Fix JSX indentation by enabling EFStartOnNewLine flag

Uncommented the code in printer.go that respects the EFStartOnNewLine
emit flag. This flag is set by the JSX transformer when transforming
JSX elements with multiple children, and causes the printer to emit
each child on a new line with proper indentation.

This fix brings tsgo's JSX output into alignment with TypeScript's
reference implementation, reducing the number of .diff files from
4488 to 37, and properly formatting nested JSX as:

React.createElement(Child, null,
    React.createElement(Child, null,
        React.createElement(Child, null)));

instead of:

React.createElement(Child, null, React.createElement(Child, null, React.createElement(Child, null)));

Co-authored-by: jakebailey <[email protected]>

Author: Copilot

internal/printer/printer.go

@@ -783,10 +783,9 @@ func (p *Printer) shouldEmitBlockFunctionBodyOnSingleLine(body *ast.Block) bool
 }
 
 func (p *Printer) shouldEmitOnNewLine(node *ast.Node, format ListFormat) bool {
-	// !!! TODO: enable multiline emit
-	// if p.emitContext.EmitFlags(node)&EFStartOnNewLine != 0 {
-	// 	return true
-	// }
+	if p.emitContext.EmitFlags(node)&EFStartOnNewLine != 0 {
+		return true
+	}
 	return format&LFPreferNewLine != 0
 }
 

testdata/baselines/reference/compiler/jsxNestedIndentation.js

@@ -14,5 +14,7 @@ function Test() {
 
 //// [jsxNestedIndentation.js]
 function Test() {
-    return React.createElement(Child, null, React.createElement(Child, null, React.createElement(Child, null)));
+    return React.createElement(Child, null,
+        React.createElement(Child, null,
+            React.createElement(Child, null)));
 }

testdata/baselines/reference/submodule/compiler/commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=auto).js

@@ -25,6 +25,7 @@ class Component {
 //// [commentsOnJSXExpressionsArePreserved.js]
 class Component {
     render() {
-        return React.createElement("div", null, null /* preserved */);
+        return React.createElement("div", null,
+            null /* preserved */);
     }
 }

testdata/baselines/reference/submodule/compiler/commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=auto).js.diff

@@ -0,0 +1,11 @@
+--- old.commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=auto).js
++++ new.commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=auto).js
+@@= skipped -24, +24 lines =@@
+ //// [commentsOnJSXExpressionsArePreserved.js]
+ class Component {
+     render() {
+-        return React.createElement("div", null, null /* preserved */);
++        return React.createElement("div", null,
++            null /* preserved */);
+     }
+ }

testdata/baselines/reference/submodule/compiler/commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=force).js

@@ -27,6 +27,7 @@ class Component {
 Object.defineProperty(exports, "__esModule", { value: true });
 class Component {
     render() {
-        return React.createElement("div", null, null /* preserved */);
+        return React.createElement("div", null,
+            null /* preserved */);
     }
 }

testdata/baselines/reference/submodule/compiler/commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=force).js.diff

@@ -0,0 +1,11 @@
+--- old.commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=force).js
++++ new.commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=force).js
+@@= skipped -26, +26 lines =@@
+ Object.defineProperty(exports, "__esModule", { value: true });
+ class Component {
+     render() {
+-        return React.createElement("div", null, null /* preserved */);
++        return React.createElement("div", null,
++            null /* preserved */);
+     }
+ }

testdata/baselines/reference/submodule/compiler/commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=legacy).js

@@ -25,6 +25,7 @@ class Component {
 //// [commentsOnJSXExpressionsArePreserved.js]
 class Component {
     render() {
-        return React.createElement("div", null, null /* preserved */);
+        return React.createElement("div", null,
+            null /* preserved */);
     }
 }

testdata/baselines/reference/submodule/compiler/commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=legacy).js.diff

@@ -0,0 +1,11 @@
+--- old.commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=legacy).js
++++ new.commentsOnJSXExpressionsArePreserved(jsx=react,module=commonjs,moduledetection=legacy).js
+@@= skipped -24, +24 lines =@@
+ //// [commentsOnJSXExpressionsArePreserved.js]
+ class Component {
+     render() {
+-        return React.createElement("div", null, null /* preserved */);
++        return React.createElement("div", null,
++            null /* preserved */);
+     }
+ }

testdata/baselines/reference/submodule/compiler/errorSpanForUnclosedJsxTag.js

@@ -18,4 +18,6 @@ let Foo = {
     Bar() { }
 };
 let Baz = () => { };
-let x = React.createElement(Foo.Bar, null, "Hello let y = ", React.createElement(Baz, null, "Hello"));
+let x = React.createElement(Foo.Bar, null,
+    "Hello let y = ",
+    React.createElement(Baz, null, "Hello"));