Foo; // Hello there ↘
+        }",
     );
 }