fix(formatter): incorrect printing of union types with comments

crates/oxc_formatter/src/ast_nodes/generated/format.rs

@@ -4377,7 +4377,6 @@ impl<'a> Format<'a> for AstNode<'a, TSUnionType<'a>> {
         if !is_suppressed && format_type_cast_comment_node(self, false, f) {
             return;
         }
-        self.format_leading_comments(f);
         let needs_parentheses = self.needs_parentheses(f);
         if needs_parentheses {
             "(".fmt(f);

crates/oxc_formatter/src/formatter/comments.rs

@@ -369,10 +369,12 @@ impl<'a> Comments<'a> {
 
     /// Checks if the node has a suppression comment (prettier-ignore).
     pub fn is_suppressed(&self, start: u32) -> bool {
-        self.comments_before(start).iter().any(|comment| {
-            // TODO: Consider using `oxc-formatter-ignore` instead of `prettier-ignore`
-            self.source_text.text_for(&comment.content_span()).trim() == "prettier-ignore"
-        })
+        self.comments_before(start).iter().any(|comment| self.is_suppression_comment(comment))
+    }
+
+    pub fn is_suppression_comment(&self, comment: &Comment) -> bool {
+        // TODO: Consider using `oxfmt-ignore` instead of `prettier-ignore`
+        self.source_text.text_for(&comment.content_span()).trim() == "prettier-ignore"
     }
 
     /// Checks if a comment is a type cast comment containing `@type` or `@satisfies`.

crates/oxc_formatter/src/utils/assignment_like.rs

@@ -554,11 +554,12 @@ impl<'a> AssignmentLike<'a, '_> {
                             _ => false,
                         }
                     };
-
                     is_generic(&conditional_type.check_type)
                         || is_generic(&conditional_type.extends_type)
                         || comments.has_comment_before(decl.type_annotation.span().start)
                 }
+                // `TSUnionType` has its own indentation logic
+                TSType::TSUnionType(_) => false,
                 _ => {
                     // Check for leading comments on any other type
                     comments.has_comment_before(decl.type_annotation.span().start)

crates/oxc_formatter/src/write/union_type.rs

@@ -52,29 +52,33 @@ impl<'a> FormatWrite<'a> for AstNode<'a, TSUnionType<'a>> {
             union_type_at_top = parent;
         }
 
-        let should_indent = {
+        let should_indent = !has_leading_comments && {
             let parent = union_type_at_top.parent;
 
             // These parents have indent for their content, so we don't need to indent here
-            !match parent {
-                AstNodes::TSTypeAliasDeclaration(_) => has_leading_comments,
+            match parent {
+                AstNodes::TSTypeAliasDeclaration(alias) => {
+                    !f.comments().printed_comments().last().is_some_and(|comment| {
+                        comment.span.start
+                            > alias.type_parameters().map_or(alias.id.span.end, |tp| tp.span.end)
+                            && f.comments().is_end_of_line_comment(comment)
+                    })
+                }
                 AstNodes::TSTypeAssertion(_)
                 | AstNodes::TSTupleType(_)
-                | AstNodes::TSTypeParameterInstantiation(_) => true,
-                _ => false,
+                | AstNodes::TSTypeParameterInstantiation(_) => false,
+                _ => true,
             }
         };
 
         let types = format_with(|f| {
-            let suppressed_node_span = if f.comments().is_suppressed(self.span.start) {
-                self.types.first().unwrap().span()
-            } else {
-                Span::default()
-            };
+            let is_suppressed = leading_comments
+                .iter()
+                .rev()
+                .any(|comment| f.comments().is_suppression_comment(comment));
 
-            if has_leading_comments {
-                write!(f, FormatLeadingComments::Comments(leading_comments));
-            }
+            let suppressed_node_span =
+                if is_suppressed { self.types.first().unwrap().span() } else { Span::default() };
 
             let leading_soft_line_break_or_space = should_indent && !has_leading_comments;
 
@@ -123,7 +127,24 @@ impl<'a> FormatWrite<'a> for AstNode<'a, TSUnionType<'a>> {
             }
         });
 
-        write!(f, [group(&content)]);
+        if has_leading_comments {
+            let has_own_line_leading_comment = union_type_at_top.types.len() > 1
+                && leading_comments.iter().any(|comment| f.comments().is_own_line_comment(comment));
+            let is_end_of_line_comment = leading_comments
+                .last()
+                .is_some_and(|comment| f.comments().is_end_of_line_comment(comment));
+            write!(
+                f,
+                [group(&indent(&format_args!(
+                    has_own_line_leading_comment.then(soft_line_break),
+                    FormatLeadingComments::Comments(leading_comments),
+                    (!is_end_of_line_comment).then(soft_line_break),
+                    group(&content)
+                )))]
+            );
+        } else {
+            write!(f, [group(&content)]);
+        }
     }
 }
 

crates/oxc_formatter/tests/fixtures/ts/union/issue-16176.ts

@@ -0,0 +1,12 @@
+export default class TestUnionTypeAnnotation1 {
+  private prop!: /* comment */
+    LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+
+  private accessor prop2!: /* comment */
+    LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+}
+
+export interface TestUnionTypeAnnotation2 {
+  property: /* comment */
+    LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+}

crates/oxc_formatter/tests/fixtures/ts/union/issue-16176.ts.snap

@@ -0,0 +1,49 @@
+---
+source: crates/oxc_formatter/tests/fixtures/mod.rs
+---
+==================== Input ====================
+export default class TestUnionTypeAnnotation1 {
+  private prop!: /* comment */
+    LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+
+  private accessor prop2!: /* comment */
+    LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+}
+
+export interface TestUnionTypeAnnotation2 {
+  property: /* comment */
+    LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+}
+
+==================== Output ====================
+------------------
+{ printWidth: 80 }
+------------------
+export default class TestUnionTypeAnnotation1 {
+  private prop!: /* comment */
+    LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+
+  private accessor prop2: /* comment */
+    LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+}
+
+export interface TestUnionTypeAnnotation2 {
+  property: /* comment */
+    LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+}
+
+-------------------
+{ printWidth: 100 }
+-------------------
+export default class TestUnionTypeAnnotation1 {
+  private prop!: /* comment */ LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+
+  private accessor prop2: /* comment */
+    LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+}
+
+export interface TestUnionTypeAnnotation2 {
+  property: /* comment */ LongLongLongLongLongLongType[] | LongLongLongLongLongLongType[];
+}
+
+===================== End =====================

tasks/ast_tools/src/generators/formatter/format.rs

@@ -31,6 +31,8 @@ const AST_NODE_WITHOUT_PRINTING_COMMENTS_LIST: &[&str] = &[
     "TemplateElement",
 ];
 
+const AST_NODE_WITHOUT_PRINTING_LEADING_COMMENTS_LIST: &[&str] = &["TSUnionType"];
+
 const AST_NODE_NEEDS_PARENTHESES: &[&str] = &[
     "TSTypeAssertion",
     "TSInferType",
@@ -109,22 +111,19 @@ fn generate_struct_implementation(
 
     let struct_name = struct_def.name();
     let do_not_print_comment = AST_NODE_WITHOUT_PRINTING_COMMENTS_LIST.contains(&struct_name);
+    let do_not_print_leading_comment = do_not_print_comment
+        || AST_NODE_WITHOUT_PRINTING_LEADING_COMMENTS_LIST.contains(&struct_name);
 
-    let leading_comments = if do_not_print_comment {
-        quote! {}
-    } else {
+    let leading_comments = (!do_not_print_leading_comment).then(|| {
         quote! {
             self.format_leading_comments(f);
         }
-    };
-
-    let trailing_comments = if do_not_print_comment {
-        quote! {}
-    } else {
+    });
+    let trailing_comments = (!do_not_print_comment).then(|| {
         quote! {
             self.format_trailing_comments(f);
         }
-    };
+    });
 
     let needs_parentheses = parenthesis_type_ids.contains(&struct_def.id);
 
@@ -171,7 +170,7 @@ fn generate_struct_implementation(
 
         let write_implementation = if suppressed_check.is_none() {
             write_call
-        } else if trailing_comments.is_empty() {
+        } else if trailing_comments.is_none() {
             quote! {
                 if is_suppressed {
                      self.format_leading_comments(f);
@@ -214,7 +213,7 @@ fn generate_struct_implementation(
             }
         });
 
-        if needs_parentheses_before.is_empty() && trailing_comments.is_empty() {
+        if needs_parentheses_before.is_empty() && trailing_comments.is_none() {
             quote! {
                 #suppressed_check
                 #type_cast_comment_formatting

tasks/coverage/snapshots/formatter_typescript.snap

@@ -2,13 +2,15 @@ commit: 669c25c0
 
 formatter_typescript Summary:
 AST Parsed     : 9822/9822 (100.00%)
-Positive Passed: 9815/9822 (99.93%)
+Positive Passed: 9814/9822 (99.92%)
 Mismatch: tasks/coverage/typescript/tests/cases/compiler/amdLikeInputDeclarationEmit.ts
 
 Expect to Parse: tasks/coverage/typescript/tests/cases/compiler/genericTypeAssertions3.ts
 Unexpected token
 Expect to Parse: tasks/coverage/typescript/tests/cases/compiler/typeAssertionToGenericFunctionType.ts
 Unexpected token
+Mismatch: tasks/coverage/typescript/tests/cases/compiler/unionTypeWithLeadingOperator.ts
+
 Mismatch: tasks/coverage/typescript/tests/cases/conformance/expressions/contextualTyping/parenthesizedContexualTyping2.ts
 
 Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/expressions/elementAccess/letIdentifierInElementAccess01.ts

tasks/prettier_conformance/snapshots/prettier.ts.snap.md

@@ -1,4 +1,4 @@
-ts compatibility: 571/602 (94.85%)
+ts compatibility: 572/602 (95.02%)
 
 # Failed
 
@@ -32,6 +32,5 @@ ts compatibility: 571/602 (94.85%)
 | typescript/object-multiline/multiline.ts | 💥✨ | 23.21% |
 | typescript/property-signature/consistent-with-flow/comments.ts | 💥 | 80.00% |
 | typescript/union/union-parens.ts | 💥 | 92.59% |
-| typescript/union/comments/18106.ts | 💥 | 90.48% |
-| typescript/union/consistent-with-flow/comment.ts | 💥 | 82.61% |
-| typescript/union/single-type/single-type.ts | 💥 | 0.00% |
+| typescript/union/comments/18106.ts | 💥 | 92.68% |
+| typescript/union/single-type/single-type.ts | 💥 | 66.67% |