fix #2805: parentheses for commented expressions

Author: evanw

CHANGELOG.md

@@ -1,5 +1,19 @@
 # Changelog
 
+## Unreleased
+
+* Fix a regression caused by comment preservation ([#2805](https://github.com/evanw/esbuild/issues/2805))
+
+    The new comment preservation behavior that was added in 0.16.14 introduced a regression where comments in certain locations could cause esbuild to omit certain necessary parentheses in the output. The outermost parentheses were incorrectly removed for the following syntax forms, which then introduced syntax errors:
+
+    ```js
+    (/* comment */ { x: 0 }).x;
+    (/* comment */ function () { })();
+    (/* comment */ class { }).prototype;
+    ```
+
+    This regression has been fixed.
+
 ## 0.16.15
 
 * Add `format` to input files in the JSON metafile data

internal/js_printer/js_printer.go

@@ -1627,6 +1627,9 @@ func (p *printer) printExprCommentsAtLoc(loc logger.Loc) {
 		return
 	}
 	if comments := p.exprComments[loc]; comments != nil && !p.printedExprComments[loc] {
+		wasStmtStart := p.stmtStart == len(p.js)
+		wasExportDefaultStart := p.exportDefaultStart == len(p.js)
+
 		// We must never generate a newline before certain expressions. For example,
 		// generating a newline before the expression in a "return" statement will
 		// cause a semicolon to be inserted, which would change the code's behavior.
@@ -1653,18 +1656,35 @@ func (p *printer) printExprCommentsAtLoc(loc logger.Loc) {
 
 		// Mark these comments as printed so we don't print them again
 		p.printedExprComments[loc] = true
+
+		if wasStmtStart {
+			p.stmtStart = len(p.js)
+		}
+		if wasExportDefaultStart {
+			p.exportDefaultStart = len(p.js)
+		}
 	}
 }
 
 func (p *printer) printExprCommentsAfterCloseTokenAtLoc(loc logger.Loc) {
 	if comments := p.exprComments[loc]; comments != nil && !p.printedExprComments[loc] {
+		wasStmtStart := p.stmtStart == len(p.js)
+		wasExportDefaultStart := p.exportDefaultStart == len(p.js)
+
 		for _, comment := range comments {
 			p.printIndent()
 			p.printIndentedComment(comment)
 		}
 
 		// Mark these comments as printed so we don't print them again
 		p.printedExprComments[loc] = true
+
+		if wasStmtStart {
+			p.stmtStart = len(p.js)
+		}
+		if wasExportDefaultStart {
+			p.exportDefaultStart = len(p.js)
+		}
 	}
 }
 
@@ -3613,7 +3633,7 @@ func (p *printer) printStmt(stmt js_ast.Stmt, flags printStmtFlags) {
 			// Functions and classes must be wrapped to avoid confusion with their statement forms
 			p.exportDefaultStart = len(p.js)
 
-			p.printExpr(s2.Value, js_ast.LComma, 0)
+			p.printExprWithoutLeadingNewline(s2.Value, js_ast.LComma, 0)
 			p.printSemicolonAfterStatement()
 			return
 
@@ -4258,20 +4278,21 @@ type PrintResult struct {
 
 func Print(tree js_ast.AST, symbols js_ast.SymbolMap, r renamer.Renamer, options Options) PrintResult {
 	p := &printer{
-		symbols:            symbols,
-		renamer:            r,
-		importRecords:      tree.ImportRecords,
-		options:            options,
-		moduleType:         tree.ModuleTypeData.Type,
-		exprComments:       tree.ExprComments,
-		stmtStart:          -1,
-		exportDefaultStart: -1,
-		arrowExprStart:     -1,
-		forOfInitStart:     -1,
-		prevOpEnd:          -1,
-		prevNumEnd:         -1,
-		prevRegExpEnd:      -1,
-		builder:            sourcemap.MakeChunkBuilder(options.InputSourceMap, options.LineOffsetTables, options.ASCIIOnly),
+		symbols:              symbols,
+		renamer:              r,
+		importRecords:        tree.ImportRecords,
+		options:              options,
+		moduleType:           tree.ModuleTypeData.Type,
+		exprComments:         tree.ExprComments,
+		stmtStart:            -1,
+		exportDefaultStart:   -1,
+		arrowExprStart:       -1,
+		forOfInitStart:       -1,
+		prevOpEnd:            -1,
+		prevNumEnd:           -1,
+		prevRegExpEnd:        -1,
+		noLeadingNewlineHere: -1,
+		builder:              sourcemap.MakeChunkBuilder(options.InputSourceMap, options.LineOffsetTables, options.ASCIIOnly),
 	}
 
 	if p.exprComments != nil {

internal/js_printer/js_printer_test.go

@@ -543,6 +543,15 @@ func TestFunction(t *testing.T) {
 		"function foo([, ,] = [, ,]) {\n}\n")
 }
 
+func TestCommentsAndParentheses(t *testing.T) {
+	expectPrinted(t, "(/* foo */ { x() { foo() } }.x());", "/* foo */\n({ x() {\n  foo();\n} }).x();\n")
+	expectPrinted(t, "(/* foo */ function f() { foo(f) }());", "/* foo */\n(function f() {\n  foo(f);\n})();\n")
+	expectPrinted(t, "(/* foo */ class x { static y() { foo(x) } }.y());", "/* foo */\n(class x {\n  static y() {\n    foo(x);\n  }\n}).y();\n")
+	expectPrinted(t, "(/* @__PURE__ */ (() => foo())());", "/* @__PURE__ */ (() => foo())();\n")
+	expectPrinted(t, "export default (/* foo */ function f() {});", "export default (\n  /* foo */\n  function f() {\n  }\n);\n")
+	expectPrinted(t, "export default (/* foo */ class x {});", "export default (\n  /* foo */\n  class x {\n  }\n);\n")
+}
+
 func TestPureComment(t *testing.T) {
 	expectPrinted(t,
 		"(function() {})",

scripts/end-to-end-tests.js

@@ -2582,6 +2582,60 @@ tests.push(
   }),
 )
 
+// Test comments inside expressions
+tests.push(
+  test(['entry.js', '--outfile=node.js', '--target=es6'], {
+    'entry.js': `
+      let foo;
+      (
+        /* x */
+        {
+          y() {
+            foo = this.y.name
+          }
+        }
+      ).y();
+      if (foo !== 'y') throw 'fail'
+    `,
+  }),
+
+  test(['entry.js', '--outfile=node.js', '--target=es6'], {
+    'entry.js': `
+      let foo;
+      (
+        /* x */
+        function y() {
+          foo = y.name
+        }
+      )();
+      if (foo !== 'y') throw 'fail'
+    `,
+  }),
+
+  test(['entry.js', '--outfile=node.js', '--target=es6'], {
+    'entry.js': `
+      let foo;
+      (
+        /* x */
+        class y {
+          static z() {
+            foo = y.name
+          }
+        }
+      ).z();
+      if (foo !== 'y') throw 'fail'
+    `,
+  }),
+
+  test(['entry.js', '--outfile=node.js', '--target=es6'], {
+    'entry.js': `
+      let foo;
+      (/* @__PURE__ */ (() => foo = 'y')());
+      if (foo !== 'y') throw 'fail'
+    `,
+  }),
+)
+
 // Test certain minification transformations
 for (const minify of [[], ['--minify-syntax']]) {
   tests.push(