Use 'static {}' for static fields when available and useDefineForClassFields is false (#47707)

Author: rbuckton

src/compiler/checker.ts

@@ -28425,29 +28425,6 @@ namespace ts {
                     grammarErrorOnNode(right, Diagnostics.Cannot_assign_to_private_method_0_Private_methods_are_not_writable, idText(right));
                 }
 
-                if (lexicallyScopedSymbol?.valueDeclaration && (getEmitScriptTarget(compilerOptions) === ScriptTarget.ESNext && !useDefineForClassFields)) {
-                    const lexicalClass = getContainingClass(lexicallyScopedSymbol.valueDeclaration);
-                    const parentStaticFieldInitializer = findAncestor(node, (n) => {
-                        if (n === lexicalClass) return "quit";
-                        if (isPropertyDeclaration(n.parent) && hasStaticModifier(n.parent) && n.parent.initializer === n && n.parent.parent === lexicalClass) {
-                            return true;
-                        }
-                        return false;
-                    });
-                    if (parentStaticFieldInitializer) {
-                        const parentStaticFieldInitializerSymbol = getSymbolOfNode(parentStaticFieldInitializer.parent);
-                        Debug.assert(parentStaticFieldInitializerSymbol, "Initializer without declaration symbol");
-                        const diagnostic = error(node,
-                            Diagnostics.Property_0_may_not_be_used_in_a_static_property_s_initializer_in_the_same_class_when_target_is_esnext_and_useDefineForClassFields_is_false,
-                            symbolName(lexicallyScopedSymbol));
-                        addRelatedInfo(diagnostic,
-                            createDiagnosticForNode(parentStaticFieldInitializer.parent,
-                                Diagnostics.Initializer_for_property_0,
-                                symbolName(parentStaticFieldInitializerSymbol))
-                        );
-                    }
-                }
-
                 if (isAnyLike) {
                     if (lexicallyScopedSymbol) {
                         return isErrorType(apparentType) ? errorType : apparentType;
@@ -34656,9 +34633,7 @@ namespace ts {
             checkVariableLikeDeclaration(node);
 
             setNodeLinksForPrivateIdentifierScope(node);
-            if (isPrivateIdentifier(node.name) && hasStaticModifier(node) && node.initializer && languageVersion === ScriptTarget.ESNext && !compilerOptions.useDefineForClassFields) {
-                error(node.initializer, Diagnostics.Static_fields_with_private_names_can_t_have_initializers_when_the_useDefineForClassFields_flag_is_not_specified_with_a_target_of_esnext_Consider_adding_the_useDefineForClassFields_flag);
-            }
+
             // property signatures already report "initializer not allowed in ambient context" elsewhere
             if (hasSyntacticModifier(node, ModifierFlags.Abstract) && node.kind === SyntaxKind.PropertyDeclaration && node.initializer) {
                 error(node, Diagnostics.Property_0_cannot_have_an_initializer_because_it_is_marked_abstract, declarationNameToString(node.name));

src/compiler/diagnosticMessages.json

@@ -3281,10 +3281,6 @@
         "category": "Error",
         "code": 2804
     },
-    "Static fields with private names can't have initializers when the '--useDefineForClassFields' flag is not specified with a '--target' of 'esnext'. Consider adding the '--useDefineForClassFields' flag.": {
-        "category": "Error",
-        "code": 2805
-    },
     "Private accessor was defined without a getter.": {
         "category": "Error",
         "code": 2806
@@ -3301,10 +3297,6 @@
         "category": "Error",
         "code": 2809
     },
-    "Property '{0}' may not be used in a static property's initializer in the same class when 'target' is 'esnext' and 'useDefineForClassFields' is 'false'.": {
-        "category": "Error",
-        "code": 2810
-    },
     "Initializer for property '{0}'": {
         "category": "Error",
         "code": 2811

src/compiler/transformers/classFields.ts

@@ -135,10 +135,13 @@ namespace ts {
 
         const shouldTransformPrivateElementsOrClassStaticBlocks = languageVersion < ScriptTarget.ES2022;
 
+        // We need to transform `this` in a static initializer into a reference to the class
+        // when targeting < ES2022 since the assignment will be moved outside of the class body.
+        const shouldTransformThisInStaticInitializers = languageVersion < ScriptTarget.ES2022;
+
         // We don't need to transform `super` property access when targeting ES5, ES3 because
         // the es2015 transformation handles those.
-        const shouldTransformSuperInStaticInitializers = (languageVersion <= ScriptTarget.ES2021 || !useDefineForClassFields) && languageVersion >= ScriptTarget.ES2015;
-        const shouldTransformThisInStaticInitializers = languageVersion <= ScriptTarget.ES2021 || !useDefineForClassFields;
+        const shouldTransformSuperInStaticInitializers = shouldTransformThisInStaticInitializers && languageVersion >= ScriptTarget.ES2015;
 
         const previousOnSubstituteNode = context.onSubstituteNode;
         context.onSubstituteNode = onSubstituteNode;
@@ -422,6 +425,11 @@ namespace ts {
 
             if (isPrivateIdentifier(node.name)) {
                 if (!shouldTransformPrivateElementsOrClassStaticBlocks) {
+                    if (isStatic(node)) {
+                        // static fields are left as is
+                        return visitEachChild(node, visitor, context);
+                    }
+
                     // Initializer is elided as the field is initialized in transformConstructor.
                     return factory.updatePropertyDeclaration(
                         node,
@@ -448,6 +456,28 @@ namespace ts {
             if (expr && !isSimpleInlineableExpression(expr)) {
                 getPendingExpressions().push(expr);
             }
+
+            if (isStatic(node) && !shouldTransformPrivateElementsOrClassStaticBlocks && !useDefineForClassFields) {
+                const initializerStatement = transformPropertyOrClassStaticBlock(node, factory.createThis());
+                if (initializerStatement) {
+                    const staticBlock = factory.createClassStaticBlockDeclaration(
+                        /*decorators*/ undefined,
+                        /*modifiers*/ undefined,
+                        factory.createBlock([initializerStatement])
+                    );
+
+                    setOriginalNode(staticBlock, node);
+                    setCommentRange(staticBlock, node);
+
+                    // Set the comment range for the statement to an empty synthetic range
+                    // and drop synthetic comments from the statement to avoid printing them twice.
+                    setCommentRange(initializerStatement, { pos: -1, end: -1 });
+                    setSyntheticLeadingComments(initializerStatement, undefined);
+                    setSyntheticTrailingComments(initializerStatement, undefined);
+                    return staticBlock;
+                }
+            }
+
             return undefined;
         }
 
@@ -1006,8 +1036,6 @@ namespace ts {
                 enableSubstitutionForClassStaticThisOrSuperReference();
             }
 
-            const staticProperties = getStaticPropertiesAndClassStaticBlock(node);
-
             // If a class has private static fields, or a static field has a `this` or `super` reference,
             // then we need to allocate a temp variable to hold on to that reference.
             let pendingClassReferenceAssignment: BinaryExpression | undefined;
@@ -1047,6 +1075,7 @@ namespace ts {
             //      HasLexicalDeclaration (N) : Determines if the argument identifier has a binding in this environment record that was created using
             //                                  a lexical declaration such as a LexicalDeclaration or a ClassDeclaration.
 
+            const staticProperties = getStaticPropertiesAndClassStaticBlock(node);
             if (some(staticProperties)) {
                 addPropertyOrClassStaticBlockStatements(statements, staticProperties, factory.getInternalName(node));
             }
@@ -1102,7 +1131,7 @@ namespace ts {
                 transformClassMembers(node, isDerivedClass)
             );
 
-            const hasTransformableStatics = some(staticPropertiesOrClassStaticBlocks, p => isClassStaticBlockDeclaration(p) || !!p.initializer || (shouldTransformPrivateElementsOrClassStaticBlocks && isPrivateIdentifier(p.name)));
+            const hasTransformableStatics = shouldTransformPrivateElementsOrClassStaticBlocks && some(staticPropertiesOrClassStaticBlocks, p => isClassStaticBlockDeclaration(p) || !!p.initializer || isPrivateIdentifier(p.name));
             if (hasTransformableStatics || some(pendingExpressions)) {
                 if (isDecoratedClassDeclaration) {
                     Debug.assertIsDefined(pendingStatements, "Decorated classes transformed by TypeScript are expected to be within a variable declaration.");
@@ -1156,6 +1185,7 @@ namespace ts {
         }
 
         function transformClassMembers(node: ClassDeclaration | ClassExpression, isDerivedClass: boolean) {
+            const members: ClassElement[] = [];
             if (shouldTransformPrivateElementsOrClassStaticBlocks) {
                 // Declare private names.
                 for (const member of node.members) {
@@ -1169,12 +1199,26 @@ namespace ts {
                 }
             }
 
-            const members: ClassElement[] = [];
             const constructor = transformConstructor(node, isDerivedClass);
+            const visitedMembers = visitNodes(node.members, classElementVisitor, isClassElement);
+
             if (constructor) {
                 members.push(constructor);
             }
-            addRange(members, visitNodes(node.members, classElementVisitor, isClassElement));
+
+            if (!shouldTransformPrivateElementsOrClassStaticBlocks && some(pendingExpressions)) {
+                members.push(factory.createClassStaticBlockDeclaration(
+                    /*decorators*/ undefined,
+                    /*modifiers*/ undefined,
+                    factory.createBlock([
+                        factory.createExpressionStatement(factory.inlineExpressions(pendingExpressions))
+                    ])
+                ));
+                pendingExpressions = undefined;
+            }
+
+            addRange(members, visitedMembers);
+
             return setTextRange(factory.createNodeArray(members), /*location*/ node.members);
         }
 
@@ -1374,27 +1418,41 @@ namespace ts {
          */
         function addPropertyOrClassStaticBlockStatements(statements: Statement[], properties: readonly (PropertyDeclaration | ClassStaticBlockDeclaration)[], receiver: LeftHandSideExpression) {
             for (const property of properties) {
-                const expression = isClassStaticBlockDeclaration(property) ?
-                    transformClassStaticBlockDeclaration(property) :
-                    transformProperty(property, receiver);
-                if (!expression) {
+                if (isStatic(property) && !shouldTransformPrivateElementsOrClassStaticBlocks && !useDefineForClassFields) {
                     continue;
                 }
-                const statement = factory.createExpressionStatement(expression);
-                setSourceMapRange(statement, moveRangePastModifiers(property));
-                setCommentRange(statement, property);
-                setOriginalNode(statement, property);
 
-                // `setOriginalNode` *copies* the `emitNode` from `property`, so now both
-                // `statement` and `expression` have a copy of the synthesized comments.
-                // Drop the comments from expression to avoid printing them twice.
-                setSyntheticLeadingComments(expression, undefined);
-                setSyntheticTrailingComments(expression, undefined);
+                const statement = transformPropertyOrClassStaticBlock(property, receiver);
+                if (!statement) {
+                    continue;
+                }
 
                 statements.push(statement);
             }
         }
 
+        function transformPropertyOrClassStaticBlock(property: PropertyDeclaration | ClassStaticBlockDeclaration, receiver: LeftHandSideExpression) {
+            const expression = isClassStaticBlockDeclaration(property) ?
+                transformClassStaticBlockDeclaration(property) :
+                transformProperty(property, receiver);
+            if (!expression) {
+                return undefined;
+            }
+
+            const statement = factory.createExpressionStatement(expression);
+            setSourceMapRange(statement, moveRangePastModifiers(property));
+            setCommentRange(statement, property);
+            setOriginalNode(statement, property);
+
+            // `setOriginalNode` *copies* the `emitNode` from `property`, so now both
+            // `statement` and `expression` have a copy of the synthesized comments.
+            // Drop the comments from expression to avoid printing them twice.
+            setSyntheticLeadingComments(expression, undefined);
+            setSyntheticTrailingComments(expression, undefined);
+
+            return statement;
+        }
+
         /**
          * Generates assignment expressions for property initializers.
          *

tests/baselines/reference/computedPropertyName.js

@@ -56,8 +56,8 @@ class D {
     constructor() {
         this[_a] = 0; // Error
     }
+    static { _a = onInit; }
 }
-_a = onInit;
 class E {
     [onInit]() { } // Error
 }