fix(formatter): fix else indentation after comment between if-else (F…

…uelLabs#3785)

closes FuelLabs#2649

Added a few test cases with comments in between, including:
- single-line comment with overindentation,
- multi-line comment with underindentation,
- single-line comment, from inline to multiline if-else

Updated `get_post_context()` with a better way to format `else` after
comment. This is a bit of a hacky fix but since the post-context concept
is currently only used for formatting `else` blocks after comment, I was
thinking this might tide us through for now (and the test suite passes
as well).

I wrote a long-form comment explaining what the new get_post_context()
does there especially because fixing the off-by-one error with
subtracting by 1 is going to look like a hacky solution (and it is,
unfortunately)

Co-authored-by: Joshua Batty <[email protected]>

swayfmt/src/formatter/mod.rs

@@ -1375,6 +1375,115 @@ fn foo() {}
 #[test]
 #[inline(always)]
 fn foo() {}
+"#;
+        let mut formatter = Formatter::default();
+        let formatted_sway_code =
+            Formatter::format(&mut formatter, Arc::from(sway_code_to_format), None).unwrap();
+        assert_eq!(correct_sway_code, formatted_sway_code);
+        assert!(test_stability(formatted_sway_code, formatter));
+    }
+
+    #[test]
+    fn test_comment_between_if_else_overindented() {
+        let sway_code_to_format = r#"contract;
+
+impl MyContract for Contract {
+    fn is_blue() -> bool {
+        if self == PrimaryColor::Blue {
+            true
+        }
+        // TODO remove this else when exhaustive ifs are checked for
+                else {
+            false
+        }
+    }
+}"#;
+
+        let correct_sway_code = r#"contract;
+
+impl MyContract for Contract {
+    fn is_blue() -> bool {
+        if self == PrimaryColor::Blue {
+            true
+        }
+        // TODO remove this else when exhaustive ifs are checked for
+        else {
+            false
+        }
+    }
+}
+"#;
+        let mut formatter = Formatter::default();
+        let formatted_sway_code =
+            Formatter::format(&mut formatter, Arc::from(sway_code_to_format), None).unwrap();
+        assert_eq!(correct_sway_code, formatted_sway_code);
+        assert!(test_stability(formatted_sway_code, formatter));
+    }
+
+    #[test]
+    fn test_multiline_comment_between_if_else_underindented() {
+        let sway_code_to_format = r#"contract;
+
+impl MyContract for Contract {
+    fn is_blue() -> bool {
+        if self == PrimaryColor::Blue {
+            true
+        }
+        // TODO
+        // remove this else when exhaustive ifs are checked for
+    else {
+            false
+        }
+    }
+}"#;
+
+        let correct_sway_code = r#"contract;
+
+impl MyContract for Contract {
+    fn is_blue() -> bool {
+        if self == PrimaryColor::Blue {
+            true
+        }
+        // TODO
+        // remove this else when exhaustive ifs are checked for
+        else {
+            false
+        }
+    }
+}
+"#;
+        let mut formatter = Formatter::default();
+        let formatted_sway_code =
+            Formatter::format(&mut formatter, Arc::from(sway_code_to_format), None).unwrap();
+        assert_eq!(correct_sway_code, formatted_sway_code);
+        assert!(test_stability(formatted_sway_code, formatter));
+    }
+
+    #[test]
+    fn test_comment_between_if_else_inline_to_multiline() {
+        let sway_code_to_format = r#"contract;
+
+impl MyContract for Contract {
+    fn is_blue() -> bool {
+            if self == PrimaryColor::Blue { true }
+        // TODO remove this else when exhaustive ifs are checked for
+    else { false }
+    }
+}"#;
+
+        let correct_sway_code = r#"contract;
+
+impl MyContract for Contract {
+    fn is_blue() -> bool {
+        if self == PrimaryColor::Blue {
+            true
+        }
+        // TODO remove this else when exhaustive ifs are checked for
+        else {
+            false
+        }
+    }
+}
 "#;
         let mut formatter = Formatter::default();
         let formatted_sway_code =

swayfmt/src/utils/map/comments.rs

@@ -220,7 +220,12 @@ fn get_comments_between_spans(
                 pre_context: unformatted_code[starting_position_for_context..comment_span.start]
                     .to_string(),
                 comment: comment.clone(),
-                post_context: get_post_context(unformatted_code, comment_span, next_line),
+                post_context: get_post_context(
+                    unformatted_code,
+                    starting_position_for_context,
+                    comment_span,
+                    next_line,
+                ),
             });
         }
     }
@@ -255,16 +260,19 @@ fn format_context(context: &str, threshold: usize) -> String {
 // We need to know the context after the comment as well.
 fn get_post_context(
     unformatted_code: &Arc<str>,
+    context_start: usize,
     comment_span: &ByteSpan,
     next_line: &str,
 ) -> Option<String> {
     if next_line.trim_start().starts_with("else") {
-        let else_token_start = next_line
-            .char_indices()
-            .find(|(_, c)| !c.is_whitespace())
-            .map(|(i, _)| i)
-            .unwrap_or_default();
-        Some(unformatted_code[comment_span.end..comment_span.end + else_token_start].to_string())
+        // We want to align the 'else' token with the above comment, so this is just
+        // same as the pre_context subtracted by 1.
+        //
+        // 1 here is somewhat a magic number. This is a result of the format_else_opt()
+        // in utils/language/expr/conditional.rs always formatting with a whitespace.
+        // We want to take that away since this 'else' will always be on a newline,
+        // and will be overindented by one whitespace if left alone.
+        Some(unformatted_code[context_start..(comment_span.start - 1)].to_string())
     } else {
         // If we don't find anything to format in the context after, we simply
         // return an empty context.