Backport: fix to extract comments to stop internal error (#3857)

Author: topecongiro

src/comment.rs

@@ -1988,6 +1988,16 @@ mod test {
         check("\"/* abc", "abc", Some(4));
     }
 
+    #[test]
+    fn test_find_last_uncommented() {
+        fn check(haystack: &str, needle: &str, expected: Option<usize>) {
+            assert_eq!(expected, haystack.find_last_uncommented(needle));
+        }
+        check("foo test bar test", "test", Some(13));
+        check("test,", "test", Some(0));
+        check("nothing", "test", None);
+    }
+
     #[test]
     fn test_filter_normal_code() {
         let s = r#"

src/items.rs

@@ -113,6 +113,57 @@ impl Rewrite for ast::Local {
         result.push_str(&infix);
 
         if let Some((init, _els)) = self.kind.init_else_opt() {
+            let base_span = if let Some(ref ty) = self.ty {
+                mk_sp(ty.span.hi(), self.span.hi())
+            } else {
+                mk_sp(self.pat.span.hi(), self.span.hi())
+            };
+
+            if let Some(offset) = context.snippet(base_span).find_uncommented("=") {
+                let base_span_lo = base_span.lo();
+
+                let assign_lo = base_span_lo + BytePos(offset as u32);
+                let comment_start_pos = if let Some(ref ty) = self.ty {
+                    ty.span.hi()
+                } else {
+                    self.pat.span.hi()
+                };
+                let comment_before_assign =
+                    context.snippet(mk_sp(comment_start_pos, assign_lo)).trim();
+
+                let assign_hi = base_span_lo + BytePos((offset + 1) as u32);
+                let rhs_span_lo = init.span.lo();
+                let comment_end_pos = if init.attrs.is_empty() {
+                    rhs_span_lo
+                } else {
+                    let attr_span_lo = init.attrs.first().unwrap().span.lo();
+                    // for the case using block
+                    // ex. let x = { #![my_attr]do_something(); }
+                    if rhs_span_lo < attr_span_lo {
+                        rhs_span_lo
+                    } else {
+                        attr_span_lo
+                    }
+                };
+                let comment_after_assign =
+                    context.snippet(mk_sp(assign_hi, comment_end_pos)).trim();
+
+                if !comment_before_assign.is_empty() {
+                    let new_indent_str = &pat_shape
+                        .block_indent(0)
+                        .to_string_with_newline(context.config);
+                    result = format!("{}{}{}", comment_before_assign, new_indent_str, result);
+                }
+
+                if !comment_after_assign.is_empty() {
+                    let new_indent_str =
+                        &shape.block_indent(0).to_string_with_newline(context.config);
+                    result.push_str(new_indent_str);
+                    result.push_str(comment_after_assign);
+                    result.push_str(new_indent_str);
+                }
+            }
+
             // 1 = trailing semicolon;
             let nested_shape = shape.sub_width(1)?;
 

tests/source/issue-3851.rs

@@ -0,0 +1,22 @@
+fn main() {
+    let before 
+      // before_comment 
+    = 
+    if true {
+     1.0
+    };
+
+    let after = 
+            // after_comment 
+    if true {
+     1.0
+    };
+
+    let both 
+      // before_comment 
+    = 
+            // after_comment 
+    if true {
+     1.0
+    };
+}

tests/target/issue-3851.rs

@@ -0,0 +1,19 @@
+fn main() {
+    // before_comment
+    let before = if true {
+        1.0
+    };
+
+    let after =
+    // after_comment
+    if true {
+        1.0
+    };
+
+    // before_comment
+    let both =
+    // after_comment
+    if true {
+        1.0
+    };
+}