fix: keep a block comment leading a later statement on its own line

src/formatter/Formatter.ts

@@ -39,16 +39,16 @@ export default class Formatter {
 
   private formatAst(statements: StatementNode[]): string {
     return statements
-      .map(stat => this.formatStatement(stat))
+      .map((stat, i) => this.formatStatement(stat, i > 0))
       .join('\n'.repeat(this.cfg.linesBetweenQueries + 1));
   }
 
-  private formatStatement(statement: StatementNode): string {
+  private formatStatement(statement: StatementNode, startsOnNewLine: boolean): string {
     const layout = new ExpressionFormatter({
       cfg: this.cfg,
       dialectCfg: this.dialect.formatOptions,
       params: this.params,
-      layout: new Layout(new Indentation(indentString(this.cfg))),
+      layout: new Layout(new Indentation(indentString(this.cfg)), startsOnNewLine),
     }).format(statement.children);
 
     if (!statement.hasSemicolon) {

src/formatter/Layout.ts

@@ -25,7 +25,7 @@ export type LayoutItem = WS.SPACE | WS.SINGLE_INDENT | WS.NEWLINE | WS.MANDATORY
 export default class Layout {
   private items: LayoutItem[] = [];
 
-  constructor(public indentation: Indentation) {}
+  constructor(public indentation: Indentation, private startsOnNewLine: boolean = false) {}
 
   /**
    * Appends token strings and whitespace modifications to SQL string.
@@ -123,9 +123,11 @@ export default class Layout {
   }
 
   /**
-   * True when some content has already been added and nothing but indentation
-   * has been emitted since the last newline, meaning the next token would be
-   * placed at the start of a fresh (non-first) line.
+   * True when nothing but indentation has been emitted since the last newline,
+   * meaning the next token would be placed at the start of a fresh line.
+   *
+   * An empty layout counts when the statement itself is preceded by others,
+   * since the formatter joins statements with newlines.
    */
   public isAtStartOfLine(): boolean {
     for (let i = this.items.length - 1; i >= 0; i--) {
@@ -135,7 +137,7 @@ export default class Layout {
       }
       return item === WS.NEWLINE || item === WS.MANDATORY_NEWLINE;
     }
-    return false;
+    return this.startsOnNewLine;
   }
 
   private itemToString(item: LayoutItem): string {

test/features/comments.ts

@@ -90,6 +90,19 @@ export default function supportsComments(format: FormatFn, opts: CommentsConfig
     expect(format(result)).toBe(result);
   });
 
+  it('keeps a block comment leading a later statement on its own line', () => {
+    const sql = 'SELECT 1; /* c */ COMMIT;';
+    const result = dedent`
+      SELECT
+        1;
+
+      /* c */
+      COMMIT;
+    `;
+    expect(format(sql)).toBe(result);
+    expect(format(result)).toBe(result);
+  });
+
   it('keeps block comments in various CREATE TABLE statement positions idempotent', () => {
     const sql =
       'CREATE TABLE /* c */ tbl (/* c */ id INT, /* c */ first_name TEXT, last_name TEXT)';